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Chip Amps Amplifiers based on integrated circuits

vintage amplifier circuit board with TDA2010 with this tone/volume control circuit
vintage amplifier circuit board with TDA2010 with this tone/volume control circuit
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Old 5th December 2017, 11:26 PM   #11
PRR is offline PRR  United States
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Quote:
Originally Posted by Mooly View Post
...you typically need two diodes per meter......
Good metering wants more than I see here, sure.

But dancing needle to dress-up a low-price set, fed the large output at a speaker, is usually resistor, one diode, and a soothing cap. Given 8V signal and 1mA meter, a few K resistor, a diode, and ~~50uFd cap so the needle is not too jumpy. Efficiency is not needed. Precision is not warranted at this price.
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Old 1st March 2018, 12:58 AM   #12
Peters8 is offline Peters8  Italy
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Quote:
Originally Posted by Mooly View Post
Yes, I would concur with PRR having looked at the second image although you typically need two diodes per meter......

This is why working from images is difficult

This shows the basic passive VU circuit (its crossed out in red because it is considered a bad design).

C1 blocks any DC present.

D1 is a clamp and conducts on the negative part of the waveform, effectively removing it by shorting it out.

D2 passes the remaining positive peaks to capacitor C2 which charges up to the peak voltage. This voltage drives the meter.

The trouble with these simple circuits is that they are very insensitive and do not work at all with low level input voltages.

Hope you are feeling better soon
Hi Mooly!
please forgive me for the delay replying to you!
Observing the amp board, I've just noticed that there're two diodes more on the circuit board: please take a look at the amp board and you'll notice two diodes behind the two grey ELNA capacitors (They're 1000uF 16V and they're the biggest ones)...on the body of the these two diodes there's a code: 1N4001 (and in the lower part of their body there's another code: 710).
Well, my question is the following: are they the two missing diodes of the vu-meters system? or they don't have any connection with the vu-meters?
Thank you very much for your patience
Best regards
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Old 1st March 2018, 07:25 AM   #13
Mooly is offline Mooly  United Kingdom
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vintage amplifier circuit board with TDA2010 with this tone/volume control circuit
I'm not sure what those diodes are tbh, at least not without seeing how they connect. The grey caps appear to be for speaker coupling and so I suppose it is possible they are meter related.

Yu would have to see where each end of the diode goes and trace the circuit out.
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Old 2nd March 2018, 12:46 AM   #14
Peters8 is offline Peters8  Italy
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OH Mooly!thank you for your fast reply, first of all.
I can confirm that one pole of each diode is welded to a side of the Elna caps (speakers coupling).
In another thread about this object, my friend Anti supposes that those diodes are a sort of "anti-pop" circuit. In fact the two Elna caps are connected to the positive poles of the speakers(and the of the vu meters) and the negative pole (I mean the ground) is provided from the power supply (I mean from from the
rectifier negative pole).
This is the other thread where we're talking about this argument:

TCA940 vintage IC:distortion please look!!!

So please, dear Mooly, could you take a look at this topic and tell us your opinion about the function of those two diodes?
What do you think?: could they be a sort of an "anti-pop" system?
I know that your opinion could be an interesting contribution to our theories.
The only thing that I can confirm is that the two vu meters worksb when I've connected the other amp circuit board based on the TDA 2010 (you can see it in the pictures) without these two 1N4001 diodes mounted on the original TBA810 amp board.
Let me know what do you think about their function, please! I'm so confused, unfortunately
Thank you once again for your support
Regards from Italy
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Old 2nd March 2018, 03:36 AM   #15
stocktrader200 is offline stocktrader200  Canada
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you need to get a schematic or draw one from the board connections then drop the 2010 into the correct pin positions.
it looks like the 810 has a gain of 100 ( 40 db ) so the 2010 needs to be set for this.
then wire in the pins to the correct holes. mount to copper plate around 810 and add extra heat sink if nesscessary
meter diodes are usually Germanium for low level sensitivity.

Last edited by stocktrader200; 2nd March 2018 at 03:46 AM.
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Old 2nd March 2018, 12:10 PM   #16
Mooly is offline Mooly  United Kingdom
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vintage amplifier circuit board with TDA2010 with this tone/volume control circuit
Hard to say what the diodes are for without seeing them drawn in on a correct circuit diagram. The devil is in the detail and you would have to draw it out.

Pop or thump suppression seems unlikely as I can't think of a way it could be configured to do anything.

Another possibility is a 'clamp' to the power supply to prevent inductive loads causing voltage spikes and possible chip damage... but its a bit tenuous on something like this.
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Old 4th March 2018, 07:17 PM   #17
Peters8 is offline Peters8  Italy
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Thank you!
You're absolutely right: as soon as possible I post a picture where I'll track the rail of these diodes on the circuit board.
Thank you guys, once again!
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