AVI Lab Series Modifications (less is more)

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ABallagh
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Re: AVI Lab Series Modifications (less is more)

Unread post by ABallagh » Sun Feb 18, 2018 10:52 am

karatestu wrote:
Sun Feb 18, 2018 8:53 am

Cool. I like a work bench shot :grin:
Yeah sod this I cant not connect it now, time to make some speaker cables.

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Re: AVI Lab Series Modifications (less is more)

Unread post by karatestu » Sun Feb 18, 2018 11:03 am

Make two cables, one for send one for return, keep them separate and well away from each other. Lower capacitance that way :grin:
Naim, Linn & Harbeth fanboy

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ABallagh
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Re: AVI Lab Series Modifications (less is more)

Unread post by ABallagh » Sun Feb 18, 2018 11:09 am

karatestu wrote:
Sun Feb 18, 2018 11:03 am
Make two cables, one for send one for return, keep them separate and well away from each other. Lower capacitance that way :grin:
Thats exactly what intend doing, ive got a drum of 13amp mains here, thinking i will use the 3 conductors per run if i can get them in some plugs, Im going to be running a parallel pair into my Augie Amps, Im hoping that doesnt upset things.

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Re: AVI Lab Series Modifications (less is more)

Unread post by ABallagh » Sat Feb 24, 2018 4:20 pm

So I couldnt wait for the LS5 and i separated my speaker cables, kept the signal and return a few inches apart and fired this up. First sound was hum, (found to be caused by me forgetting the signal return between the amp and volume control Doh!) Then the squeeling started, now ive never heard oscillation before so I dont know if thats what it was but it was pretty scary, I cut the power immediately. I doubt the noise was anything to do with the missing return lines so I guess the AVI isnt that stable into a pair of speakers and a couple of plate amps high level inputs. I did test it on the bench with some cheap speaker cable after I put the returns in and that played fine, I wasnt going to test it again on my main speakers. So for now the inductor circuit is back in but everything else is as modded and no zobal network on the output, this now plays beautifully into the full speaker system Augies included. Definitely a worthwhile bit of modding, now i have to think about resurrecting my JLH monoblocks, considering these played for years with the output inductor removed and I had 2.5mtrs of Electrofluidics monolith 20/20 on them, (basically heavy duty goertz) they must be bloody bomb proof, this is going back nearly 20 years before I was aware of the true nature of the inductors job, I was told it was for difficult to drive speakers, we live and sometimes learn. In the mean time I have truly scary scale, width I didnt think possible and I wonder how the hell can this get better........

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Re: AVI Lab Series Modifications (less is more)

Unread post by karatestu » Sat Feb 24, 2018 4:55 pm

Try the AVI with out inductor again with the LS5 arrives. Squealing does indeed sound like oscillation to me. My avondale power amps are running absolutely fine without input coupling cap, zobel and output inductor. Inductor damping resistor bypassed as well
Naim, Linn & Harbeth fanboy

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Re: AVI Lab Series Modifications (less is more)

Unread post by ABallagh » Sat Feb 24, 2018 5:05 pm

karatestu wrote:
Sat Feb 24, 2018 4:55 pm
Try the AVI with out inductor again with the LS5 arrives. Squealing does indeed sound like oscillation to me. My avondale power amps are running absolutely fine without input coupling cap, zobel and output inductor. Inductor damping resistor bypassed as well
I've asked Doc to hold off on the LS5, I'm in an indecisive state of mind right now, if I go monos then the speaker cable will be too long, I realise I could take advantage of the trade in scheme but it doesn't make sense to get him to make them if I'm going to give them back, I'm sure he has enough to do as it is. 😁 At the moment music is making me smile again for the first time in a very long time. I am also contemplating a80s as I'm finding I have less and less time for DIY these days.

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Re: AVI Lab Series Modifications (less is more)

Unread post by _D_S_J_R_ » Sun Feb 25, 2018 1:56 pm

ABallagh wrote:
Fri Jan 26, 2018 9:14 am
"When you removed the output inductor from the JLH did you remove a resistor in parallel to it as well. Mine has a resistor within the coil which is in parallel. Naim amps have 0R22 on the output but no inductor."

Yeah I removed the resister too, but I left in the 0r22 that was in circuit just before, all the output transistors had 0r22's on the outputs too. The AVI has 0r22s on each output transistor but no additional one just before the Inducter/resistor. I dont know how safe it is but I ran the JLH's for about 10 years like that until one of the power supplies failed, I did run the 2 boards with one power supply for a while but never got round to sorting it out.

All I want to say is that AVI's designer is one of the few electronics design engineers who I feel would only put in what was needed for good stable working and I don't remember his amp or digital designs being full of ignorant bullshit as so many domestic designs are. I remember he progressively seemed to simplify his amp designs as time and better devices came along and his mouthpiece-partner Ashley loved that aspect as they could make more money on simpler designs than exotic creations with ten output transistors a channel and so on. The inductor would be part of the design for best reliability for the amp and its often ignorant end-users causing it to be designed in there. The performance may well be ruined with its removal (this isn't a butchered 1950's 50W? PA amp circuit that was messed with long before Naim took it on and made it even more compromised). Martin could tell you precisely why it was there - in plain and simple English (no obfuscation) and tell you precisely what would happen - or not - if it was removed without making adjustments for its loss. He's one of the proper designers out there, without an inflated ego - his business partner had enough for both of them at the time ;)

On the other hand-

NVA isn't for the uninitiated 'for example.' NVA owners should be bright enough to know what the amps are about and willing to use them as designed, where they're totally reliable for years usually. AVI was sold to all-sorts, using all manner of speakers and cables to connect it all up and not knowing one end of a 4mm banana plug from a RCA phono connector, although this is where the supplying dealer should come in as part of the situation (and we tried our best). Ashley's reaction at the time to the very few AVI amps that went wrong shows that the inductor being there for protection for both sides was almost certainly a very good idea :grin: - oh, and our main issue with Ash was over over-rated case-FUSES they fitted because at the time, the mains went iffy in the late 90's and all kinds of amps would pop mains fuses, even otherwise utterly reliable Audiolab amp case-fuses - I don't know what was going on, but the situation was real for a year or so... This particular amp suffered a short bridge-rectifier (it happens) and the case fuse didn't blow to prevent the amp board melting down/components catching fire..

