Audio Innovations AI500 - low volume phono stage

[bard61]

Hello all...looking for some possble diagnoses and hopefully remedies!

My Audio Innovations AI500 has become very volume shy when I play records. I've connected my turntable to a backup amp and it plays fine, and all the other outputs on the AI500 are also working fine. There's no apparent change in brightness for any of the valves, so it doesn't look like a simple matter of valve replacement. Grateful for any advice.
Brad

 

[Alan4411]

Hi Brad,
''Brightness'' unfortunately isn't a test for how well a valve is working. (Unless it is not glowing at all...)
Might well be worth trying a couple of replacements first. I think they are ECC82s / 12AU7 from memory.

Alan

 

[JonSnell Electronic]

There are two differences on theses, phono wise, as Richard changed the RIAA slope. They both use ECC83 valves. An ECC82 has not enough gain to work properly.
Check the decoupling capacitors, pre- 1991 2nd cathode of ECC83, 1991 onwards both cathodes.
They are 100u 10v.

 

[soulmerchant]

The AI500 had two ecc83‘s using a passive riaa correction. There were at least three variations of the circuit, but all used ecc83‘s

If ecc82‘s are in place, swap them for ecc83. Do not change the pcc88‘s (or ecc88‘s) with ecc83.

Yes, the cathode by-pass caps might need replacing. Originals were blue philips ones that are pretty old now. Do NOT buy nos capacitors. Get new production caps of the same value.


Ian

 

[JonSnell Electronic]

We changed a few component values, at the factory in Weymouth , due to stock shortages but generally only two variants were built.

 

[bard61]

Thanks so much all. I'll try replacing the valves first as per suggestions, if no luck there I'll send it in for repair - my skill level is very limited! Really apreciate all your help. Best, Brad.