Differences in passive preamps?

[Tony L]

@Tony L did build those TKD pots into a sandwich box I think. Why did you change them, Tony? Was there any difference?

I built that one for a specific task rather than buy yet another Audio Synthesis (which are not especially cheap or common second hand). At the time I was playing about with a pair of Decca Kelly horns as “supertweeters” on my Tannoys and was powering them from a second 303, I built the Tupperware passive as a level control for them. It is very, very good, but the AS stepped attenuators are better (at many multiples of the price).

 

[SONDEKNZ]

Is there more than one Tisbury? Here's a quote from an article relating to it:

When asked about the input and output impedance of the Mini Passive II, Young clarified that, though the 10 kΩ input impedance remains constant, “…output impedance varies from 0 to 2.5 kΩ depending on volume position” or knob setting.

That is what an ordinary 10k (resistive) pot would do, without any "impedance matching tricks".

Perhaps you are right.

Our TISBURY has always performed so well, that I assumed there is more to it.

I confess that I've never taken it apart to check.
(Not like me really... )

 

[mandryka]

Is this true? No passive pre-amp could ever be truer than a direct connection from source to power amp, and digital volume control/balance. Let's assume satisfactory impedance matching.

 

[richards13]

Is this true? No passive pre-amp could ever be truer than a direct connection from source to power amp, and digital volume control/balance. Let's assume satisfactory impedance matching.

Transformers provide isolation of ground related noise, making some source components sounding better than a direct connection. My speculation after getting a MFA preamp. Which made both my phonostage and digital source sound better and with less hash.

 

[Jim Audiomisc]

I’ve used both 10k and 20k pots and pres with 606s with no problem. They work great with a passive.

The context should be the 'externals' like the cable capacitance, etc.

 

[Eoin]

I use a Nordost cable for no other reason than it was cheap on eBay, I’d need to check its capacitance

 

[the caretaker]

I tried a Tisbury to get a feel for passives and it is good for the money. The Khozmo was a step up to these ears (both with a Leak ST20). I use a dual mono Khozmo but have a stereo spare if you'd like to borrow it.

Think the khozmo would be a good choice..Alex knows a lot of stuff, I would go with his recommendation..

 

[beammeup]

Is this true? No passive pre-amp could ever be truer than a direct connection from source to power amp, and digital volume control/balance. Let's assume satisfactory impedance matching.

That’s an interesting question - perhaps if you are playing 16bit CD quality music then a digital volume control direct should be better - all things being equal with good impedance matching.

Interesting that it’s possibly the transformer in the MFA stopping the ground noise in the system which is of benefit.

 

[vacuum_tubes]

I thought that digital volume control was pretty much always better than analogue and the whole "digital volume reduces quality/resolution" was a red herring.

 

[Alex S]

As far as I understand it, digital works just fine but does not attenuate noise so you could run into a problem at very low volume. Active preamps can have channel balance issues at very low volume.

Some say a passive lacks dynamics and I know what they mean with one of my amps. Definitely does not apply with the Leak.

 

[SONDEKNZ]

@foxwelljsly

As you will know, the rather fabulous little LEAK Stereo 20 has absolutely loads of gain.

My own experiments with it - many moons ago - with my 12dB (low) gain tubed preamp were unsuccessful, due to noise from this excess of gain.

On that basis, you might be well served by an active, tubed, preamp which offers variable gain - down to zero gain (unity gain), if necessary. As others have attested, the variation of gain allows you to dial-in slightly different tonal balances. Season to taste, so to speak.

Here is such a machine... (I've heard very good things...)

I have built these TRANSCENDENT designs previously and they are extremely fast, transparent and neutral. Definitely NO syrupy "classic tube" sound with the TRANSCENDENT stuff...

Variable Gain Tubed Preamp

Just a thought...

