News:

GroupDIY is currently under construction.
Some parts of the site may not work properly.



RedNoise

ART PRO VLA - Kenetec mod
« on: March 04, 2009, 02:23:31 PM »
Hi guyz... :P

Several monthes ago I made some "parts replacement" in my ART Pro Vla.
I changed resistors for metal 1% , also changed caps for audio ones or good YXF around psu.I swaped 553X for socketed OPA .Finally I add a couple of Mullards.
Those maintenance (not really mods) were really improving sound (to my taste).

In another website I read a thread about "Kenetec mod".It apparently consist of bypassing Opamp input for two Stancor WF30.
Two weeks later , my evilbay Stancor arrived. ;D

As I'm not really at ease with electronics generaly speaking , I thought I should ask here before trying to put these babies in the VLA.

So , guyz , could someone help me to wire them correctly?
How should I proceed?

I know this forum is essentially a forum for advertised people (towards electronics) .I actually try to concentrate all my free time to learn about it.I have to admit I need more time to become an amateur electronician , but what's better than practicing? :D
So : any help for f***** noob greatly appreciated!Cheers.
T.
« Last Edit: March 04, 2009, 04:22:44 PM by RedNoise »
If your neighbour is hunger : don't give him fish , teach him how to fish ...
if you don't like it don't buy it ;-)  [Wolker Texas Ranger] ( ;-) )


rodabod

Re: ART PRO VLA - Kenetec mod
« Reply #1 on: March 04, 2009, 03:46:27 PM »
We need more information. Is the Stancor a transformer?

Datasheets / schematics would answer a lot of questions.
Quote from: tv
punchy fat bastard chip

stitch-o

Re: ART PRO VLA - Kenetec mod
« Reply #2 on: March 04, 2009, 04:07:44 PM »
Here's what I dug up on the Stancor WF30 (which is indeed a transformer) as I have a VLA hotrod in mind as well:
WF series: HI-FI: Shielded:

WF30:

Application: Mixer, Mic , Pickup or Line to Line.
Impedance in ohms: Same for input and output: 500-600/333/250/200/125-150/50
Audio watts: +7db
Termination: Lugs (in and out)
DC Resistance in ohms: Pri. = 80 Sec. = 84.2
Overall Turns Ratio: 1:1
Frequency Response in cps +- 3 db: 30-20K
RMS test voltage: 500
Dimensions: H-2 W-1 1/2 D-1 1/2
Weight: .6 lb.

The UTC A-20 is apparently a drop in replacement for the Stancor's you have.
You can find UTC info HERE

I think the idea is to bypass the TLO72s on the rearpanel.

Here is the VLA schematic:::
I'll apologize in advance

RedNoise

Re: ART PRO VLA - Kenetec mod
« Reply #3 on: March 04, 2009, 04:19:38 PM »
Wow!!
Thanks for interest.

I read about the Kenetec mod here :
http://www.gearslutz.com/board/gear-shoot-outs-sound-file-comparisons-audio-tests/332227-art-vla-pro-ii-kenetek-mod-vs-stock.html

Some "schem" are laying around scrollin down the first page.

I'll re-read this thread and understood this WF30 (audio input tx) just "took" a wire from the ribbon cables coming from opamp input boards.I imagine this wire is to be connected to output tx.So:
XLR->Tx input->Wire from ribbon.


IIRC Joe Electro've done that mod.The problem is that I do not exactly understand how a tx is working....He!
I'll try to host the schem and pics I found @ Gearslutz!

I'll be less tired tomorrow , will try to explain myself more clearly! :P

If your neighbour is hunger : don't give him fish , teach him how to fish ...
if you don't like it don't buy it ;-)  [Wolker Texas Ranger] ( ;-) )

rodabod

Re: ART PRO VLA - Kenetec mod
« Reply #4 on: March 04, 2009, 07:06:04 PM »
Here's that section of the schematic you mention:

http://i510.photobucket.com/albums/s344/norman_nomad/ProVLAInputTransformerSchematic.jpg

Having thought about it, I don't really think that a line source having to go through a couple of TL072s in a typical configuration is really the end of the world. Which makes me wonder, would simply putting some iron in series with the original input provide a similar sound to this modification?
Quote from: tv
punchy fat bastard chip

outoftune

Re: ART PRO VLA - Kenetec mod
« Reply #5 on: March 04, 2009, 11:44:24 PM »
FWIW...i popped a couple opa2604's in place of those tl072's. definitely made a difference, sounds like a slightly nicer pro vla. roger foote suggested this and a few other mods here on the board, have a search.

i was going to try to replace all the signal lytic caps with higher quality ones, but the big main board is just so difficult to get at. the tl072's on the I/O are on a small, easily accessible pcb, the rest of the stuff was way too much hassle for me to go digging at. but that's yer call!

while i was poking around in there, i was considering trying to replace the psu...using a nice torroid and ditching the voltage doubler setup that is in there now...might make some improvement...
« Last Edit: March 04, 2009, 11:53:18 PM by outoftune »

stitch-o

Re: ART PRO VLA - Kenetec mod
« Reply #6 on: March 05, 2009, 09:59:51 AM »
roger foote suggested this

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)
I'll apologize in advance

RedNoise

Re: ART PRO VLA - Kenetec mod
« Reply #7 on: March 06, 2009, 04:57:32 AM »
Stitch'o : Thanks for reminding me the RogerFoot mods.They're effctively what I did first.

