Sound Skulptor forums

Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: rob@roblanter.com on February 06, 2021, 11:31:33 PM

Title: Channel A Distorted
Post by: rob@roblanter.com on February 06, 2021, 11:31:33 PM: Hi JP,

I am getting distortion in channel A. I followed the tests in the "In case your CP4500 doesn't work as expected (https://www.soundskulptor.com/forum/index.php?topic=3.0)" I got some strange readings:

Step2:
TP2: -.7 VDC
TP4: -1.1 VDC
TP11: -6.5 VDC
TP12: - 6.0 VDC

Step 6:
U6 pin 1: -.7

Any suggestions?

Thanks,
Rob
Title: Re: Channel A Distorted
Post by: JPK on February 09, 2021, 08:12:15 AM: Start by the usual suspects (https://www.soundskulptor.com/forum/index.php?topic=11.msg11#msg11) and IC's in the wrong place (https://www.soundskulptor.com/forum/index.php?topic=4.msg4#msg4).
Are the +/-16V and +/-12V correct?
Remove all IC's except U21 and check again TP11 = 0VDC
Title: Re: Channel A Distorted
Post by: rob@roblanter.com on February 09, 2021, 03:36:50 PM: Hi JP,

Usual suspects are fine, IC's are in the right place, I am getting +16.15V, all others are between 15V and 16V

I removed all IC's except U21, TP11 = 4.3DC

I am getting sound in channel A and all the controls are working, there is just some distortion, where as Channel B is perfectly clean.

Thanks,

Rob
Title: Re: Channel A Distorted
Post by: rob@roblanter.com on February 10, 2021, 02:43:28 PM: Hi JP,

Can you please help me debug this issue?

Thanks,

Rob Lanter
Title: Re: Channel A Distorted
Post by: JPK on February 10, 2021, 04:09:19 PM: Quote
I am getting sound in channel A and all the controls are working, there is just some distortion, where as Channel B is perfectly clean.
Do you mean you get compression? and on channel B too?
Quote
TP11: -6.5 VDC
This is not compatible with the previous statement. With this value, the meter needle should be stuck to 20
Title: Re: Channel A Distorted
Post by: rob@roblanter.com on February 10, 2021, 04:53:30 PM: Hi,

I get compression on Channel B. I am not sure about channel A because of the distortion.

I had a typo in the previous reply...TP11 was 6.5VDC, NOT -6.5VDC, Then the second time I measured TP11 was 4.3DC.

Rob
Title: Re: Channel A Distorted
Post by: JPK on February 11, 2021, 08:29:48 AM: Please redo the measurements. Check the negative voltmeter probe is well connected to the 0V.
It is just impossible to get any compression with +6.5V on TP11.
Do you see the meter needle moving when compressing?
Regarding the distortion try putting U11 (THAT1246) in U1, in case U1 is damaged.
Title: Re: Channel A Distorted
Post by: rob@roblanter.com on February 11, 2021, 04:03:28 PM: Hi,

I am getting +4.6VDC on TP11.
I switched U1 with U11...same problem.

I am definitely getting compression on both channels. Though Channel A has some slight distortion.

I am attaching a short audio file so that you can hear what I am talking about.

https://www.dropbox.com/s/7yil2tongebu5gp/DistortionExample.mp3?dl=0

Any other suggestions as too what might be causing distortion?

Thanks,
Rob
Title: Re: Channel A Distorted
Post by: rob@roblanter.com on February 12, 2021, 02:55:57 PM: Also, the meter needle does move when compressing. It moves as I would expect it to move when changing the Threshold.

Rob
Title: Re: Channel A Distorted
Post by: JPK on February 12, 2021, 03:08:18 PM: Try swapping IC's between channels until the distortion changes side.
This in case the distortion is caused by a defective IC.
Title: Re: Channel A Distorted
Post by: rob@roblanter.com on February 12, 2021, 05:45:23 PM: Hi JP,

Good news...I was able to move the distortion to the other side...the 1646 chip is bad...I will replace it and hopefully the problem will be solved. I am going to wait to replace it after I finish building the two 501 eq's I purchased in case I need to order more than just the IC 1646 chip.

Thanks for your help.

Rob Lanter