Preamp ramblings: Active, Passive, TVCs, Birds, And Bees
- Thread starter bazelio
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DaveC said:
Beautiful preamp!
I think a decent resistor based volume control can equal a copper tvc but silver tvc is the best possible solution. The next preamp I build will use silver TVC + a tube buffered output.
Passive pres are a good option but they depend on the source having a robust output section.
Dave, why would you combine a silver TVC with a tube buffer? If you're going to do an active preamp with buffer, why not use a resistor ladder or shunt type attenuator since they'd be lower in distortion than transformers? If you're going to do a TVC/AVC, why would you add a buffer? The TVC solves most impedance issues itself.
Beautiful preamp!
I think a decent resistor based volume control can equal a copper tvc but silver tvc is the best possible solution. The next preamp I build will use silver TVC + a tube buffered output.
Passive pres are a good option but they depend on the source having a robust output section.
Dave, why would you combine a silver TVC with a tube buffer? If you're going to do an active preamp with buffer, why not use a resistor ladder or shunt type attenuator since they'd be lower in distortion than transformers? If you're going to do a TVC/AVC, why would you add a buffer? The TVC solves most impedance issues itself.
bazelio said:
Dave, why would you combine a silver TVC with a tube buffer? If you're going to do an active preamp with buffer, why not use a resistor ladder or shunt type attenuator since they'd be lower in distortion than transformers? If you're going to do a TVC/AVC, why would you add a buffer? The TVC solves most impedance issues itself.
With a TVC the output depends on volume. This may or may not be a big deal depending on both source and what the TVC is driving.
IMO a silver tvc is still the best volume control and loses less information vs others. I'm currently using LDR, and it's good but not as good. I don't want to go far OT, but afaik Thomas Mayer uses the silver slagleformer tvcs in some of his active pres. Maybe when I built the preamp I'll talk more about it...
A lot of it is that I've built preamps and understand how to make an excellent tube buffer that sounds better vs not having the buffer.
Industry Affiliation:
I own ZenWave Audio
zenwaveaudio.com
dave@zenwaveaudio.com
Furutech Dealer
Dave, why would you combine a silver TVC with a tube buffer? If you're going to do an active preamp with buffer, why not use a resistor ladder or shunt type attenuator since they'd be lower in distortion than transformers? If you're going to do a TVC/AVC, why would you add a buffer? The TVC solves most impedance issues itself.
With a TVC the output depends on volume. This may or may not be a big deal depending on both source and what the TVC is driving.
IMO a silver tvc is still the best volume control and loses less information vs others. I'm currently using LDR, and it's good but not as good. I don't want to go far OT, but afaik Thomas Mayer uses the silver slagleformer tvcs in some of his active pres. Maybe when I built the preamp I'll talk more about it...
A lot of it is that I've built preamps and understand how to make an excellent tube buffer that sounds better vs not having the buffer.Industry Affiliation:
I own ZenWave Audio
zenwaveaudio.com
dave@zenwaveaudio.com
Furutech Dealer
#18
@DaveC In every attenuation scheme, output depends on volume. I don't know what you mean. We care about the voltage swing, current drive and impedance matching between source and amp. Impedance issues are ameliorated by a TVC in most cases with only the wimpiest of sources needing an active pre amplifier. The reflected load of the amp is cut in half for each 3dB of attenuation of a TVC. In most cases where you have sufficient system gain, the load becomes infinitesimal and you're left with the inductive reactance of the TVC - which for a Slagle AVC gapping is around 15k-20k. Even with a source output impedance as high as 3k (such as OTL phonos), this is working well. Bass is strong.
Anyways, a TVC, silver or otherwise, is going to be higher in distortion than a shunt or ladder type stepped attenuator. Although, passive resistor attenuators can be problematic in terms of impedance issues for many chains. So my point is if you're going to build an active device which fixes impedance mismatches, then why not use the lowest distortion attenuator? There's no need for a TVC at that point, and all you're doing is further distorting the signal as compared to a simple resistor based attenuator. On the other hand, if you're going to build a passive device, then it makes sense to go for an AVC or TVC in order to avoid likely impedance issues.
