Passive Preamps

steve williams

steve williams

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I remember several years ago when passive preamps such as Placette were all the rage whereas now I just don't seem to hear people talking about them

I seem to remember that Mike Lavigne had a Placette that he raved about.

I also remember the issue that if a passive preamp is used it needs short interconnects in the system.

Anyone here using a passive preamp and what are your thoughts
 
Was lent one of these:

http://www.mfaudio.co.uk/classic.htm

Transparent as might be expected, but doesn't seem to drive my ARC 210 amps. Have a Bel Canto DAC3 at the moment too -- it works as an active preamp as well as a DAC and mates much better to the ARCs.
 
apparently the Steve McCormack passive preamp is VERY good. i know someone who has replaced some very high end preamps with it. problem is it was like 7k when it came out and now is 14k. ridiculous.
 
and maybe not passive---but i have considered buying a Berkeley Audio DAC and running it direct into my Shindo amplifier. although, i do really enjoy my Bryston dac.

my favorite system i had back in the day was a Wadia direct into tube amp---Steve, similar to your Krell KPS direct.
 
KeithR said:
and maybe not passive---but i have considered buying a Berkeley Audio DAC and running it direct into my Shindo amplifier. although, i do really enjoy my Bryston dac.

my favorite system i had back in the day was a Wadia direct into tube amp---Steve, similar to your Krell KPS direct.
Click to expand...


I remember it well
 
The Lightspeed Attenuator sold by an australian guy has received a lot of applause lately.
http://members.optusnet.com.au/~georgehifi/
The cost is $470 which includes international shipping.

Part of the challenge with a passive pre is the impedance match. From what I understand, if this is not matched properly the sound will lack dynamics and sound lean. Another challenge is of course the fact that the sound becomes more transparent and faults in the system will then be more revealed. This may be the reason why people actually prefer some distortion.
 
I had my passive preamp time some years back, I tried a lot ranking from the very good and inexpensive Axiom to the best I had (a First Sound) modified by Emmanuel himself.

At the end I always had some lack of dynamics and punch compared with having an active preamp, I ran at least three power amps (CJ Premier 8A, Pass Labs X 250 and Audio Note P4s).

Now I am back to integrateds where I belong :)
 
I've got a Slagle Autoformer in my system now while I await my new Experience Music Line stage. It's pretty good!
 
Sources are designed for active pre-amps. Most if not all lack the drive to handle the load that these pre-amps put on them. The dynamics suffer the most and distortion increases.

One thought might be to use sources with balanced outs. Those have much higher drive given the larger voltage swings that balanced interconnect brings.
 
Amir,

Some newer sources are now tuned to drive power amps direct (at least they claim). In your view would a source with output voltage around 3-5v, 100-600hom, present a problem with modern amps?

Thanks!
 
3-5 Volts should be good as that is nearly double the drive out of a mass market source.

That said, I think the way to know for sure is to test it with a normal pre-amp and compare the bass. Any old pre-amp should do as you are not checking for fidelity per-se but rather, whether there is an impact to dynamics/low frequencies.

Another would be to see a chart of distortion vs level. See this measurement example:

Dacscompared2.jpg


Clearly the device on the left will do better than the one on the right.
 
Amir,
Thanks.
Is it that right the lower freq suffered from impedance miss match?
Do you have a rule of thumb? I've seen many, don't know which one to use.
 
There is some general confusion regarding impedance match. In audio world, you do not want to strive for matching impedance. But rather you always want the input of a circuit to have high impedance and its output, low. That gives the device most flexibility to match others before or after it. This is also why active pre-amps have such an advantage. They provide a much higher input impedance relative to their output and in that sense, almost remove the load presented from the source.

Matching impedance is important in high frequency areas where we worry about reflections and such.

So it is not a mis-match that is causing an issue here but loading down the output of the source. If there is not enough drive, the dynamics suffer the most as that is when you need maximum power transfer.
 
Bjorn said:
The Lightspeed Attenuator sold by an australian guy has received a lot of applause lately.
http://members.optusnet.com.au/~georgehifi/
The cost is $470 which includes international shipping.

Part of the challenge with a passive pre is the impedance match. From what I understand, if this is not matched properly the sound will lack dynamics and sound lean. Another challenge is of course the fact that the sound becomes more transparent and faults in the system will then be more revealed. This may be the reason why people actually prefer some distortion.
Click to expand...

I agree with this! The presentation is very transparent. Btw, i'm using a 5mtr interconnect with no sign of signal loss.
 
Tjaderman said:
I agree with this! The presentation is very transparent. Btw, i'm using a 5mtr interconnect with no sign of signal loss.
Click to expand...

I too find the transparency addictive. You can hear it from the first few notes and no need to convince yourself about it.

However, in my system I experienced first hand the mismatch, perhaps it's the impedance. My Tranquility DAC has output Z of 600ohm (mid-high) and my class D amp has input Z of 22kOhm (low), while the Lightspeed in/out Z varies greatly with volume levels.
- The frequency extremes, especially 50hz down, are rolled off
- Dynamic becomes very flat at lower listening levels.

Another problem I have is a very distinct distorted ringing with high piano note transients echoes. I am not sure whether it is from the DAC or the Lightspeed, or the Class D amp.
If I change the DAC, it's no longer there. If I keep the DAC but substitute the Lightspeed with an active preamp (EAR834L and Pass X2.5), it's gone. I am at a puzzle but may be it's the interplay of both. Have not tried swapping the amp though.

I just ordered a TVC passive from StereoKnight and will see whether it deals with matching components better in this system or not.
 
Seta said:
I too find the transparency addictive. You can hear it from the first few notes and no need to convince yourself about it.

However, in my system I experienced first hand the mismatch, perhaps it's the impedance. My Tranquility DAC has output Z of 600ohm (mid-high) and my class D amp has input Z of 22kOhm (low), while the Lightspeed in/out Z varies greatly with volume levels.
- The frequency extremes, especially 50hz down, are rolled off
- Dynamic becomes very flat at lower listening levels.

Another problem I have is a very distinct distorted ringing with high piano note transients echoes. I am not sure whether it is from the DAC or the Lightspeed, or the Class D amp.
If I change the DAC, it's no longer there. If I keep the DAC but substitute the Lightspeed with an active preamp (EAR834L and Pass X2.5), it's gone. I am at a puzzle but may be it's the interplay of both. Have not tried swapping the amp though.

I just ordered a TVC passive from StereoKnight and will see whether it deals with matching components better in this system or not.
Click to expand...
An input impedance of 22k is too low. You need an amp with 50k or higher to use with the Lightspeed attenuator. If you like class D, you can try Hypex which has 100k.
http://www.hexateq.com/products.html
The DAC/CD player should have lower then 200k.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html
 
Bjorn said:
An input impedance of 22k is too low. You need an amp with 50k or higher to use with the Lightspeed attenuator. If you like class D, you can try Hypex which has 100k.
http://www.hexateq.com/products.html
The DAC/CD player should have lower then 200k.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html
Click to expand...

Understood.

There's another LDR-based preamp but with JFET buffers (in/out) from Serbia called "The Myth". Anyone had come across this before?
 
An input impedance of 22k is too low. You need an amp with 50k or higher to use with the Lightspeed attenuator. If you like class D, you can try Hypex which has 100k.
Click to expand...

Is this applicable also with chip amp?

Currently using a gainclone with an input imp of 22k paired with Lightspeed Passive attenuator. Extentions and decay on the extreme frequencies are unbelievable but on a very realistic presentation. Mids are to die for.:cool:
 
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