Balanced pre amps..

[Non-Smoking Man]

I'm interested in balanced pre amps, both active and passive, solid state and valve.

Having said that the interest in passives in this thread will be limited to TVCs - i think they have won the battle over regular passives on grounds of better impedance matching.

There are plenty of balanced active solid state pre amps around (e.g., my Ayre K-5xeMP) and some active valve pres (e.g., Audio Research) and a number of TVCs such as those from Audiozone, Audio Music, Music First Audio, and the Django, that incorporate balanced circuitry.

What the market is sorely lacking is a balanced VALVE pre amp. I know B.A.T (Balanced Audio Technologies U.S.A.) do one and a local Wammer Ian possesses one, though I haven't heard it. In a recent conversation with a leading Wammer and DIY amp builder, it was explained to me that the difficulties in matching the output and transconductance of the valves mitigates against this type of design, not to mention the extra expense of having 2 of everything, increasing component cost.

Ive been discussing this type of component with Jessica_k for some time - Jess's RCA connected PRE 1 has been well received on the bake off circuit and I have been badgering her to come up with a balanced version of the valve pre amp design.

It appears from various discussions that a key feature of balanced pre amps is the volume control. For a fully balanced pre you need a 4 gang stepped attenuator - and a good one that can match all 4 parts of the thing for a phase correct performance. Alps, Goldpoint and Elma do them and you can buy them in a basic form and solder the many film resistors yourself at a pinch. I recently heard such a (SS) pre using an op amp board and a 4 gang attenuater comprising 0.1% film resistors (where 0.5 % are more common off the shelf). Jessica is interestingly working on a similar pre but this one will be valved, arguing that ss components also go off spec (though more slowly) too and that valves can be swapped out relatively cheaply (6sn7 and 6sl7s presumably)to preserve accurate matching

I have at my place doing a spell in the horn system (where such a pre is destined) a kind of halfway-house' one-off built specially for a customer by Juancho, of this parish. Its a Satchmo based design and uses a pair of 6SL7s, one for each channel, that gets round the purist balanced 4 gang control, by using a pair of Cinemag transformers at each end - the first set unbalances the incoming signal, sends it through the SE 'guts' as Dave puts it in a pm, and the second set rebalances the signal to be sent on. It sounds pretty good.

So, there are a number of ways to skin this cat and I seem to be accumulating a few different examples (you know how it goes..). Enough for a group test at some point..?

So what do I want from you guys?

We like theory, so any theoretical discussion of the merits and demerits of different approaches is welcome;
Second, if you are using a balanced pre in your system we would like to know about it; and, even better,
Third, would it be possible to add your precious example to the Group Test (to be held at mine, at some point in the future, in the 5 way horn system).

Jack NSM

Suggested reading: TNT - Audio review of the Audio Music TVC on the internet.
Hifi Pig Baby Reference MFA V2 review

 

[wizmax]

Audio Research Ref 3 of any interest Jack?

 

[Non-Smoking Man]

That'll do nicely, Robin...

jack NSM

 

[Juancho]

I don't have much to contribute to this thread I'm afraid Jack. There's few balanced valve amps around so I've never had the demand to build one apart from the hybrid you now own, which went between solid state amplification. Why do you need a balanced pre in your set up exactly?

I can't cite any references but arguments go both ways and advantages for domestic use seem few or non existent when weighed against the added complexity.
David

 

[Ian b]

Hi jack
I’d be happy to bring along my B.A.T. Vk5i pre to the balanced pre bake-off if the date works in with my shift patterns for work
Ian

 

[Non-Smoking Man]

I don't have much to contribute to this thread I'm afraid Jack. There's few balanced valve amps around so I've never had the demand to build one apart from the hybrid you now own, which went between solid state amplification. Why do you need a balanced pre in your set up exactly?

