Audio Innovations Alto

[canfixit]

Wanted...Help with schematics/service manual or bias current setting.

Despite hours of searching I can find nothing on the web about the Audio Innovations Alto, there's only the odd passing comment even on this site.

I bought one not working and on inspection found previous repair bodging that had damaged a number of pcb tracks and very bad soldering where new transistors had been installed + some wrong equivalents. Anyway cut a long story short - fixed all that re-wiring tracks as necessary, replaced all the caps etc and got it running and sounding OK.

Problem is I can find no information about setting the bias and normal procedures for what I presume is a fairly standard class B design don't seem to be working. There are two trimmers per channel and I would normally expect one to control DC offset and one bias current. The amp runs ok and doesn't get too warm if I leave them as found but that gives output offsets of 200 and 500mv ish. Adjusting the trimmers will get that down to near zero but then the output transistors get very hot, very quickly and Collector current is climbing indicating runaway.

Only unusual design feature I've noticed is 3 (i think) signal diodes arranged in a sandwich between pcb and output transistor heatsink. N.B. Each transistor has separate board mounted sink with bias transistors attached. What's that about?

Can anyone help, does anyone have one of these amps they can take some measurements off. There may yet be something else wrong I haven't located yet.

Thanks.

[hotiron]

Has anybody ever found a schematic for this piece of junk?

It would appear to be a JLH design but the layout and casing suck.


Edit:
sorry didn't mean to use the man's name in vain!

[jaycee]

Audio Innovations is a brand of Audio Partnership plc, the same people that make Cambridge Audio.

The signal diodes are probably being used for temperature sensing, instead of the VBE device itself.

[eggontoast]

Originally Posted by jaycee

Audio Innovations is a brand of Audio Partnership plc, the same people that make Cambridge Audio.

It is now but it wasn't when the first series of Alto amplifiers (grey ones) were manufactured. The silver version is a re-hashed version under the Audio Partnership regime and is of much poorer quality than the originals, the matching cd/tuner is a right bag of poo. I have repaired a few of these but have never managed to find a schematic unfortunately

[sparrowSG]

Hi,

I also have one of these nice looking but very unreliable amps (now on my 2nd) and it has died on me. Does anyone know of somewhere I can get it fixed please, or at least someone to look to see if it can be/is worth fixing? I've been wondering whether just to give up and get something else but it seems a shame to just dump it if it's something simple that's wrong.

Thanks all.

[thoglette]

Originally Posted by sparrowSG

... but it seems a shame to just dump it if it's something simple that's wrong.

Don't do it - send it to me!

On that front, the only information I have been able to find is a gramaphone review of July 1994 which states that it is a quasicomplimentary AB design with a DC blocking capacitor.

Oh, I would love to get some dead ones to play with!

[sakis]

THIS is actually a small nice amplifier .. normally a few milliamps will do ....something like 50 ma only problem is that you will need a scope to tune i properly ...if memory serves properly one trimmer is for symmetry while he other is for the bias

still for an amp like that i would change the capacitors to anything bigger may fit in the case ...4700 for that total power supply is barely enough and inside a snap 10.000 mfd could be easily placed while in the output 4700 instead of 2.200 or even more

beyond the damage one way ore another some of these amps had soldering issues and you need to be careful

since also heatsink is small be careful with the bias ...when finished you will see that beyond low power the little crap actually sounds very decent

[Ludwik]

[getdowncdg]

Hello.
Thank you for the diagram. Strangely, my circuit-board is a bit older (labeled KA043/9, not KA043/7). Purchased around 1995... And the procedure does not seem to be the same. Would you have this newer service information, please?