Author Topic: Distorted output - also in bypass

April 28, 2022, 05:13:44 PM
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koos

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Hi!

I made 2 units this week but apparently not very succesful. 
They both have a distorted output (also in bypass), from which one of the units the low freqs appears to be gone. At lower levels the outputs appears 'gated'. VU meter is working. Drive seems to be working. Checked IC's/networks/ resoldered suspicious joints, but no success.

Voltages are (both units):
V+ 15.6
V- 15.9

Not sure how the measure the units test points though!

Hope you can help me out.

Koos

April 30, 2022, 09:43:57 AM
Reply #1

JPK

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95% of the issues are due to bad solder joints. The other 5% are misplaced components.
So I would recommend reflowing all the solder joints.

Without input signal, check that you have no DC voltage on TP1, TP2, TP3, TP4, TP5, TP6, TP7.

With all switches to the left, except bypass to the right, potentiometers on max, send a 0.25VAC signal to the input (measured while connected to the unit).
You should get against 0V:
TP1 = 0.9VAC
TP2 = 3.8VAC

TP3 = 1.5VAC
TP4 = 1.5VAC
TP5 = 1.5VAC
TP6 = 1.3VAC
TP7 = 4.8VAC
+/- 15%
JPK

May 03, 2022, 02:15:57 PM
Reply #2

koos

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Hi JPK, thanks for the reply and clearing things up.

Here's my test report:

(DC seems zero on all points.)
(VAC readings: 0,25 VAC sine wave)

MODULE 1

TP1 1.4
TP2 7.1
TP3 3.2
TP4 3.1
TP5 3.1
TP6 2.7
TP7 0

MODULE 2


TP1 1.3 
TP2 6.9
TP3 3.3
TP4 3.2
TP5 3.1
TP6 2.8
TP7 0

I reckon this doesn't seem too good..
I had some problems soldering U13 in the first place but after a reflow of this and other joints I still got these readings

Hope there is something to say about this!


Regards, Koos

May 04, 2022, 05:07:39 PM
Reply #3

JPK

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There is something wrong with the output stage.
Can you report the DC voltages on the pins of U12 and TP7, against 0V ?


JPK

July 23, 2023, 01:38:15 PM
Reply #4

koos

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Bit late on my side but I can confirm that this problem was indeed caused by myself: Reversing the placement of Q1 power transisor.
Reversing again it solved it! Sorry for replying to this so late..

July 25, 2023, 10:41:50 AM
Reply #5

JPK

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JPK