I can't cite any references but arguments go both ways and advantages for domestic use seem few or non existent when weighed against the added complexity.
David

Because the 5 way active horn system uses XLR only Ashly analogue crossovers, and with such a complex system with 14 plug in items there is a plethora of cables in behind - this adds up to a compelling case for a totally balanced system, first to avoid hum loops, and, second, to achieve common mode noise rejection. (And, third, controvertially, a plausible increase in SQ.)

See my thread 'A Fiveway Horn System' in 2 channel.

Jack

P.s. your balanced Satchmo is, indeed, between 2 solid state components - an Ayre P-5xe and an Ashly XR4001 XO.

 

[Jazid]

I also have little to add but will waffle on anyway.

The Vacuum State RTP3 is a fully balanced differential valve circuit, and when I heard it the system it was in sounded excellent. However, it requires eight tightly matched ECC88s, this one had eight curve tracer matched NOS Telefunken CCa tubes. Plainly this was not a cheap option, and will not get cheaper in future. It feels like balanced valve preamps in home audio are a solution looking for a problem.

But, since for you there is value in the less trouble prone connectability of balanced connectors, it is a simple thing to make transformer balancer/unbalancer boxes, and use a SE preamp or whatever into that, with balanced cables out. I recall studio shops having these things for small change, and if better were required a good trafo could be wound up to impedance match whatever you are going from and to with it?

 

[pmcuk]

Read Morgan Jones "Valve Amps" on volume controls for balanced systems. I don't have my copy handy, but if I recollect he just puts a variable resistance between the 2 legs. That's not a "4 gang" control.

I'd never think of using a balanced system using tubes - far too much work and real estate. Solid state maybe. But for a simple domestic system I frankly don't see the point when unbalanced systems, especially SE amps, work perfectly well. Sure - you could use loads of transformers for the inter-connections but good ones are costly and they all degrade the sound to some extent. Seems to me more an intellectual exercise than a necessity.

I suppose you could make a case for a zero hum system when using extremely high sensitivity horns or very long cable runs, but again that's unusual in a domestic system.

 

[Non-Smoking Man]

Response to PMCuk:

Thankyou for posting..
I quite agree with this - "I don't see the point..of balanced systems..for a simple domestic system".
But as I have explained the 5 way horn system is neither 'simple' nor 'domestic'. If you read my posts on the horn system you will find that it is a dual-purpose system, designed for both pro audio and domestic situations (there are larger lounges in this world than either you or I inhabit sir!).
And, nor is just an 'intellectual exercise' (though it is partly that hehe..).

Talking of degrading sound...have you heard this system? Its very good indeed even in a tight space.
The point of this exercise is precisely to test out what you, me and others presume or suppose, or theorise to be the case.
Hence my assembly of the various options. Lets see, or hear, them in action. And anyone bringing their component along can hear what the horns can do (or can't do) compared with what they have at home.

We shall see..
And I intend to own an example of the most affordable winner because it will advance the system.

Jack NSM

 

[pmcuk]

Thanks for the reply, Jack. I read with envy the bit about "larger lounges than you or I inhabit" as I sit in my 4.5 by 3.5 metre listening room......

I reckoned it was partly an intellectual exercise, but isn't that exactly what we do when we try and create something different and interesting? A 5 way horn system is somewhere between amazing and bonkers, but I've been guilty of some bonkers systems in the past like stacked quads in a 3.5 by 4.5 metre room, such that I couldn't see out of the window let alone walk about the floor.

Yes - I can see a reason for a balanced system the way you put it, especially for a much larger listening space. Standard studio practice. But the idea of 5 valve amps all with double the contents to make them balanced just makes my head hurt. I'm down to 4 signal tubes these days - 2x 2a3 and 2x 10Y with a 1:4 input transformer. But since I have my bonkers side too, the power supplies and filament supplies are pretty large.

Once you have a dream in your head the practical realities can take you to places you never saw in the magic of the dream......

