Altec 436 / compression distortion?
« on: March 19, 2021, 04:35:47 AM »
Hi guys! I know this site is chock-full of 436 posts, but care for one more?

I built a an Altec 436 clone according to this slightly modified circuit. (I added a compression on/off switch between R12 and P4 that grounds the open end of the R12 resistor when the compression is bypassed.)

The amplifier sounds good when the comp is bypassed, no hums or buzzes, and during compression the controls do what they should, the meter moves and compression curve itself sounds about right.

However, when the compression kicks in (i.e. the meter moves) the signal clearly distors and it sounds quite ugly. This happens only during the transients (small & big), but not when the unit holds down compression. What could be causing this? Thanks in advance.


Re: Altec 436 / compression distortion?
« Reply #1 on: March 19, 2021, 07:15:56 AM »
Have you measured voltages on the tubes and checked against the schematic ?

Have you tried different tubes and checked the balancing at the 6bc8 is set correctly ?

Heikki

Re: Altec 436 / compression distortion?
« Reply #2 on: March 19, 2021, 07:33:44 AM »
What could be causing this?

Huge common-mode voltage clipping V2.

EmRR

Re: Altec 436 / compression distortion?
« Reply #3 on: March 19, 2021, 03:27:36 PM »
Sounds like imbalance in the 1st tube, have you trimmed the control per Dave's instructions?
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


 

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