VHT - Valvulator

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
User avatar
theehman
Cap Cooler
Information
Posts: 686
Joined: 16 Aug 2007, 16:52
Location: Clear Creek, IN
Has thanked: 84 times
Been thanked: 88 times
Contact:

Post by theehman »

Thought someone might enjoy these shots of the VHT Valvulator. I've got it apart right now replacing the poorly designed power transformer. The tranny solders to the PCB which rests on it's side in the housing. Gravity and normal use take their toll and the wires break off the solder pins. Can be fixed but it's often temporary. Any unit you see that's listed as broken will likely have this problem.
Feel free to ask any questions.
Attachments
VHTcomp.jpg
VHTboard.jpg
Ron Neely II
Electro-Harmonix info: http://electroharmonix.vintageusaguitars.com
Home of RonSound effects: http://www.ronsound.com
fx schematics and repairs

User avatar
lolbou
Old Solderhand
Information
Posts: 2757
Joined: 18 Nov 2008, 21:38
Has thanked: 295 times
Been thanked: 192 times

Post by lolbou »

Great Ron!

Thank you for sharing!!
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

User avatar
theehman
Cap Cooler
Information
Posts: 686
Joined: 16 Aug 2007, 16:52
Location: Clear Creek, IN
Has thanked: 84 times
Been thanked: 88 times
Contact:

Post by theehman »

Here's a schematic I put together. Can someone check it and see if it looks right? This is just the buffer section as I figured no one was really interested in the pedal power supplies.
Attachments
VHTValvulator.jpg
Ron Neely II
Electro-Harmonix info: http://electroharmonix.vintageusaguitars.com
Home of RonSound effects: http://www.ronsound.com
fx schematics and repairs

User avatar
lolbou
Old Solderhand
Information
Posts: 2757
Joined: 18 Nov 2008, 21:38
Has thanked: 295 times
Been thanked: 192 times

Post by lolbou »

Well, I would be interested (or simply curious) to know about the pedal power supply somehow...

If you do have it, then feel free :D ! Thanks again for the schem...
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

User avatar
bajaman
Old Solderhand
Information
Posts: 4416
Joined: 26 Jun 2007, 21:18
Location: New Brighton, Christchurch, NZ
Has thanked: 474 times
Been thanked: 1725 times

Post by bajaman »

from the picture - the pedal power supplies are four independent diode bridges feeding four electrolytics and four dc socket outputs.
not rocket science!
bajaman
be kind to all animals - especially human beings

User avatar
theehman
Cap Cooler
Information
Posts: 686
Joined: 16 Aug 2007, 16:52
Location: Clear Creek, IN
Has thanked: 84 times
Been thanked: 88 times
Contact:

Post by theehman »

bajaman wrote:from the picture - the pedal power supplies are four independent diode bridges feeding four electrolytics and four dc socket outputs.
not rocket science!
bajaman
Yeah, they're just your basic regulated supplies. There was a 12v supply but I changed it into a 9V.

There's also a .01uF cap across the AC supply I didn't add in.
Ron Neely II
Electro-Harmonix info: http://electroharmonix.vintageusaguitars.com
Home of RonSound effects: http://www.ronsound.com
fx schematics and repairs

User avatar
lolbou
Old Solderhand
Information
Posts: 2757
Joined: 18 Nov 2008, 21:38
Has thanked: 295 times
Been thanked: 192 times

Post by lolbou »

bajaman wrote:from the picture - the pedal power supplies are four independent diode bridges feeding four electrolytics and four dc socket outputs.
not rocket science!
bajaman
:oops: I didn't look closely to these round things, and thus expected all bridge rectifiers to be squary devices...

Thanks bajaman, sharp eyes as always!

I know power supply is a common thing, but I -stupidly :) - assumed that these VHT ones were good quality ones as regards to the unit's price...

So there's no regulators in there... Can a simple filtering be good quality enough to get rid of residual oscillations in the voltage output? Are these VHT power supplies noisy??

If these are poor, I can't understand why they add them... If these are good, then what makes them efficient, 'cause I thought a regulator was the best way to get a clean DC?

ps: I'm actually into rockets (and gravity and satellites...) this week with some of my pupils, you know... :lol:

edit: thanks too ron... did you changed the 12V by tweaking a resistor to the 9V circuit values?
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

User avatar
theehman
Cap Cooler
Information
Posts: 686
Joined: 16 Aug 2007, 16:52
Location: Clear Creek, IN
Has thanked: 84 times
Been thanked: 88 times
Contact:

Post by theehman »

lolbou wrote:
So there's no regulators in there... Can a simple filtering be good quality enough to get rid of residual oscillations in the voltage output? Are these VHT power supplies noisy??

If these are poor, I can't understand why they add them... If these are good, then what makes them efficient, 'cause I thought a regulator was the best way to get a clean DC?


edit: thanks too ron... did you changed the 12V by tweaking a resistor to the 9V circuit values?
3 of the regulators for the pedal supplies are TO-92 sized 9v regulators. You can see them behind the power outputs.
The 12V was a TO-3 which I just replaced with a similar 9V unit.
I'll toss a schematic together and post it tomorrow.
Ron Neely II
Electro-Harmonix info: http://electroharmonix.vintageusaguitars.com
Home of RonSound effects: http://www.ronsound.com
fx schematics and repairs

User avatar
lolbou
Old Solderhand
Information
Posts: 2757
Joined: 18 Nov 2008, 21:38
Has thanked: 295 times
Been thanked: 192 times

Post by lolbou »

I think I need my glasses.

I think I need some sleep.

