How long is piece of string? Same relevance as your question.
SET amp owners thread
- Thread starter bonzo75
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How long have you been self employed as Ralph’s minister of propaganda ?
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Gentlemen, please stop. We are better than this.
Tom
Tom
I would be interested to know what kind of 8 ohm load that was (8 ohm load resistor or a speaker dummy load with capacitors & coils and resistors). If it was the former, even a poorly designed amplifier can do it. The real problem with set amps is that they amplify to different levels without negative feedback and follow the impedance curve and phase response of the speaker. The poor negative feedback reduces this problem, now it's about finding the right level without it damaging the sound. If you don't want feedback, then you build an RCL element into the speaker that smooths out the impedance curve if the manufacturer hasn't already done that. The disadvantage of this solution is that you lose speaker efficiency. Then you'll hear your set amp amplifying evenly, just as the designer intended.
Exsample real world impedancedummy load of a speaker
Hi team - I have two technical questions I am hoping you can explain to me in a way that is easy for a realtively bright but electrically ignorant audophile to understand.
First is what differentiates Class A2 from Class A. I understand what Class A is and therefore why when I hear a Class A amp (or one heavily biassed to Class A) I tend to like it. But I am not sure what differentiates Class A2 from pure Class A.
Second is why would an SET power amp use an XLR input (with a transformer immediately behind it). As a follow up to that, to what extent to RCA-XLR adapters degrade things? I don't have any balanced outputs in my signal chain so I know there is nothing to be gained there by switching to a dedicated XLR cable.
First is what differentiates Class A2 from Class A. I understand what Class A is and therefore why when I hear a Class A amp (or one heavily biassed to Class A) I tend to like it. But I am not sure what differentiates Class A2 from pure Class A.
Second is why would an SET power amp use an XLR input (with a transformer immediately behind it). As a follow up to that, to what extent to RCA-XLR adapters degrade things? I don't have any balanced outputs in my signal chain so I know there is nothing to be gained there by switching to a dedicated XLR cable.
Agreed. From what I've seen this forum has definitely become more abusive over the last 18 months.
Just had a look at some recent REW sweeps and I have 0.5% distortion at 30Hz 90dB measured in room at the listening chair. That is not at the amplifier output measured into a resistor but where my ears are in the room with a microphone, which honestly is the only place that really matters. Amplifier is six channel SET monoblocks with circa 9watt output for each of the three bass channels.
Not entirely sure how that distortion number compares to systems elsewhere, but the bass here sounds textural, fully fleshed, immense, and soft as butter.
SET amps can do bass. With the right speakers.
Not entirely sure how that distortion number compares to systems elsewhere, but the bass here sounds textural, fully fleshed, immense, and soft as butter.
SET amps can do bass. With the right speakers.
Most speakers that have suitable sensitivity for SETs will also usually be relatively mild in terms of impedance and therefore frequency response errors...a very minor problem and less than most speakers base response anyway. I would never put such a network in front of my high sensitivity speaker. My Hornings work amazingly well with as little as a 3.5 watt 2A3 amp...no need for help and they are only horn in the bass (DTQWT). Same thing with my Odeons and my DIY horn speakers.
Class A2 is when the grid of the output triode is driven positive voltage. Normally it is biased negative and the driver stage drives it progressively closer to 0V. Driving it positive gives significantly more power but it also generates significantly more distortion. I would think of it more as a reserve tank for large peaks where increased distortion would be less audible.
A SET amp only needs an XLR input for compatibility to preamps/sources that have balanced outputs. If transformers are used, then you have another passive component in the chain that might degrade the sound. Unless it is true balanced it won't provide any benefit from a noise/hum reduction...
A1 means the control grid is always negative wrt the cathode. No significant grid current flows. A2 means the grid can be driven positive for some part of the duty cycle and grid current will flow while it is positive. A2 can give much more power than A1. The input impedance drops dramatically from, say, 1 meg when the grid is negative to less than 1k when it is positive. It acts like a diode.
To use A2, you need an output tube that can safely draw grid current without the grid deforming or melting and a driver circuit that can supply the grid current, usually either a direct-coupled cathode follower or an interstage transformer.
Avoid long sine/square wave measurements in A 2 mode because the maximum power loss(tube) can be reached quickly. The tube dies, and that is the spectacle you don't want see it live.
You lose some interference immunity with the adapter when transporting signals over long cables, e.g. preamp to amp. The only thing that helps is to try it out.
+1
I wanted to show a way that even speakers that are not perfectly suited for this purpose still work to enjoy music
Better bass? what tube have you used with Cary 2a3? I found many of 6sn7 variant design is lacking volume in bass. It does go deep but just lack of the punch. I got few 2a3 SET amps. One with Tango XE-20s using interstage NC-15 with 12bh7, 12ax7 input and One with Tamura F2007 output transformers using 6v6 triode strapped and 6922 input. The best result I got out of these 2a3 SETs is with JJ 2a3-40 tube. It is basically a 2.5V version of a 300B tube. What is interesting is that they sound better than the JJ 300B in a same amp I have with switchable output tube.