 

[Alex S]

Nice idea but it’s a kit that without valves costs more than a good passive (apart from Townshend and TVC). I really think a passive is all the Leak needs since it doesn’t need variable gain, it needs none. If you have several amps variable gain could be useful.

Going back to digital attenuation, when I got the Topping Pro Sabre I was down at -40dB late night so I got the Pre90. I probably didn’t need to but It’s certainly not worse.

 

[SONDEKNZ]

Nice idea but it’s a kit that without valves costs more than a good passive (apart from Townshend and TVA). I really think a passive is all the Leak needs since it doesn’t need variable gain, it needs none.

If you have several amps variable gain could be useful. Actually, I have several amps but also several preamps.

Going back to digital attenuation, when I got the Topping Pro Sabre I was down at -40dB late night so I got the Pre90. It’s certainly not worse.

Revealing my firm tubed persuasion...

 

[Woodface]

I tend to use the digital volume on my Innuos to even out recordings, some are very, very loud. I can get finer degrees on the digital side. Useless for vinyl obviously.

 

[mandryka]

That’s an interesting question - perhaps if you are playing 16bit CD quality music then a digital volume control direct should be better - all things being equal with good impedance matching.

Interesting that it’s possibly the transformer in the MFA stopping the ground noise in the system which is of benefit.

I shouldn't have said "better".

The point I really wanted to make is that if a passive preamp can't be more truthful to the source than no preamp at all, then you have a benchmark by which to assess one aspect of the sound quality of passive preamps. First find out what it's like with the source direct into the power amp and digital volume control. Then listen to some passive amplifiers.

But on reflection, this would have been glib. The power amp's distortions may be compensated by the preamp's distortions! It was a silly point, it goes nowhere interesting.

 

[les24preludes]

Shunt volume controls can sound good. Put one ultra high end resistor e.g. around 8K in the series position and use a decent 10K pot for the shunt. This wouldn't sound as good as no series resistor when a traditional stepped attenuator is on maximum, but it might sound as good when the series resistance is 8K or more. That would be more typical in normal use.

Always remember that the passive is in parallel with the input resistor to ground in the amp when you figure out values. A 10K pot into 100K would be 9K.

 

[Avon]

What’s the considerations with my 606. Input impedance is 20k.?

I’ve just built a passive preamp using a TKD 2CP-601 10k potentiometer. It’s feeding an Avondale NCC220, which has an input impedance of about 19k. Cable is a standard 1.25m 4-pin Naim black SNAIC. In comparison with my NAC72 active preamp, its frequency response extends slightly higher, meaning it’s not an issue. That’s with the pot at its mid-point, where the output impedance is highest (5k). Input is a Rega DAC.

So it’s worth trying, just to get an alternative presentation.

 

[NeilK]

I'm quite a fan of passive pre amps.
I've used many from a 'pot in a box' to my current MFA. The standouts (at different price points) were a little Tisbury (only -ve was its small size and light weight meaning heavy or chunky cables could be awkward), a lovely Khosmo 'dual mono' with z-foils and silver wiring but the real stand out has been the Music First Classic -transformer based so no problems with impedence matching or longer runs of interconnect. I can't see me replacing this any time soon!

 

[matt j]

I generally find them a bit hit and miss, the Allegri was a stand out though, fantastic bit of kit.

 

[Fourlegs]

I'm quite a fan of passive pre amps.
I've used many from a 'pot in a box' to my current MFA. The standouts (at different price points) were a little Tisbury (only -ve was its small size and light weight meaning heavy or chunky cables could be awkward), a lovely Khosmo 'dual mono' with z-foils and silver wiring but the real stand out has been the Music First Classic -transformer based so no problems with impedence matching or longer runs of interconnect. I can't see me replacing this any time soon!

Agreed with you about the Music First transformer based passives. I worked my way up their range until finally I got the Baby Ref V2 which rather put the rest of the range into perspective. My only advice would be to buy the best in the range that one can afford - it is worth it in terms of sound quality.