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In Reply to: Re: Audio Innovations Series 500 vs. Antique Sound Lab AV-8/AQ2004DT posted by jackcpsu on June 22, 2001 at 09:54:18:
The center valve on the 500 is the line input amplifier, and was an ECC83/12AX7 on the amps I saw. On the left of it, there were two more ECC83's for the phono stage, which had MC gain (fantastic!) and a ton of hum (erm...not so fantastic!). In the end, you could only use an MM cartridge because the hum was so bad.
The valves on the right of middle one were PCC88/7DJ8's. I subbed to 6CG7's, finding the sound to clean up substantially by doing so. The phase inverter circuit is crude and assymetrical, and sounds better with some speaker loads than with others. With most, the amp sounds a bit tatty & nasty, with a fair amount of grain. It was also highly unreliable, and outrageously coloured.
The biggest problems in the 500 are that the filament voltages for the valves are dead wrong, being WAY too high. No doubt this inspired Mark or a previous owner to sub the output valves to 6L6/5881, which is a far inferior sounding valve to any EL34. But it is TOUGHER, so I can see the point for that reason.
But subbing valves for tougher ones is not the appropriate solution, fixing all the stupid design liberties, blatant mistakes of the highest idiocy imaginable, IS.
That means lowering the output valve filament voltages from 7.0 to 6.3, and the driver stage voltages from 7.5 to 6.3 as well.
That will clean things up, make the beast run cooler, and tighten up the bass and improve the treble. The amp will sound more RELAXED, as well. Also, even with that, the output valves are still overbiased, and I would recommend replacing the cathode resistors on them with values 20% higher, and replacing the bypass condensers with ones rated at 63VDC. I had problems with the valves occasionally running away even AFTER I corrected the filament voltages. And the bypass condenser failing with the excess voltage across it, and spewing smoke & flames!
Signal coupling condensers are of decent quality, made by Roederstein (Ero) of Austria. Unfortunately, they are the green polyester ones, and a substantial sonic improvement can be made by subbing them for polypropylene ones.
The amp is an absolute BEAR to work on, dismantling it is quite a nightmare. The earthing scheme is also horrid, and this would be an epic undertaking to correct.
The 500 is only a classic because it looks cool. The sound is OK, WHEN IT WORKS. If you can live with its fiery temperment, then it probably will sound a little better than an ASL amp, at least stock vs. stock. But to fix it up, the amount of effort & cost would be better spent in doing the same or similar things in an ASL amp, which won't have all the glaring engineering screwups of an AI piece. Passive parts quality is probably worse, but the layouts look alot better and replacing such parts in a mechanically well-designed unit can be quite pleasant...
As it stands, if you have 6L6 outputs in your 500 and the circuit is otherwise unmodified, I'd spring for the ASL amp instead.
No power cords or sorbothane puck things are going to save it, and you'll still need to keep a fire extinguisher handy...
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Follow Ups
- Re: Audio Innovations Series 500 vs. Antique Sound Lab AV-8/AQ2004DT - Joe Rosen 11:43:23 06/22/01 (2)
- Re: Audio Innovations Series 500 vs. Antique Sound Lab AV-8/AQ2004DT - seventymillimeter 15:46:29 06/22/01 (1)
- Re: Audio Innovations Series 500 vs. Antique Sound Lab AV-8/AQ2004DT - Joe Rosen 09:10:09 06/23/01 (0)
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