DC link vs DC block wima caps

[schrobbelbop]

Is it wrong to use the wima MKP4 DC LINK 10uf caps for audio HV? for example my sta-level
needs 2x 10uf  in the HV supply and the audio thumps when compression is starting.

Might need DC blocking caps (wich is normally used for audio?)

or shouldn't it matter?

 

[JohnRoberts]

Thumps associated with dynamics processing is typically caused by DC control voltage  feedthrough in gain elements.

JR

 

[abbey road d enfer]

Is it wrong to use the wima MKP4 DC LINK 10uf caps for audio HV? for example my sta-level
needs 2x 10uf  in the HV supply and the audio thumps when compression is starting.

Might need DC blocking caps (wich is normally used for audio?)

or shouldn't it matter?

There is nothing to gain using film caps instead of lytics in the HT rails.
As JR mentioned, control voltage feedthrough is a known problem with vari-mu compressors - not only, FET and VCA compressors suffer that to a lesser degree.
Making sure the circuit is perfectly balanced is paramount. However, the Sta-Level has no way to balance the two halves of the vari-mu tube, which may have drift.
You may want to read this thread.
https://groupdiy.com/index.php?topic=64047.0

 

[schrobbelbop]

There is nothing to gain using film caps instead of lytics in the HT rails.
As JR mentioned, control voltage feedthrough is a known problem with vari-mu compressors - not only, FET and VCA compressors suffer that to a lesser degree.
Making sure the circuit is perfectly balanced is paramount. However, the Sta-Level has no way to balance the two halves of the vari-mu tube, which may have drift.
You may want to read this thread.
https://groupdiy.com/index.php?topic=64047.0

I've read this, and tried 10 diffrent JJ 6386's the ones wich gives te least compression seem to be most stable, it doesnt really matter how balanced they are. might be an unbalance between the 12AT7 and 6V6 output stage? 6V6's are balanced.

Im working on some T-bar's to put in 6BA6 pairs instead of the 6386. In my 670 the JJ 6386's struggeld
in the beginnen, but after burn in and some shuffeling them around no more weird thumbs over there.

 

[abbey road d enfer]

I've read this, and tried 10 diffrent JJ 6386's the ones wich gives te least compression seem to be most stable,

That is predictable.

  it doesnt really matter how balanced they are.

  Probably because of unbalance in the following stages.

might be an unbalance between the 12AT7 and 6V6 output stage? 6V6's are balanced.

The 6V6's are balanced for DC current. In order to minimize thumps, it's the gain of each half of the output stage that must be balanced. You need to check the balance of the 6V6 and each triode in the 12AT7.

 

[gyraf]

Please try to get NOS 6386 tubes at some point.

A friend of mine struggled for a long time with getting  a known-good vari-mu circuit behaving straight. Worked through a rather big stack of JJ's, went through the trouble of minutely curvetracing them all in order to find good matches, but never really got it working even halfway decently (he knows all too well how a 670 should behave).

Then he tried a set of NOS/genuine ones, and results were spot on. He told me that the new production tubes did not even resemble the curve behavior of the old ones.

This was some 3-4years ago, hopefully tube production got their act together since then, but somehow I doubt it.

Jakob E.

 

[Rob Flinn]

I have made 5 or 6 sta levels using point to point construction &  original 6386 & have never had an issue with thumping.  As Abbey suggests you can null any problems out to some extent with the trimmer on the output valves, but I have just matched the cathode voltages & never had an issue.

 

[schrobbelbop]

I've got the 6BA6 running, no difference. still thumping.

Plate HI/LO voltages seem to fluctuate between 298-315v when the tumping occurs.
is this normal, i might go dig in to the 300V psu? or something is shorting?

 

[Rob Flinn]

I've got the 6BA6 running, no difference. still thumping.

Plate HI/LO voltages seem to fluctuate between 298-315v when the tumping occurs.
is this normal, i might go dig in to the 300V psu? or something is shorting?

Have you several 6BA6 to try.    Sometimes you need to use a few to find a pair.    Although I once built a P2P prototype sta level using a pair of 6BA6that I had, and had no issues with thumping.

 

[abbey road d enfer]

I don't get it. Are there 6BA6's in a Sta-Level?

 

[schrobbelbop]

I don't get it. Are there 6BA6's in a Sta-Level?

Not in the original design but the double triode 6386 can be substituted for 2 6ba6 tubes