LM1875 power supply

[Chricket]

Hi everyone,

This forum seems to be very active a and helpful to novices. I have a question about lm1875 power supply. because I currently have an 18-0-18 6amps transformer(pls disregard the T1 value on the diagram). Can I use the circuit below for the tranny?

[sofaspud]

It ought to work okay, but since you only need 18-0-18 why create it twice? Just use a more robust bridge rectifier. Once.

[AndrewT]

Hi,
the dual amplifier (stereo/two channel) running from that common transformer has a common connection to ground.

Each amplifier will connect to ground via the PSU and again via the input interconnect.
These are big ground loops. You will get buzz and hum.

either use a dual secondary and dual bridge rectifiers and dual Disconnecting Networks or
use a centre tapped single dual polarity supply and connect all channels to the same ground.

Even following either of those advice routes and you may still get buzz and hum, but at a lower level.

[wintermute]

I've done this without any problems, However The zero volts returns from both channels are to a point exactly central to the two half's of the power-supply.

My original reasoning for using separate rectifiers and cap bank for each channel was that I thought it would reduce channel crosstalk. As I never built a single bridge supply for the amp I can't say whether or not it really does make a difference.

layout of the board is attached below, as well as an actual picture. The amp does have some very low level hum, but it is only possible to hear it with an ear right up against the speaker.

Tony.

[Chricket]

Thanks for the responses. I just saw that power supply circuit at (url removed by moderators) and thought I might use a single transformer for two channels.

The original power supply circuit is this
(link removed by moderators)

and the amp's cicuit is this
(link removed by moderators)
Would a separate transformer for each channel be better?

[Chricket]

will this work or there will be a hum too in this configuration?

[Leolo]

Hum and ground is a complex topic. You might want to read this article about Audio Component Grounding and Interconnection

[Greg Erskine]

Originally Posted by Chricket

Thanks for the responses. I just saw that power supply circuit at (URL removed by moderators) and thought I might use a single transformer for two channels.

The original power supply circuit is this


and the amp's circuit is this


Would a separate transformer for each channel be better?

Hi Chricket,

Here's the original source of this amp.

Silicon Chip Online - Schoolies Amp

BTW: The original article only describes a mono amp.

BTW: These people seem to be ripping off Silicon Chip. The pictures they reproduce are exactly those published in the SC article except any reference to "Silicon Chip" has been erased.

regards

[wintermute]

Greg, is the power supply in the original post also SC copyright? I haven't seen the article. Just pondering how to fix the issue....

Tony.

[AndrewT]

Cr,
post5:
the 22uF NP in the feedback loop is far too small.
Try >=100uF. I would suggest 220uF.