Passive, buffered or valve preamp

[Hummer]

What thoughts or preferences do you have regarding preamp design. I have used everything from completely passive solid state to tube. Which topology do you think works best.
1. Passive
2. Passive with solid state buffer or tube buffer.
3. Tube.

I think I know the pros and cons for each and my preference is Tube which I know adds a richness and slightly holographic quality to the sound stage but maybe not as accurate to the source material. I have tried passive but although it is revealing and probably more precise,its rendition of the recording is too thin and neutral for my liking. Maybe a Buffered passive is the way to go in order to get a good compromise? What are your thoughts?

 

[garn63]

It's entirely down to what kind of signal you like to listen to ? I like a passive Pre but am happy with a valve that's implemented in the choke psu of my Dac. You might like a valve used in the output of a Dac ? Have a play & try to dem/borrow stuff. Choose what you like

 

[uzzy]

It matters not to me what the topology of a preamp is, be it passive or active, be it valves, hubrid of valves and SS, or SS.
The answer as with any aural reproduction is to get your ears around the gear and compare and buy what they like the best.
This is a discussion that will go round in circles as there is our thoughts will have no influence on the actual sounds and so many have preconcieved ideas that one topoloy sounds better than another.
The best preamp I ever heard was a Paragon Valve preamp .. the best sounding preamp I could afford (and I preferred to just about every other preamp available in the 70s was an Audionics B2. (which was solid state). One of the worst preamps I tried was a Beard giant of a thing (valves).
Just get out there and get your ears around stuff to determine what they like

 

[rabski]

Depends more than anything on the power amplifier it's feeding. Do you need gain? Do you need a specific change of impedance to match properly?

The one I would avoid personally is any buffer. A 'true' buffer is simply an impedance matching device, but get the system matching correct in the first place and it's unnecessary, not to mention that it's putting more components directly in the signal path. A lot of the things that are advertised as 'buffers' are more like effects boxes, usually running a grotty double triode valve at well outside it's correct operating point with the aim of adding non-linearity and some harmonic distortion.

Every passive preamp has it's own potential problems with impedance matching and component quality as well, though they can be excellent. But then so can some valve and solid-state active gain stages.

There is no universal right and wrong.

 

[hifinutt]

As you hummer i have had a LOT of pre amps . some better at holographics than others . totally depends on synergy . just now using a BC dac pre which has good holographics . so much choice as rabski says . at one point i had the tube based arc ref 5 and music first baby ref v1 . both had stunning dynamics and fab holographics . not a huge amount in it and the mfa was half the price of the arc

 

[Hummer]

I like a bit of gain from a preamp and to be honest I like the coloured distortion valves give to music. I have heard flat accurate sounding passive preamps and they leave me cold but with a bit of gain they can sound OK. Of course as a number of you have mentioned everything is both system dependent and personal and I agree there is no right of wrong, just a preference for how you like you music to sound.

 

[Norfolkman51]

My experience - I tried various passive preamps into my EAR899 (now superseded with an 861) including a Prometheus, Slagle and Townsend Allegri. Unfortunately none offered the dynamics and tonality of an EAR 864 that I borrowed. I now use a Nelson Pass designed DIY Korg B1 that sandwiches a modern low voltage triode between two jfet buffers. I'm very pleased with it, and even more so having replaced the original twin mono volume controls with a Khozmo ladder type stepped attenuator. I've been lucky in being able to try out the various alternatives curtesy of friends in my local group. My preference is definitely for active preamps with my power amp, but of course this is not to say that others wouldn't prefer passive.

 

[pmcuk]

As Rabski says, start with the amplifier and work backwards. In terms of a valve preamp....
- If you have a valve amplifier or solid state amp with an input impedance of 100K, then your preamp could have an output impedance of say around 7K or 8K. That would typically be something like a 6SN7 at around 7.5K, or also nice would be a 2P29L DHT at 3K. This would not need a buffer. So you save on one added stage.
- if you have a solid state amp with input impedance of 10K you want a low output impedance preamp around 1K. This could be a 2a3 or 6B4G/6C4C without a buffer. I've built one and it sounds very nice to me.
- if you have a solid state amp with input impedance of 10K as above and want to use something like a 6SN7 or a DHT like a 26 you will need a buffer, typically a cathode follower, or a step-down transformer.