I'll crawl back under my stone now - forgive the rant above - as you were...
...I have renounced the worldly bustle and live in peace at a quiet place,
I live alone in this my heaven, in my love (and) in my songs.

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ABallagh
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Re: AVI Lab Series Modifications (less is more)

Unread post by ABallagh » Sun Feb 25, 2018 2:50 pm

_D_S_J_R_ wrote:
Sun Feb 25, 2018 1:56 pm
All I want to say is that AVI's designer is one of the few electronics design engineers who I feel would only put in what was needed for good stable working and I don't remember his amp or digital designs being full of ignorant bullshit as so many domestic designs are. I remember he progressively seemed to simplify his amp designs as time and better devices came along and his mouthpiece-partner Ashley loved that aspect as they could make more money on simpler designs than exotic creations with ten output transistors a channel and so on. The inductor would be part of the design for best reliability for the amp and its often ignorant end-users causing it to be designed in there. The performance may well be ruined with its removal (this isn't a butchered 1950's 50W? PA amp circuit that was messed with long before Naim took it on and made it even more compromised). Martin could tell you precisely why it was there - in plain and simple English (no obfuscation) and tell you precisely what would happen - or not - if it was removed without making adjustments for its loss. He's one of the proper designers out there, without an inflated ego - his business partner had enough for both of them at the time ;)

On the other hand-

NVA isn't for the uninitiated 'for example.' NVA owners should be bright enough to know what the amps are about and willing to use them as designed, where they're totally reliable for years usually. AVI was sold to all-sorts, using all manner of speakers and cables to connect it all up and not knowing one end of a 4mm banana plug from a RCA phono connector, although this is where the supplying dealer should come in as part of the situation (and we tried our best). Ashley's reaction at the time to the very few AVI amps that went wrong shows that the inductor being there for protection for both sides was almost certainly a very good idea :grin: - oh, and our main issue with Ash was over over-rated case-FUSES they fitted because at the time, the mains went iffy in the late 90's and all kinds of amps would pop mains fuses, even otherwise utterly reliable Audiolab amp case-fuses - I don't know what was going on, but the situation was real for a year or so... This particular amp suffered a short bridge-rectifier (it happens) and the case fuse didn't blow to prevent the amp board melting down/components catching fire..

I'll crawl back under my stone now - forgive the rant above - as you were...
No forgiveness needed, I appreciate you taking the time to post. I guess I was acting on my previous experience which was more than positive without any issues on the JLH. Is Martin approachable? I dont follow all the forums, no time but I was told by a very good friend what a well respected designer he was. I may take a look at that fuse then, I have replaced all the rectifiers with MUR820's as I have a load in my parts bin, hopefully that should hold off any premature failures. I am more than happy that i'm heading in the right direction with the part replacement and removal already done, I've got tracks that I have been listening to throughout the last 30 years and I didnt think there was anymore information on them and thats only part of what I consider to be improvements in SQ. This has always been my goal, right from when i removed the xovers on my Townshend Glastonbury's nearly 20 years ago, at 52 I know my hearing has taken a big hit at the top end and I thought It might be time to sell up and simplify the system, not now. :grin:

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Re: AVI Lab Series Modifications (less is more)

Unread post by _D_S_J_R_ » Sun Feb 25, 2018 6:27 pm

I'm going back before the Lab series to the Bristol-made S2000 models and the 140W mono's did seem fairly simple inside although I think there was an ic op-amp in the input side (either in the signal path or in the feedback loop, I don't know). Your amp was made in Sth Wales but the company (if I have it right) has moved to the south midlands I think. Being a nosey dealer for them at the time and visiting the nearby ATC factory regularly, I got to know them both rather well.

Martin G usually stays well in the background and at the time, you always had to go through Ashley. Now the company has changed and moved, you'd need to go through main-man Martin Hill now. Not sure how any of them would deal with a punter who's taken a finished product apart to customise for himself - sorry... despite said product now being fifteen years or so old. A third party now deals with servicing said 'separates products' (legacy indeed!) and all they're really bothered with is the active speakers they make now.

You know, I still think you'd have loads of good learning fun working on some of the Pass kits and designs. He's another true enthusiast who designs solid, tough, reliable and stable products for his Top End and pro clients and has some considerable fun on the side with innovative kit designs for 'us' to play with... Just a thought.
...I have renounced the worldly bustle and live in peace at a quiet place,
I live alone in this my heaven, in my love (and) in my songs.

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ABallagh
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Re: AVI Lab Series Modifications (less is more)

Unread post by ABallagh » Sun Feb 25, 2018 7:29 pm

Thanks _D_S_J_R_. I've been toying with building Pass stuff for years, never got round to it. I think I'm getting to the stage where learning fun isn't fun any more. I've re-worked a lot of stuff over the years, probably all the wrong stuff but I had fun. I still have my class D and KT88 amps and it's all about synergy isn't it, I have some speakers that demand a high current amplifier now, I did have diy 96db Hawthorn Audio jobs that anything could drive, it's all fun though I guess. 😁

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