Suppo Audio -- New Chinese EL84 PP amp for CHEAP.

[OneyedK]

Originally Posted by Wavebourn

Please explain why matching pair of tubes is so critical, why someone would seriously consider matching all of them.

This amp consists of 3 stages. All of them determine the distortion characteristics of the amp.
A (big) difference between the distortion produced by each channel, destroys or at least distorts the imaging.

2 out of 3 stages are determined by the driver/phasesplitter section around the 6N1.
The first stage already has a rather low anode-cathode voltage, so even smaller differences
between tubes will create a different opearing point. Different operating point means
different distortion spectrum.
That's the reason why I want those 6N1P's (or equivalents) to be matched.
In this case, they don't have to be internally balanced, but matched between tubes.

To a lesser extent, the same thing goes for power tubes.
But a matched quad is not more expensive than two matched pairs...
So why would I buy two pairs?

btw, I found nothing bad on the stock chinese 6P15's, they were properly matched (or it was just my lucky day).
The chinese 6N1P's were far worse! (badly constructed and totally different from each other) Replaced them with Siemens E88CC - yes, matched pair.

[Wavebourn]

Originally Posted by OneyedK

This amp consists of 3 stages. All of them determine the distortion characteristics of the amp.
A (big) difference between the distortion produced by each channel, destroys or at least distorts the imaging.

The keyword is (big)

How big is the difference if output pairs are not matched? Is it audible at all?

This is the question.

[OneyedK]

Originally Posted by Wavebourn

How big is the difference if output pairs are not matched? Is it audible at all?

This is the question.

Thing is, I don't know what the maximum allowed mismatch between channels is.
(maybe it's bigger than I assume now)
But if you bias one channel slightly hot and on slightly cold (changing cathode resistors), the effect is clearly audible.
- male voices crawl to the hot channel, female voices to the cold -

[Wavebourn]

How deep is feedback in the amp?

[OneyedK]

Originally Posted by Wavebourn

How deep is feedback in the amp?

If I'm correct, open loop gain is around 21, closed loop gain around 8.
That's -8.4dB.

Why the question?

[Wavebourn]

Originally Posted by OneyedK

If I'm correct, open loop gain is around 21, closed loop gain around 8.
That's -8.4dB.

Why the question?

How big will be the difference in gain if tube pairs are unmatched when this feedback is applied?

[imnewbie]

Originally Posted by OneyedK

Wow, I overlooked the 200V limit of g2.

This means that the Suppo Golden Voice, supplied with Chinese 6P15 tubes is actually wired in "self destruct" mode. (original schematic)
Lucky for Joe we all voided warranty

Only peepz with JJ EL84's are safe.

I pretty much do NOT understand anything on page 31 tubesteve's post (#308) and oneyedk's post(#310).

oneyedk, what all this means? (tubesteve's and your post). I don't understand any technical discussions. Can you do an outline in simple understandable language for people like me? Is Suppo golden voice with 6P15 tubes bound to die after short service duration? So does this mean only safe tube choice is the JJ EL84's?

[OneyedK]

Originally Posted by Wavebourn

How big will be the difference in gain if tube pairs are unmatched when this feedback is applied?

Euhm... There will be no difference in gain...

Problem is not the difference in gain, but the difference in "colour" between channels.

Originally Posted by imnewbie

Is Suppo golden voice with 6P15 tubes bound to die after short service duration? So does this mean only safe tube choice is the JJ EL84's?

On paper, the only safe choice is JJ EL84.
(JJ EL84 is the best current production EL84 on the market, available at a fair price)
In practice, the stock 6P15's of the suppo seem to survive the theoretical abuse. Mine are still triode strapped without lowering g2 voltage.
If they would die a little early, it's not a big deal, they don't cost an arm or a leg (if you stay with 6P15-EV's or JJ EL84)

[imnewbie]

Originally Posted by OneyedK

On paper, the only safe choice is JJ EL84.
(JJ EL84 is the best current production EL84 on the market, available at a fair price)
In practice, the stock 6P15's of the suppo seem to survive the theoretical abuse. Mine are still triode strapped without lowering g2 voltage.
If they would die a little early, it's not a big deal, they don't cost an arm or a leg (if you stay with 6P15-EV's or JJ EL84)

The impression I got was that using 6P15 meant shorter life for the amplifier itself. That's really not the case right?

[OneyedK]

Originally Posted by imnewbie

The impression I got was that using 6P15 meant shorter life for the amplifier itself. That's really not the case right?

Difficult to answer that question...
Nobody knows how much these particular 6P15's can take, mine show no signs of decay after about 6 months of use (or abuse, if you like).

The people at Suppo are very helpful and friendly, so if you run the amp with stock tubes and it fails after a short while, I'm sure they will help.

On the other hand, this amp is fairly simple, so if a failing tube would take out some components, they are replaceable.

we don't choose tube amps for their reliability, nor do we read and post on DIYaudio to leave amps as they were