You might start with an amplifier with 100K input impedance and then want to switch to one with 10K input impedance, in which case you would need to revise your preamp.

One important factor is to choose the best sounding valve for your preamp. Preferably not a 12au7 and certainly nothing like a 12ax7 or 12at7. Much better options can be used. A 6SN7 is pretty much the minimum quality you would want, and even then there is better, not only DHTs but some more obscure indirectly heated valves. You get a lot of 12a*7 valves in commercial equipment because of the prevalent concept that you can find replacements in places like Timbuktu and Perpète-lès-Oies, but with plenty of valves available on auction sites this is a bit lame.

 

[Lawrence001]

As Rabski says, start with the amplifier and work backwards. In terms of a valve preamp....
- If you have a valve amplifier or solid state amp with an input impedance of 100K, then your preamp could have an output impedance of say around 7K or 8K. That would typically be something like a 6SN7 at around 7.5K, or also nice would be a 2P29L DHT at 3K. This would not need a buffer. So you save on one added stage.
- if you have a solid state amp with input impedance of 10K you want a low output impedance preamp around 1K. This could be a 2a3 or 6B4G/6C4C without a buffer. I've built one and it sounds very nice to me.
- if you have a solid state amp with input impedance of 10K as above and want to use something like a 6SN7 or a DHT like a 26 you will need a buffer, typically a cathode follower, or a step-down transformer.

You might start with an amplifier with 100K input impedance and then want to switch to one with 10K input impedance, in which case you would need to revise your preamp.

One important factor is to choose the best sounding valve for your preamp. Preferably not a 12au7 and certainly nothing like a 12ax7 or 12at7. Much better options can be used. A 6SN7 is pretty much the minimum quality you would want, and even then there is better, not only DHTs but some more obscure indirectly heated valves. You get a lot of 12a*7 valves in commercial equipment because of the prevalent concept that you can find replacements in places like Timbuktu and Perpète-lès-Oies, but with plenty of valves available on auction sites this is a bit lame.

Do I take it you have little time for Croft Micro preamps then?

 

[pmcuk]

Do I take it you have little time for Croft Micro preamps then?

I believe the Croft preamps use 12ax7? This is a perfectly good valve for a phono stage but I don't know why you would use it in a line stage. I haven't heard the preamp you mention so clearly I can't say if I would like the sound or not.

 

[karlsushi]

I use an LDR passive with a valve buffer (a clone Musical Fidelity X-10D). I tried a variety of passives on their own for a bit and enjoyed the transparency, but ultimately I was left cold and fatigued by them. The buffer (placed after the passive) has been a revelation and I now use one in each of my two systems.

Whilst I don't have the experience with preamps as many here on the Wam, I haven't heard a better preamp than the ones I use.

To my ears it's the perfect combination of transparency, but with the body and dynamic authority that a passive on its own never seemed to provide.

If you need some gain, then it isn't going to be the right pre, but otherwise, it feels like the perfect pre. Too many preamps over-complicate matters if you ask me. All you really need is a volume control and an input selector which does lend itself to the passive idea, but it does seem that the buffer has been essential for me in my systems, presumably as a result of impedance matching.

 

[dave]

The buffer (placed after the passive) has been a revelation and I now use one in each of my two systems.

I think this is a valid way of doing things, no mater how many boxes are used. I use a valve preamp, but it is a pot and a valve buffer in one box and I like it very much. I feel the important quality is the way the cable is driven and that can be a make or brake. Passive pres and some solid state are at a disadvantage here IMO.

 

[rabski]

Croft preamps seems to come in so many flavours that it's hard to generalise. The only one I've looked at in detail (a minor repair) used a 12AX7 for the phono section and a 12AU7 for the linestage. That sounded very decent actually, but young Mr Croft is careful and clever with layout and (crucially) power supplies.

