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cowana 29th June 2012 02:35 PM

DIY preamp component choice
I recently purchased a set of Tannoy V4 speakers to run with a Quad 405-2 amplifier. I'm an electronic engineer with lots of experience with digital electronics - however I'm fairly new to the world of audio.

The Quad 405-2 amplifier has no controls or variable attenuator on it, so requires an external volume control. The amp currently takes a 0.5v input - I plan to convert it to a standard 1.5v input.

So, I need to make a box that will:
- Provide volume control
- Provide adjustable balance (L/R)
- Provide adjustable bass/treble levels
- Allow for input selection of line level analogue inputs (PC/Mp3 player/etc)

As digital electronics is an area I'm familiar with, I plan to have:
- A graphic LCD display showing current settings
- A rotary encoder and user interface for the graphic LCD
- Presets, selectable with a remote control

I've been searching for chips that provide volume/balance/tone control through a digital interface (such as SPI or I2C). I have found several chips which look suitable, however the datasheets all mention 'car audio' rather than 'hifi audio'. I'm concerned that I could spend a few months designing and making this product, then find that it degrades the audio signal so much that it is unusable.

Does anyone have any experience with any of the below chips, or if not, do the specifications look suitable for home audio?

PT7313 - I2C control of volume, tone, gain and input
LC75342 - SPI control of volume, tone, gain and input
TDA7313 - SPI control of volume, tone, gain and input (mentions hifi, but no distortion figures)

The only digitally controlled part I could find that has excellent specifications and would definitely be suitable for hifi applications is the PGA2311 - however this doesn't provide any control of bass or treble. If the other options are going to distort the signal too much I could just use the EQ built in to the MP3 player/PC/etc, however I would prefer if the preamp had it's own settings.

Any thoughts or opinions are much appreciated!


indianajo 4th July 2012 12:58 PM

Good luck. I've never heard a car audio system I thought sounded good. The whole industry dove headfirst off a cliff when car audio became popular. Who thinks "buzz buzz buzz buzz" is even music. First Circuit City drove the audio stores out of business, now thank goodness they are bankrupt themselves, just like all those dead "audio" systems in the little f**t cars sold at the height of the craze. How were you supposed to listen to anything in a 5 sided room? And Best Buy demonstrates in a concrete warehouse with metal ceilings, just like your living room, right? Bah, humbug.
I've got a tube dynakit PAS2 preamp that sounds good, and a heavily modified op amp disco mixer that sounds almost as good. Digital control of input relays for source selection sounds doable and useful, and I like the idea of a remote control device to turn the system on and off, but the simpler analog treatment of audio is more my style. Digital sources can be okay, and my HDTV puts out a decent concert sound with a PBS program source, but the amp circuits and speakers of that are tinny and due for an upgrade as soon as I figure out how to get the case open on my Peavey mixer (which will balance the volume from the six various audio sources to my TV) and upgrade the op amps etc.

homemodder 10th July 2012 06:30 AM

You would be surprised how good it can be, there are systems that are not designed for buzz buzz buzz. You should listen to mine, Me and friends I spend more time listening to my system in the car then the system in my house and that is based on electrocompaniet separates. That should tell you all.

reactivepower 12th July 2012 02:49 AM

Look into the NJR MUSES72320 volume IC. it doesn't have tone controls, but will probably be one of the better volume control ICs you can find. No experience with it myself though. No word on availability either.

Lin0 18th September 2015 01:35 AM


Hey, just built the LC75342
I like its functionality(& its loud), however I am not yet sure of the audio quality. Seems to be introducing a lot of hiss(not hum). Maybe its my fault as I'm powering it with a transformer from a Fischer tape deck and am unsure how install a filter circuit inline to address the high frequency hiss. And I can't use the remote function with my tv because the remote for the tv also controls the LC75342

AndrewT 18th September 2015 12:46 PM

Have a look at Wapo's LED/LDR volume control. A digitally controlled analogue volume adjustment.
Or consider the Pass B1, a buffered volume potentiometer. A hand controlled analogue volume adjustment.

rsavas 21st September 2015 09:56 PM

have you checked out this thread

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