Outoftune : Yeahh , opa rules in this machine.I though sound was really wide , more high end opened , the low frequencies were also more "tensed"

Rod' : This schematic is effectively exactly what I need.How would you "calculate" this termination resistor?I imagined it's soldered directly between WF-30 pins.


At the back of the WF30 I have 13 pins.
Number 13 is the ground.
I now have to find what are the other 12 pins for , which one should I use for this "mod".
Maybe some of you could point me out a good link to learn how a tx is workin??

Thanks again.
 ;D
If your neighbour is hunger : don't give him fish , teach him how to fish ...
if you don't like it don't buy it ;-)  [Wolker Texas Ranger] ( ;-) )

diyfanatic

Re: ART PRO VLA - Kenetec mod
« Reply #8 on: August 05, 2009, 06:04:34 AM »
hi RedNoise, have you done the kenetec mod?

I got a vla pro 2 for cheap (200$), Mullard 12at7wa are on the way and OPA also.
I wanted to know if the Stancors satisfied you!

I'm thinking buying some Utc A-20 for this guy.

the stock compressor is not so bad (it surprised me) but I want it to be a big nice dirt box since I have no time to start my D-AOC and My La-2a!

Jr.

Re: ART PRO VLA - Kenetec mod
« Reply #9 on: August 06, 2009, 01:51:08 AM »
Considering what you're probably going to pay for A-20's or the Stancors I wouldn't recommend it.  These are fairly clean transformers so if by "dirt box" you meant distortion I doubt you'll get much.

If you want to improve the audio quality I'd go with the info in Stitch-o's post.  If you want the nice little transformer thickness bump you could save some dough and get a WSM 600:600 from Edcor for 10.23 USD. I don't think those vintage units are going to blow you away in this particular application and they won't change the circuit that follows it.  I've tried some vintage Merits, Jensens and the Edcors. The Edcors did the job just fine for a fraction of the cost of the Jensen.  And besides, the A-20 was once a $20.00 apiece transformer not too long ago . . . . .



RedNoise

Re: ART PRO VLA - Kenetec mod
« Reply #10 on: August 06, 2009, 02:36:33 AM »
@ Diyfanatic : I didn't receive notifications for this thread (?) thanks for reminding me!I haven't done the tx mod at the moment , but I swear OPA and cap mod (I've done resistors too) is really improving the general audio capabilities of this comp.
Before , I essentially used it with bass or guitars , now I love it on MANY sources.I've done several A/B (I only mod one channel) and it was (to me) a real "upgrade".
I also found pairs of Telefunken 12AT7A (IIRC) , but I'm not sure about the result.Maybe Mullard will be "enough".

@Iassoharp : I've had a pair of Stancor 6 monthes ago for 60 usd (shipped to France).It's not "so" expensive . For sure , The OPA mod (and cap mod) is certainly the more audible.
I'm experiencing problems with Edcor Tx (LA2A) , it seems they are HPFing and LPFing the signal , what # of 600:600 are you recommending?

JoeElectro , are you out there to comment about the tx mod ?
If your neighbour is hunger : don't give him fish , teach him how to fish ...
if you don't like it don't buy it ;-)  [Wolker Texas Ranger] ( ;-) )

RedNoise

Re: ART PRO VLA - Kenetec mod
« Reply #11 on: August 06, 2009, 02:39:07 AM »
Diyfanatic : Try to find audio comment about UTC vs Stancor ...Apparently (I haven't A/B'd) Stancor are the most prefered...
If your neighbour is hunger : don't give him fish , teach him how to fish ...
if you don't like it don't buy it ;-)  [Wolker Texas Ranger] ( ;-) )

diyfanatic

Re: ART PRO VLA - Kenetec mod
« Reply #12 on: August 06, 2009, 03:57:29 AM »
@Rednoise hey thanks for the reply!!  ::)

no doubt that an opa upgrade should improve the overall sound
franchement je suis sur le cul, la petite machine marche vraiment pas mal... 8)

Quote
HPFing and LPFing
that's why I try to put some decent transformer...jensen or cinemag are useless for my application...too clean


@lassoharp
UTC are not cheap this days, so some on ebay for at least 80$/pair...so you say for what I want they are overated?
I got the gear for very small fee, 200$ (in France it's sold between 350 and 400€  :o )so I can afford Utc and in the futur I could use them in other Diy stuff.
when I say dirt box, I say distortion but I want something versatil so something who could be clean but colored and dirty when you push the input...and I have an issue with edcor so...
I don't know if you try this comp, but I was very suprised that it work very well for a chinese machine...but the idea is to bypass the crappy input...
for the output I've got some sowter 600:600, very clean...I think I will drop them into!
and opa upgrade could be good.

