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Old 10th February 2004, 07:48 PM   #1
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Default Audio Innovations 800 (series 2)

Hi guys and gals!
i bought this amp used and ive started to restore it and upgrade anything i feel i have to..

-what i want is info, any tip is welcome!

somewhere i read that this isn't a good amp, that the original 800 (not series 2) is better, whats the difference between these two?

appreciate any help!
/Ludvig.
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Old 11th February 2004, 09:01 AM   #2
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Default Re: Audio Innovations 800 (series 2)

Quote:
Originally posted by Mr. Triatic
Hi guys and gals!
i bought this amp used and ive started to restore it and upgrade anything i feel i have to..

-what i want is info, any tip is welcome!

somewhere i read that this isn't a good amp, that the original 800 (not series 2) is better, whats the difference between these two?

appreciate any help!
/Ludvig.
Hi
Here you have the schematic fo the AI 800 I and the 800 III....
http://www.drtube.com/audioamp.htm#AI
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Old 11th February 2004, 08:36 PM   #3
Jax is offline Jax  Sweden
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A few years ago I restored an AI 500 first version for a friend. It motorboated at around 3 Hz. I found the reason to be the low phase margin in the lows.

I added the low frequency compensation you can see on the 800 schematic at the site linked in previous post, the 10nF in parallel with 1.5Mohm. That stopped the motorboating.

I can't for my life remember if 500/800 mk2 had ECC83/82 or ECC88.

Whatever you do with your amplifier, do not omit that compensation, that motorboating ruin the EL34's. My friend had to replace all of them. Compare the different schematics on that site and find which version you have.
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Old 12th February 2004, 06:16 PM   #4
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Thanks!
-Jax, the series 2 (no schem. for mk2 on the link..) indeed has 4 of E88CC (ECC88) and 4 of EL34 also, i guess, and the same OPT as mk1 with the 2ohm tap.
The rumour says that the mk2 was a not-so-good amp and that soon the mk3 replaced it on the market, i cant see why, it sounds good... 8-)
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Old 12th February 2004, 07:46 PM   #5
SY is offline SY  United States
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The MkI schematic shows the diff amp running with no grid leak on one side. If true, that's a terrible idea. The low freq poles should be staggered to minimize motorboating tendencies. And the power supply decoupling looks marginal; that would be something high priority to attack.
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Old 12th February 2004, 10:15 PM   #6
Jax is offline Jax  Sweden
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It's most likely an error in the schematic, the 500 I restored had a grid leak.
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