LDRs are a solution looking for a problem. They minimize mechanical contacts in the signal path. My friend pointed out, this is the same "problem" that TOSLINK solved. How well did that work? LOL. I just got done playing with LDRs myself, and quite honestly, once you buffer them they sound fine. But there again, once you're buffering, then there is no intuitive advantage of an LDR over regular resistors. But there are many disadvantages, like non-linearity, drift, etc.
At the end of the day, a line stage should be a low noise, low distortion device. Passive TVC/AVC solutions solve the noise problem, and do reasonably well in terms of distortion at "consumer" signal levels for most of the frequency range. As soon as we go active, even by merely inserting a buffer, then we start fighting noise (and additional distortion). So if we're going to buffer, a tube doesn't seem like the best choice. Perhaps a low noise op amp like the OPA1611 configured as a voltage follower. It would best any tube any day in terms of noise and distortion.
Last edited: Yesterday at 9:01 AM
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@DaveC In every attenuation scheme, output depends on volume. I don't know what you mean. We care about the voltage swing, current drive and impedance matching between source and amp. Impedance issues are ameliorated by a TVC in most cases with only the wimpiest of sources needing an active pre amplifier. The reflected load of the amp is cut in half for each 3dB of attenuation of a TVC. In most cases where you have sufficient system gain, the load becomes infinitesimal and you're left with the inductive reactance of the TVC - which for a Slagle AVC gapping is around 15k-20k. Even with a source output impedance as high as 3k (such as OTL phonos), this is working well. Bass is strong.
Anyways, a TVC, silver or otherwise, is going to be higher in distortion than a shunt or ladder type stepped attenuator. Although, passive resistor attenuators can be problematic in terms of impedance issues for many chains. So my point is if you're going to build an active device which fixes impedance mismatches, then why not use the lowest distortion attenuator? There's no need for a TVC at that point, and all you're doing is further distorting the signal as compared to a simple resistor based attenuator. On the other hand, if you're going to build a passive device, then it makes sense to go for an AVC or TVC in order to avoid likely impedance issues.
LDRs are a solution looking for a problem. They minimize mechanical contacts in the signal path. My friend pointed out, this is the same "problem" that TOSLINK solved. How well did that work? LOL. I just got done playing with LDRs myself, and quite honestly, once you buffer them they sound fine. But there again, once you're buffering, then there is no intuitive advantage of an LDR over regular resistors. But there are many disadvantages, like non-linearity, drift, etc.
At the end of the day, a line stage should be a low noise, low distortion device. Passive TVC/AVC solutions solve the noise problem, and do reasonably well in terms of distortion at "consumer" signal levels for most of the frequency range. As soon as we go active, even by merely inserting a buffer, then we start fighting noise (and additional distortion). So if we're going to buffer, a tube doesn't seem like the best choice. Perhaps a low noise op amp like the OPA1611 configured as a voltage follower. It would best any tube any day in terms of noise and distortion.
Last edited: Yesterday at 9:01 AM
Likes: sfoclt
@DaveC said:
No, output doesn't depend on volume for every attenuation scheme. I don't think you're quite getting this.
Good luck with whatever you want to do... I've experimented a lot, built several preamps, etc... I know what I like and what I feel is best.
“LDRs are a solution looking for a problem. They minimize mechanical contacts in the signal path. My friend pointed out, this is the same "problem" that TOSLINK solved. How well did that work? LOL. I just got done playing with LDRs myself, and quite honestly, once you buffer them they sound fine. But there again, once you're buffering, then there is no intuitive advantage of an LDR over regular resistors. But there are many disadvantages, like non-linearity, drift, etc.”
I’m enjoying my LDR or should I say Optocoupled volume control. The Java Triple Shot uses a novel circuit according to their blurb and sounds very transparent to me. Certainly more transparent than the Bespoke I heard for a short time.
Dartzeel and Aqua Acoustic both use optocouplers so I’m in quite good company I think.
I’m enjoying my LDR or should I say Optocoupled volume control. The Java Triple Shot uses a novel circuit according to their blurb and sounds very transparent to me. Certainly more transparent than the Bespoke I heard for a short time.