 

[Mr.Ian]

Graaf 13.5b2 is a fantastic fully balanced valve pre amp

 

[Mr.Ian]

No longer made, i reckon £2k would buy one in good condition, if you can find one

 

[hifinutt]

funnily enough i was only looking at one today

https://2ndhandhifi.co.uk/product/graaf-13-5b-mkii-pre-amplifier/

 

[Disarmamant]

How about a balanced version of the Pass B1 buffer preamp, and a Balanced Neurochrome buffer Preamp?

 

[Norfolkman51]

How about a balanced version of the Pass B1 buffer preamp, and a Balanced Neurochrome buffer Preamp?

I have a friend who has a balanced version of the Korg B1 preamp and we've compared this to my single ended version of the same pre. They are almost identical in sound, with perhaps a tiny bit more definition in the top end in my version, probably due to it having a Khozmo stepped attenuator.

Other possible balanced valve preamps are the EAR 868 and EAR 912.

 

[hifinutt]

as you know i just love bel canto pre amps . am i right in thinking the bel canto pre 5 is a balanced pre amp . the pre 3 vb is quite popular with some who use active speakers . it can be highly modded with better psu

http://belcantodesign.com/home/eone/pre5-preamplifier/

 

[Non-Smoking Man]

as you know i just love bel canto pre amps . am i right in thinking the bel canto pre 5 is a balanced pre amp . the pre 3 vb is quite popular with some who use active speakers . it can be highly modded with better psu

http://belcantodesign.com/home/eone/pre5-preamplifier/

The BC Pre 5 is balanced Phil.

Jack

 

[Bodgit]

I guess there is another type of balanced pre-amp, and that's a digital one incorporated with a DAC. My Wadia 861 is of this type. Not what you're looking at/for, but may be another idea to throw into the mix.

I dare say this kind of pre-amp will sound totally different to a pure valve pre-amp.

Of course this works best with digital front ends and an ADC would be needed for analogue front ends. So not what you're after...but, might be useful even if to discount

 

[Andrei]

I have been using a balanced pre-amp for a few years now. It is the solid state Emm Labs Pre 2. It receives balanced signals via XLR from my DAC and from my CD player. It has a balanced output, again via XLR, into my power amp. It is low noise and I am happy with it.

Two weeks ago I decided to swap in my Ayon Eris pre-amp. It is valve based with a pair of 6H30s. It has single ended inputs only. But it does have an XLR (presumably balanced or why bother) option for output to the power amp. The difference in output is subtle. No blind tests or measurements but it just seems to have the edge over single ended.

I prefer the Ayon for vocals or small ensemble pieces. I will go back to the Emm Labs as it is better for orchestral.

Ayon do have a few fully balanced range. The Ayon Auris which has balance inputs and outputs would surely be a great option as it is balanced and it is a later model compared with the Eris.

On the other hand I have compared my Daniel Hertz M6 pre-amp, single ended inputs and outputs only, with the balanced Emm Labs. My ears cannot detect any difference in quality.

 

[dave]

Because the 5 way active horn system uses XLR only Ashly analogue crossovers,

I would be fairly confident the crossover is unbalanced inside...... And if it was mine, in your position I would be tempted to think about bypassing the input banacing stage, but it would probably make little difference to just running an unbalanced signal from a pre, if the lengths for that wire were sensible.

Anyway thought experiment shunt volume balanced pre, not too complicated. I am not as precious as some, I did work in BSS for a couple of years, one of the early pioneers of active crossovers in the UK, so I know what goes on inside these type of boxes.



A bit simplified, but something like this would work. Would use ECC88s personally or similar, and kep anode resistors fairly low, sub 10k, and it would need quiet stabilised power supplies.

would also be tempted to make output SRPP



or a PP output transformer for true balanced. Whatever, it could be made simpler or more complicated, but does mean you can use a normal stereo log pot, although it would not be as log... sometime we must suffer for our art.