This is a subject I tend to rotate round to every few years. The latest spark is becasue I've just spent the day restoring a couple of old 1970's Rotel amps. Unfortuately one is looking positively past its sell-by date, which always begs the question "why don't I put something funky into it". Power amp replacements are straight forward, preamp replacements are more tricky. Anyway...
What I'm think of is a modern, practical pre-amp which has:
I'm not talking about audio-purism here: it needs to be practical, usable and affordable.
QUESTION: Am I covering old ground here?
Using semiconductor volume controls and source-selects gets rid of exotic pots/switches and also allows remote operation. No obsure components which can't be bought for Digikey/Mouser. Almost certainly require a microcontroller to handle the interfaces, but thats pretty straight forward (my posion is TI's MSP430's - I've already done a remote control interface for one using an AppleTV remote - very obtainable). The question is then to handle the rest of the system?
THOUGHTS?
There is one option which would make for a very simple circuit, but I suspect I may be burned as witch for even suggesting it: using an Audio Codec chip and 'normalising' everything into digital for processing!!! Something like the Cirrus CS4245: it'll take 6 Analogue Inputs (line level), 1 Digital Input, level balance, volume balance, mute and protect. The only issue is that the audio will be chopped into 24bit/192kbps then reconvertered
6x Line In >> CS4245 >> Audio Out
1x SPDIF Rx >>
Remote/Front Panel >> uC ^
To my mind, thats a 3 chip solution (Codec, uC and SPDIF Reciever) to cover some very substantial functionality
IS THIS MADNESS?
Just collecting ideas and thoughts. If I pursue this through, does it value anyone else?
Mat
What I'm think of is a modern, practical pre-amp which has:
- volume control
- source select
- line-level inputs
- option for front-panel control or remote control
- both digital and analogue inputs
- option for RIAA/phono
I'm not talking about audio-purism here: it needs to be practical, usable and affordable.
QUESTION: Am I covering old ground here?
Using semiconductor volume controls and source-selects gets rid of exotic pots/switches and also allows remote operation. No obsure components which can't be bought for Digikey/Mouser. Almost certainly require a microcontroller to handle the interfaces, but thats pretty straight forward (my posion is TI's MSP430's - I've already done a remote control interface for one using an AppleTV remote - very obtainable). The question is then to handle the rest of the system?
THOUGHTS?
There is one option which would make for a very simple circuit, but I suspect I may be burned as witch for even suggesting it: using an Audio Codec chip and 'normalising' everything into digital for processing!!! Something like the Cirrus CS4245: it'll take 6 Analogue Inputs (line level), 1 Digital Input, level balance, volume balance, mute and protect. The only issue is that the audio will be chopped into 24bit/192kbps then reconvertered
6x Line In >> CS4245 >> Audio Out
1x SPDIF Rx >>
Remote/Front Panel >> uC ^
To my mind, thats a 3 chip solution (Codec, uC and SPDIF Reciever) to cover some very substantial functionality
IS THIS MADNESS?
Just collecting ideas and thoughts. If I pursue this through, does it value anyone else?
Mat
So how do you make a good no-EQ analog amplifier for the cartridge?
It needs low 1/f noise for sure. How much analog gain?
me? I was lazy and got some boards form Wayne Kirkwood. Gain I am still playing around with but noise hasn't been an issue so far.
Ok, so it's a balanced instrumentation amplifier, with 12dB to 40dB gain.
It couldn't really have more mm gain than that without risk of overloading.
It couldn't really have more mm gain than that without risk of overloading.
I have the balanced MC card as well. But yes oodles of gain depending on your view on headroom required.
Looks like a very nice project. But my Quad ESLs need new power supplies, so that's gonna occupy me for a while.
Hmmm, after reading the responses, bit more research needed.
If I head down the digital route, then actually the ADAU1701 is a brilliant fit: it almost does bloody everything in one chip. However, as this is starting to feel like more work than art, then a TDA7440 would give a good analogue solution (with uC strapped to it).
To be clear, the reason I'm doing this as a 'compromise' design is to have a standard building platform to upgrade old amps with. Given my work so far with the Rotel, I've got a plethora of choices of power amp designs (including a Tripath board sitting in the shed which is tempting), but most of the failures in the old Rotel are preamp/signal path related. (some previous DIY-Audio'er decided to replace the electrolytics, but has badly fobar'd the PCB in the process).
If I head down the digital route, then actually the ADAU1701 is a brilliant fit: it almost does bloody everything in one chip. However, as this is starting to feel like more work than art, then a TDA7440 would give a good analogue solution (with uC strapped to it).
To be clear, the reason I'm doing this as a 'compromise' design is to have a standard building platform to upgrade old amps with. Given my work so far with the Rotel, I've got a plethora of choices of power amp designs (including a Tripath board sitting in the shed which is tempting), but most of the failures in the old Rotel are preamp/signal path related. (some previous DIY-Audio'er decided to replace the electrolytics, but has badly fobar'd the PCB in the process).
