AVI Lab Series Modifications (less is more)

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ABallagh
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AVI Lab Series Modifications (less is more)

Unread post by ABallagh » Thu Jan 18, 2018 11:19 pm

Ok, so my first post outside of the welcome section and im looking for advice/help, please treat me like someone who doesnt really know what there doing, I aint too bright but I can solder, ask me the best way to hang a big TV on a dot n dab wall and im yer man. lol.

I have decided to do some tweaking to my perfectly healthy AVI AMP. Here is the schematic of the power amp section.
S21 MI AMPLIFIER CCT_.PDF
(170.35 KiB) Downloaded 13 times
I have removed the pre amp, input switching and control/mute circuits, I have changed the reservoir caps for DNM slit foils and I have removed the output inductor/resistor but I have also removed the zobal too. My speakers appear to have zobal networks on them,
Photo from Alan Ballagh.jpg
Photo from Alan Ballagh.jpg (80.57 KiB) Viewed 685 times
From what I understand the amp should be stable after doing the mods providing I keep the speaker cable capacitance low, so how low is low? and how does this look?

3 x braids of 16 x 5/0.09mm stranding
Hollow PE central core of 1.5mm OD
Jacket OD - 4.00mm
Wire gauge 17 AWG
Cross-sectional area - 1.50mm²
Loop resistance - 0.025 Ω/m
Capacitance - 17pF/m
Inductance - 0.69 µH/m
Dissipation factor - 0.0006

If it depends on the amp then I will have to try it I guess, I have no scope so I will have to rely on my ears, oh and the AVI has temperature sensors on the heat sinks, these are pretty simple and form a loop on the centre of the TRX Primary. I havnt listened to the modded amp yet as I am in the process of putting it in a bigger case and adding my remote LDR volume control and input card both from BTFSystems, the front plate is still on the AVI to keep it stable for now, the TRX is pretty big, it sits very close to the big caps but it does have what looks like a thick goss band.
Image
Heres the new input switch. Image As you can see my main goal is short signal paths.

Another section I would like to mod is the input, I havnt touched it yet but I would like to know what I can safely do here to reduce components in the signal chain, I havnt actually measured the output of my sources yet but I think I would like to keep a DC blocking cap at the very least, so can anyone tell me the drawbacks of removing the filter and say just have a single cap on the input? at the moment there is a 22uf Tant doing the duty while forming part of the filter, I would like to change that to a film for sonic benifit and small to keep down cost, maybe 4.7uf?

I know that this is a complicated design, I had no desire to buy such a thing, I was happy modding class D and I was about to put the lid on my chip amp build, Image when my best mate sends me an ebay link to a pair of speakers, i nabbed em for almost half the cost of the crossovers and I have been grinning from ear to ear since. Unfortunately the new speakers are hungry, they are based on the Zaph Audio SB12.3.
So Im looking for any tips, advice and mostly help with getting as much information from my source material as possible which involves doing a bit of a makeover on the AVI, dont get me wrong though, ive got the best reproduction ive ever had in my audio life right now and thats at a point in time that my hearing has seen better days, Ive tested myself at about a 16khz roll off but lets not go there, this is my hobby and I dont want a little HF loss to stop me enjoying it, I know i can still be gobsmacked, the new speakers prove that...

Alan

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

Unread post by karatestu » Fri Jan 19, 2018 10:36 am

Helo Alan,

I see you have removed the power amp output zobel and inductor. NVA speaker cables are low capacitance but I don't know what the figures are. As low as you can find is the way to go. 17pf/M sounds low to me but then I am no expert.

I would try the amplifier out as soon as possible to see if all is stable. I try (not always successfully) to make one change at a time and then listen. Otherwise how do you know what has done what? I see you have done quite a few changes all at once. Changing the reservoir caps is a good thing.

Do you really need remote control ? It is adding extra complexity and does not fit in with the KISS approach. It is a good thing to keep the heat trip sensors on the heat sinks until you know everything is ok - oscillation that is not audible will cause heat and your amp will hopefully shut down before any damage is done.

What is an input card from BTFS - preamp or input switching ?

