Balanced pre amps..

[Non-Smoking Man]

OO,, where did you spring from?
On paper looks worth investigating , but above my paygrade.

(Thanks for the contribution, Dave.)

Any observations, comments?
Jack.

 

[dave]

OO,, where did you spring from?

I live here mate.

 

[Non-Smoking Man]

Graaf 13.5b2 is a fantastic fully balanced valve pre amp

Have you got one..?

Jack.

 

[hifinutt]

hoping to get a BC pre 5 before end of jan . be good to see how it compares with the pre 3 vbs . shame cant bring to any bakeoff though

 

[GLB]

https://www.ebay.co.uk/itm/374464176035 Their is a fresh one on eBay today Jack

 

[Non-Smoking Man]

Graaf 13.5b2 is a fantastic fully balanced valve pre amp

I did a bit of digging around about the Graaf 13.5B and found some very negative comments re noise and reliability from Graham Tricker on a Forum.
However, some users rate them highly. The Graaf uses 6 double triodes which could be hard to match because one thing we are aware of is the need for the valves and other components to be closely toleranced/matched in a balanced circuit.

Jack NSM

 

[Non-Smoking Man]

Dave (Incurable Thinker) - have you any more thoughts on your claim that the Ashly XR4001 and the rest of the Ashly range of crossovers are not balanced?

Jack

 

[Non-Smoking Man]

For wont of something better to do, Ive pepperred the internet with Ashly searches and haven't found anybody mentioning doubts about the balanced technology.
I DID discover they have an internal jumper that operates a 25Hz filter that prevents sub bass cone flap. That's useful to know as Ive lost one 18" JBL driver already.
Most users rate them, as I already knew.

Jack NSM

 

[Non-Smoking Man]

Eastbourne-based Ian B is popping over on Sunday a.m. with his B.A.T. valve pre amp,
In situ is the reference Ayre K-5xeMP.
This will be an interesting comparison.
It follows the Django TVC (Stevens & Billington TX102 trannies) and the one-off balanced Satchmo (equipped with the lovely Tung Sol 6SU7 valves) that I got from nut recently.

Obviously all these pres are balanced as the horn system has to be balanced as the favoured analogue crossovers are balanced connections only.

(Mixing RCA and XLR equipment in such a complex system can lead to hum/noise problems which are only exacerbated in a 100 - 116 db driver set up. Any sound quality benefits from being balanced are probably down to a lower noise floor and the greater attention paid by manufacturers like Ayre to their balanced circuitry as opposed to their RCA option. I use Ayre's P-5xe phono stage as well as the Ayre pre. Ayre themselves are very clear about this in their handbook.)

Jack NSM

 

[Juancho]

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. Wherever, 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.

At a quick glance these look a lot like the Broskie balance /unbalancer circuits. If so, I've experimented quite widely with these for tube output stages, either to balance or unbalance. Whilst decent sounding they were not spectacular and I don't think offer any sonic advantages over transformer conversion as used in Jack's Satchmo balanced. YMMV

 

[dave]

At a quick glance these look a lot like the Broskie balance /unbalancer circuits. If so, I've experimented quite widely with these for tube output stages, either to balance or unbalance. Whilst decent sounding they were not spectacular and I don't think offer any sonic advantages over transformer conversion as used in Jack's Satchmo balanced.

Hmm. That Broskie, wants to lay claim to all possible valve circuit IP, it feels, virtually any original thought, he seems to have thought of it (creative sulk). I know everything has been invented already but...

I am not sure he builds them all. I thought I would "copy" one of his circuits, when it was very similar to an idea I had. It didn't work very well, so I went back to cooking it up my self.

I have been thinking about the above thought experiments, and may well have ago at making one. I was reacting to having two complete double "balanced" circuits, like some seem to favour. I liked it having just one pot. That should also apply for filtering as well, rather than having two ultra closely matched.
The problem the circuit could have is saturating the longtail pair before the volume control, but should not be insurmountable. And how quiet?

Thanks for your comments.

 

[dave]

Dave (Incurable Thinker) - have you any more thoughts on your claim that the Ashly XR4001 and the rest of the Ashly range of crossovers are not balanced?