Dartzeel and Aqua Acoustic both use optocouplers so I’m in quite good company I think.
I think the success (or not) of using a passive either TVC or resistor stepped type is more down to the power and drive of the source component. Most (all) decent sources have at least 2v output which 'should' meet the peak power requirement of almost any power amplifier. BUT it isn't just about voltage, is is about current, drive and also impedance. Plus capacitance in the cables.
In my system the Kassandra DAC has a high 10v output and uses OPTs, so has plenty of 'drive' and can handle long interconnects. Using a passive has so far, been successful. I am about to have the Genus integrated and can then see if a preamplifier stage in that amp plus the power stage will beat the passive. In theory it shouldn't but I have the feeling it will and resoundingly so.
A common sign of a passive struggling is a lower dynamic range, weak bass and slightly tipped up treble. Also I notice a passive can accentuate treble detail at lower levels, possibly due to phase shift or impedance matching. Set at say 7 o'clock the passive will have a high impedance load obviously, so the source will see possibly 150K or more. As you up the volume, the impedance drops and things calm down, probably as the source now sees 50K load.
I am unsure if the old theory of 2 loads being seem at the source is true, many seem to state that about passives. I have also read it can see just one load, as the passive is 'inline' to the input impedance for the power amp, so they become a sum of those.
I haven't tried a TVC, but imagine the transformers need to be of very high quality to not increase distortions or issues. In theory a passive using 2 highest quality resistors should be the ultimate solution, as opposed to adding a pre-amplifier, as if we have 2v already, why drop that down in the pre-amplifier to then amplify it back up to 2v or more?
I think the attraction of a passive is simpliicy, save money (unless you buy the Be-spoke passive) and transparency.
YMMV and lets get more posts in this thread on experiences in the subject. I find it quite fascinating.
In my system the Kassandra DAC has a high 10v output and uses OPTs, so has plenty of 'drive' and can handle long interconnects. Using a passive has so far, been successful. I am about to have the Genus integrated and can then see if a preamplifier stage in that amp plus the power stage will beat the passive. In theory it shouldn't but I have the feeling it will and resoundingly so.
A common sign of a passive struggling is a lower dynamic range, weak bass and slightly tipped up treble. Also I notice a passive can accentuate treble detail at lower levels, possibly due to phase shift or impedance matching. Set at say 7 o'clock the passive will have a high impedance load obviously, so the source will see possibly 150K or more. As you up the volume, the impedance drops and things calm down, probably as the source now sees 50K load.
I am unsure if the old theory of 2 loads being seem at the source is true, many seem to state that about passives. I have also read it can see just one load, as the passive is 'inline' to the input impedance for the power amp, so they become a sum of those.
I haven't tried a TVC, but imagine the transformers need to be of very high quality to not increase distortions or issues. In theory a passive using 2 highest quality resistors should be the ultimate solution, as opposed to adding a pre-amplifier, as if we have 2v already, why drop that down in the pre-amplifier to then amplify it back up to 2v or more?
I think the attraction of a passive is simpliicy, save money (unless you buy the Be-spoke passive) and transparency.
YMMV and lets get more posts in this thread on experiences in the subject. I find it quite fascinating.
LDR I'm using is Tortuga's, with connections soldered to pcb.
LDR is interesting as the LDRs themselves don't measure well. IMO, they have a capacitive element and are probably closer to a resistor with a small cap bypassing it. I also want to give credit to Folsom for this idea, he brought up this possibility probably a couple years ago when discussing why LDR should sound any different vs resistors... it's not just the lack of switches, it probably is capacitance in the LDR it's self and maybe other things too that cause the somewhat questionable performance of an LDR based volume control. Check link below for more info:
https://www.neurochrome.com/tortuga-audio-ldr3/
Despite these issues most do feel the LDR is subjectively better vs resistor based attenuators. I know a few others who have compared it to a Bent pre based on copper slagleformers and feel they are comparable. Possibly/probably because both add some amount of desirable distortions.
