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Audio Innovations Alto
Audio Innovations Alto
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Old 28th May 2009, 01:03 PM   #1
canfixit is offline canfixit  United Kingdom
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Default Audio Innovations Alto

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.

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Old 23rd March 2011, 11:40 PM   #2
hotiron is offline hotiron  Scotland
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Default Audio Innovations Alto

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.

sorry didn't mean to use the man's name in vain!
If you give up easily Dont start!!
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Old 24th March 2011, 12:46 AM   #3
jaycee is offline jaycee  United Kingdom
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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.
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Old 20th April 2011, 11:33 AM   #4
eggontoast is offline eggontoast  England
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Originally Posted by jaycee View Post
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
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Old 30th January 2012, 02:36 PM   #5
sparrowSG is offline sparrowSG
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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.
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Old 7th May 2012, 01:56 PM   #6
thoglette is offline thoglette  Australia
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Originally Posted by sparrowSG View Post
... 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!
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Old 8th May 2012, 08:31 AM   #7
east electronics is offline east electronics  Greece
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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

Click the image to open in full size.

Click the image to open in full size.
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Old 8th May 2012, 11:29 AM   #8
Ludwik is offline Ludwik  Poland
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Attached Images
File Type: jpg ALTO1.jpg (121.8 KB, 1342 views)
File Type: jpg ALTO2.jpg (157.0 KB, 1259 views)
File Type: jpg ALTO3.jpg (160.6 KB, 1244 views)
File Type: jpg ALTO4.jpg (168.5 KB, 874 views)
File Type: jpg ALTO5.jpg (182.8 KB, 878 views)
File Type: jpg ALTO6.jpg (116.3 KB, 712 views)
File Type: jpg ALTO7.jpg (227.4 KB, 525 views)
File Type: jpg ALTO8.jpg (134.3 KB, 512 views)
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Old 13th May 2012, 07:54 AM   #9
getdowncdg is offline getdowncdg
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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?
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Old 27th November 2012, 05:06 PM   #10
ultraprime is offline ultraprime  Netherlands
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Hi, good stuff here with the diagram!
May someone can give me a hint with my problem. I do have Volt Meter, can solder, but transistor/components knowledge is low/rusty...

I have an Alto amplifier with main board K4043/6 and since sunday an issue...
During normal operation all of a sudden both channels, no sound anymore. powerled still on.

Opened it up, no smell, no visible blown parts, no blown fuses.
But also not the output delay click!!..

Going through the schematics, I do have 60V on the fuses FS1 and FS2.
I do measure 30V at R21-R22-R25-R26. (Alto4picture).
Then the part that confuses me, at both W11 and W18 (or W8 and W5 at Alto5picture) I do not measure anything, that is after the 2 capacitors C8 and C9. Is there supposed to be a DC voltage there (so close to the speaker connections)? Also no DC voltage at R3 - R4.

It all leads to the little delay switch RL1a-RL1b an Omron G2R-2 24VDC that does not do anything... or would the capacitors C8 and C9 still be suspicious? (both both at the same time is weird).

Any experrience or suggestions would be welcome! also on some quick other check points ;-)

I really love the sound of this amplifier, got it connected to 2 JMlab Electra 905. A match from heaven ;-)
)ps, although mine is chrome, it is the same as the black one, not tha later am1 version)
Cheers from holland
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