Some interesting circuits i found

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weiss

Well-known member
Joined
Jun 16, 2014
Messages
1,436
Location
Germany
I found 3 schematics online that got my attention and i wanted your opinion about these circuits. Are they suitable for testing or do they show any major faults? Wasn't able to get in touch with the designer so no help there..


Vari Mu compressor (it isn't clear to me where the tubes should get their voltage from)
gYNnnNr.png




opto type compressor
IFEokt2.png




some kind of solid state pultec style equalizer:
GXzSOgP.png

 
pucho812 said:
in the varimu design there is a HV connection labeled  p3 it appears between r14 and r15. . The heaters are standard 12VDC .  It does not list the B+ voltage.

I see. Could be worth trying?
 
The first one has obvious flaws and shortcomings. It will thump (common-mode swing on plates exceeds CM range of recovery amp; CMRR of recovery amp is dubious with finite source impedance). The "Link" simply ties opamp outputs together, they will fight. With *two* opamps it only gets half-wave rectification, which does not justify such a fancy build (and tends to thump/motorboat). I will say it "gets plate voltage" from the magic "HV" connector. How much HV? No clue.

These are sketches, incomplete.
 
Looks to me like some sort of theoretical simulation game.

It will not be able to work very fast, which is usually the niceyness of varimu - control voltage at the tube grids is added through 33K, charging a 1uF. This is why input transformers for varimu is a good idea :)

And ECC81 is not a good tube for this - something like ECC82 or even '88 would be much better, while still staying in the "widely available" category..

Jakob E.
 
The values for the pots are as follows:

RV1 10k
RV2 1M
RV3 50k
RV 4 1k

I was able to track down a corrected schematic for the vari mu with unit in action, unfortunately it's in spanish: https://www.youtube.com/watch?v=G9WqPUMsE_c
Seems the ECC81 was used intentionally. Still doesn't show anything about the HV though..
 

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weiss said:
I was able to track down a corrected schematic for the vari mu with unit in action, unfortunately it's in spanish:

def not Spanish..... sorta........

Google translate shows Portuguese....

cool language......


I understood side chain......lol

be cool to hear what he's saying.....


 
scott2000 said:
def not Spanish..... sorta........

Google translate shows Portuguese....

cool language......


I understood side chain......lol

be cool to hear what he's saying.....
of course! my bad.
 
in his link his schematic is listed as corrigido which means adjusted.  ;)
The video is called compressor vari-mu in detail...
hmmmm I would be curious to know what he is saying.  perhaps I will talk to my Portuguese friends and see if they can translate
 
pucho812 said:
in his link his schematic is listed as corrigido which means adjusted.  ;)
The video is called compressor vari-mu in detail...
hmmmm I would be curious to know what he is saying.  perhaps I will talk to my Portuguese friends and see if they can translate

i used youtube's auto translate function with subtitles.. quite handy but not completely correct. although i begin to understand some things
 

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