Val_r
Well-known member
6V6 connected in ultra-linear mode.
Is it possible?
Can it give benefits?
Is it possible?
Can it give benefits?
Ultralinear connection in the sta-level output
- Thread starter Val_r
- Start date
Help Support GroupDIY Audio Forum:
I'm just wondering if you have used or built a sta level ?
They sound pretty good without modifications.
They sound pretty good without modifications.
Val_r
Well-known member
[quote author="Rob Flinn"]I'm just wondering if you have used or built a sta level ?[/quote]
Yes
Sure.
But my question was:
are there any drawbacks in using screen FB in the output stage of a variable mu limiter with pentode output tubes, such as the sta-level?
Respect,
Val.
Yes
Sure.
But my question was:
are there any drawbacks in using screen FB in the output stage of a variable mu limiter with pentode output tubes, such as the sta-level?
Respect,
Val.
I was just asking because in your other thread about changing the input transformer the last thing was that you were having problems with it clipping, & I was wondering if you had resolved them ?
> any drawbacks in using screen FB in the output stage of a variable mu limiter
I wrote a long theoretical reply, but, ya know.... for a two-6V6 line driver, the color of paint on the OT probably makes more difference than any UL connection.
Loudspeaker amps are different.
I wrote a long theoretical reply, but, ya know.... for a two-6V6 line driver, the color of paint on the OT probably makes more difference than any UL connection.
Loudspeaker amps are different.
SSLtech
Well-known member
Hmmmmmph...
As a result of my recent tube-limiter building frenzy I seem to have contracted a case of 'must-buy-exotic-tube' syndrome, and I have a 6386 here, and I was considering building a Sta-level clone to house it.
Not knowing much about the Sta-Level -and not being overly concerned with authenticity- I was wondering what the cost-effective input, output and power trannies would be... -Sowters look look they'd cost about $400 for just the power and output transformers... -not cost-effective, I suspect.
Any alternative suggestions, anyone?
Keith
As a result of my recent tube-limiter building frenzy I seem to have contracted a case of 'must-buy-exotic-tube' syndrome, and I have a 6386 here, and I was considering building a Sta-level clone to house it.
Not knowing much about the Sta-Level -and not being overly concerned with authenticity- I was wondering what the cost-effective input, output and power trannies would be... -Sowters look look they'd cost about $400 for just the power and output transformers... -not cost-effective, I suspect.
Any alternative suggestions, anyone?
Keith
AnalogPackrat
Well-known member
Keef,
For power transformers, check out the various manufacturer's for guitar amps. Looks like a 275-0-275V @90+mA with 5V @2A and 6.3V @3A would do it the job. Check out the Hammonds at AES/Tubes and More. Looks like under $50 will get you there. There's lots of NOS Stancor, Chicago, and similar PT stuff on eBay, too. I've picked up a few similar types over the years for under $20ea.
If you want quality, but more affordable (than J, L, or S) input iron, ask the guys at CineMag what they would recommend. Maybe a CMMI-8C? They may also be able to help with the output, but eBay may be your best bet for 5k:600.
Good luck!
A P
p.s. Sta-Level Schematic in case anyone needs a reference...
For power transformers, check out the various manufacturer's for guitar amps. Looks like a 275-0-275V @90+mA with 5V @2A and 6.3V @3A would do it the job. Check out the Hammonds at AES/Tubes and More. Looks like under $50 will get you there. There's lots of NOS Stancor, Chicago, and similar PT stuff on eBay, too. I've picked up a few similar types over the years for under $20ea.
If you want quality, but more affordable (than J, L, or S) input iron, ask the guys at CineMag what they would recommend. Maybe a CMMI-8C? They may also be able to help with the output, but eBay may be your best bet for 5k:600.
Good luck!
A P
p.s. Sta-Level Schematic in case anyone needs a reference...
> any drawbacks in using screen FB in the output stage of a variable mu limiter
> Hmmmmmph...
Well, if you are going to get grumpy....
The output stage is just an amplifier. The vary-Mu stage gives it a signal, after that is is just a Line Amp, a small speaker amp.
But note that while speaker amps are necessarily worked up to (or past) 100%, line stages such as this are 8-Watt amps typically worked below half-watt. Design focus should be different.
UltraLinear reduces the impedance at the OT. Not enough to damp a speaker or make a line-out solid, so we always have overall NFB. UL helps there because it damps the OT's HF resonance locally, allowing more overall NFB before instability. But the gain we give to the UL (a UL's gain is around half of a pentode) come out of the overall NFB budget. It's all just NFB, trading-off gain for other benefits. Where you take the gain-loss is a practical detail.
UL arose when Hi-Fi guys were going nuts with more and more overall NFB. If you are trying to get 30dB-40dB NFB around a transformer, UL is useful.
The merits of massive NFB have been debated for decades, and fashion has swung back and forth.
In loudspeaker work, the high damping (>20dB NFB) does have some advantage.
In line driving, a super low output impedance is not important, not even desirable. Even when chips allow <1 ohm Zout, we pad them up to 50 or 60 ohms. Super-NFB amplifiers don't like to see cables directly. Modern custom is to not load the far end (load >10K) and if we also have zero Z on the source, reflections never die. 60R is a broadcast custom; in small studios your Zout hardly matters (stay below a few K).
The Sta-Level output amp is designed to be good enough, not flippin' phantastic. Does the job, easy to produce, easy to troubleshoot. If you want a gold-lilly limiter, you might re-think it, even ground-up. If you just want to house your 6386 (sorry to hear of your syndrome), toss a Edcor 10KPP:600 OT on there, leaving room for a UTC or Sowter later.
> Hmmmmmph...
