This is not just another gainclone

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#1,321
fresh news:

the speaker that has hum (audible at 1m when the room is quiet), is the one connected to the channel with the 2 new filtering caps


and this hum is a little bit reduced when I disconnect the other speaker (the one connected to the channel without the 2 220uF caps)


I hope that when I'll add the caps to the other channel, hum will go

Non symmetry is certainly amplifiing this hum
 
#1,322
Hi, A newbie question

While I am waiting for my plitron transformer to come (+18,0,-18), 300VA, I've already got the LM3857T and OPA548, because the OPA548 allows very low voltage like +-4V, and I am so eager to do some test before my transformer arrive, I found out an old computer server power supply which reads:

OUTPUT
+5V 55.0a
+12V 16.0A
-12V 1.0A
-5V 1.0A

Can I just use this one to do a quick try run on OPA548? If I can, do I need 1000uf capacitors? I guess this PSU is already regulated.
Thanks
 
#1,324
power supply

Hi all,

I want to build a gainclone and keep the power supply external. Is it ok to connect the amp to the power supply by way of a power cord in the way that one would have a detachable power supply cord to a CPU which in turn plugs into an outlet. In other words, have a male socket on the amp which connects to a female end of a power cord. Then the male end of the power cord plugs into a female socket on the power supply unit. Is this OK or would it be too noisy? I view the power supply circuitry as an inetgral part of an amplifier's. I'm not sure if this is a "clean" enough connection.

Thanks,

vic
 
#1,325
And always put a resistor (10 watt or so) between +5 and -5 volts, otherwise a lot of computer supplies don't "accept" any connections to the +-12V (like no motherboard connected)...

Tried that once for a car amplifier, didn't work at first, only with load on +-5V...

Bye,

Arndt
 
#1,326
I have couple of questions.

Peter Daniel said:
I guess you can try +/- 12V on sypply. Although it's already regulated, placing 1000u or at least 220u at the pins wouldn't hurt and might actually prevent possible oscillations.
Click to expand...

Is it to prevent an oscillation or hum noise from power supply? I think those two are quite different.

Cradle22 said:
And always put a resistor (10 watt or so) between +5 and -5 volts, otherwise a lot of computer supplies don't "accept" any connections to the +-12V (like no motherboard connected)...
Click to expand...

Is there any possibility that it is because the ground levels of +/-12V and +/-5V are too far apart? If so, can one simply tie those two ground levels together? Well... I'm not sure whether I understood what you meant correctly. 🙂
 
#1,327
Hi!


I think I explained it wrong. The computer supply must have a load on some pins (I don't know them right now) on the motherboard supply connector, otherwise (although a multimeter shows the actual voltage of +-12 and +-5 volts on the other supply connectors with no load connected) the supply voltage drops as soon as you connect a device to the supply.

At least for ATX supplies this applies, don't know about the others. But sorry, I can't verify it right now...


Bye,

Arndt
 
#1,328
I want to build a gainclone and keep the power supply external. Is it ok to connect the amp to the power supply by way of a power cord in the way that one would have a detachable power supply cord to a CPU which in turn plugs into an outlet. In other words, have a male socket on the amp which connects to a female end of a power cord. Then the male end of the power cord plugs into a female socket on the power supply unit. Is this OK or would it be too noisy? I view the power supply circuitry as an inetgral part of an amplifier's. I'm not sure if this is a "clean" enough connection.
Click to expand...

I'm not quite sure where a CPU comes into this, I presume that you meant PSU.

This is a straight choice between sound quality and convenience but do you really need to have the umbilical detachable from both the PSU and amp?

The only justification for that would be to facilitate the easily substitution of different umbilicals to see which one sounded best.

Otherwise, I would go for a flying lead on either the amp or the PSU and a plug/socket arrangement to attach the umbilical to the other.
 
#1,329
SlouGan said:
Hi, A newbie question
+12V 16.0A
-12V 1.0A

Can I just use this one to do a quick try run on OPA548? If I can, do I need 1000uf capacitors? I guess this PSU is already regulated.
Thanks
Click to expand...

Hi,
dont do this. Minus 12V is weak, you can make unbalance in rails voltage on louder listening. Anyway, computer PSU works stable only when +5V is under big load.IMO

Regards
 
#1,333
moamps said:


Hi,
dont do this. Minus 12V is weak, you can make unbalance in rails voltage on louder listening. Anyway, computer PSU works stable only when +5V is under big load.IMO

Regards
Click to expand...

But OPA548 can even work with a single voltage supply, as long as the voltage difference between + and - is >=4 V (application notes). So even just using +12 V and ground should work...


Bye,

Arndt
 
#1,335
Grounding issues.

Bricolo,

It will not matter how much capacitance you use for filtering or what values you use for bypass if you do not address all the issues listed in the application notes of the TDA7294 datasheets it is almost guaranteed that you will have noise issues. I think this topic has been beaten about in the thread several times and the conclusions I have gleaned from the discussions almost always point to circuit construction rather than component selection (i.e. build it by accepted practices.)

Look at other techniques that members have used for their construction and emulate that construction. I do not know if you have changed your current "layout", if you have not, I can tell you from experience that your problems likely lie in the several unecessary feet of interconnections you have used for circuit construction. Sort it out, eliminate any unecessarily long connections, and practice proper grounding techniques.

Good Luck,
 
#1,336
Re: Grounding issues.

stadams said:
Bricolo,

It will not matter how much capacitance you use for filtering or what values you use for bypass if you do not address all the issues listed in the application notes of the TDA7294 datasheets it is almost guaranteed that you will have noise issues. I think this topic has been beaten about in the thread several times and the conclusions I have gleaned from the discussions almost always point to circuit construction rather than component selection (i.e. build it by accepted practices.)

Look at other techniques that members have used for their construction and emulate that construction. I do not know if you have changed your current "layout", if you have not, I can tell you from experience that your problems likely lie in the several unecessary feet of interconnections you have used for circuit construction. Sort it out, eliminate any unecessarily long connections, and practice proper grounding techniques.

Good Luck,
Click to expand...
my setup has changed since I posted the photo

now I connect the TDAs with cat 5E wire (8 wires, shielded by pair, and a global shield) and with a 0.75mm² wire to speakers
 
#1,337
I'm about to order the parts for my first pair of Gainclones which will be built as stand-alone power amps.

What I need to know is what resistors to place on the input in place of the pot? I know this was asked once before but this thread has got ratrher too large to go back and find the answer!
 
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