mjrippe

Berglund Vari-Mu
« on: November 22, 2019, 04:51:29 PM »
Has anyone else read this article from 1997?  I found it in my archives.  It appears to be a hi-fi/audiophile magazine but he lays out a vari-mu circuit with a twist.


EmRR

Re: Berglund Vari-Mu
« Reply #1 on: November 23, 2019, 10:19:57 AM »
Interesting, never seen that before. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

abbey road d enfer

Re: Berglund Vari-Mu
« Reply #2 on: November 28, 2019, 12:48:48 AM »
Has anyone else read this article from 1997?  I found it in my archives.  It appears to be a hi-fi/audiophile magazine but he lays out a vari-mu circuit with a twist.
The claim for low distortion seems to lack substance. Indeed the push-pull arrangement does somewhat reduce 2nd-order distortion, but not more than any other push-pull arrangement, as found in many reputed compressors, such as Gates StaLevel, CBS Audimax, Collins 26, UA176, any Western Electric limiter, and indeed the famous fairchild 660/670.
The few non-push-pull implementations of Vari-mu exhibit not only 2nd-order distortion, but also control-voltage feedthrough that creates thumps in the audio.
In the proposed schematic, the side-chain rectification is only single-wave, which makes it prone to LF distortion under compression.
The fact that no measurements are published indicates that claims of superior performance are but wishful thinking.

The only noticeable thing in this schemo is how the ratio is increased by applying the control voltage to a LTP carrying signals of opposite phase. I would think it's not favourable to the noise performance, though.
« Last Edit: November 28, 2019, 01:13:22 AM by abbey road d enfer »
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

gyraf

Re: Berglund Vari-Mu
« Reply #3 on: November 28, 2019, 02:42:55 AM »
Agree, I always suspected it to be some kind of a simulation exercise. When I tried quickly setting it up on perfboard, sound and performance was subjectively underwhelming. Don't take my word for it, it's a simple enough circuit with cheap parts - quick to wire up.

My main show stoppers, other than the subjective performance:

Very dependent on ECC189 tube selection, no trim for CV break-through

Output is post passive attenuator, 100K Ohms from a ECC88 cathode. Who would do that for audio?

/Jakob E.
..note to self: don't let Harman run your company..

abbey road d enfer

Re: Berglund Vari-Mu
« Reply #4 on: November 28, 2019, 04:12:26 AM »
Agree, I always suspected it to be some kind of a simulation exercise.
Like it is very often with these articles. Nobody double-checks the content.

Quote
Very dependent on ECC189 tube selection, no trim for CV break-through
In order to make it acceptable, it would be necessary to add balance controls.

Quote
Output is post passive attenuator, 100K Ohms from a ECC88 cathode.
As you know, HiFi is a different world, 100mV 100kohms...
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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