PICS of diy bd from low right channel amp

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PICS of diy bd from low right channel amp

Postby alcors3 » Fri Nov 22, 2013 9:02 am

Here are some pics of the board and the amp. I have not removed the board to test each component, instead I have a function generator board level, and a hand held oscilloscope. I am not sure what the maximum input voltage for the scope is, documentation is sketchy and the web site is in chinese..
Can you tell me assuming I can use this scope, what points on the board I should look at the for the signal?
My own ideas were
j7, v1 pin2, v1 pin 1, c2, v2 pin2, v2 pin 1 and 8, c8 and c10 r20 and r22, j2 and j1
If that is incorrect can you point me in the right direction..
Thanks
Attachments
diy-bd-3.jpg
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diy-bd-2.jpg
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diy-bd-1.jpg
diy-bd-1.jpg (271.15 KiB) Viewed 5740 times
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Re: PICS of diy bd from low right channel amp

Postby Shannon Parks » Tue Nov 26, 2013 2:16 pm

1) Disconnect the negative feedback at J12 & J13 so they don't screw up your test.
2) Jumper J7 and J17 (both left and right channels). Now you can hop between the halves and immediately see the difference without measuring the absolute value with your scope.
3) Attach resistive loads to the amp.
4) Set the function generator to a low sine wave value. 1kHz @ 50mV would be good.
5) Drive J7 & J17.
6) Compare the following (with a 10X probe) and tell me where we have the drop (all of the following should be the same on voltage on the oscope):
V1-1 and V1-6
V2-2 and V3-2
V2-1 & V2-6 & V3-1 & V3-6
J1 & J2 & J22 & J23

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Re: PICS of diy bd from low right channel amp

Postby alcors3 » Fri Nov 29, 2013 9:40 am

Thanks Shannon, I will do this soon, I spent about 3 half days trying to get the DSO Nano scope to work, a lot of time on the web looking for new firmware which I found but could not install. Finally ordered a different scope which uses a PC for a display and has 2 traces..should be here soon. So I will have some data soon..
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Re: PICS of diy bd from low right channel amp

Postby Shannon Parks » Fri Nov 29, 2013 10:57 am

You can use a DMM on AC mode instead of a scope and it will actually be a simpler test setup. Just use 400Hz instead of 1kHz. Your readings will be pretty accurate.

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Re: PICS of diy bd from low right channel amp

Postby alcors3 » Sat Dec 07, 2013 11:52 am

Shannon finally got to do this, I spent a bunch of time using the scope on a Sansui AU505, trying to find a fault. I felt easier about using the scope on a lower voltage amp for the first time. Anyway here is the data, it doesn't look to me as though there are any real differences. One thing though, to begin with I set up the dummy loads w/ no heat sink, I was just finishing measuring J23 when I realized I needed heat sinking, so I shut it down and proceeded with setting up a sink. However when I made the first set of measurements on J1,2,22,23 all the the V maxes were closely clustered around 12V, as you can see in the data when I turned the amp on for the second time the V maxes were clustered around 48.

V1-1 = 50.2 V2-2 = 16.3vmax, 32.6 P-P, 11.2 RMS
V1-6 = 50.2 V3.2 = 16.3VMAX, 32.6 P-P, 11.2 RMS
V2-1 = 50.2
V2-6 = 50.2
V3-1 = 50.2
V3-6 = 50.2

J1 = 47.7 VMAX, 99.8 P-P, 29 V RMS
J2 = 48 VMAX, 100 P-P, 29 V RMS
J22 = 49.6 VMAX, 102 P-P, 30 V RMS
J23 = 46.4 VMAX, 98.5 P-P, 29 V RMS

INPUT 1KHZ 627mV
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Re: PICS of diy bd from low right channel amp

Postby Shannon Parks » Mon Dec 09, 2013 6:26 am

OK, with feedback removed all your grid to power tube voltages look perfect. Now hook up the feedback again and retake those last four voltages. And then take those voltages right at pin 5 of the EL34s, too. Then also take the voltages at the speaker terminals.

