41Hz Tripath makes noise when on same SMPS as SB3

[topa]

Hello!

I have succesfully assembled a "41Hz.com" Amp6 Basic which works perfectly with my Skynet 8080 SMPS. (12v output)

Now I wanted to use the 5v output of the SMPS to power my Squeezebox SB3 at the same time. Power rating is not an issue, the SMPS is well over sized.

The result however is not so good, there is quite some noise when running both simultaniously. Interestingly, the noise is reduced when I dimm the display of the SB3. A second constant back ground noise cannot be altered though. Noise doesn't change with distance between units, I gather the SB3 spills out some form of noise back into the SMPS via the power cable?

I want to stress that all parts work just fine when not running together. If I power the SB3 with a different Powersupply, there is no problem either.

Maybe it helps you to know that the same SMPS powering the SB3 and a (12v) NOS DAC instead of the Amp works excellently too. No problems here.

I contacted Jan at 41hz.com who made a guess and advised me to put a cap in parallel to the SB3, but that makes no difference unfortunately.

Any other ideas? I'de hate to give up the idea of powering both units off one SMPS. It would make such a small setup!

Thank you,
Tobi.

[v-bro]

You seem to have a similar ground loop problem I've had and solved before. I made a usb charger supply from 12V for my mp3 player on 41hz AMP32. When I used separate supplies there was no problem, but with the amp and player on the same supply (even battery!) I had noise.

I solved two problems with one solution.

I placed two small transformers between the source and amp with 1:4 rating. The galvanic separation made the noise completely disappear. The sound also became very dynamic and refined, but also a bit louder. Just what I needed!

I posted this somewhere on the forum before, will look it up and place a link here if you like....if you haven't found it before me allready.......

Maybe there are other solutions like placing a diode towards one of the devices, I don't know (yet). Information about the issue I've found sofar all seems a bit mysterious. Nobody came up with really good other solutions yet....

[v-bro]

Here:More MP3 power!

[v-bro]

By the way, the same transformer can also be connected to have 1:1 rating (when you don't need more gain).

If you can spend 30EUR. per channel Lundahl transformers are the best, I got my OEP transformers from an old board. And I am fully satisfied with them.....

The transformers I used can be bought for about 15EUR. each, you need one per channel....

Edit: I recently built one for a friend that is only 3.5x3.5x7.5 cm for a stereo unit. with 2x RCA-in and 2x RCA-out in aluminum box (wish I had a camera....).

I can give you the details to build one yourself, or even build it for you. Mail me....

[topa]

Hi!
Hey, a transformer sounds like a good idea, yes!
Would these work here? (Pretty cheap&small):

"Transformer (German Reseller)"

Diodes.... might order something along with the transformers just to try. I don't understand the cause for the ground loop, so it's basically trial&error without any theory behind it.

Thanks for the offer with the amp! I'm in the process of installing it into aluminium cases, Amp is done, now I'm boxing the (external) SMPS.

Regards,
Tobi.

[topa]

Apparantly my link is not correct.
Just search for "NFU 1-1" on www.reichelt.de

It's a small print version of a NF transformer, 1:1 rated at 4,6 Ohm going for 2,35 EUR

[v-bro]

Still haven't been able to access your link, the impedance makes me suspect it is a speaker impedance transformer, but the price is right

Though I don't expect it to be very high quality for the price, the OEP has excellent freq. response.

[nicoch58]

hi vbro

which model and where buy OEP?

[v-bro]

Hi you can google on OEP A262A2E and find lots of shops that sell them (some even sell a shielding case and bottomplate to avoid 50hz hum from mains transformers that are near...)



Here's an example:
http://www.canford.co.uk/commerce/Pr...oductID=23-054
And here:
http://www.oep.co.uk/audio_transform...rformance.html

This transformer is meant for other use, but works great and has lots of options because it has double primary and secondary. (1+1:2+2, you can do several options parallelling or series connecting the windings )

I measured frequency response myself with ARTA and it shows an excellent linearity from 30hz to over 25khz....

[nicoch58]

fine thanks!