blueNan

recap oscillation? problem
« on: April 16, 2019, 03:25:40 AM »
Hi, i am almost new to electronics. I have soldering gear and humble soldering chops.

I have recapped a circa 25 years old stereo compressor (Estec Twincomp) using Nichicon KZ capacitors of the same specs, to replace original Thompson capacitors. I did only the audio board.

It was sounding fine at the beginning, just felt that the signal lose a tiny bit of "size" if that makes sense, when passing through the compressor (subtle difference). The task looked easy so i decided to try with expensive capacitors.

Once finished, the compressor exerts a constant hum, which frequency variates (basically making weird noises) if i inject audio. I have examined the board but it looks fine.

So i don't know what to do now... i heard from the previous owner that the designer himself, Sonny Schneid, told him that if he was to build again the compressor he would have used Panasonic FM. So i am tempted to give it a try replacing the Nichicons with FM, but do not know what  to solve this hum problem...




jensenmann

Re: recap oscillation? problem
« Reply #1 on: April 16, 2019, 04:08:58 AM »
Doublecheck if the new caps are installed with the right polarity.
« Last Edit: April 16, 2019, 04:55:52 AM by jensenmann »
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

blueNan

Re: recap oscillation? problem
« Reply #2 on: April 16, 2019, 07:08:20 AM »
Doublecheck if the new caps are installed with the right polarity.

I double checked, and just did it again now. Polarity is ok.

blueNan

Re: recap oscillation? problem
« Reply #3 on: April 16, 2019, 07:30:59 AM »
Besides the replacement of the 5 x Thompson capacitors per channels with Nichicon KZs, i replaced also 2 capacitors per channel that i assume are related to power the opamps and VCAs, because the designer used here standard Jamicon ones.

For this replacement, i used Panasonic FM. Perhaps the low ESR of the Panasonic FM can be the cause for this oscillation?

I attach a picture of one channel of the audio board with the replacements i did. The controls that govern the VCA are in a physically separated board, connected to this one via ribbon cable.

scott2000

Re: recap oscillation? problem
« Reply #4 on: April 16, 2019, 10:25:01 AM »
So it Did it work well before the upgrades?

Is the new problem on both channels ??

pucho812

Re: recap oscillation? problem
« Reply #5 on: April 16, 2019, 11:07:17 AM »
if the problem is on both channels. look for something common to both channels? start with the power supply.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

blueNan

Re: recap oscillation? problem
« Reply #6 on: April 17, 2019, 06:16:09 AM »
Yes it worked very well before i messed up with it.   The problem affects both channels. I did not touch the psu, and it has two Philips LQ capacitors supposed to be of the finest quality, according to the info i could find about.

The unit does not pass audio unless i feed a very strong signal, then the hum derives into weird noises rhythmically related to the music i am playing.

I think I will remove one channel's Panasonic FMs and solder the original Jamicon back in place to see if it works... as they are less in number.  Discouraging results for a first recap project!

« Last Edit: April 17, 2019, 06:23:53 AM by blueNan »

scott2000

Re: recap oscillation? problem
« Reply #7 on: April 17, 2019, 06:15:20 PM »
Strange.......

Those weren't some back alley deal caps????

Doesn't make sense....... unless you goofed some trace or bridged  something with solder...,,maybe disturbed something during disassembly/assembly....magnifying glass with bright light is good to check.....etc.
« Last Edit: April 17, 2019, 10:13:31 PM by scott2000 »

pucho812

Re: recap oscillation? problem
« Reply #8 on: Today at 12:13:40 AM »


The unit does not pass audio unless i feed a very strong signal, then the hum derives into weird noises rhythmically related to the music i am playing.



again check the power supply. it's not about a recap,yet, it's to confirm it outputs the correct voltages and such...
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

ruffrecords

Re: recap oscillation? problem
« Reply #9 on: Today at 04:31:49 AM »
Also check for solder splashes or track bridges. It is unlikely to be the type of electrolytic you have used. More likely something much more simple.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


 

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