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Re: PICS of diy bd from low right channel amp

Postby 20to20 » Mon Dec 09, 2013 10:51 pm

Is your speaker (-) binding post actually grounded to the chassis? It looks isolated and I can't see the wire that would ground it. I see the black tranny wire (-) and another coming off the terminal that looks like the wires from both are cut short, disconnected.
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Re: PICS of diy bd from low right channel amp

Postby alcors3 » Tue Dec 10, 2013 12:10 pm

Thanks for looking 20 to 20, yes each ground post is at chassis ground, the white wires from the center posts each go to the star ground.

The voltages I measured today are

J1 = -30.1
J2 = -30.1
J22 = -30.1
J23 = -30.1
THESE V NUMBERS ARE THE ONES USED IN THE DYNACO LITERATURE
V2 = -30.1
V3 = -30.7
V6 = -30.7
V7 = - 30.1 V6 BOUNCED AROUND ABIT BETWEEN 30.1 AND 30.7

OUTPUTS
LEFT 7.53 V 15.1 P-P
RIGHT 7.53 V

I don't see any great variations there either..I hope this was not all a wild goose chase.
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Re: PICS of diy bd from low right channel amp

Postby 20to20 » Tue Dec 10, 2013 1:04 pm

alcors3 wrote:Thanks for looking 20 to 20, yes each ground post is at chassis ground, the white wires from the center posts each go to the star ground.

The voltages I measured today are

J1 = -30.1
J2 = -30.1
J22 = -30.1
J23 = -30.1
THESE V NUMBERS ARE THE ONES USED IN THE DYNACO LITERATURE
V2 = -30.1
V3 = -30.7
V6 = -30.7
V7 = - 30.1 V6 BOUNCED AROUND ABIT BETWEEN 30.1 AND 30.7

OUTPUTS
LEFT 7.53 V 15.1 P-P
RIGHT 7.53 V

I don't see any great variations there either..I hope this was not all a wild goose chase.



If these checks were made without the GNFB, and the outputs are equal now, then the possibilities are narrowed to a speaker itself or the FB circuit components. Sometimes in the real world of troubleshooting just the manipulation of components "fixes" things. It exposes the intermittent connections that need ferrited out with a stick poked around. It never lasts.

Do you have equal volumes if you hook the speakers back up for a test?

ADDENDUM... In your prior post you said you used a 1K Hz input signal. Your meter may not be able to accurately read that. Try bringing your input frequency back down to the 400 Hz. range Shannon suggested. Depending on your meter it may even need to come down to 200 Hz. The manual for it should specify its accuracy and highest frequency allowable for an A/C voltage..
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Re: PICS of diy bd from low right channel amp

Postby alcors3 » Tue Dec 10, 2013 2:19 pm

Well it is not the speakers, they perform well with 3 other amps. The negative feedback is back in the circuit for this last reading. The meter is a Hantek scope attached to a PC and the frequencies are all right on. I think now I will reinstall the amp in the system. The preamp is a VTA SP6 and it works well with the other ST70 which is a rebuilt original, with a VTA driver board..I will repost after hooking it up.
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Re: PICS of diy bd from low right channel amp

Postby alcors3 » Tue Dec 10, 2013 4:24 pm

OK all who have devoted time to this, thank you. I placed the amplifier in the system this afternoon and voila everything was fine.I can only assume that a massive brain fart started all this, I certainly have no other explanation..now perhaps on to some svetlana winged c and some cleartops and maybe a well regarded 12ax7
Thanks all great support
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Re: PICS of diy bd from low right channel amp

Postby Shannon Parks » Fri Dec 13, 2013 3:37 pm

alcors3 wrote:OK all who have devoted time to this, thank you. I placed the amplifier in the system this afternoon and voila everything was fine.I can only assume that a massive brain fart started all this, I certainly have no other explanation..now perhaps on to some svetlana winged c and some cleartops and maybe a well regarded 12ax7
Thanks all great support


No prob at all. It's a pleasure to spent a couple minutes answering questions when someone takes the time to set up tests, take measurements and then reports back. Kudos to you, and enjoy some music. (b)

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Re: PICS of diy bd from low right channel amp

Postby dannyr » Fri Apr 11, 2014 11:49 am

I appreciate this thread. I have a Fisher 400 that has a louder channel even with a new volume pot that I have to get to one day. I fix it with the unit's balance but I'd like to figure it out sometime.
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