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Post by gouge on Jun 22, 2014 0:19:38 GMT -6
I've started on my tinkering way with my art pro vla.
so here it is, a hacks guide to .......
I opened it up to find someone had already dropped a pair of jan Phillips tubes into it. I bought it second hand. now that's a good outcome. I've got some other tubes to roll so time wil tell.
ok, a hacks guide to hacking up an art vla.
why, "because why not"
first up is power supply.
I'm recapping it with low esr fm caps. leaving all values as stock other than
1. voltage rating I used either 50v in lieu of 16v or 25v or 100v in lieu of 63v. 35v may have been better as the 50v almost didn't fit but I have a bag of 50v so here we are. 2. I changed the 2 10uf caps (C25, C24) after the regulators in the power supply to 100uf 50v 3. changed the tube power (C9) 100uf 63v to 220uf 100v as that all I had. 4. all 1N4003 diodes replaced with 1N4007 diodes.
the diodes were difficult to replace. I pulled one trace during that process and had to sub a wire in to fix it. other than that everything seems ok. yet to power up the unit as I'm waiting on 4 more caps in the post. I cross my fingers.
although I did botch a few things here and there the process helped my skills a lot so I'm feeling like it was worth the risk.
audio path upgrades....
I replaced the opto with as per the mod floating around online. once I make sure I haven't destroyed the power supply i'll get into the audio path mods. will do one channel at a time and make some test comparison's. that should be fun because i'll have to learn how to use the oscilloscope sitting in the corner as well as the distortion meter.
more to follow. |
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Post by henge on Jun 22, 2014 5:57:17 GMT -6
Nice!! I have a vla, not a bad unit, and I'd be interested in how the upgrades go.
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Post by gouge on Jun 22, 2014 7:25:42 GMT -6
will do,
all up I like the vla, had it for as long as I can remember as it was my first compressor.
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Post by gouge on Jun 24, 2014 6:13:20 GMT -6
update,
I ordered some 3300uf caps to replace the 2200uf caps in the power supply so I can finish that part of things off.
added a .01uf ceramic bypass cap to c9, c24, c25
sowter input transformers have arrived.
will post photos once I get back into the unit. wife has taken back ownership of the dining table so the project is on hold until extra caps arrive. :-)
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ericn
Temp
Balance Engineer
Posts: 16,107 
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Post by ericn on Jul 2, 2014 11:14:25 GMT -6
There's been one of these sitting in one of the local pawn shops that keeps tempting me, don't really need it but ...
So I'm staying tuned to your tuneing!
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Deleted
Deleted Member
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Post by Deleted on Jul 5, 2014 7:14:27 GMT -6
Just a short side comment on the rectifier diode upgrades...
If the rectifier diodes were not erroneously dimensioned, you won't gain any advantage replacing IN4003 with IN4007 diodes.
An alternative would be replacing IN400x diodes with UF400x ultrafast switching rectifiers instead...
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Post by gouge on Jul 5, 2014 21:06:24 GMT -6
Thanks smallbutfine.
is it the uf rectifiers that are the low noise ones?
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Deleted
Deleted Member
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Post by Deleted on Jul 6, 2014 16:19:42 GMT -6
Well, IF the rectifier diodes upgrades have a positive effect on an audio circuit, THEN it is often due to faster recovery times, not higher voltage rating. the difference between the different IN400x types is just that, different voltage rating. Different power rating also does not make a difference. (edited, confused late at night..;-) ) the UF type diodes have the faster recovery times as can be looked up in the datasheets, while still beeing cheap. You only have to have 4 of them in a normal rectifying psu. Or you have a bridge rectifier. These can also be replaced by faster types btw. SOMETIMES you get a benefit from that, that is audible. Since it's no big deal by any means financially to buy faster types for diy, just use them always as a replacement. Here is a nice not too scientific article about that to get a clearer picture what rectifier diode upgrades in audio are all about. www.audiodesignguide.com/Ibridone/Sen_Semi_Diode_Apps-quik108.pdfIn rare cases rectifiers are really known to be flakey and prone to fail or wrongly dimensioned by design. E.g. some of the smaller FoH consoles from Soundtracs have bridge rectifiers that unfortunately fall in this category. When they fail, they damage mostly parts of the psu pcbs due to burning resistors - ugly stuff! In these cases you are 100% better off to replace e.g. against better quality glass bridge rectifier anyway preventively. But cases like these are rare, and most of the time you gain little by replacing rectifier diodes IMO. But since it's cheap it doesn't hurt..... BUT, and this is a quite big "but(t)" - rectifier diodes and higher wattage bridge rectifiers can be very ugly beasts to desolder - as you might have experienced already - several times i damaged PCBs, you are not alone with that. So i read and think twice before i replace existing ones in a psu and mostly leave them alone... ...and i think much more about local decoupling, grounding schemes and the other obvious upgrade possibilities... Best regards, Martin |
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Post by gouge on Jul 7, 2014 0:14:05 GMT -6
Thanks martin, really appreciate you advice.
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Post by keymod on Oct 22, 2014 17:32:02 GMT -6
So how are the mods turning out? Did you ever finish?
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