In any case, all volume controls have some issues with them. Technically, a resistor based attenuator using high quality resistors and switches will be the best choice. Subjectively I feel a silver avc is the best.
As far as buffers, one of the attractions of choosing the Tortuga is adjustable input impedance. There are others like it includes microprocessor controlled calibration of the LDRs and source switching... but the adjustable input impedance is interesting as it allows you to test sources and see if they are indeed sensitive to this. Turns out some are... these sources, when used with an avc based VC (volume control), will result in sounding different depending on the volume setting. Others, like my Sony HAP-Z1ES, sound exactly the same from 10-100k ohm input impedance and are a far better choice for a source driving a passive pre vs a source that is sensitive to impedance.
The thought that avc corrects impedance mismatches is not correct. It may to some degree, but having this depend on volume settings and the source's output makes it a poor solution imo... it's still very possible for the system to sound different depending on volume settings. So I'd consider this a possible side-effect but not a real solution to the fact that impedance mismatchs can effect the sound.
As far as using an op-amp based voltage follower as a buffer, if that's what floats your boat then great. It can work very well if it's properly implemented. But so can anything. What's interesting is recently, a company that specializes in buffers and DACs recently gave away a bunch of interconnect cables with a cheap USB-powered buffers in it to members of a particular forum in exchange for reviews. The number of folks reporting large improvements from inserting a very cheap USB powered op-amp based buffer was unbelievable. This shows how much sources can vary and how much impedance mismatch, or poorly designed source output stages, can really effect a system and that they are VERY COMMON. This is also why I believe very few mfg'ers offer passive preamps. If you want your preamp to sound the same regardless of what system it's in it needs to be active, it's as simple as that. If you want to base your system around a passive pre, it's going to take more consideration to make sure you get proper results, and your selection of appropriate sources will be reduced. Also, good luck finding those appropriate sources and figuring out a way to test them to make sure they really are an ideal candidate for a passive pre.
So while not easy, it is definitely possible to have a buffer or active preamp section that sounds great, often better vs it not being in the chain. I've even heard of some folks putting more than one preamp in series because they like it.
LDR is interesting as the LDRs themselves don't measure well. IMO, they have a capacitive element and are probably closer to a resistor with a small cap bypassing it. I also want to give credit to Folsom for this idea, he brought up this possibility probably a couple years ago when discussing why LDR should sound any different vs resistors... it's not just the lack of switches, it probably is capacitance in the LDR it's self and maybe other things too that cause the somewhat questionable performance of an LDR based volume control. Check link below for more info:
https://www.neurochrome.com/tortuga-audio-ldr3/
Despite these issues most do feel the LDR is subjectively better vs resistor based attenuators. I know a few others who have compared it to a Bent pre based on copper slagleformers and feel they are comparable. Possibly/probably because both add some amount of desirable distortions.
In any case, all volume controls have some issues with them. Technically, a resistor based attenuator using high quality resistors and switches will be the best choice. Subjectively I feel a silver avc is the best.
As far as buffers, one of the attractions of choosing the Tortuga is adjustable input impedance. There are others like it includes microprocessor controlled calibration of the LDRs and source switching... but the adjustable input impedance is interesting as it allows you to test sources and see if they are indeed sensitive to this. Turns out some are... these sources, when used with an avc based VC (volume control), will result in sounding different depending on the volume setting. Others, like my Sony HAP-Z1ES, sound exactly the same from 10-100k ohm input impedance and are a far better choice for a source driving a passive pre vs a source that is sensitive to impedance.
The thought that avc corrects impedance mismatches is not correct. It may to some degree, but having this depend on volume settings and the source's output makes it a poor solution imo... it's still very possible for the system to sound different depending on volume settings. So I'd consider this a possible side-effect but not a real solution to the fact that impedance mismatchs can effect the sound.
