Chip amp power supply- a beginners guide

[!]

Originally posted by tent
Hi again,
ok current status is: I checked with 3.15A fuses and they did also blow and now with 4A fuses I have a stable setup even by turning on and off several times, so this seems the best for my two 200VA 2x13.5V toroids, and now I can read after the bridge a 18.7V between V+/- and GND.
Next step will be connecting amp and then speakers.. after I connect amp and check how many milliamps there are on the output for the speakers, can I do it simple as is with my multi or is it better to put some load between them like a 10ohm 5W resistor?

I don't think you really need to measure the mA output to the speakers, but if you want to a resistor would be better and you'll have to have a RMS capable meter.

So now the missing questions for me are:
- Is it possible to use two bridges with my setup? (is it non sense? just parallel the out on two bridges, etc.)
- Is it possible to use just one of my two 13.5V toroids (with single secondaries) and the one bridge? (connectng only AC1 and AC2_, nothing on the 0V?)
- Would it be wiser/sinically better to change the 1500uF caps with some 10000uF or any other value? I also put under the current 1500 caps a 2200 resistor at 2W.
- Is it wise/sonically better to snubber the bridge? If so would you suggest me on this PSU+trafos something like a 2.2nF between the secondaries coming out the toroid?

Thanks in advance,
tent:wq

- Yes it's possible, but it seems a growing amount of expense and time for a 20W mono amp. Since the pair of 200VA transformers and 10,000uF capacitance is quite a lot for a 20W mono amp, you will probably have good regulation and have minimal benefit from a second bridge rectifier. This is audio though, the only way you can really know is to audition it both ways.

- It's possible to use only one of your transformers but would require building the amp itself a different way with coupling capacitors on the output to the speakers because then the amp output would swing between V+ and Gnd instead of V+ and V-. I would not recommend doing it this way, coupling caps large enough to handle the output power tend to become lossy at higher frequencies.

- 10,000 uF is overkill for a mono 20W amp, I would go with about 2,000 to 4,000uF at most, but some people have in the past felt that their 60W+ gainclones actually sound better if those use small 1,000uF capacitors so to duplicate their result you would use even less with a single channel at 1/6th the total output power.

Essentially everyone likes something different but my recommendation is roughly 220uF low-esr caps as close to the chip pins as possible, then about 2200uF on the PSU board. In other words the more capacitance you have on the amp board the less is needed on PSU board. Even then you are building a power supply that is overkill for this amp, personally I would save the PSU board for the next amp and just put a plain silicon diode and pair of 2200uF caps on a stripboard for this amp as you don't even need the thicker traces or wire holes for the size wire carrying this lower level of current.

- Some say they can hear a difference with a bridge snubber, some say they can't. Some say put just a single cap right after the bridge, others across each diode, others put a series resistor with any cap. If you have the caps lying around you might as well use them, and the suggested value seems to be in the ballpark, but there is another topic that shows how to calculate them but I can't remember the name of it, maybe someone else will remember or a forum search will find it.

[tent]

Hi !
well thanks a lot for your answers, and yes: you convinced me to finish asap with this amp (I'm almost finished and will post the photos) and go on further with a LM3886 one asap!

tent:wq

PS: going to stick to 1500uF and some snubbers here and there and seeing what changes.

BTW: any idea where is the PLUS of the C2 eletrolythic cap??
http://www.chipamp.com/images/lm1875-3.jpg

[korben69]

Originally posted by tent
Hi !
well thanks a lot for your answers, and yes: you convinced me to finish asap with this amp (I'm almost finished and will post the photos) and go on further with a LM3886 one asap!

tent:wq

PS: going to stick to 1500uF and some snubbers here and there and seeing what changes.

BTW: any idea where is the PLUS of the C2 eletrolythic cap??
http://www.chipamp.com/images/lm1875-3.jpg

You won't find + or -, this cap is "Non Polarized" or "Bipolar" one.
I've used a 22µF/50v Nichicon MUSE ES as C2.
Can be found here :
http://www.minisemi.com/Nichicon%20M...apacitors.html

[tent]

Originally posted by korben69


You won't find + or -, this cap is "Non Polarized" or "Bipolar" one.
I've used a 22µF/50v Nichicon MUSE ES as C2.
Can be found here :
http://www.minisemi.com/Nichicon%20M...apacitors.html

Uff you're right! completely overseen it..

tent:wq

[tent]

Hi all,
so I finally managed to finish the thing and plug it to my cd player!
I attach here some fotos of the current result before finishing the casing.



The only thing I have to say is that really the humm that is annoying me now is this trafo humming!! The loudpeakers and the rest seem really quiet.. but could it really be I have two really noisy toroids? are there differences between them? And of course, I now agree with ! that the power of this amp really limited is.. but anyhow I'll quickly move to a LM3886 now..



tent:wq

[tent]

underside (I added thos two bigr resistors under the caps..)

tent:wq

[tent]

the two tiny amps (no C2 cap for now.. where for the zobel nw)..

tent:wq

[tent]

mounted on the ground plate I'm testing it out now!
the two LM1875 are "hanging" from the two heatsinks..

tent:wq

[tent]

the two heatsinks are at V+ since no mica or such insulation was used to better dissipate and get better sound (somebody states this at least.. and so I simply decoupled it on the bottom plate by using plasic washes and screws (PVC) so nobody gets hurt..
The two trafos on the background are really huge and heavy..

tent:wq

[tent]

detail of those two 1500uF caps (not the best of the world but the best I could find.. pitty they are just 35V.. a bit few.. but I'd like to test soon with 2200uF and with 220uF @ 100V !

tent:wq