Questionable voltage readings, should I proceed?

GilSt · 2104

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Offline GilSt

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on: January 17, 2012, 08:04:18 AM
Hello.

First, let me express my deep appreciation of your work. Being my first DIY project, stock Crack assembly was easy and it sounded great!

Yesterday I finished the speedball upgrade, plugged in and the left PC board didn't lit its LEDs.

After rechecking I found my mistake - attached black wire to wrong terminal: instead of G - to a near-by R4 one. (bottom image on Page 22 of the manual)
After the correction, everything lit up properly, and I started with the voltage check.
Those are the voltage readings:

Terminal   Expected   Actual
1             75             84      
2             170             155
3             0                0
4             170             155
5            75             108
6             0                0
7             100             101.7
8             0                0
9             100             117
10             0                0
11             0                0
12             0                0
13             170             154.3
14             0                0
15             185             173
            
20             0                0
21             206             192
            
A1             75             107
A2             0                0
A3             1.56             1.54
A4             0                0
A5             0                0
A6             75             83.4
A7             0                0
A8             1.56             1.54
A9             0                0
            
B1             75             83.3
B2             170             153.3
B3             100             101
B4             75             108
B5             170             153.5
B6             100             117
B7             0                 0
B8             0                 0

Some of the readings exceed even 15% margin.

Should I proceed to final check?

Thanks!   

Note: We ordered a batch of 3 kits. Another member reports very similar results (haven't been able to contact thrid member yet). He also reports a slight static noise in left channel.
« Last Edit: January 17, 2012, 08:55:40 AM by GilSt »



Offline Bolivar

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Reply #1 on: January 17, 2012, 08:48:22 AM
I had very similar voltage readings at first with my crack + speedball. Replacing the 12AU7 driver tube solved the issue.

Valtteri Nurmi

AMB Gamma2 DAC --> Crack --> Beyerdynamic DT880


Offline Paul Joppa

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Reply #2 on: January 17, 2012, 09:52:05 AM
Yes, it looks like one section of the 12AU7 is low on transconductance. It may come around in a while - like, 50 to 100 hours of operation. New tubes sometimes do not have the cathode emission fully developed. Nothing is so far out of line that it will cause harm.

Paul Joppa


Offline GilSt

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Reply #3 on: January 17, 2012, 10:36:22 AM
Thanks for the replies.
As advised I replaced stock tube to a JJ 12AU7  (also new) and the readings are now fine (except 170V are all 155V).

The sound is now amazingly crispy. Sennheiser veil is long gone.