As far as using an op-amp based voltage follower as a buffer, if that's what floats your boat then great. It can work very well if it's properly implemented. But so can anything. What's interesting is recently, a company that specializes in buffers and DACs recently gave away a bunch of interconnect cables with a cheap USB-powered buffers in it to members of a particular forum in exchange for reviews. The number of folks reporting large improvements from inserting a very cheap USB powered op-amp based buffer was unbelievable. This shows how much sources can vary and how much impedance mismatch, or poorly designed source output stages, can really effect a system and that they are VERY COMMON. This is also why I believe very few mfg'ers offer passive preamps. If you want your preamp to sound the same regardless of what system it's in it needs to be active, it's as simple as that. If you want to base your system around a passive pre, it's going to take more consideration to make sure you get proper results, and your selection of appropriate sources will be reduced. Also, good luck finding those appropriate sources and figuring out a way to test them to make sure they really are an ideal candidate for a passive pre.
So while not easy, it is definitely possible to have a buffer or active preamp section that sounds great, often better vs it not being in the chain. I've even heard of some folks putting more than one preamp in series because they like it.
My comments are based on a line stage "preamp" having only two fundamental functions. One is source selection. The other is volume control. It is very easy for preamps to do a lot of damage as they amplify, distort, inject noise, attenuate and then pass forward this "new" signal to subsequent gear to once again amplify. The best preamp is no preamp.
If we have clean well-regulated DC, a very simple topology with 600R stepped resistor attenuator on either side of precision op amp buffers will give us high input impedance, low output impedance, low noise and low distortion. Hypothetically, this should be very difficult to surpass.
A passive AVC or TVC will be higher in distortion than the active buffer line stage above, but lower in noise. Absolute THD at 20Hz and less than ~8V signal levels is actually very good, though. And we'd never expect >8V with non-pro gear to my knowledge. The reason to use transformer based volume control is indeed to avoid needing buffers, power supplies, etc. You're mistaken about impedance compensation. Their output impedance is low and stable at less than 100R up to -10dB attenuation (which in my system, would blow my speaker drivers almost assuredly). Even at -5db, they're still only around a couple hundred ohm OI. Where I normally use mine, probably around -25dB, I recall measuring it at ~8R. Systems shouldn't rely on preamp *gain* in the first place. IMO.
Let's look at some possible -3dB frequency points for a Slagle AVC (125H) based on different source output impedance:
Source OI of 100R = 0.12 Hz
Source OI of 500R = 0.64 Hz
Source OI of 3000R (such as a tube OTL phono) = 3.9 Hz
The -1dB point is at 2x these frequencies. So the worst case -1db rolloff point is going to be around 8 Hz. assuming a direct coupled output and a maximum of 3kOhm output impedance. The high end performance is flat to 200kHz or beyond always. Now we need source signal swing. Select manufacturers clearly want you to buy their preamps. I have seen two examples. But, minus a few, source signal swing is usually suitable. Still, I agree with your point about designing for the wild wild west, and wanting to avoid system incompatibilities at the fringe. I just want to avoid the sound quality degradation that results. Slagle, MFA, Bespoke, et al are offering products that would work great for most people.
Lastly, a purely passive resistor ladder attenuator line stage will be a problem for most people most of the time, with clearly audible deficiencies. These types of passive attenuators are probably what give "passive" a bad name in general. It's too easy to use them in systems where they don't belong. Maybe they also give resistor attenuators in general a bad name. Yet resistor attenuators should be the first choice in most active preamps since they're the cleanest option. Just don't use goofy audiophile resistors. $0.30 metal films work great.
This probably can't be true, unless "most" have compared apples to apples Tortuga LDR vs Tortuga resistor ladder. As TomC's measurements reveal, the LDR's input cap varies non-linearly and creates THD within the audio frequency range that approaches 10% (!!) as you adjust the volume. You worry about different sound at different volume levels?!? Nothing I've ever seen can touch the LDR's ability to achieve this.
Have you heard of "The Truth" preamp? I've been playing music through and measuring one of these recently. It's using a photo cell based attenuator also. Arthur Salvatore waxes poetic about it here.
If we have clean well-regulated DC, a very simple topology with 600R stepped resistor attenuator on either side of precision op amp buffers will give us high input impedance, low output impedance, low noise and low distortion. Hypothetically, this should be very difficult to surpass.
