Sound Skulptor forums

Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: mjc7900 on October 25, 2022, 02:50:19 AM

Title: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on October 25, 2022, 02:50:19 AM
So the whole setup process went really well until I was passing audio through the unit and checking the sound (and liking it a lot) with some drum loops.  At this point I switched off of the 10:1 ratio down to 2:1.  At 2:1 and 2:1 only the dB Compression meter jumps up to 4dB of compression and stays there as a new baseline.  What is the likely culprit here?  Everything else works as expected, sounds completely clean, and functions normally.  Only the meter in 2:1 mode doesn't work as expected.
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: JPK on October 25, 2022, 09:37:14 AM
Is it only the display with the sound being compressed normally in 2:1?
Does the meter needle move from the +4 position when audio is sent?

You could check that diodes D1 and D2 are in the correct direction.
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on October 25, 2022, 03:28:28 PM
The meter does move in 2:1.  Its like the meter sees 4dB as the new "zero" when in 2:1 mode.  The meter will respond to input signal though.  I will check the diode position again.
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on October 26, 2022, 04:48:31 PM
just checked D1 & D2 and they are oriented correctly.
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on October 26, 2022, 05:45:54 PM
Is it time for an isopropyl bath - and if so:



Thank you!

Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: JPK on October 27, 2022, 11:02:37 AM
Not sure for the isopropyl. The issue would be there for the 3 ratios.
Do you get the same meter shift without the channel 2 installed?
Do installing channel 2 modifies the shift level?
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on October 27, 2022, 07:45:22 PM
I'll have to check.  Just pull the second channel, keep JP1 in place, and do the same test?
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: JPK on October 28, 2022, 11:22:31 AM
Yes exactly.
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: ReadyToRockAudio on October 31, 2022, 03:50:20 AM
I'm having the EXACT same issue. Everything seems to work perfectly, except On 2:1 my meter rests at about 3db.  4:1 and 10:1 rest at zero.
I'll be watching this thread.

Chris
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: ReadyToRockAudio on November 02, 2022, 02:44:49 AM
JPK,
    I went back and checked D1 and D2.   I did have them in backwards!   It was the one part of the instructions I glossed over.  Oops.  K means Cathode (aka black ring, negative).
Mine is working perfectly now.  Sounds great!   I hope MJC7900 can get his figured out.

Thanks so much!
Chris
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on November 03, 2022, 02:29:01 AM
Well my diodes are correctly oriented and the unit behaves in the same way whether there is one or two channels installed...

Glad to hear you got yours working though, Chris!
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: JPK on November 04, 2022, 06:34:59 PM
What is the DC voltage on TP5 and TP11 (only channel 1 installed)?
Check that the resistors R5 to R9 are in the correct position.
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on November 09, 2022, 11:32:00 PM
TP5 @ .367vdc
TP11 @ .006vdc

I just confirmed also that R5-R9 are correctly placed as well.

Thank you!
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: JPK on November 10, 2022, 12:57:02 PM
Try removing Q1, it might be damaged (Its function is to stop the meter moving when the compressor is bypassed).
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on November 21, 2022, 04:18:12 PM
Should I just remove it and plug the compressor back in to check?
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: JPK on November 22, 2022, 07:36:20 AM
Yes.
Heat the 3 pins together with a big blob of solder.
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: mjc7900 on December 02, 2022, 06:23:51 PM
Replaced the 2N7000 (I had some available), still behaving the same way.  Where the meter hovers is dependent on the release time as well.  Another interesting development - the release potentiometer housing now spins freely on the soldered pins and the detents are now essentially useless and the potentiometer is likely not functioning correctly.  Pretty inexplicably too.  I didn't do anything to prompt that behavior.  
Title: Re: Meter works as expected except on 2:1 ratio, where it stays on 4dB GR minimum
Post by: JPK on December 06, 2022, 09:22:40 AM
Please check again this value: TP11 @ .006vdc. It seems too low.

The release rotary switch needs to be replaced. Please contact me at jpk(a)soundskulptor.com.