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Old 14th May 2007, 07:47 PM   #1
EAH is offline EAH  Panama
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Default Two pots

Some years ago I made 1 amp (tda 1554Q 2x22w) for my computer.
In the input, I put a pot of 50K ohm for gain control, It still functioning OK with a pair of JBL control 1 speakers.

, now my soon wants 4 outputs with the same 1554 amp, He wants to control 2 pair of speakers, each pair independently.
I allready made 2 amps in a case but:

1- Need to use 2 independent volume control, can I apply the same input signal to each 50 k ohm pot or do I have to

2- increment the value of each pot
3- decrement the value of each pot

As long as I know the input signal (is) seen by each amp will be is/2 ??

TY
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Old 15th May 2007, 02:59 AM   #2
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Default Re: Two pots

Quote:
Originally posted by EAH
Some years ago I made 1 amp (tda 1554Q 2x22w) for my computer.
In the input, I put a pot of 50K ohm for gain control, It still functioning OK with a pair of JBL control 1 speakers.

, now my soon wants 4 outputs with the same 1554 amp, He wants to control 2 pair of speakers, each pair independently.
I allready made 2 amps in a case but:

1- Need to use 2 independent volume control, can I apply the same input signal to each 50 k ohm pot or do I have to

2- increment the value of each pot
3- decrement the value of each pot

As long as I know the input signal (is) seen by each amp will be is/2 ??

TY
The load seen by the source will be the value or the two volume pots in parallel together with the impedance of the power amplifiers in parallel. This may mean you should use a buffer (or two).

A lot of unity gain stable opamps make great buffers.

A few examplesin no particular order)

LM4562
OPA2227
AD8620

I would put those buffers directly after the two pots, feeding the power amplifiers with a nice low output impedance.

With the buffers in place you could easily use 22 or 47K pots.

You may not need the buffers, but they probably will not hurt...

More details = better answer.

Best of luck!

Cheers!
Russ
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Old 15th May 2007, 03:28 PM   #3
EAH is offline EAH  Panama
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Join Date: Apr 2007
Default TY for your answer

Russ:

Sorry about my english, it is not very good so I will try to explain myself

I was thinking on this

My son will use the amp with one source at the time, and it could be:
1- Computer
2- Sony mp3 walkman

So I want to use just one input RCA conector and then split the signal in 2. Conecting from the rca to the pot1 and pot2
Then from each pot to its corresponding amp input.

So everyting is going to bo seen in parallel by the source.
the worst case will be at max volume on each pot:
50k pot1, 50k amp1 input, 50k pot2, 50k amp2 input = 12.5k seen by the source.

Is it too low impedance seen by any of the sources my soon will use???
The volume obtained in each amp will be less, at a given set in the source volume, comparing using the pots at max and not using the pots at all???
The courent demanding from the charge will be too high in order to run out of baterries to soon????

Thanks again

EDUARDO AH.
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