The (high-cap.) unregulated PSU for chipamps

[jkeny]

Is it a given that UCD180 is better?

Roibm,
I believe it is a given - just a matter of how much better - maybe Matjans can answers this?

John

[matjans]

i don't think it's a given per se. you can't compare the two, really. the ucd is a plug-n-play amp, a clone you have to build yourself.
the ucd delivers 9,5A continously whereas a single lm3875 delivers way less.

I can only say that my ucd based amp sounds way better than every clone i've built. a linn klimax is a chipamp too.

[roibm]

After looking through the "UCD180 questions" thread(18 BIG pages...), I can't really say who would be able to tell the story by it's name(i.e. what is better and why...)
And let's not forget, better is relative, and personal taste can influence the result a lot.

[roibm]

After looking through the "UCD180 questions" thread(18 BIG pages...), I can't really say who would be able to tell the story by it's name(i.e. what is better and why...)
And let's not forget, better is relative, and personal taste can influence the result a lot.

PS: bug in vBB, see the timestamp of the two posts

[carlosfm]

Originally posted by matjans
the ucd delivers 9,5A continously whereas a single lm3875 delivers way less.

I can only say that my ucd based amp sounds way better than every clone i've built. a linn klimax is a chipamp too.

Have you ever tried an LM3886 with regulated PSU?
The LM3875 is not suited to drive most modern speakers, just forget it.

[yuri777]

Hi Carlos

Could you describe the function of R1 and R2 on your unregulated PSU schematic?
Are R3 and R4 there to discharge the caps once the power supply has been turned off like Dejan suggests in his articles?

Thanks

[SheldonD]

I am not Carlos, but to answer your questions:

R3 and R4 are in series with a small capacitor, these can not pass DC which is what is stored inthe large filter caps. They do provide a very low impedance to high frequencies, as such will short out high frequency transients and suppress high frequency oscillation.

R1 and R2 are however a conducting path across the storage capacitors, and will in a short time drain the caps after shut down.

For Carlos: I am glad to see you are pursuing this area. But the problem can not be simply the higher inductance of larger caps as adding more caps to existing caps will lower the inductance. as inductors in parallel become smaller not larger.

[carlosfm]

Originally posted by SheldonD
I am not Carlos, but to answer your questions:
R3 and R4 are in series with a small capacitor, these can not pass DC which is what is stored inthe large filter caps. They do provide a very low impedance to high frequencies, as such will short out high frequency transients and suppress high frequency oscillation.

R1 and R2 are however a conducting path across the storage capacitors, and will in a short time drain the caps after shut down.

I've been out, thanks Sheldon.

Originally posted by SheldonD
For Carlos: I am glad to see you are pursuing this area. But the problem can not be simply the higher inductance of larger caps as adding more caps to existing caps will lower the inductance. as inductors in parallel become smaller not larger.

Maby there are other reasons too, I'm open to suggestions.
Anyway, on the chip there are 100uf caps bypassed with 100nf ceramics.
I've made many amps with several chips, several implementations, and tried too many combinations regarding unregulated PSU.
2x3,300uf per rail sound worse than single 4,700uf caps per rail.
Really.
2x4700uf sound as awful as 10,000uf.
Go lower to 1,000~1,500uf per rail/chip and that's the sweet spot.
But then most probably it won't drive your speakers.
This snubber lets me go higher in capacitance without mucking up the sound.

[yuri777]

Thanks alll for your answers.
I thought the discharge resistors had to be in front of the capacitors like on Dejan's schematics, which is why i asked.

Anyway, i have more questions:

1-Carlos, why didn't you implement the snub capacitors across each one of the bridge diodes like on Dejan's schematic?
I know Nuuk also recommends doing this on his web pages...

2-How come nobody here building PSUs recommends using at least one termistor (Digikey Part#KC006L-ND) to limit the Inrush current in the PSU?
From what i have read, it has many the benefits..
I know Nelson Pass has termistors in at least one of his PSU designs

Thanks

[scottw]

Having a little trouble understanding why the R in the snubber has to be such high wattage. Regardless of the interaction with filter capacitor inductance, isn't it still just "snubbing" high frequency? In the case of Carlos' schematic with 1R/0.120uf snubber the f > 1MHz. Can there be this much energy at high frequency in the PSU or is there something else going on?

Veselinovic was using up to 17 watt R's for 50 to 100 watt amps(me thinks). Did some digging. The original design of the Otala inspired amp that Veselinovic based his usage of the RC snubber on used 1 watt R's:

http://home.online.no/~tsandstr/Otal...20original.htm

and the production design built by Electrocompaniet used 0.5 watt R's for the snubber:

http://home.online.no/~tsandstr/sche..._ec_25w_am.htm

This was a 25 watt amp.

I understand a little wattage headroom will be a good idea for a stable filter but shouldn't two watts be enough for a 30 to 50 watt GC?

And thanks Carlos for pointing out this filter.

scottw