No, but seeing as you seem interested, I had a quick look to see if I could find a circuit. It has electronically balanced inputs, i.e. an opamp circuit (TL072 if I am not mistaken), that converts balanced to unbalanced, then unbalanced all the way through, and then has "pseudo" balanced outputs, i.e. unbalanced outputs. Pseudo balanced is fine and will give some noise cancelation if fed into a properly balanced input, but will only manage half the voltage swing of fully balanced, but no problem.
Pseudo balanced is how unbalanced would be done if it was done "correctly" from a shielding perspective.

schematic

Retrospective edit 23/02/23, There seems to be confusion between balanced and symmetrical / differential, in my self at least. The above "psuedo balanced" is balanced, in that the requirements to be "balanced" is that the two signal lines in the XLR have the same output impedance, which allows noise cancelation at the differential input at the other end of the wire.

 

[Sir_Franc]

Jack, you're welcome to give my MFA Classic silver version a try. If you want to let me know when you're in the area and you can collect it.

 

[hifinutt]

i recall many years ago having the first bel canto pre 3 and bought one of these mfa silver classic pre amps which just blew away the pre 3 for dynamics and clarity . great little pre amps

then i got the pre 3vbs which was probably just as good as the classic and it had a decent remote control unlike mfa !!!

Today the latest analogue pre amp from bel canto landed [ balanced ] the pre 5 . i must say i was sceptical that it would be not as good as the pre 3vbs with the external psu . well first impressions are extremely good . very smooth pre without being soft , lovely control of bass and realism . i am somewhat impressed i must say . certainly a pre amp to put up against many others .

 

[Non-Smoking Man]

Jack, you're welcome to give my MFA Classic silver version a try. If you want to let me know when you're in the area and you can collect it.

Ooo, yes please Rick.
One interesting point is whether Music First use 4 transformers for balanced as in the Stereo Knight or whether they connect up with half of the winding, as in the Django, using just a pair of trannies. It is 'balancing' but use of only half the tranny's capability (see the TNT review of the Django).
We will arrange collection when I'm that way - be nice to see you old chap.
I'll lend you the Django so you have sounds..
I have heard a Silver Classic - it got 20 mins in my system at Kegworth. It was Fourlegs's. Not 20 mins cos it was no good, but because he wanted it back sharpish like!

Jack

 

[Sir_Franc]

Ooo, yes please Rick.
One interesting point is whether Music First use 4 transformers for balanced as in the Stereo Knight or whether they connect up with half of the winding, as in the Django, using just a pair of trannies. It is 'balancing' but use of only half the tranny's capability (see the TNT review of the Django).
We will arrange collection when I'm that way - be nice to see you old chap.
I'll lend you the Django so you have sounds..
I have heard a Silver Classic - it got 20 mins in my system at Kegworth. It was Fourlegs's. Not 20 mins cos it was no good, but because he wanted it back sharpish like!

Jack

You're most welcome. I think it uses two rather than four transformers. I'm using an integrated so don't currently have a need to try any other pre-amp thanks.
Message me when you know you'll be in the area.

 

[Non-Smoking Man]

Ian b has just been round with his B.A.T. balanced valve pre amp.
It was up against the resident Ayre K-5xeMP pre, which is a JFet SS pre (fully balanced also).

There was not a lot in it is the punchline - swings and roundabouts really. The BAT was a little lusher and fleshed out Joni Mitchell's (Blue) voice and guitar slightly better, but it would be picky and would require a lot of effort to separate them.

I did like the B.A.T. a lot and what impressed me was the low residual noise into 103+ db horns. I suspect there was a bit of scope for improvement via valve rolling, which Ian hasn't done (yet).

We tried 2 different postions of the knob(s) that control 'gain'. In the initial audition Ian advised turning the 2 smaller knobs to full gain. There is one for each channel so they are equalisers for each channel. Then using the large middle knob to control the volume.

Next we tried the 2 equalising knobs to just 10 0'clock (instead of all the way round) (which introduces them..?) and then used the volume knob to operate the output. The sound was different and we both preferred it this way. I'd want more time playing with these options.

Jack NSM

Vinyl: Ike Quebec 'Blue & Sentimental' Blue Note
Led Zep 'Lad Zep Untitled, 'Black Dog';
Grace Jone 'Walking In The Rain' from 'Nightclubbing;
Joni Mitchell, 'California' from 'Blue';
Michael Jackson 'Off The Wall' from 'Off The Wall' (Epic).