This is not just another gainclone

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#1,341
just got my GC chips! they said it would arive tuesday, but as it was free, 1 day late dosnt bother me 😀

i got 2xOPA541, 2xOPA547, 2xOPA548 and 2xOPA549.

will start constuction tonight 🙂

i was rooting through my component boxes and found only one pot, it was a dual one and it was 50k! how lucky was that! i found 2 matching pairs of 4700uf capacitors for the power lines, and 2 pairs of 1000uf capacitors for on the chip. i also have all the other components so im not bothering to buy any expensive ones unless it sounds really bad.

i cant believe TI would give away such a load of stuff and pay the postage for you :bigeyes:
 
#1,342
Cradle22 said:
Hi!

At least for ATX supplies this applies, don't know about the others.

Arndt
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Sorry gangs if this is a bit off topic,

The problem for this PSU is, it comes off from an old server and the power switch is controlled by motherboard. Which means I have to find from the maze of power cords which pair is the turn-on cords....When I plug it in, I could not get any measure out so I think there must be some wires that need to be shorted first. :scratch: , do you have any suggestion?
 
#1,344
SlouGan said:

Sorry gangs if this is a bit off topic,..., do you have any suggestion?
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I would suggest to wait for the Plitron transformer (unless it takes very long). It will take a lot of time to get this working. And even then it will not work very good, because of the low voltage, low current capability (1A) and because of the switching power supply inside...

I am aware this is not very helpful, but...

Fedde
 
#1,347
Matttcattt said:
i have 2 OPA541s, with the current limiter circuit, what do i do?

i have looked at the datasheet but it doesnt say what i connect the current limit setting pin (pin 8) to if i dont to use the max power limit.

the datasheets for OPA547, OPA548, and OPA549 say that i should connect it to -V.
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This is because the OPA547/8/9 is set to the max I_lim if you put V- on it (internal R) This feature insn't present in the OPA541, so in order to have I_lim (and short-circuit protection), you MUST use a resistor. The size if this R i determined by the SOA chart. Please read the datasheets...

😉 You could ommit the R ofcourse (as I did in my test-setup), but then you're not protected...
 
#1,349
mhennessy said:
Bricolo,

Your problems are almost certainly due to layout. Even just a short length of wire can act as inductor, which will provoke oscillations in any high-gain op-amp circuit. My GainClone has no Zobel network at the moment, and is perfectly fine.

However, I will add them to the final versions, as they will help to ensure stability into awkward loads. It shouldn't harm the sound quality, and you shouldn't be afraid to use them. But it is wise to ensure that your amp is stable without them...

Mine take about 25-30mA per IC at idle, and run cold. Take a close look at the pictures on this thread (and on my GainClone page) for examples of good layout practice. It really does matter!

Post us a picture of your current setup, and we'll try to help 😉 If the above picture is yours, then definately rebuild it!


Fedde,

I didn't mention the sound as the post seemed a bit long, and I'd put some comments on my homepage. But, first impressions are really encouraging - really clean, detailed, dynamic. Even with just one 120VA transformer...
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I'll try the zobel (I bought a 10R 10W resistor and a 0.1uF MKH cap)


Has polarity (RC or CR) an importance?
where do I put the zobel? close to the chip or close to the speaker?
 
#1,354
I think I need some holydays 😀


I dont' understant anything anymore :bawling:



I added a zobel (10R+0.1uF) at each speaker (at the speaker side, not amp side) and the residual oscillation is only a little lower



a strange thing (with and without the zobel)
I have very little 666khz oscillation (10mV) when the volume pot is 5%, at 50% it's much greater, and at 100% it's lower than at 50% volume


I'll try to remove my 220uF caps and keep the zobel
 
#1,356
Peter Daniel said:
Why didn't you add it at amp side?😉

I'm asking the question again: where is your common ground point for both channels?
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it was easier for me to add it to the speakers plug

but I'll try at the amp




I already answeared you: my gound point is at the bridge's ground, directly soldered to the bridges





I tested without the 220uF caps:
without the zobel: 2Vpp oscillation
with the zobel: very low oscillation (but still goes up when turning the volume pot up) but one of the 2 sides buzzed a lot
 
#1,360
i am having the same problems, however i feel it is more to do with the fact that youy are not using a chasis and have extra wires, shorten the wires as much as you can and see if that helps anything

i will be rebuilding my amplfier into a metal chassis, this should also improve things.
 
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