I saw some Tamura 1:1 for half the price


Quote
Frequency range of TK-1 is 50 - 10000 Hz +/-0.5dB and maximum operation level is 10dBm

Quote
Frequency range of TD-1 is 30 ~ 20000 Hz +/-0.2dB and maximum operation level is 13dBm

Re: ART PRO VLA - Kenetec mod
« Reply #13 on: August 06, 2009, 10:42:41 AM »
Those sowters would be very nice and full range on the input as well.  I've never used the Tamuras but I would guess they're a good sounding transformer.  Yes, the Edcors are not as hi-fi sounding as say a Jensen.  Sounds like you prefer the cleaner hi-fi sound

If you've got the iron already, may as well use it. If you use the Stancor, you could wire the primary for full range selection of all the impedances/coils.  This would require a 4P5T rotary switch. The WF-30 will give you 5 different impedance configurations, all of which will step-up the gain when the secondary is left connected for 500/600 ohm operation.  This would provide you with a useful and fun way to hit the input of the amp circuit a little harder.

A diagram of the coil connections should be printed on the side of the xformer.  My guess is that it's similar to the A-20s with pins 3 and 4 = pri C.T , and 9 and 10 = sec C.T

Here's a catalog link:

http://www.bunkerofdoom.com/xfm/stancor1968/stan_68_010.jpg

If you're interested in using the 4P5T switch let me know and I'll post a diagram of the wiring for it. 

diyfanatic

Re: ART PRO VLA - Kenetec mod
« Reply #14 on: August 06, 2009, 12:30:23 PM »
thanks for the catalog !!

Quote
If you've got the iron already
no I haven't bought it , waited to know if it will worth it.

Quote
his would require a 4P5T rotary switch. The WF-30 will give you 5 different impedance configurations
this is very interseting!so basically the swith will step up the impedance from 50 to 600ohm and the less ohm at the transformer input the more it will distort?

Quote
If you're interested in using the 4P5T switch let me know and I'll post a diagram of the wiring for it. 
please do!!!  ;)

cheers.
Jr.



Re: ART PRO VLA - Kenetec mod
« Reply #15 on: August 06, 2009, 03:21:31 PM »


Well this certainly qualifies as one of the most badly drawn diagrams on the forum but hopefully it gets the job done.

This is correct for the UTC A-20 and assumes that pins 3 & 4 are the center tap.  I'm not 100% the WF-30 uses the same pin outs as the A-20 but they're probably very close.

A-20 connection guide                                    Diagram Guide

1 to 6  (3 to 4)  = 500 ohm                          Pole 1  =  XLR  pin 2 (+)
1 to 5   same     = 333 ohm                         Pole 2  =  XLR pin 3 (-)
2 to 5   same     = 200 ohm                          Pole 3  =  transformer CT (pin 3)
1 to 3   4 to 6    = 125 ohm                          Pole 4  =  transformer CT (pin 4)
2 to 3   4 to 5    = 50 ohm

 Numbers 1,2,5 and 6 are connected directly to the corresponding transformer pins.

Green denotes the starting position (500 ohm) and proceeds clockwise to 50 ohms

Sorry for the messy drawing.  If anyone can recommend a more suitable drawing program for this app, let me know and I'll re-post it                                                           

diyfanatic

Re: ART PRO VLA - Kenetec mod
« Reply #16 on: August 06, 2009, 04:33:26 PM »
Quote
I'm not 100% the WF-30 uses the same pin outs as the A-20
I read that the stancor is a exact replacement of the Utc so it should be true

Quote
one of the most badly drawn diagrams
I've seen really worse!!  :D

thanks for the effort.

I let you know.
Peace.
Jr.

RedNoise

Re: ART PRO VLA - Kenetec mod
« Reply #17 on: August 07, 2009, 03:57:00 AM »
Thank you so much lassoharp !  :D
If your neighbour is hunger : don't give him fish , teach him how to fish ...
if you don't like it don't buy it ;-)  [Wolker Texas Ranger] ( ;-) )

Silvas

Re: ART PRO VLA - Kenetec mod
« Reply #18 on: November 29, 2009, 01:59:23 PM »
Hello

I´m about to buy a VLA for less than $ 200, in great shape.  :D

I want to perform some of the mods described here (but not any trafo mod)

Someone has a hi res schemo of this compressor? I want to understand what i´m going to do !

Thanks so much !


tommypiper

Re: ART PRO VLA - Kenetec mod
« Reply #19 on: December 04, 2009, 10:15:23 AM »
roger foote suggested this

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)


Why replace the 300 R resisters with 200 R?  Or is that a typo?  (Which resistors?)
Imagine a wet, slightly chilled from its gas release and decompression, with water droplets condensing, sucking surface tension, slowly sliding down the side, capped by a healthy virgin froth on top..