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Audio Innovations 800 (series 2)

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Mr. Triatic

Mr. Triatic

Member
Joined 2002
Hi guys and gals!
i bought this amp used and i´ve 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, what´s the difference between these two?

appreciate any help!
/Ludvig.
 
Tube_Dude

Tube_Dude

Member
Joined 2002
Mr. Triatic said:
Hi guys and gals!
i bought this amp used and i´ve 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, what´s the difference between these two?

appreciate any help!
/Ludvig.
Click to expand...

Hi
Here you have the schematic fo the AI 800 I and the 800 III....
http://www.drtube.com/audioamp.htm#AI
 
J

Jax

Member
Joined 2003
crude.axing.se/
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.
 
Mr. Triatic

Mr. Triatic

Member
Joined 2002
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... :cool:
 
SY

SY

Ex-Moderator
Joined 2002
SYclotron.com
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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