Quality passive preamp?
- Thread starter Rosewind
- Start date
YNWOAN
100% Analogue
I believe the Pass DCBI is a unity gain buffer combined with a passive volume pot, but am happy to be corrected. As such it’s not passive because there is an active stage but, it’s not like an active pre-amp either because there is no added gain. The unity gain buffer bit is supposed to act as an ‘impedance buffer’ (I believe) in the same way as transformer passives claim.
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Strictly speaking I’m not sure there is such a thing as the Pass DCB1 as I believe the DCB1 is a modification, by the DIY Audio forum, of the circuit of the Pass B1 - so not strictly a Pass design. So I think there is either the Pass B1 or the DCB1, but this is largely a semantic issue.
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Rosewind
Lost in Translation
You are right. I thought that Nelson Pass had made a version of the DCB1 himself, but he has only commented on the modification of his B1 buffer pre. There is also a DIY DCB1 Turbo version in existence.
My DIY Build of the DCB1 has a valab stepped attenuator. But the level of detail it retrieves is astonishing. It is better than the Pass B1 clone which I had in my system for a month or so. So in many ways, this is as good as I would expect music to sound.
Still, I have heard good things about Audiopax Model 5 and Tom Evans The Vibe. So ...
My DIY Build of the DCB1 has a valab stepped attenuator. But the level of detail it retrieves is astonishing. It is better than the Pass B1 clone which I had in my system for a month or so. So in many ways, this is as good as I would expect music to sound.
Still, I have heard good things about Audiopax Model 5 and Tom Evans The Vibe. So ...
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YNWOAN
100% Analogue
A friend built a B1 and I have to say it really didn’t do it for me; yes it was sweet, delicate and subtle, but I also found the produced sound to be quite bland and lacking dynamic contrast (even when accounting for gain differences). By the time my friend sold the B1 it had been ‘maxed out’ with a host of high quality components - but all that just enhanced the strong qualities of the B1 and didn’t alter my criticism.
An an aside, Avondale Audio do a unity gain stage for the Naim Nac72 pre-amp that they call the 821 board. When I tried this option I felt very much the same as I did regarding the B1 above (so not for me). Now it’s possible that what I’m preferring is colouration but if it is it’s a type of colouration/mechanism I’m not familiar with.
An an aside, Avondale Audio do a unity gain stage for the Naim Nac72 pre-amp that they call the 821 board. When I tried this option I felt very much the same as I did regarding the B1 above (so not for me). Now it’s possible that what I’m preferring is colouration but if it is it’s a type of colouration/mechanism I’m not familiar with.
I just hope you have not limited yourself to uncovering little shimmers and things in Beatles' records over all these decades as there is a wide, very wide, range of music out there, new and old. Degustibus etc. I know. I am still amazed at discovering the amazing musical talent and so often genius of Jazz, anything from the beginning of stereo to current musicians, but hey that is me and you are you. So often I read on sites such as this guys buying every known recording, pressing of always the same old same old rock groups, the same albums as though secret messages are to be found through better equipment, epiphenomena is of strictly limited interest as I age. Obsessing about tiny bits of go-to recordings to me is like what experiencing prison food over a long sentence must be like, any little variation is thrilling, I guess.
For me it's about discovering music and being amazed, confounded and at times perplexed by it, not artifacts in reproduced sound.
Recently discovered Ahmad Jamal and have been delighted by his playing.
It's a voyage of discovery of music not artifacts of sound reproduction.
A good recording is great but has to be appreciated as a whole not just bits and chunks.
I am a crazy difficult old man so don't mind me.
Rosewind
Lost in Translation
Thanks. That makes sense. I am all for musicality over micro details. So I have no axe to grind there. I also love discovering new music by artists that I wish I had known about decades ago. I just get enthusiastic when new details are present without detracting from enjoyment.
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Guest432
Guest
I had a Khozmo stepped attenuator pre while the M3 was being serviced and while it was good at higher volumes it was rubbish at low volume.
When I put the M3 back in I remembered how good an active pre really is, it blew the passive away completely.
Personally now I have no interest in trying any passive preamps.
Arkless Electronics
Trade: Amp design and repairs.
Personally I have zero interest in active pres! Passives win in every way including dynamics.
eastone
pfm Member
This can't surely be an absolute, Jez? My power amp requires an input of 3V for full power. Its input impedance is set to 'expect' the signal from a valve preamp. It certainly sounds good enough when used with a passive but with my active preamp is on a different level entirely.
Arkless Electronics
Trade: Amp design and repairs.
No distortion, no excess noise (that's a technical definition), no limit on dynamics (they can't clip or compress).
Some power amps require an unusually high input level so an active pre will be needed.
Some power amps (solid state usually) have unusual input characteristics (I'll spare you the technical details) which means they will only give their best performance when driven by a very low impedance source but that's not the pre 's fault.
Usually when people prefer an active I reckon it's a case of them choosing a very coloured active pre because they simply like the colouration and inaccuracy!
Having said all that I will point out that an active pre is by far the simplest and easiest part of a system to design and build and it's also dead easy to get "near as damn it perfect" performance out of one to the extent that you would not expect it to have any audible sound signature.
How easy? Take a dual op amp and 2-3 resistors per channel and you're there! You just need a power supply (which doesn't need to be anything special) and of course a pot or switched attenuator... That simple to make an active pre with (depending on op amp used) 0.001% THD, DC - >100KHz frequency response and very low noise.
Edit: And if you just want a buffer you can do it without the resistors! A dual op amp and a pot... that's it.... oh well you need a power supply of course
mandryka
pfm Member
This colour that the active preamp gives to the sound, it could be something that the amp designers have planned for, something that was part of their total conception. I’m thinking of the Radford STA and SC22, for example. Or indeed the pre component of any well designed integrated amp.
The pre/power combination could be part of the “magic” that the amp designers are trying to create.
I wonder how the Musical Fidelity Nu Vista 300 would sound without its pre.
The pre/power combination could be part of the “magic” that the amp designers are trying to create.
I wonder how the Musical Fidelity Nu Vista 300 would sound without its pre.
Arkless Electronics
Trade: Amp design and repairs.
No definitely not.
No idea about Nu-Vista 300 as I used it with a passive. A pot in a box to be precise. It sounded amazing!
Arkless Electronics
Trade: Amp design and repairs.
It's a two box power amp, transformers and some housekeeping circuitry is in one box and power amp itself in the other.
What it does have is a valve stage ahead of the main power amps. This is the bit with the Nuvistor valves in it (that's the correct spelling of the valve type, made by RCA) and probably a buffer.
Mr Underhill
pfm Member
I am using a Townshend Allegri which I have used in combination with an EAR534 and a CB250 and currently with an Avondaled CB250, it is SUPERB. No lack of detail or dynamics.
