Pro VLA Mod!

[franklinh]

Any word on the big upgrade?

 

[featherpillow]

Yes, it nearly lives. I gutted everything, changed the tube over to a 6GM8, changed the plate and cathode resistor values but I can't remember what the new values are off the top of my head--you have to change the voltage divider on that tube plate. The wimpy NPN darlington that gets used as a regulator has to be changed out because the current draw on the 45 volt rail goes up substantially (from 14ma to ~800).

Instead of a push-pull arrangement, I used a Zetex medium power transistor as a single ended output from the tube to drive that transformer. It's biased to drive a load as low as 150 ohms before it runs out of current.

I'm just waiting on word from Cinemag regarding an output transformer, but you could use an Edcor 600:600 if you wanted to.

My work schedule causes delays, but hopefully it will be done eventually.

 

[Svart]

any word on this?

 

[franklinh]

I'm planning my own, simpler upgrade - to be incrementally applied:

Replace input ICs with Iron
Replace output ICs with a THAT balanced line driver
Upgrade signal path capacitors and amps

I'm going to do one channel and copy it to the other if the end result is an improvement. I often use my VLA as a vocal comp. I don't want a new animal as much as I'd like it to pass a little more HF information. Trading out the 12AX7s for an older pair of "quality" bottles made a small but noticeable improvement. Based on my experiences so far, this should open the window a little more.

Frank

 

[jdiamantis]

FYI, you can find the schematic here:

http://www.blacklionaudio.com/art_pro_vla_schem.html

jD

 

[Morrow]

I did the mod to the rear I/O card that RogerFoote described. It's pretty doable and it sounds great. Increased depth and subtle increase in frequency range (more kick, and sizzley cymbals, but subtle).

I recorded a short mono clip before and after through Channel 2. I'm not really sure how to post it, but can figure it out if anyone's really into it.

Chris

 

[outoftune]

gearing up to do some mods to my pro vla....

i was wondering if it is possible to add a HPF around 100hz to the detector circuit?

 

[rascalseven]

A little OT here, but can anyone tell me what kind of meters are in the ART Pro VLA? Are they legit VU meters, or are they something else?

Thanks,

JC

 

[RedNoise]

Gearing up to do some mods too...
Intersted in the mod concerning a HPF too...
Sorry for poor english!!

 

[tommypiper]

JC, not having opened mine up in a long while nor looked at any docs... so I'm just guesstimating... they are most certainly not high budget meters, and I doubt they are "true" VU ballistic meters. More closer to the Sifam "Audio Level" type of meter, I would venture...

If you're thinking of scavanging them, it's not worth it. If you're thinking of replacing them, probly good idea, but not really necessary.

 

[RedNoise]

mine are sifam...

 

[RedNoise]

Finally working with some mods (OPA 2604 , 22µf 50v...)I didn't undestand why I couldn't change the 5532D JRC nor with OPA 604 , nor with 5532 AP (it burns) , only a 5532P goes...Is anyone able to explain me why??and what reference of BB could I put instead of the JRC (on the motherboard , i precise i didn't change any caps in here)
thx.
schem on lionaudio site.
http://www.blacklionaudio.com/art_pro_vla_schem.html

 

[Gert]

5532 are dual opamps
OPA604 is single opamp
You CAN'T replace a 604 for 5532

 

[RedNoise]

yes thx for that precision , i noticed it today having a "close" eye on the datasheet!!!.
any reference to replace the 5532?a different one than op275(I can't find it!)...
I also noticed A1 were not on the signal path.;;(right???)
Sorry for my newbie questions , thx for the help...

 

[Gert]

These are the mods Rogerfoote suggested at the beginning of the tread:

Main Board:
Replaced 4-NE5532 with OP275
Replaced 2-TL072 with OPA2604
Replaced 2-TL074 with TLE2074 (probably not needed)

Rear I/O Board:
Replaced 2-TL072 with OPA2604
Replaced 6-10 uf @50V electrolytics with Panasonic FC 22uf @ 63V
Replaced 8-300 Ohm 5% Carbon film resistors with 200 Ohm 1% Metal film
(The caps are marked C35,C38,C41,C56,C58 AND C63) : :razz:

 

[RedNoise]

thx Gert , that s with this part (the one you mentioned) that i started my mods on the ProVla...Actually I can't find a dealer in France for the OPA275 , so i was looking for another ref. :razz:
Why is it intersting to change the mainboard's TL072 while it looks like being there only for the vu meter???no???...same thing for the 5532 (A3)???
I m not used to read schematics , so apologies if I m wrong!
thx.

 

[Snapcase]

I gutted everything, changed the tube over to a 6GM8, changed the plate and cathode resistor values but I can't remember what the new values are off the top of my head--you have to change the voltage divider on that tube plate.  The wimpy NPN darlington that gets used as a regulator has to be changed out because the current draw on the 45 volt rail goes up substantially (from 14ma to ~800).

Instead of a push-pull arrangement, I used a Zetex medium power transistor as a single ended output from the tube to drive that transformer.  It's biased to drive a load as low as 150 ohms before it runs out of current.

Sorry to resurrect a very old topic.

I'm about modding my two VLAs following Roger Foote's guidelines. But I'd like to do something with the starved plate tube too. Anything new about the 6GM8 mod implementation? I think I can deal with making the tube performing right, but I'm a bit lost about the darlington thing. I'm only a hobbyist who tampers old tube gear and this thingy falls away from my limited knowledge.

Any help will be welcome.

 

[jmejia]

Again - sorry for the old thread resurrection - but did anyone happen to mirror the VLA schematic that blacklion used to host? Thanks!

 

[Spencerleehorton]

Hi,

I am really interested in this mod and how it sounds, i have read through what everyone has put and tried the links to the schematics but links dont work.
Are there more clear instructions for this, i would be able to work form the notes and the schematic but it may be better to put together a clear mod run through?
I'd be happy to help, also as i have the MK1 version with the fast/slow attack/release buttons, is there a way to change them to rotary controls as per the MK2?

any help will be appreciated.

regards

Spence.