Sound Skulptor forums

Build help and troubleshooting => SK25/SK99 Discrete Op-Amp => Topic started by: DUYBuilder on November 28, 2023, 04:41:11 AM

Title: SK-25 half as loud as it should be
Post by: DUYBuilder on November 28, 2023, 04:41:11 AM

I have built 6 5176 Comps. 5 are working wonderfully after I embarrassingly figured out the bypass button. One is not and I determined, by swapping the DOA, that the DOA was the problem.
I re flowed ll points (used 40/60 solder). All diodes are pointed the right way. All the resistors measured correctly with exception of R2 and 3, but their bands were correct. Not sure what is wrong but with the other DOAs I was able to get outputs at 14AC and this one only allows ~6 regardless of the setting of P6.
(https://i.ibb.co/ygXjc6Y/IMG-20231127-193028320.jpg)
(https://i.ibb.co/7pvM2MC/IMG-20231127-193040647-HDR.jpg)

Title: Re: SK-25 half as loud as it should be
Post by: JPK on November 28, 2023, 05:10:28 PM

Did you check these (https://www.soundskulptor.com/forum/index.php?topic=9.msg9#msg9)?
What values do you get for R2, R3? 
50 ohms would be correct.
Does the DOA sound OK outside the output level? The DOA gain is set by R19, R20 on the compressor.

Title: Re: SK-25 half as loud as it should be
Post by: DUYBuilder on November 28, 2023, 09:34:12 PM

Quote from: JPK on November 28, 2023, 05:10:28 PM

Did you check these (https://www.soundskulptor.com/forum/index.php?topic=9.msg9#msg9)?
What values do you get for R2, R3?
50 ohms would be correct.
Does the DOA sound OK outside the output level? The DOA gain is set by R19, R20 on the compressor.

I checked as much as I could - it's a bit hard to see the transistors with it built.
50 ohm for R2 and 3 - all others read what is printed on the bands.
It sounds awful - audio drops in and out and its quite distorted.
I don't think it is R19 and 20, but I'll double check - but swapping the DOA fixes it so I assume the fault is there.

Title: Re: SK-25 half as loud as it should be
Post by: DUYBuilder on November 29, 2023, 01:11:49 AM

Just verified all other parts on the SK25 - they are correct.

Title: Re: SK-25 half as loud as it should be
Post by: JPK on November 29, 2023, 05:50:15 PM

Yes the fault is in the DOA.
Are you sure about your connections between the base and the vertical PCB's?

Title: Re: SK-25 half as loud as it should be
Post by: DUYBuilder on December 06, 2023, 09:38:19 PM

BY vertical do you mean the PCB with the potentiometers? i feel pretty good about them, because when I swap the DOA everything is good.
I've re-flowed the DOA (many times) and now it's better but still very distorted. It sounds like the speaker is torn.

Title: Re: SK-25 half as loud as it should be
Post by: DUYBuilder on December 06, 2023, 09:42:32 PM

https://youtube.com/shorts/puYFpGsn6fE?feature=share Shows the current state

Title: Re: SK-25 half as loud as it should be
Post by: JPK on December 07, 2023, 09:26:57 AM

BY vertical do you mean the PCB with the potentiometers?
No, I mean the 2 side PCB's, acting as heatsinks, on the DOA