Audio Innovations 800 (series 2)

Mr. Triatic · 10th February 2004, 08:48 PM

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 · 11th February 2004, 10:01 AM

Quote:

Originally posted by Mr. Triatic
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.

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

Jax · 11th February 2004, 09:36 PM

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 · 12th February 2004, 07:16 PM

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-)

SY · 12th February 2004, 08:46 PM

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.

Jax · 12th February 2004, 11:15 PM

It's most likely an error in the schematic, the 500 I restored had a grid leak.

10th February 2004, 08:48 PM	#1
Mr. Triatic diyAudio Member Join Date: Feb 2002 Location: SWE EU	Audio Innovations 800 (series 2) 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. __________________ www.joddla.net/audio/

11th February 2004, 09:36 PM	#3
Jax diyAudio Member Join Date: Nov 2003 Location: South Sweden	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. __________________ Jan

12th February 2004, 07:16 PM	#4
Mr. Triatic diyAudio Member Join Date: Feb 2002 Location: SWE EU	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-) __________________ www.joddla.net/audio/

12th February 2004, 08:46 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	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. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

12th February 2004, 11:15 PM	#6
Jax diyAudio Member Join Date: Nov 2003 Location: South Sweden	It's most likely an error in the schematic, the 500 I restored had a grid leak. __________________ Jan

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