Source Selection IC

[danward79]

Thanks, I'll have a look

[mikesnowdon]

Hi.

I have a Cambridge Audio amp using the TC9163AF for input switching. Im looking into some mods and one of area I'd like to improve on is this. I believe this ic to be the most limiting factor in terms of how much SQ I can get out of the Cambridge amp.

Does anyone have any opinion on this IC's quality? Is there any kind of drop-in replacement which would give better SQ?

Ideally I'd love to replace the whole thing with relays but getting them to work off the buttons on the front panel (and remote) is beyond my expertise. Finding a pin compatible replacement ic which would give lower distortion than the current one would be the easiest solution.

Any ideas?

[mikesnowdon]

Anyone? The chip im trying to improve on is a TC9163AF ?????

Mike.

[Mooly]

Originally posted by danward79
Hi All,

Thanks for the responses.

I like the idea of using a summing amplifier with the input shorted.

Looking at the analogue switch ic's available in DIP packages it seems I am a bit stuck for choice. All the decent ones are smd's.

Does it have to be an IC ?
I designed this for my MOSFET amp, works better than any relays, the "off" isolation is too high to be measurable.

[mikesnowdon]

Hi Mousy.

Ive no idea what that is or how it works! Im just a modest tweaker/bodger at the moment mate.

I was hoping for a 'drop in' upgrade to the current ic as it would be the easiset thing. Alternatively some kind of 'kit' that works off buttons rather than a rotary switch would be good. I suppose it dosent have to be relays as long as its an improvement over an ic in terms of ultimate sound quality.

I have a srvice manual for the Cambridge amp. It shows the schematics and PCB layout etc. Ive been studying the input selector to try and figure out how its controlled by the microprocessor but its way over my head.

If anyone would care to take a look and see if I can use the existing micro processor (control circuit) to control relays PM me and I'll send a copy.

Mike.

[Mooly]

Mousy, who's Mousy

Right then Mickey just pulled the data sheet for the IC you mention. It's unique, no replacements, no drop in's
It's really just an array of bi-lateral CMOS swithes with a clever logic driver that enables easy ( for a microprocessor ) interfacing.
To be honest it's how it's implemented that is likely to be the limiting factor ie do the switches "see" any signal voltage across them in use.
As in my discrete version above which uses JFET's for the switch elements ( it would work just the same using your IC switches instead of the Fets ) they are arranged so that they are at the input of a virtual earth opamp.
See you ask about using relays driven from the microprocessor.
Anythings possible, but it's just not worth it IMO. You would need a decoder to emulate the logic in the switching IC. It's all done with serial logic a bit like the I2C bus.

[mikesnowdon]

Cheers Moggy!!!

I just had a barnstorming idea!!

Relays work on a voltage pulse that closes or opens the switch right? (I know its somthing like that) How about using the existing ic to contol an array of relays? Instead of the audio signal passing through the ic I pass a voltage through it which is directed to the appropriate relay thus swithcing the signal? Do you get the idea? Is is it do-able?

Mike.

I'll get your Name right from now on. He,He!

[Mooly]

A bit of lateral thinking there Zippy. That's certainly do-able.
Is it really really worth it though.
Best bet may be SIL style relays. Pick a supply voltage value, say 5 or 12v and choose the appropriate relays. Disconnect all the IC switches from the PCB. Feed your 5 or 12 volts to the "top end" of each switch. Take the output to ground via a 100 k resistor. Use 2n7000 FET's to switch the relays directly, gate of FET via 1 meg to the 100 k's --- easy.
It's easy to introduce problems too such as hum pickup etc. Just be careful how you do it. There are many ways to drive the relays, you could connect them in series ( coils for each input that is ) to enable them to run off a higher supply. You can get them with 24 volt coils, diode suppression built in.
You have to use a driver of some sort, like the FET, as the on resistance of the gates is too high for passing a relay current directly through it -- unless you found some ultra low power relays.

[mikesnowdon]

Is it really really worth it though.

I duuno really Mooly. This is all based on the assumption that relays sound better than a switching ic. I have thread running, all about possible mods to my Cambridge amp and those in the know have advised that one of biggest compromises to the sound quality is the signal switching. Im looking at ways to overcome this issue so as to warrant further mods like a bigger Trafo etc.

What do you reckon?

Mike.

[mikesnowdon]

CA 340A SE Modding.