A passive AVC or TVC will be higher in distortion than the active buffer line stage above, but lower in noise. Absolute THD at 20Hz and less than ~8V signal levels is actually very good, though. And we'd never expect >8V with non-pro gear to my knowledge. The reason to use transformer based volume control is indeed to avoid needing buffers, power supplies, etc. You're mistaken about impedance compensation. Their output impedance is low and stable at less than 100R up to -10dB attenuation (which in my system, would blow my speaker drivers almost assuredly). Even at -5db, they're still only around a couple hundred ohm OI. Where I normally use mine, probably around -25dB, I recall measuring it at ~8R. Systems shouldn't rely on preamp *gain* in the first place. IMO.
Let's look at some possible -3dB frequency points for a Slagle AVC (125H) based on different source output impedance:
Source OI of 100R = 0.12 Hz
Source OI of 500R = 0.64 Hz
Source OI of 3000R (such as a tube OTL phono) = 3.9 Hz
The -1dB point is at 2x these frequencies. So the worst case -1db rolloff point is going to be around 8 Hz. assuming a direct coupled output and a maximum of 3kOhm output impedance. The high end performance is flat to 200kHz or beyond always. Now we need source signal swing. Select manufacturers clearly want you to buy their preamps. I have seen two examples. But, minus a few, source signal swing is usually suitable. Still, I agree with your point about designing for the wild wild west, and wanting to avoid system incompatibilities at the fringe. I just want to avoid the sound quality degradation that results. Slagle, MFA, Bespoke, et al are offering products that would work great for most people.
Lastly, a purely passive resistor ladder attenuator line stage will be a problem for most people most of the time, with clearly audible deficiencies. These types of passive attenuators are probably what give "passive" a bad name in general. It's too easy to use them in systems where they don't belong. Maybe they also give resistor attenuators in general a bad name. Yet resistor attenuators should be the first choice in most active preamps since they're the cleanest option. Just don't use goofy audiophile resistors. $0.30 metal films work great.
This probably can't be true, unless "most" have compared apples to apples Tortuga LDR vs Tortuga resistor ladder. As TomC's measurements reveal, the LDR's input cap varies non-linearly and creates THD within the audio frequency range that approaches 10% (!!) as you adjust the volume. You worry about different sound at different volume levels?!? Nothing I've ever seen can touch the LDR's ability to achieve this.
Have you heard of "The Truth" preamp? I've been playing music through and measuring one of these recently. It's using a photo cell based attenuator also. Arthur Salvatore waxes poetic about it here.
That's quite high. Can it be trimmed down? A lot of transformers are not designed for 10V.
Yes, the Kassandra also has 6v output SE or XLRs, selectable by an external switch.
Can you expand on that, why would it be so?
If a 'typical' active pre-amplifier has the pot at the input of the gain stage, then that is very different to one that has the pot at the output. I wonder how common it is to have one at the output? This would then replicate what a passive resistor ladder is doing.
Your views on what a preamp should be are your own. Definitely not mine. I can build a preamp that does none of what you claim, and is better than no preamp. I bet everyone on this site has enough experience with high end gear to understand exactly what I'm talking about. I've heard what you're saying a million times, and heard it recanted a million times after the person has experienced what a good active preamp can do for a system.
Also, your ideas about the abilities and effectiveness of a trafo or autoformer to make up for poor output stages of many sources is simply not correct. It all depends on what's downstream of the preamp. Maybe it involves multiple amps with low input impedances? In any case, the frequency of mismatchs is far higher than you may think and that cable with the buffer built in is a solid example of tons of folks getting what they consider major improvements from simply inserting a cheap buffer, and the cable parts are canare so that end of it is likely worse that what the person had before. It's not the "wild, wild west". We're talking about not simply measurements but actual, real experiences. In real life, things are often different than measurements would lead you to believe as measurements don't fully define what people hear. In real life, the end results of a source driving the system is often not ideal, and this not some far off outlier, it's very common.
