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Micro processor controlled preamp, how is it done?

Zombie

pfm Member
I have a Quad Artera Pre which claims to be "old school" analogue, but uses a microprocessor to, I assume, set and control different settings for all inputs and outputs.
How is this done?
Does it control some kind of variable resistance/capacitance components?
Or is it done in the digital domain?
Switching inputs is now done with relays, though. Would be interesting to see a schematic.
 
My Audiolab 8000Q is real old school it does have a remote but that controls motors to turn the volume control and also to select the input
 
It's always a bad idea and usually it means compromises have been made to sound quality in order to get greater convenience and ability to remote control it etc.
Microprocessor can control sealed silver contact relays for source switching and discreet resistive volume ladders, like my Emotiva and others. Or it can control Cirrus Logic line stage volume chip.

No compromises.

Keep those stereo and balance analogue pots far away from me. :)

If you want true old school, buy Goldpoint switch box and passive discreet attenuator volume controls - based on silver Elma switches and laser trimmed SMD resistors.
 
You can do CMOS input switching and digitally controlled potentiometer with cutting measurable corners, if designed with thought.
For design purity you can use telecom relays to switch inputs and a motor controlled pot or even switched ladder attenuator. If nothing else it gives the reviewers something to write about.
The microcontroller can go into deep sleep unless woken by an infra red code, so it should not affect the sound
 
Microprocessor can control sealed silver contact relays for source switching and discreet resistive volume ladders, like my Emotiva and others. Or it can control Cirrus Logic line stage volume chip.

No compromises.

Keep those stereo and balance analogue pots far away from me. :)

If you want true old school, buy Goldpoint switch box and passive discreet attenuator volume controls - based on silver Elma switches and laser trimmed SMD resistors.

CAN.... but often doesn't. Often abominations like the Cryrus Logic vol chip are used and other much worse examples also. It's usually a way, in mass produced kit, of saving money as good quality analogue controls, and especially things like switched attenuators, are very expensive.
 
So how is it done, then? Making and saving settings for five inputs in the analogue domain?
 
Hi Guys;

Like dual gang volume controls, Microprocessor Controlled solutions can vary greatly in cost and quality.

If you want to know how they actually work just google it and start reading. In short; it’s a resistor ladder that is usually switched by semiconductors (usually contained on a single Integrated circuit) or more exotic versions can use an array of relays, (expensive and mechanically noisy).

A small microprocessor, usually another IC, will take the output from the remote-control receiver or rotary encoder and switch the ladder to the desired setting. A more desirable execution of this design will have the Microprocessor go into standby when it is not receiving a control signal and thus eliminating electrical noise and unnecessary power draw.

Which is better? That’s a loaded question; like everything in this world cost will be the overriding driver of quality. A properly executed Microprocessor Controlled solution will outperform a cheap volume pot, it can easily track within 0.1 of dB across it’s entire range. Even Mid-priced Volume pots will struggle to maintain its balance within 2dB at the lower end of it’s travel. A Microprocessor Controlled solution also has no moving parts to wear out (except for Mechanical relay switching).

For the DIY’er; a good quality volume pot is the easiest solution, to build a Microprocessor Controlled setup requires the ability to design and make your own Printed Circuit Boards or at the very least you can purchase and assemble a pre-packaged kit. I have a cheap 200-dollar Chinese made receiver that uses a single Microprocessor Controlled “no-name” IC that provides Volume, Bass/Treble, Balance and input switching, Its overall performance is nothing more that “adequate” for casual listening if slightly noisy. My Arcam Amplifier uses one of the Burr-Brown Chips. It’s dead silent, offers individual input level trimming, channel balance within 0.1dB across it’s entire range as well as remote control operation, something you can’t do with a motorised volume Pot. I also have a NAC72 that uses the Alps "Black Beauty" volume pot. It has a silky smooth operation, channel balance tracks very well and it functions perfectly even though its nearly 30 years old.

Like many things, the execution of the technology often is more important than the technology itself.

LPSpinner.
 
That's what I suspected. Advertising the relays to switch sources, but still using the good old 4066 approach but in other forms elsewhere.
 
Hi Zombie. A quick google search for internal photos and reviews suggests that your Quad Artera Pre uses a Burr-Brown PGA4311 4 channel Audio Volume control integrated circuit.

The audio section is a purely analogue and there is no digital processing of audio. The only digital circuity is the Logic controller, the -106 dB (independently measured) noise floor would suggest that QUAD have this well and truly isolated and under control.

Google the data sheet and check the specs. You can see that like all the PGA series, it has an internal gain stage with the variable resistor in the NFB loop to set the overall gain.

LPSpinner
 
The Beomaster 8000 released in 1980 had all that, plus remote and Datalink. It still works perfectly today.
I have often wondered how it would perform with no cmos microprocessor-controlled volume attenuator (it uses an optoelectronic wheel that counts pulses) and source selectors.

Beomaster 8000 on Beocentral.
 
The Beomaster 8000 released in 1980 had all that, plus remote and Datalink. It still works perfectly today.
I have often wondered how it would perform with no cmos microprocessor-controlled volume attenuator (it uses an optoelectronic wheel that counts pulses) and source selectors.

Beomaster 8000 on Beocentral.

An earlier model (I assume it's earlier!) did the job properly with relays under control of CMOS logic. It is very similar to a design of my own which uses TTL logic to do the same thing.
 


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