Output DC offset
I have both shunty and pumpkins running. The output offset is very sensitive to air currents and causes a number of volts negative offset when cooled. The culprit is the constant current source transistor Q9.
My question I have is about stabilizing the offset using the same techniques used on the Aleph-X where a resistor is placed between the output and returned to the source of the differential pair Q1 and Q2. If this would work what values might be appropriate. Another technique used was a resistor from the outputs to ground. On the pumpkin R2 and R4 seem to provide this function.
Any ideas
BDP
I have both shunty and pumpkins running. The output offset is very sensitive to air currents and causes a number of volts negative offset when cooled. The culprit is the constant current source transistor Q9.
My question I have is about stabilizing the offset using the same techniques used on the Aleph-X where a resistor is placed between the output and returned to the source of the differential pair Q1 and Q2. If this would work what values might be appropriate. Another technique used was a resistor from the outputs to ground. On the pumpkin R2 and R4 seem to provide this function.
Any ideas
BDP
A proper servo would be interesting.
I tested a few values of resistors from the outputs to the differential pair sources and it did help to stabilize the output offset. I started out using 100K ohms. This slowed the rate at which the offset would occur, but it still varied a couple of volts when I blew across the board. The last value I tried was 47.5K ohms and this stabilized the output offset to .5 volts and slowed the rate of change even more when blowing across the board. I wouldn't expect this much air flow when mounted in its case. The R2 and R4 values at the outputs to ground were left at 10K ohms. The gain remained much the same along with the frequency response. I didn't do any distortion measurements.
I am still planning on using input caps.
BDP
I tested a few values of resistors from the outputs to the differential pair sources and it did help to stabilize the output offset. I started out using 100K ohms. This slowed the rate at which the offset would occur, but it still varied a couple of volts when I blew across the board. The last value I tried was 47.5K ohms and this stabilized the output offset to .5 volts and slowed the rate of change even more when blowing across the board. I wouldn't expect this much air flow when mounted in its case. The R2 and R4 values at the outputs to ground were left at 10K ohms. The gain remained much the same along with the frequency response. I didn't do any distortion measurements.
I am still planning on using input caps.
BDP
Hello.
I´m looking for transformer for my Pumpkin and I´d like know if is better one for each channel or no be sonic difference. Anybody make tests about this?
Best regards
Jose
I´m looking for transformer for my Pumpkin and I´d like know if is better one for each channel or no be sonic difference. Anybody make tests about this?
Best regards
Jose
Hi Jose 😉
one xformer is more than good enough 😉
in fact - you'll have that much isolation between channels with dedicated Shunty's that you'll not hear difference between one vs. two xformers
one xformer is more than good enough 😉
in fact - you'll have that much isolation between channels with dedicated Shunty's that you'll not hear difference between one vs. two xformers
more is always better 😉
or is it bigger is always better .......
we must ask that our better halves
yup - everything is written in Cook Book ;
or is it bigger is always better .......
we must ask that our better halves
yup - everything is written in Cook Book ;
Looks is the animal time.
Big donkey walk or no walk.🙂
Yes, I saw over the bird and part list, the first look an ant and the second one elephant. I´ll choose the elephant. 2x42,2.5A in my custormer´s tranformers.
One parts minus.
Thanks a lot
Big donkey walk or no walk.🙂
Yes, I saw over the bird and part list, the first look an ant and the second one elephant. I´ll choose the elephant. 2x42,2.5A in my custormer´s tranformers.
One parts minus.
Thanks a lot
Jose - first - Happy NY 😉
I didn't received reply from you ; your LS&other package leave my borders on 26.12.
I think that postman is near your doors , if not already .
I was not satisfied with the pre implemented in my Accuphase 213, so I bought Dave Slagles attenuator and got much better highs and more room in the sound.
Later I looked for different ebay Honkkong pre kits with fets, nice sound but not really better in my chain.
I build up UGS pre, that was a step in the right direction, very detailed, easy to build.
Pumpkin was ordered earlier, but it took more time to be build, took the first place now.
More colour, more dynamics.
Dave Slagles attenuator has good coherence, may be, still more room, but pumpkin is really alive!
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I understand the A-213 is an integrated and you use as power amp. I´d like some day heard attenuator with transformers. At this moment I get the best sound with DACT attenuator, I´ll can compare with PSMLS in few times. Nice race!
Whats heatsinks are you put in Pumpkin?
No my power amp is F5! The A-213 is in the corner, a little bit damaged from my experiments.😡
I will sell it, after recovering in a good state.
I have the impression the less people can manage electronics at all, the more important the shine surface, cables, capacitors all what is in your range to change gets.
So I will get no good price.😱
I am only on the kit level, but it is such a pleasure to look at the circuit diagram understanding more and dreaming of the things to come.
I also used a DACT and was overwhelmed by the details as a passive attenuator.
I put it also in the front of pumpkin and compared it to the ebay attenuator on the output of Pumpkin. You can see on the picture the yellow relais. Worked a little better for me.
Heatsinks, I took all what Zen Mod recommended in the .pdf.
My problem was that the transformers gave about 2 x 52V. So I had to fight with much heat.
I put the transistors with the small heatsinks an the alu chasis. Here they feel well.
I will sell it, after recovering in a good state.
I have the impression the less people can manage electronics at all, the more important the shine surface, cables, capacitors all what is in your range to change gets.
So I will get no good price.😱
I am only on the kit level, but it is such a pleasure to look at the circuit diagram understanding more and dreaming of the things to come.
I also used a DACT and was overwhelmed by the details as a passive attenuator.
I put it also in the front of pumpkin and compared it to the ebay attenuator on the output of Pumpkin. You can see on the picture the yellow relais. Worked a little better for me.
Heatsinks, I took all what Zen Mod recommended in the .pdf.
My problem was that the transformers gave about 2 x 52V. So I had to fight with much heat.
I put the transistors with the small heatsinks an the alu chasis. Here they feel well.
I´m in the kit level too and with the help of people, ZM and others I enjoy a lot.
You say 2x52V dc in the output of Shunty or ac in transformers?
In the second case, can you get the +-36vdc?
You say 2x52V dc in the output of Shunty or ac in transformers?
In the second case, can you get the +-36vdc?
2 x 52V AC in the transformers, I suppose, that is difficult to handle. I will try to go back to 2 x 42V AC.
first - you always need good ventilated case for
second - mount (first) mosfets in Shunty series regs (Q1 and Q1A) on bottom of case (with insulators , gate resistors near gates ) and do not worry about their dissipation ;
sturdy little buggers - they are ......
first - you always need good ventilated case for
unfortunately my expensive case is very closed, may be i put only a grid on it as a top!🙁
second - mount (first) mosfets in Shunty series regs (Q1 and Q1A) on bottom of case (with insulators , gate resistors near gates ) and do not worry about their dissipation ;
I am happy to tell you that it was what I did, now the whole case fells cozy warm!😎
sturdy little buggers - they are ......
little buggers, but very energetic like their father!
