Author Topic: SK-25 half as loud as it should be

November 28, 2023, 04:41:11 AM
Read 262 times

DUYBuilder

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
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.


« Last Edit: November 28, 2023, 04:50:42 AM by DUYBuilder »

November 28, 2023, 05:10:28 PM
Reply #1

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 969
  • Karma: +28/-0
    • View Profile
Did you check these?
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.
JPK

November 28, 2023, 09:34:12 PM
Reply #2

DUYBuilder

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
Did you check these?
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.

November 29, 2023, 01:11:49 AM
Reply #3

DUYBuilder

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
Just verified all other parts on the SK25 - they are correct.

November 29, 2023, 05:50:15 PM
Reply #4

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 969
  • Karma: +28/-0
    • View Profile
Yes the fault is in the DOA.
Are you sure about your connections between the base and the vertical PCB's?
JPK

December 06, 2023, 09:38:19 PM
Reply #5

DUYBuilder

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
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.

December 06, 2023, 09:42:32 PM
Reply #6

DUYBuilder

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile

December 07, 2023, 09:26:57 AM
Reply #7

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 969
  • Karma: +28/-0
    • View Profile
BY vertical do you mean the PCB with the potentiometers?
No, I mean the 2 side PCB's, acting as heatsinks, on the DOA
JPK