Audio Filing, under "D"


(Andy Wootton) #1

A couple of years ago, one of the channels on my Hi-Fi amp blew. It was only supposed to be a make-do because the previous one blew up. When I got it home, I discovered it was a modern take on the original, with just an X appended to the model number. Things seem to have moved faster since then.

I borrowed my daughter’s amp but was surprised to discover that it had no phono channel, so I was expecting any new amp to need a phono pre-amp. When I started looking, I was reminded about https://en.wikipedia.org/wiki/Class-D_amplifier models that seem crazy-cheap. I imagine these are what is going in the stand-alone speakers everyone seems to be buying. I think the tech is related to the switching transformers you get in phone chargers now.

I realised that if I ordered a pre-amp, I could plug it into a desktop line-in or listen through headphones, so I started messing about. This morning I had my tuner playing through macOS and Debian. In both cases I had to use an audio recorder then play it back. I seem to need some sort of software mixer to route the (analogue) line-in to the (analogue) line-out. I read that an ALSA mixer can be configured with a ‘loopback’ to make this happen but I’m not sure how. I have no problem with playing CDs to line-out, obviously. They are already digital.

I always thought of myself as a hi-fi separates person but I’ve realised a conventional amp is a phono pre-amp, a switch and an amplifier with tone/equalisation controls.

Does anyone have any helpful observations? Has anyone tried a small, £50 Class-D amp?


(Jon) #2

If you want good sound quality, don’t use headphone or phono outputs on a computer. They don’t use particularly good digital to analogue converters. Use USB as an audio out with a dedicated DAC, ideally with optical out, if your amplifier has an optical in. Or use a DAC with quality phono plugs and a good quality (and short) interconnect to the amplifier.

I use a cheap Linux netbook with a Cambridge Audio DAC Magic and a Cambridge Audio amplifier, in the above configuration, and the results are pretty good even with low-bitrate MP3s.

I don’t know if this helps with your specific problem. If you can give some specs on your current amplifier, including what input or output connector is not working, folks might be able to give you ideas on getting it working. :slightly_smiling_face: :headphones:


(Andy Wootton) #3

The amp is a Sansui AU-X117. Smell of burning, I think :slight_smile: Something similar happened to my AU-117. I paid about £40 to get one side fixed and the other side went. The new amp cost £70, so I’m not convinced it is worth mending.

I’m not really looking for hi-fi, just noise without the mains hum when silent I get from the cheap PC amp I’m using now. I don’t really listen when I’m using a computer. My headphones came from B&Q. I mainly listen to CDs by bands who probably used the line-in on a Mac to record.

I found a note on the ALSA loopback. It’s an 'orrible command line hack. Linux sound is complicated! I’ve been planning to play with Jack for about 10 years. Maybe this time.

btw I have worked out that I won’t get an equivalent hi-fi amp for £70 any more.


(Jon) #4

In that case, I suggest plugging headphones into the computer itself, and a Bluetooth speaker if you want to hear your music out loud. I agree that there’s a point when one should give up on old equipment!

I got one of these speakers recently, so I can listen to podcasts while doing the washing up. I think it was around £50, and the audio performance is pretty good for the size.


(Andy Wootton) #5

The new toy I didn’t say I’d ordered has arrived. https://www.gear4music.com/PA-DJ-and-Lighting/Behringer-PP400-Microphono-Phono-Preamp/796?origin=product-ads&campaign=PLA+Shop+-+GENERIC&adgroup=GENERIC&medium=vertical_search&network=google&merchant_id=1279443&product_id=9402d1&product_country=GB&product_partition_id=111959081119&gclid=EAIaIQobChMI7rS5p5bJ2gIVxJUbCh1gSAXwEAQYAyABEgJrVfD_BwE
My current PC amp doesn’t allow me to comment meaningfully on quality (I’m not even sure my ears do) but I can at least hear what the reckids are now. It’s UB40’s ‘Reefer Madness’ on 12" 45.
I forgot it had line-out as well as RCAs. That’s saved me some knitting.