hi everyone, does anybody have service manual of PA 7000?
I got this clone preamp of 7000 and have distortion problem on one channel and bad quality on other.
removed "keys part" from circuit (SC I mean), quality of right is fine but still have huge distortion on left output of first opamp.
here some pics I downloaded:
I got this clone preamp of 7000 and have distortion problem on one channel and bad quality on other.
removed "keys part" from circuit (SC I mean), quality of right is fine but still have huge distortion on left output of first opamp.
here some pics I downloaded:
Attachments
the distorted channel has around 10v dc and I dont know why,
suplly is +/-12v. almost checked everythind,
the tone control section has a feedback but dc apears in L chanell
suplly is +/-12v. almost checked everythind,
the tone control section has a feedback but dc apears in L chanell
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pcb is realy bad quality one, and had several disconnections.
I think the distortion was for filter cap went out of circuit
but theres a question, why output of device has smaller signal than opamps output,
is this natural?
output of opamps are very loud with headphone and another question,
can I use opamps output for headphone?
I think the distortion was for filter cap went out of circuit
but theres a question, why output of device has smaller signal than opamps output,
is this natural?
output of opamps are very loud with headphone and another question,
can I use opamps output for headphone?
Hello.
This is protection against DC "plop".
Output will be shorted to GND until 4,7uF full charged.
This is protection against DC "plop".
Output will be shorted to GND until 4,7uF full charged.
That is not an output stage. It is a MUTE. One transistor and diodes senses power supply rise and/or fall. It switches a transistor on each channel to short the output.
tnx for the answer
hence there is a dc protection circuit can I remove coupling caps?
I suppose not right??
This is not DC protection.
I don't know if you can remove the capacitor, you must check if there's voltage at output before the capacitor, between pin 7 and GND .
I don't know if you can remove the capacitor, you must check if there's voltage at output before the capacitor, between pin 7 and GND .
The 3-band (Bass, Middle, Treble) EQ _is_ active. 3 bands is about all this type of EQ can manage.
Why?
If the capacitor is bad, replace it with a good capacitor.
There is no large DC here, but small DC will increase (what Samsara calls) "plop". I am *sure* Gemini did not spend 5 cents for a cap without a reason. In PA mixers, caps are often wanted to reduce scratch and plot when controls are moved during the show. It is a fine design but not a "super hi-fi" design and I do not think random part changes will make it "better".
first of all tnx again for your time and answer.
whats the difference between 10uf coupling cap and 4.7uf? I have seen different caps for coupling. which is better? bigger or smaller?
I simulated this circuit and coupling 4.7uf at the output made huge differences. but I didn't get how muting section works
what about another opamp like opa27 or so? in simulation opa27 was about 40ms faster!
can you give me some guidance on hi-fi designs?
Impossible. (A 40 milli-Second delay requires an actual Delay Line; tape, BBD, 40 feet of pipe, or digital storage.) Re-read what the sim is telling you.
Anyway pure delay is not a problem. When I listen to an LP there is a 30-40 YEAR delay from recording to playback.
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