The issue is, you're trying to base your beliefs on some math and measurements and think that's all there is to it. Your example of 2 opamp buffers with a VC in between is a perfect example of what's theoretically good but is likely to sound very poor in real life. It reminds me of something Toole would say. Half right but not getting the full picture. Another example is insisting metal film resistors are just fine. Have you listened to many resistors? I have. Your statement makes me believe you've never compared resistors at all and are simply looking at specs. If you truly believe that Blue Jeans has all the cable you could ever need. The specs of the LC-1 are pretty good!
I've actually built a lot this stuff and experimented with it. I've built my entire system from source to speaker driver, and not only measured but listened. I've rebuilt and modded my SET amp and preamps many times. I've experimented with most every part in them. I'm an engineer and actually understand the math and theory, but I also believe that'll only get you so far. A good system requires more than good measurements and to assume you actually know it all based on some math is a surefire way to miss a lot.
Anyways, arguing and justifying my design decisions isn't really what I had in mind and I'm gonna bow out of this conversation.
Also, your ideas about the abilities and effectiveness of a trafo or autoformer to make up for poor output stages of many sources is simply not correct. It all depends on what's downstream of the preamp. Maybe it involves multiple amps with low input impedances? In any case, the frequency of mismatchs is far higher than you may think and that cable with the buffer built in is a solid example of tons of folks getting what they consider major improvements from simply inserting a cheap buffer, and the cable parts are canare so that end of it is likely worse that what the person had before. It's not the "wild, wild west". We're talking about not simply measurements but actual, real experiences. In real life, things are often different than measurements would lead you to believe as measurements don't fully define what people hear. In real life, the end results of a source driving the system is often not ideal, and this not some far off outlier, it's very common.
The issue is, you're trying to base your beliefs on some math and measurements and think that's all there is to it. Your example of 2 opamp buffers with a VC in between is a perfect example of what's theoretically good but is likely to sound very poor in real life. It reminds me of something Toole would say. Half right but not getting the full picture. Another example is insisting metal film resistors are just fine. Have you listened to many resistors? I have. Your statement makes me believe you've never compared resistors at all and are simply looking at specs. If you truly believe that Blue Jeans has all the cable you could ever need. The specs of the LC-1 are pretty good!
I've actually built a lot this stuff and experimented with it. I've built my entire system from source to speaker driver, and not only measured but listened. I've rebuilt and modded my SET amp and preamps many times. I've experimented with most every part in them. I'm an engineer and actually understand the math and theory, but I also believe that'll only get you so far. A good system requires more than good measurements and to assume you actually know it all based on some math is a surefire way to miss a lot.
Anyways, arguing and justifying my design decisions isn't really what I had in mind and I'm gonna bow out of this conversation.
DaveC you are addressing bazelio I think?
I think you may be correct about passives. I am going to see how it goes dropping mine out of my system for the first time in 5 years. This subject seems to also align with headphone amplifiers or DAC output to headphone. I have tried a few DACs direct output to high end headphones (not my Kassandra) and it always sounds best with an amplifier. So in that case, where in 'theory' 6v on balanced should be enough it probably wasn't. Maybe enough volume, but not enough drive, something else.
So possibly a passive and it's location inline after the source is the thing that is not working here? Active pre-amps could have the pot in the circuit at the input of part way through it seems, possibly less at the output. Thus a passive is an unnatural item in the chain and may be causing havoc with impedance, current limiting and phase shift / FR shift?
That is my theory at the moment. I am not talking a huge amount, maybe lets say 10% of quality loss as a rule of thumb here. The apparent extra transparency and seemingly increase in speed maybe the typical passive attraction. I wonder if we are loosing stuff in all the other areas instead?
In a budget setup, this increase in transparency can be a free lunch, but in higher end as active pre-amps get better, probably the passive is left behind somewhat. So quite possibly passive as best in low to mid fi, not 'elevated' to high end systems. Caveat, I haven't heard the BeSpoke Audio passive.
I think you may be correct about passives. I am going to see how it goes dropping mine out of my system for the first time in 5 years. This subject seems to also align with headphone amplifiers or DAC output to headphone. I have tried a few DACs direct output to high end headphones (not my Kassandra) and it always sounds best with an amplifier. So in that case, where in 'theory' 6v on balanced should be enough it probably wasn't. Maybe enough volume, but not enough drive, something else.