Well, if you are going to get grumpy....
The output stage is just an amplifier. The vary-Mu stage gives it a signal, after that is is just a Line Amp, a small speaker amp.
But note that while speaker amps are necessarily worked up to (or past) 100%, line stages such as this are 8-Watt amps typically worked below half-watt. Design focus should be different.
UltraLinear reduces the impedance at the OT. Not enough to damp a speaker or make a line-out solid, so we always have overall NFB. UL helps there because it damps the OT's HF resonance locally, allowing more overall NFB before instability. But the gain we give to the UL (a UL's gain is around half of a pentode) come out of the overall NFB budget. It's all just NFB, trading-off gain for other benefits. Where you take the gain-loss is a practical detail.
UL arose when Hi-Fi guys were going nuts with more and more overall NFB. If you are trying to get 30dB-40dB NFB around a transformer, UL is useful.
The merits of massive NFB have been debated for decades, and fashion has swung back and forth.
In loudspeaker work, the high damping (>20dB NFB) does have some advantage.
In line driving, a super low output impedance is not important, not even desirable. Even when chips allow <1 ohm Zout, we pad them up to 50 or 60 ohms. Super-NFB amplifiers don't like to see cables directly. Modern custom is to not load the far end (load >10K) and if we also have zero Z on the source, reflections never die. 60R is a broadcast custom; in small studios your Zout hardly matters (stay below a few K).
The Sta-Level output amp is designed to be good enough, not flippin' phantastic. Does the job, easy to produce, easy to troubleshoot. If you want a gold-lilly limiter, you might re-think it, even ground-up. If you just want to house your 6386 (sorry to hear of your syndrome), toss a Edcor 10KPP:600 OT on there, leaving room for a UTC or Sowter later.
Keith, the StaLevel audio transformers are nothing to write home about. Anything you might find with acceptable specs will do the job. I'm certain there are some off-brand unknowns that could be had used for $10-$20 apiece that would meet or beat performance, if you feel like fishing around.
Thanks for your thoughts, PRR. I was thinking previous to your post that, with a side-chain redesign, there might be a fraction of a benefit that could be squeezed out of the side-chain simply by accident with UL connection. But, that a side-chain redesign in of itself would easily do far far more.
Thanks for your thoughts, PRR. I was thinking previous to your post that, with a side-chain redesign, there might be a fraction of a benefit that could be squeezed out of the side-chain simply by accident with UL connection. But, that a side-chain redesign in of itself would easily do far far more.
Val_r
Well-known member
[quote author="Rob Flinn"]I was just asking because in your other thread about changing the input transformer the last thing was that you were having problems with it clipping, & I was wondering if you had resolved them ?[/quote]
Oh yes, you're right!
The clipping problem is because the input attenuator has wrong resistor values: the in Z that the soundcard 'sees' is too low, so it clips at high level. I was using this: (R37 and 39 are 301R actually)
I think that raising R36/38 value a bit will solve that problem.
[quote author="PRR"]I wrote a long theoretical reply, but, ya know.... for a two-6V6 line driver, the color of paint on the OT probably makes more difference than any UL connection. [/quote]
Oh could you please show the link to your article?
[quote author="SSLtech"]Not knowing much about the Sta-Level -and not being overly concerned with authenticity- I was wondering what the cost-effective input, output and power trannies would be...[/quote]
As you can see, I am using a 1:1 input trafo, a Lundahl LL1540, with good results, so you can try any 1:1 of your favour.
As for output trafo: I am currently using a Hammond 1650G, 6K6 p-p wired for 250R secondary, with satisfactory results. Someone is winding another OT for me, it is a 8K p-p with ct in each primary, so I can experiment with UL connection (even if 50% is objectively too much).
I am using some 5749 (6BA6) that I bought some time ago, they seem pretty similar to the 6386 published curves. Here is what I get with these tubes:
I also bought some 6BJ6 (Sylvania), but I feel the 6BA6 curves are closer to the 6386.
Unfortunately I have never had the pleasure to get my hands on genuine 6386's, so I cannot make any comparative listening test.
If anyone has some experience with that can post impression.
Thank you,
Val.
Oh yes, you're right!
The clipping problem is because the input attenuator has wrong resistor values: the in Z that the soundcard 'sees' is too low, so it clips at high level. I was using this: (R37 and 39 are 301R actually)
I think that raising R36/38 value a bit will solve that problem.
[quote author="PRR"]I wrote a long theoretical reply, but, ya know.... for a two-6V6 line driver, the color of paint on the OT probably makes more difference than any UL connection. [/quote]
Oh could you please show the link to your article?
[quote author="SSLtech"]Not knowing much about the Sta-Level -and not being overly concerned with authenticity- I was wondering what the cost-effective input, output and power trannies would be...[/quote]
As you can see, I am using a 1:1 input trafo, a Lundahl LL1540, with good results, so you can try any 1:1 of your favour.
As for output trafo: I am currently using a Hammond 1650G, 6K6 p-p wired for 250R secondary, with satisfactory results. Someone is winding another OT for me, it is a 8K p-p with ct in each primary, so I can experiment with UL connection (even if 50% is objectively too much).
Great! Is it a genuine one? You could post the characteristic curves to check for substitutes.
I am using some 5749 (6BA6) that I bought some time ago, they seem pretty similar to the 6386 published curves. Here is what I get with these tubes:
I also bought some 6BJ6 (Sylvania), but I feel the 6BA6 curves are closer to the 6386.
Unfortunately I have never had the pleasure to get my hands on genuine 6386's, so I cannot make any comparative listening test.
If anyone has some experience with that can post impression.
Thank you,
Val.