WRT one comment above, it's my favourite (not) suggestion, that valves give coloured distortion. They certainly can, but then so can solid state. All you need to do is design things to sound crap, and as if by magic, they will. A great many properly designed valve preamps have a near ruler flat frequency response and distortion massively below the limits of being audible. They also tend to be more linear and have faster response than solid state.

A buffer (properly designed) can do this, but I stand by my earlier suggestion. It can work fine, but a passive preamp with a good valve buffer stage is basically a decent valve preamp with the disadvantages of more boxes, more connectors and more interconnects.

 

[THOMO]

Hummer from your description a Supratek valve preamp [6SN7 or DHT] will give you the sort of sound you are after.I use one of each in different systems.Very room filling 3D sound but not obviously valvey sounding-just very clear and open.Other preamps lack depth and vibrancy by comparison-even far more expensive ones I have compared.

 

[Hummer]

Hummer from your description a Supratek valve preamp [6SN7 or DHT] will give you the sort of sound you are after.I use one of each in different systems.Very room filling 3D sound but not obviously valvey sounding-just very clear and open.Other preamps lack depth and vibrancy by comparison-even far more expensive ones I have compared.

Thanks for the suggestion THOMO but I actually use a Croft 25R modified preamp which fits the bill perfectly. It is all valve with valve regulation and and valve phono stage using mainly ECC83s but the line stage is 12BH7a. It sounds so open and very transparent which gives incredible insight into recordings, they almost sound live with plenty of guts and tremendous resolution.

 

[bencat]

Why have a pre ? My favourite is a direct digital connection then control the volume from the digital device . Sounds good to me but no doubt others will mention things like digital volume reducing bits etc . This was the system used in the early days of digital but all the devices I have currently do not use this method so digital volume control (if you only use digital sources which I do ) is the best .

 

[karlsushi]

Don't you just love this hobby. No sooner than I wrote my response to this thread about my perception that an LDR passive plus buffer being the best thing since sliced bread, a few days loan from the very generous @Fourlegs of a Chord DAVE and that theory is well and truly put to bed.

I've carried out a few tests using the DAVE straight into a power amp (using the DAVE's internal volume control) Vs using it with a buffer after and then also using it with fixed line output and using my LDR passive as a pre.

Don't get me wrong, the LDR is very transparent, but absolutely no question, the LDR and buffer are adding something.

So I would hereby like to amend my earlier response to "without doubt, the best solution is to use a DAC with its own internal volume without a preamp". Especially if that DAC is a Chord DAVE. Wow.

Obviously a different situation for vinyl, but no doubt this is the best solution I have ever heard for digital. Phenomenal.

 

[pmcuk]

Hummer from your description a Supratek valve preamp [6SN7 or DHT] will give you the sort of sound you are after. I use one of each in different systems. Very room filling 3D sound but not obviously valvey sounding-just very clear and open. Other preamps lack depth and vibrancy by comparison-even far more expensive ones I have compared.

I'm using a 6SN7 stage to drive my 2a3 output tubes, and it's everything you say - very clear and open with depth and vibrancy. This 6SN7 stage is exactly the same circuit as a 6SN7 line stage I use for other purposes. I've used a lot of DHTs but I have to say that in this case I don't really miss them too much. The 6SN7 can sound very good indeed.

 

[Lawrence001]

I believe the Croft preamps use 12ax7? This is a perfectly good valve for a phono stage but I don't know why you would use it in a line stage. I haven't heard the preamp you mention so clearly I can't say if I would like the sound or not.

That's a good point, I haven't owned one for years but the ECC83s may have been in the phono stage rather than the line stage.

 

[Hummer]

That's a good point, I haven't owned one for years but the ECC83s may have been in the phono stage rather than the line stage.

Yes the ECC83 is used in the phono stage but also in the line stage in some of the Croft 25 preamps.