Dc blocking caps are best got rid of IF you can. If the active preamp (if you have one) also has a DC blocking cap on it's output then you can get rid of one of them I think. If you are set on keeping it then just be aware that going too low in value will roll off the bass. I would take a film cap over an electrolytic any day of the week but making them fit is often the problem. Removing signal coupling caps is a popular tweak in the Naim bodging community. R34 and C13 are a low pass filter with the corner frequency being 1.1 MHz, which is fairly high and probably not worth messing with.

Get rid of the Mains IEC socket and hard wire the mains in to the unit.

That is my view, could be wrong though.

Stu
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 » Fri Jan 19, 2018 10:13 pm

Hi Stu, Many thanks for the input, its very much appreciated.

I see you have removed the power amp output zobel and inductor. NVA speaker cables are low capacitance but I don't know what the figures are. As low as you can find is the way to go. 17pf/M sounds low to me but then I am no expert.
I did read a post by Doc where he stated what capacitance the cable should be for his amps but Ive lost it, been looking for it using search but theres a lot of posts to get through and theres only so many free hours in a day...

I would try the amplifier out as soon as possible to see if all is stable. I try (not always successfully) to make one change at a time and then listen. Otherwise how do you know what has done what? I see you have done quite a few changes all at once. Changing the reservoir caps is a good thing.
Oh and I changed all the power supply rectifier Diodes. To be honest I used to do that many years ago, I dont have the time I did back then, im on wife number 3 too so i try to balance my time, I have many things that take it up.

Do you really need remote control ? It is adding extra complexity and does not fit in with the KISS approach. It is a good thing to keep the heat trip sensors on the heat sinks until you know everything is ok - oscillation that is not audible will cause heat and your amp will hopefully shut down before any damage is done.
I really do! Im getting so fricken lazy in my old age, when I finnish work I just want to sit down. I dont mind extra complexity if its not adding parts to the signal, The LDR volume control keeps things as simple as it gets as far as the signal is concerned, there is one resistor in series and zero switching, the designer of this one has done things a little different to mr lightspeed, he uses current change to vary the resistance, im pretty sure all the others use voltage and they operate above the recommended limits for the devices, (this is what i understand) these should last more than one lifetime.... I am able to keep the signal path very short with the LDR control. Oh and it has L/R balance adjustment and an OLED display, and the signal still only has one passive component in series, obviously it also has a shunt one too.

What is an input card from BTFS - preamp or input switching ?
Its a remote input switch, it doesnt require any additional power, Karl from BTFS has programmed the OLED display board to control the input board via a chip swap, plug and play, again the signal is kept very short only passing through a relay to the LDR board.

Im not sure I can get rid of the DC blocking cap, my AV amp has been known to cause the odd thump now and again and I switch this for front chanels, I dont have a separate preamp. The other problem is the Dc blocking cap forms a high pass filter doesnt it so Im messing with things i dont know enough about here. The same applies to signal coupling caps, I dont even know which ones they are and I would want to be sure that the theory is good for all amp designs before I started doing that, at the very least I would like to see whats been used and maybe insert a "better" cap there.
My hifi buddy has just replaced c7/8 with a 2.2 film, he reports no loss in bass, his Tannoys are capable of 33hz but I guess there are other factors like the room to consider here, the bottom line is he said he aint going back from that little mod... ...

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Dr Bunsen Honeydew
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Re: AVI Lab Series Modifications (less is more)

Unread post by Dr Bunsen Honeydew » Fri Jan 19, 2018 10:20 pm

"I really do! Im getting so fricken lazy in my old age, when I finnish work I just want to sit down. I dont mind extra complexity if its not adding parts to the signal, The LDR volume control keeps things as simple as it gets as far as the signal is concerned, there is one resistor in series and zero switching, the designer of this one has done things a little different to mr lightspeed"

LDRs are shite, they really mess with the signal IMO. AND more to the point because the LDR contains cadmium they are illegal to sell in the EU, which includes the UK.

