Sound Skulptor forums
Build help and troubleshooting => CP5176 FET compressor => Topic started by: mwhitlock on January 25, 2024, 02:09:14 PM
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I have built a stereo pair of the CP5176. Seems both are operating on their own, but one unit has significantly higher input level than the other. For them to match up in stereo I need to put e.g. input to 2 on one and 5 on the other.
I saw there was a similar issue reported on another thread, but that was regarding a mismatch on the output. Any hint where I should focus initial fault search?
Thanks in advance!
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Isn't this a problem caused by adjusting the P6 trimmer in setup step 7?
Do you have the same difference when the side chain is inhibited: jumper in 2-3 ?
Compare the input signal level on TP1 with input pot at max on both units.
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Hi again,
Isn't this a problem caused by adjusting the P6 trimmer in setup step 7?
---> I've redone calibration on both units, with the same results.
Do you have the same difference when the side chain is inhibited: jumper in 2-3 ?
---> Yes, with a jumper on 2-3 there is still a difference.
Compare the input signal level on TP1 with input pot at max on both units.
---> With the same input signal (1 kHz sine measured to 0.334VAC) I get 0.659 VAC on TP1 with one unit and 0.217 VAC on the other. (Input volume set to max on both).
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Check the resistor value of P1 on each unit (between TP1 and 0V with pot at max).
Check the input resistance on each unplugged unit between fingers 8 and 10 (2kohms). Verify that there is no resistance leak between these and the 0V.
Check that the transformer is in the correct direction in both units (logo pointing up).
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Check that the transformer is in the correct direction in both units (logo pointing up).
--> Both have logo pointing up
Check the resistor value of P1 on each unit (between TP1 and 0V with pot at max).
--> Unit A measures 1.64 kohm between TP1 and 0V. Unit B measures 1.740 kohm.
Check the input resistance on each unplugged unit between fingers 8 and 10 (2kohms). Verify that there is no resistance leak between these and the 0V.
--> Here we seem to have an issue... Unit A measures 2.15 kohm between 8 and 10, while unit B only measures 55 ohm... None of them seem to leak between 8/10 and 0V.
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Check the name on the input transformer: CMLI - 15/15PCA
If OK, remove (very carefully) the input transformer and
measure the resistor value between pin 1 & 4 : ~ 2k2
measure the resistor value between pin 5 & 8 : ~ 2k2
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Hi!
Unit A unfortunately has a very bad print on the input transformer, so I can't see anything else than the CineMag logo. That is however the unit demonstrating the correct (2.2kohm) resistance between PIN 8-10 so I assume it is the right one.
Unit B, the one that only shows 55 ohms between fingers 8-10, has a readable print. But it does not seem to be the right one... The label on the input transformer says "CM-75101APC". So I guess it is the wrong one...?
Darn... I double checked basically all other components with multimeter before soldering in place, but obviously I never thought of checking that the input transformer that it was the right one...
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I am sorry, we just realized that Cinemag mixed up a few CM75101 in our last batch of CMMI 15/15.
Please contact me (https://www.soundskulptor.com/en/content/6-contact) for a replacement.
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OK, good to have the cause of the issue sorted out. Thanks for great support JPK!
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New transformer arrived quickly, and has now replaced the wrong one. Works like a charm together with the stereo pair now after another setup. Many thanks!!!
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(https://fonts.gstatic.com/s/e/notoemoji/15.0/1f44d/32.png)