non-oversampling dac to gainclone - coupling/filter caps worthwhile?

[sharpi31]

I have a TDA1543 non-oversampling dac with passive I/V conversion feeding a standard LM3875 chipamp with 1000uF panasonic FM power supply caps.

I've tried 4uf russian pio coupling caps, which rounded off the sound a bit - I ended up removing them.

My question is this: is it worth using a small RC network between the dac and chipamp to drain off some of the ultrasonics? Would this help the LM3875 by removing RF and other nasties from the input? I'm torn as I appreciate much of the quality of non-os dacs comes from a lack of intrusive filtering, but I think a parallel RC network would act as a 1st order passive high pass filter which may not be too bad.

Any experience would help. I have some low value russian teflon caps to play with, and am happy to experiment. Please tell me if this is a waste of time.

Thanks :-)

[Nuuk]

What type of chipamp are you using?

And what type/value of volume control?

[sharpi31]

Hi Nuuk.

Standard chipamp.com revision 3 LM3875 with external PSU using 1x 225VA toroid with twin 18V secondaries. I wanted my first unit to be a standard gainclone so I can have a reference for the next one...

I have an Alps blue 20K pot between input and chip, so passive preamp only. I have read that TDA1543 dacs with passive I/V prefer 20-25K potentiometers, hence my choice.

I love the sound of this system. I can't believe the quality for the investement. I used to work for a high-end manufacturer and a couple of high-end hifi retailers, so I have owned/played with lots of highly rated expensive kit. I love my new setup and can't help but laugh when I think about the stuff that gets sold for silly money! All my speakers are full-range fostex/tang band etc. so I won't be getting any ultrasonics out of the speakers anyway, but I'd be interested if doing what I suggested allows the amp to work better.

Your help is much appreciated.

[Nuuk]

That's all OK then and good to see you have done your homework!

I don't know about the filter. I have tried an LPF in conjunction with a buffer (please refer to my site) but don't use one at present.

It sounds to me as though you just have to 'discover' the 'right' cap for the job.

As you have saved all that money by not buying commercial, it may be worth investing in a few good coupling caps until you find the one that works best for you.

[sharpi31]

I take it from your response that you think a coupling cap is worthwhile?

Thanks again.

[Nuuk]

Well.... if you are not using a pre-amp and are confident that there is no DC on the output of the DAC.....

Why were you using the PIO's?

[sharpi31]

I was confident there was no dc offset to worry about but always like to experiment (like us all!). I'm happy without coupling caps, but it just bugged me that ultrasonics could be removed simply and this might give the amp an easier time (giving me better sound overall). This is pure speculation but we all know that removing HF nasties can help amps in many situations. This is not because I'm concerned about these frequencies coming out of the speakers (since owning non-os dacs I'm convinced this is a massively over-rated concern, and anyway my full rangers don't give out much over 20K anyway) just that I hypothesised this might allow the amp to do a better job.

If I'm talking cr*p please tell me, it just seemed an intuitive area to explore and I wondered if others had been down this road before.

Thanks again.

[Nuuk]

Your idea about removing the highest frequencies is correct, at least in theory. That was the reasoning behind the buffered LPF that many of us tried with out GC's. So if you want to try it it for yourself it's not difficult to implement.

My current speakers have helper tweeters that are supposed go up to 40K and I don't hear any 'nasties' from my NOS DAC.