[helge]

Hi people,

Just finished my bugle, but theres no sound.. My bad, but any help would be greatly appreciated. I get a normal pop sound when turning on and off, but no music. My DVM reads:

Pin1: 7.65V (Out A)
Pin2: 6.42V (- in A)
Pin3: 6.56V (+ inA)
Pin4: 7.20V (V-)

Pin5: 6.55V (+ in B)
Pin6: 6.44V (- in B)
Pin7: 7.44V (Out B)
Pin8: 8.61V (V+)

(on all 3)

I know at least the out values are incorrect, but dont know what it means. Have checked resistor color codes and they comply with schematics, solder joints looks ok and PS electrolyts have right polarity.. Please anyone - are my opamps gone??

I want music...

Thanks,
helge

[hagtech]

There should be no dc on the outputs.  Supply voltages look really low, too.  Try one opamp at a time.  Pictures look ok.

jh

[helge]

Thanks,

Ok. Voltage readings on pins, starting with the one closest to the inputs:

1: 7.80 (out A)
2: 6.76 (-in A)
3: 6.88 (+in A)
4: 7.50 (V-)
5: 6.84 (+In B)
6: 6.72 (-In B)
7: 7.55 (Out B)
8: 8.72 (V+)

middle:
1: 7.75 (out A)
2: 6.61 (-in A)
3: 6.76 (+in A)
4: 7.37 (V-)
5: 6.72 (+In B)
6: 6.60 (-In B)
7: 7.50 (Out B)
8: 8.67 (V+)

outputs:
1: 7.72 (out A)
2: 6.54 (-in A)
3: 6.68 (+in A)
4: 7.31 (V-)
5: 6.66 (+In B)
6: 6.56 (-In B)
7: 7.52 (Out B)
8: 8.64 (V+)



Helge

[hagtech]

It's like the opamps are in backwards.  But look ok in photo.  Take opamps out and make measurements.  Then add one at a time for each position.  Something is driving the to the rails.  Like the + input is floating.  Not making sense.

jh

[helge]

OK...This is what I get on the 3 sockets without amps:

1: 0 (out A)
2: 0 (-in A)
3: 0 (+in A)
4: 1.80 (V-)  [dropping 0.01V for every second i keep the DVM connected]
5: 0 (+In B)
6: 0 (-In B)
7: 0 (Out B)
8: 8.86  (V+)

Then, mounting one amp in the first position and measuring the pins on (the same) socket

1: 7.88 (out A)
2: 6.76 (-in A)
3: 6.85 (+in A)
4: 7.47 (V-)
5: 6.81 (+In B)
6: 6.69 (-In B)
7: 7.64 (Out B)
8: 8.81  (V+)

Which is approximetly same as before. Tried to swap amps to se if that changed anything, but got same results.

Did the same, one amp only, in 2nd and 3rd position with similar results, only slightly lesser voltages when moving from one position to the next (typicaly - 0.05V) nothing significant I guess, only batteries or something.

Ok.. keeping one amp in first position and measuring the empty socket in pos 2:

1: 0 (out A)
2: 0 (-in A)
3: 7.63 (+in A)
4: 7.24 (V-)
5: 7.41 (+In B)
6: 0 (-In B)
7: 0 (Out B)
8: 8.70  (V+)

and socket 3:

1: 0 (out A)
2: 0 (-in A)
3: 0 (+in A)
4: 7.12 (V-)
5: 0 (+In B)
6: 0 (-In B)
7: 0 (Out B)
8: 8.670  (V+)


Then, mounting one amp i 2nd position:

1st socket:

1: 3.32 (out A)
2: 0.3 (-in A)
3: 0 (+in A)
4: 7.17 (V-)
5: 0 (+In B)
6: 0.3 (-In B)
7: 3.27(Out B)
8: 8.66 (V+)

3rd:


1: 0 (out A)
2: 0 (-in A)
3: 0 (+in A)
4: 7.24 (V-)
5: 0 (+In B)
6: 0 (-In B)
7: 0 (Out B)
8: 8.66  (V+)

With amps in pos 1 and 2, this is what I read on socket 3:

1: 0 (out A)
2: 0 (-in A)
3: 0 (+in A)
4: 7.11 (V-)
5: 0 (+In B)
6: 0 (-In B)
7: 0 (Out B)
8: 8.64  (V+)

(If I measure same sockets as the amps are mounted on I get similar results as before)


 

Have I understood you correctly? Anything else I should try or check?

Thanks again,
helge

[hagtech]

Doh!  I misread your previous numbers.  You are missing the negative supply!  Or somehow one battery is installed backwards (although I don't know how that is possible.

Without opamps, get the negative supply rail working.  Then you will be ok.

jh

[helge]

Youre absolutely right. Pulled out the battery, got same readings and I can see theres a 'clip'-thing missing in one batter yholder, so no connection to the battery..

Thanks

now I only have to try to find a new batteryholder...

[helge]

Well, actually the missing part resides inside the -pole on the battery I removed 


Ok.. think Ill manage.  Thanks 

[helge]

I got the negative supply working, and sweet music appeared

Early celebration...

The right channel was about 2/3 down compared t the left. Hmm... Swapped L and R on inputs, same result. Swapped L and R on outputs and got the same, but on opposite channels as expected. Hooked up my NAD phono and things were ok. So back to the BUGLE (which no doubt will sound better than the NAD ) Even took out the amps, and swithed positions but no effect. Resistors look perfectly mirrored L/R valuewise..

Any Ideas what could be wrong?

I really feel like the amateur I am now...

Thanks,
Helge

[hagtech]

All I can think of is a resistor.  Do the channels have the same sounding EQ?  Is it only a volume difference?

jh

[helge]

No, the weak channel has no treble/upper mid also..

H

[hagtech]

Check input loading.  Is it 47k?  Could also be any of the R or C values.

jh

[helge]

Measurements:

Input load 44k6 on both channels. close enough?

Resistors values measures the same on both channels (+-5%)

I dont know about the capacitors.. it possible to measure them?

Thanks again Jim for your time and support.

Helge

[hagtech]

Shux, I dunno here.  It could be a cap.  Really, just need to look at the lettering on the side.  You've tried swapping input cables?  You can also short inputs together, that way they get identical signals.  See if that leads to a clue.

If you get stuck, you can send it to me for repair.  Depends on how much agony you want to endure.  But hey, this is how we all got started, too.  Believe it or not, you're learning very useful debugging skills.

jh