So possibly a passive and it's location inline after the source is the thing that is not working here? Active pre-amps could have the pot in the circuit at the input of part way through it seems, possibly less at the output. Thus a passive is an unnatural item in the chain and may be causing havoc with impedance, current limiting and phase shift / FR shift?
That is my theory at the moment. I am not talking a huge amount, maybe lets say 10% of quality loss as a rule of thumb here. The apparent extra transparency and seemingly increase in speed maybe the typical passive attraction. I wonder if we are loosing stuff in all the other areas instead?
In a budget setup, this increase in transparency can be a free lunch, but in higher end as active pre-amps get better, probably the passive is left behind somewhat. So quite possibly passive as best in low to mid fi, not 'elevated' to high end systems. Caveat, I haven't heard the BeSpoke Audio passive.
There is a new preamp just being launched by Townshend audio which I think will be worth looking out for.
The Enigma is a two box unit with separate power supply and available in black and silver.
About £10k retail in the UK and hearing good things about it.
Details at townshendaudio.com
The Enigma is a two box unit with separate power supply and available in black and silver.
About £10k retail in the UK and hearing good things about it.
Details at townshendaudio.com
One more thing... I'm not dogmatic about it... I believe there are systems that might be best using a passive pre. It may both measure and sound better too.
astrostar, yes... addressing bazelio. Also, your experiences are common, not that it doesn't work, it just doesn't work as well... you subjectively lose something even if measurements and theory says it should work fine. Not all the time, but I've heard what you're saying a lot.
astrostar, yes... addressing bazelio. Also, your experiences are common, not that it doesn't work, it just doesn't work as well... you subjectively lose something even if measurements and theory says it should work fine. Not all the time, but I've heard what you're saying a lot.
Headphones are a very different type of load and dedicated headphone amps serve a purpose. Planars can be very current hungry, for example. Headphone loads typically range between 32R and 300R, and within the audio band can have significant (100s of ohms) variation. The headphone amp itself should be chosen based on its ability to drive the particular headphones you're using.
This is a different topic than preamps driving amps.
@DaveC , I'm trying to extract what you think active preamps add to a system (and why). Not considering cases where we're running parallel low impedance amps with weak sources in the chain, etc. I'm aware these cases exist. But I'd rather consider the many cases where a system's source is capable of driving the amplifier.
Yeah, I've played with caps, resistors, etc. I like Vishay naked foil resistors and Koa Speer metal film. I've played with all sorts and am aware they affect sound. But the boutique audiophile resistors I find add varying degrees of color and veil. Audio Note tants are pretty nice, but colored. Also absurdly priced. I like Jupiter and V-Caps, but I dislike caps in the signal path in general as none are transparent. Among the problems I have with tube buffers is that the ones I've seen have cap coupled outputs. I'm not basing everything on math and specs.
Yeah, I've played with caps, resistors, etc. I like Vishay naked foil resistors and Koa Speer metal film. I've played with all sorts and am aware they affect sound. But the boutique audiophile resistors I find add varying degrees of color and veil. Audio Note tants are pretty nice, but colored. Also absurdly priced. I like Jupiter and V-Caps, but I dislike caps in the signal path in general as none are transparent. Among the problems I have with tube buffers is that the ones I've seen have cap coupled outputs. I'm not basing everything on math and specs.
Yes I agree, I was saying it is similar in the fact it should in 'theory' have enough drive for the HP, and likewise so should most standard 2V DAC outputs for a power amplifier. But it seems there is more to this than that. The problem in a passive IMO is the fact the pot it at the output, not in the circuit or at the input of the pre-amp. In my mind this could be the issue, though I am not an engineer.
Maybe we need to have more examples of a good pre v a good passive rather than argue on the technicals, wether provable or theory. I must admit, I have read a lot of cases where an owner tried the passive route to great lengths then went back to actives. Die-hard passive users seem to be in limited numbers.
I wonder if something happens when you hit the output of a source with an inline pot, and at the highest impedance setting (low volume on the pot) the signal gets damaged? I guess that is why designs using a transformer try to get around that.
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