My Silvercore amp with interstage transformer has huge punch from a 2A3 amp. The input tube is a 6C45P, which is a darn good sounding tube.
Ooh which Silvercore amp is that? I didn't know he made one with a 2A3 output tube
It's an old one...they no longer make it. Nice design though with tube rectifier, choke filtering and all non-electrolytic caps. It is 6C45Pi tube with interstage transformer coupling to 2A3 output. All transformers and chokes are from Silvercore.
Apparently morricab can't see what is on the page at the link. The plots do not show the bandwidth of the amp at full power (which seems to be about 15-16 Watts). How it works is that as you increase the output power at low frequencies, the lack of inductance in the output transformer starts to look like a short to the power tube so output drops off. If you measure the primary winding resistance, you can see how this is so. Its usually just a few hundred Ohms, while the load impedance needed for the tube to make power is usually several thousand Ohms.
FWIW Speltz's ZERO autoformer has helped out a lot of SET owners too. The problem is that many speakers these days are 4 Ohms in the bass and 8 Ohms in the mids and highs. SETs struggle with a load like that as any zero feedback tube amp does. The ZERO is a problem solver; Steve McCormick, who makes very competent solid state amps which can drive 4 Ohms with ease, sent Paul a letter stating that while his amps do so, that isn't the same as saying they sound their best. Steve found that his amps sound better driving 4 Ohms thru the ZEROs; the lesson being that 4 Ohms isn't good for most amps if high quality reproduction is your goal.
The comments Brad makes on his own and about Otala are rubbish: the problem is that any feedback network must be carefully designed to allow the feedback to do its job with the amp properly without the load being able to mess with it (cause oscillation or the like). Clearly Mr. Otala didn't have such an amp at his disposal (and this was a problem in the 1970s and 80s- some amps would oscillate and blow up as described). Poorly designed feedback loops are a problem in audio- most of them really don't do the job. I have laid out what the problems are that have given feedback a bad name. None of them have to do with feedback itself; they have to do with execution.
Brad's comments about 'that back signal' is problematic. He is referring to 'back EMF' if I read that correctly. It most definately messes with the amp (whether OTL or SET)! The 'heat' is created in the power tubes themselves, raising their temperature. IOW they run hotter with a more diffcult load. Many people think that an output transformer isolates the tube from the load; this is only true of DC. Transformers transform impedance which is how they got their name. It goes in both directions, not one (otherwise Kirchoff's Law, a basic law of electronics like Ohm's Law, is violated, which would create a new branch of physics
). So an adverse load that might generate back EMF is messing with the power tube(s) directly. It heats them up, causes distortion and shorter life. If you don't beleive me get a thermal camera (cheap on ebay), put the amp on different loads, play it and you'll see.If anyone reading this wants a more technical explanation of what goes on with feedback, why high feedback amps of the 70s and 80s sucked and so on, read this article. FWIW, since the 1970s and 80s, technology has marched on; we use things like the web that we take for granted. Why could amps not also evolve in that time?? The idea that the problems of the 70s and 80s designs haven't seen some progress is frankly ridiculous.
There's no reason a high feedback amp has to oscillate if the feedback network (usually multiple ordered) is properly designed. A class D design can take a simpler approach though by using the feedback to actually cause the amp to oscillate- and the oscillation is then used as the switching frequency. Of course the feedback network has to be properly designed so the amp can only find one oscillation solution. The formula for that is called the 'oscillation criteria'.
Finally, the 'psychoacoustic findings' I've mentioned in the past are well known and consistent (for example that the 2nd harmonic is interpreted by the ear as 'warmth' or 'bloom'). These are the same findings that are why people like SETs. Brad seems to be shooting himself in the foot here.
Your prior statement you 'don't care' is contradicted by your continued attacks; its obvious to anyone you do care else you would not continue posting. I've found that when someone contradicts themselves in this manner, the comments are never relevent to the thread itself.
As for whether it works for me or not, I've been doing the same stuff for 47th years now, not just 30...
WRT the Internet these are the rules I use:
stick to the truth
don't take anything personally (you have no idea what sort of problems the person on the other end of an argument has)
don't make personal attacks; 'attack the post, not the person' is a principle rule on any website.
Over time people learn who you are. I started on the Internet in 1990 before the web. So yes, it works for me.
Cool! I have Christoph's 833s in my system and adore them!
It is all about the match isn't it! I agree that with the proper speakers a quality SET can produce very nice bass and a realistic soundstage too. When I think of a matching system I would also have to include the interaction of the room, which is probably the cause of poor sounding bass in many cases.
Well not yet but having seen how this can evolve I understand where you are coming from. So far the commentary has been interesting and the bias for the most part obvious.
Until it wasn't...sadly!
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