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

Unread post by ABallagh » Fri Jan 19, 2018 10:55 pm

Dr Bunsen Honeydew wrote:
Fri Jan 19, 2018 10:20 pm
LDRs are shite, they really mess with the signal IMO. AND more to the point because the LDR contains cadmium they are illegal to sell in the EU, which includes the UK.
Forums are full of the "that product is shite" opinion on a LOT of hifi but it doesnt stop people enjoying the music that equipment makes, and they are also full of very happy customers who after purchasing said equipment dont look back. The LDR volume control is one of those, I know it has a lot of haters but it also has a lot of lovers, I was fully aware when i purchased it that it was claimed (and rightly so) by the non subjective clan to be less accurate than a pot but we learned a long time ago measurements and accuracy dont always make the best music. I know there are 2 types of LDR and Karl choose one over the other for technical reasons, I am also aware they are illegal to sell in the uk, I have read more than one such comment from irate small manufactures who hate that they have to adhere to those regulations while people like George get away with it, or maybe im been cynical and theres a genuine concern for our welfare, hey they might even scrap that when we brexit! (ok they probably wont but i dont care)

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Re: AVI Lab Series Modifications (less is more)

Unread post by Dr Bunsen Honeydew » Fri Jan 19, 2018 11:41 pm

Why do you think they only sell kits, to try and get around the law which is disgraceful. I have listened to, built and designed my own version because this became very controversial when I made public the illegality a couple of years ago, I was seriously attacked (per usual) by ignorant people. I can tell you I was shocked at how bad they were, for me it is similar to a bad valve amp, it changes the music. They are unreliable, they drift with age and temperature, and they are unsafe, what more do you want. I do not use measurement, to make my decisions I use MUSIC.

Your system you list IMO is flawed in many ways, so the LDR just adds to and changes those flaws. You are trying to change it and even trying to apply NVA principles to products that are just not suitable. Again, IMO, you need to start again. BUT you are welcome to do and say what you want on this forum as long as within the rules and so am I.

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

Unread post by ABallagh » Sat Jan 20, 2018 1:53 am

Doc, did you build this version? The designer isn't here to defend it but he has done extensive testing and there is ZERO drift, he hasn't cloned lightspeed, the ldrs dont even need matching, anyway it doesn't matter because you have your opinion on it. You ask what do I want, if you read my thread which I'm guessing you have then you know what I want, i won't keep asking because I'm not into begging. I know you could answer all my questions and I understand your reluctance but you don't own the principles, I removed the crossovers from my Townsend glastenburry speakers 15 years ago, I'm not trying to impart NVA principles to my gear, I'm doing what I've been doing for 30 years without even knowing you existed, this isn't the first amp I've removed caps, inductors and stripped parts from, that's what I really liked about your philosophy, but the fact that you make money from it doesn't mean you invented those principles, that's rich even for you. I am interested in the "many flaws" in my system though, I have listed a crossover, an AVI amplifier and the volume control that you don't like, I genuinely would like to know what you think of the the rest of my listed system?

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

Unread post by ABallagh » Sat Jan 20, 2018 2:08 am

Just to be clear Doc, I'm not been sarcastic, I would like to know where the flaws are.

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

Unread post by ABallagh » Sat Jan 20, 2018 2:10 am

And what's wrong with the bloody forum, not one single email to let me know someone is trashing my gear......grrrr

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Re: AVI Lab Series Modifications (less is more)

Unread post by Dr Bunsen Honeydew » Sat Jan 20, 2018 10:22 am

My main motivation is to see the letters LDR, this became a pet subject because of all the abuse I received. We are known here for telling the truth and giving honest opinions. I have seen this bullshit before, each time someone like stereo coffee comes up with what they call a new version the nonsense starts all over again "we have now solved the problems" over and over again to the point I just take no notice of it. The *principle* of the design is fatally flawed, and the components they *have* to use are declared illegal in the EU due to the dangers involved with Cadmium. You can go and find the official documents relating, I did. The reasons given is that the release of the severe poison Cadmium can occur in two case. 1/ an internal fire in the unit, this is possible because the unit is mains powered. 2/ The end of life disposal as it can't go into ground fill or be burnt, no one has control of what happens so it is better to ban it. The penalty under EU law for illegal disposal is prison!!! and if you sell it on, you as the first illegal purchaser are responsible for what any future owner does with it.

It is a complete bag of nails, why do you want to get involved in it. The other two things you talk about again IMO!! 1/ crossover - throw the bloody thing away and do it properly by matching and doping 2/ I have no problem with your amp, for its type it is one of the better ones, it is just unsuitable to do the things I have done i.e. NVA principles to it, as I said better sell it and start again if you want to go down the KISS route.

As I said you can say what you want, recommend what you want, there is nothing wrong with what you did or said regarding the forum BUT so can I and any member can do the same. I see that as constructive criticism, you see it as trashing.

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