Pro VLA Mod!

Hello ladies/ guys. Have any of you modded the Pro VLA other than just tube swaps? I know of several people saying they hear improvements with just changing out the tubes, but I'm talking maybe caps, op-amps, power supply upgrade, etc. Thanks!

Try the Black Lion "Levelar" Mods.
Upgrade signal caps and resistors.

I opened mine up the other day to have a look. Quite a few TL072s in there. The tubes in mine are EH 12AX7s. I don't feel the need to replace them, but I'm sure others are putting NOS tubes in and raving about the difference it makes.

Has anyone experimented with opamp replacements? The signal path resistors looked like metal film already, but maybe cap replacements will help.

Any photos?

[quote author="rf"]I did some serious experimentation replacing chips in the Pro VLA...
I ended up replacing ALL Ic's in the signal path, but the ones that had the most effect in improvement terms were the TL072's on the rear I/O apron.

Just replace them with BB OPA2604's. Also any electrolytics in the signal path would be a place to make changes.

Be aware that ART uses very tiny traces and pads on their PCB's and are very difficult to de-solder without a vacuum pump de-soldering station.

Also, the Yugo tubes that came stock can be upgraded with something better. I used NOS Mullard's and it is quieter. I also tried Groove Tubes GT12AX7C's and they are almost as good as the Mullards.

Good Luck[/quote]"Be aware that Art uses very tiny traces"....... Hey Roger, I'm not technically inclined "at all" but I've noticed this! Not in just Art gear but most "Prosumer" gear. They have small traces compared to "High-End" gear! What is the technical reason for this? Got to be one! :thumb:

[quote author="Snatchman"]What is the technical reason for this? Got to be one! :thumb:[/quote]

Cheep-niss!

[quote author="jrmintz"][quote author="Snatchman"]What is the technical reason for this? Got to be one! :thumb:[/quote]

Cheep-niss![/quote]

Most of the layouts I get from boutiqueaudio manufacturers show signs of being layouts that have originally been drawn by hand, or something that can be etched in a simple setup. Whenever I get something from larger "prosumer" style companies they will most often be drawn out by a professional who does nothing but this. I dont know any technical reason for the traces to be thinner other than that you can keep the layout neater and smaller, but its definitly not to save money they are being made that way - cuz the price wont be any different. When you get below a certain trace size itll actually be more expensive.

Gustav

The annular ring on @RT PCBs are really small and the holes are small. This makes it hard to transfer heat to the solder and when the solder does melt, its hard to get the lead out. Its just a standard way of doing things that they continue to do for some reason.

There is no difference in PCB cost to the manufacturing company for smaller traces, but it costs more in chemicals to the company that actually makes the PCB because you gotta etch more copper off the raw board.

HTH!
Charlie

So... then there's no degradation of sound/signal quality with smaller traces huh?.. :? Dang, I thought I was justifying why some of the "Prosumer" gear suck!.. :green:

Not saying that layout cannot influence the sound of a circuit, but there are a lot of things that influence it more such as component choice.

HTH!
Charlie

Here is a link to an old thread about this topic. It was on another forum.

http://www.musicplayer.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=3;t=005632;p=

Jason

Seems to me the biggest problem with this unit is the tubes running at sub standard, low voltage which takes them out of linearity and what I hear is a smearing of the audio. (This apparently is appealing to some who term it "tube warmth" and is how ART was marketing the units.) Have you heard any improvement in this smearing?

[quote author="rf"]I don't run it hot enough to let the tube come into play much... There is a substantial improvement in just the solid state mods though.

I doubt anything will help the sound of a "starved plate" tube circuit overdriving. The question is, how much does the tube have to do with the sound if run at nominal levels?[/quote]

It's not a question of overdriving. I don't overdrive the levels, but I still hear a smearing of the audio which is due to the starved plate voltage the tube is operating in. You will never get a clean or unsmeary audio in a tube that is running so far outside of its intended linear range - or so I've been told. And my ears tell me something is fundamentally wrong. It's subtle, it's not frequency, it's not compression or level related, it's a blurring/smearing character. If you don't listen carefully it sounds like a smooth character. But it's not smooth, its smeared. My question is, has this changed with the mods?

cheers,
t

Can we get a visual description on the location and values of the four caps that you would replace? And what brand would you recommend on this RF?


Thanks

GREAT! I have one of these on the way. Thanks Roger.

:sam:

I'm looking at the schematic for this, and here's what I'd like to see done:

Say farewell to A5 and A7, and all associated components.
Replace it with a unity-gain single-ended discrete FET/bipolar stage powered from the +47vdc rail

Say farewell to R58 and R73. Replace with 330 ohm and 47 ohm 1 watt resistors configured as a divider. Or, replace U1 and U2 with 7805 and 7905 (that's probably easier)

Say farewell to the 12AX7 tube. Replace with a 6GM8 tube

Turn R62 and R98 into a voltage divider by adding a 25K resistor

Say farewell to A2 and A10 and associated components.
Replace with a dicrete bipolar push-pull stage powered from the 47vdc rail as well, and an output transformer.

So essentially, you'd get rid of the starved plate tube (since the 6GM8 will run properly on 35vdc, and it's a 9-pin octal like the 12AX7), you'd increase the headroom of the solid state portions, and you'd be adding an output trafo.

I've got one of these coming to me in a week or so. I think I'll do it. If anyone is interested, I'll post the results.

[quote author="featherpillow"]I'm looking at the schematic for this, and here's what I'd like to see done:[/quote]
:shock: You just ran with it. :sam:

[quote author="featherpillow"]I've got one of these coming to me in a week or so. I think I'll do it. If anyone is interested, I'll post the results.[/quote]
Please do, this is very interesting. Less involved mods seem to have had lukewarm results. It's very cool that you are considering the 6GM8 tubes. They are available and cheap. Can't wait to hear how they work.

It's very cool that you are considering the 6GM8 tubes

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Actually, I'm surprised that ART didn't consider it. Starved plate sounds like doo-doo. The biggest drawback is the increased current draw on the heaters--it's like 350ma@6vdc. But since the opamp stages would be gone, it's going to completely eliminate any other current draw off of that rail. Plus, the existing draw off the 47vdc supply is what, 14ma?

The big trick is going to be putting together a push-pull output stage to drive the transformer.

Also, I've something I've noticed with the ART stuff is lowering johnson noise by upgrading to better resistors (vishay comes to mind). I'd definitely suggest using something fancier than the stock brand, although some may see that as guilding the sow's ear so to speak.

Featherpillow, great ideas.

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Thanks, RF :grin:

I've worked with some of the ART stuff before--overly crammed boards, tiny pads...some of the Rane stuff is just as bad, as is Crest. I use one of those flux pens, and I've also noticed that a tiny bead of solder melted onto the wick helps draw the solder out of those tiny holes.

I'll post results when I'm done.

Yes and it also helps a lot to basically re-solder each pad

Click to expand...

I've noticed that to be especially true with the IC's on these boards.