As I can't have both at one time, I'll go for the second at once, and will come back with the first tomorrow... 8)

Cheers Ron, and good night! :tired
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

User avatar
soulsonic
Old Solderhand
Information
Posts: 3820
Joined: 27 Jun 2007, 03:38
my favorite amplifier: Stopped using amps mostly...
Completed builds: too many!
Location: Homer, NY
Has thanked: 128 times
Been thanked: 330 times
Contact:

Post by soulsonic »

Thanks, Ron!
I might play with this. I like tube stuff.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

User avatar
Nyquist5
Breadboard Brother
Information
Posts: 55
Joined: 08 Jan 2008, 08:15
my favorite amplifier: The amps I build
Location: Lille, France
Been thanked: 3 times
Contact:

Post by Nyquist5 »

Thanks for that schem EHMan!
I think you have a mistake on R5 and R6. C4 should probably be before them, otherwise they constitute a voltage divider with R3 and the anode of the first triode won't see the proper voltage.
I think their purpose is to attenuate the amplified signal before they hit the second triode, hence their probable location after C4.
Also, the succession of C5 and C6 seem strange.

User avatar
theehman
Cap Cooler
Information
Posts: 686
Joined: 16 Aug 2007, 16:52
Location: Clear Creek, IN
Has thanked: 84 times
Been thanked: 88 times
Contact:

Post by theehman »

Nyquist5 wrote:Thanks for that schem EHMan!
I think you have a mistake on R5 and R6. C4 should probably be before them, otherwise they constitute a voltage divider with R3 and the anode of the first triode won't see the proper voltage.
I think their purpose is to attenuate the amplified signal before they hit the second triode, hence their probable location after C4.
Also, the succession of C5 and C6 seem strange.
I checked it again visually and by continuity and the schematic is correct as far as R5, R6, C4, C5, and C6 go. I thought it looked strange, too. :scratch:
Ron Neely II
Electro-Harmonix info: http://electroharmonix.vintageusaguitars.com
Home of RonSound effects: http://www.ronsound.com
fx schematics and repairs

User avatar
Nyquist5
Breadboard Brother
Information
Posts: 55
Joined: 08 Jan 2008, 08:15
my favorite amplifier: The amps I build
Location: Lille, France
Been thanked: 3 times
Contact:

Post by Nyquist5 »

:hmmm: ...

User avatar
theehman
Cap Cooler
Information
Posts: 686
Joined: 16 Aug 2007, 16:52
Location: Clear Creek, IN
Has thanked: 84 times
Been thanked: 88 times
Contact:

Post by theehman »

Here's a merged image of both sides. Please let me know if you find an error. :hmmm: :scratch:
Attachments
VHTmerge.jpg
Ron Neely II
Electro-Harmonix info: http://electroharmonix.vintageusaguitars.com
Home of RonSound effects: http://www.ronsound.com
fx schematics and repairs

Tube2stomp
Breadboard Brother
Information
Posts: 63
Joined: 14 Dec 2007, 12:53
Been thanked: 3 times

Post by Tube2stomp »

What's the B+/HT and the measured input stage plate voltage?
Never saw one before but hoped it was a bit more "clever" then this for a dedicated tube buffer [smilie=a_reading.gif]
Also does it really have R1 before the grid bleed resistor and not after like a normal grid stopper?
And that input cap... oy vey

crispycircuit
Information
Posts: 6
Joined: 04 Feb 2010, 02:37

Post by crispycircuit »

I've been searching for a Valvulator schematic since mine is blowing fuses, those tiny cylinder plug-in's. They're not very common and have to be ordered. 250ma @250V. I was hoping a schematic would help make it easier than tracing the double sided circuit board. Help is greatly appreciated.... Mine is a Valvulator 1 with circuit board R1.2......

crispycircuit
Information
Posts: 6
Joined: 04 Feb 2010, 02:37

Post by crispycircuit »

Update, I just tested it out on the bench. I ended up hooking up my meter set on ma AC in line with the AC cord. It's running fine, however, since I changed the 12ax7 it draws a lot at turn on. I put a EI 12ax7 and did you ever notice some European tubes glow bright when turned on? It's intial draw is more than the stock tube. Plus the fact I ordered fast blow instead of slo blow. So I'll order 300ma 250V slo blow fuses. Keep it mind if you change you tube...

Tube2stomp
Breadboard Brother
Information
Posts: 63
Joined: 14 Dec 2007, 12:53
Been thanked: 3 times

Post by Tube2stomp »

At turn-on the heaters are cold, there is less resistance and so current draw is higher.
It's normal and happens with all heat type resistances... even light bulbs at home.
Mulards and Mulard style built tubes do flash harder at startup.
Maybe in the past they didn't care much because parts were cheap, but when ever I see my NOS Mulards flash it flips my stomach :mrgreen:

There are ways to couter that current rush and old tube books sometimes do mention that issue, but I don't remember seeing "old" amps or schematics that implemented such methods.

User avatar
mictester
Old Solderhand
Information
Posts: 2923
Joined: 11 Sep 2008, 20:29
my favorite amplifier: Mesa Boogie, Roost Sessionmaster, AC30
Completed builds: Hundreds! Mostly originals, a few clones and lots of modifications.
Location: Somewhat closer to Amsterdam than before!
Has thanked: 33 times
Been thanked: 758 times
Contact:

Post by mictester »

crispycircuit wrote:Update, I just tested it out on the bench. I ended up hooking up my meter set on ma AC in line with the AC cord. It's running fine, however, since I changed the 12ax7 it draws a lot at turn on. I put a EI 12ax7 and did you ever notice some European tubes glow bright when turned on? It's intial draw is more than the stock tube. Plus the fact I ordered fast blow instead of slo blow. So I'll order 300ma 250V slo blow fuses. Keep it mind if you change you tube...
Back when I was a kid, and all my amplifiers were glass-mode types, it was common to put a resistor in series with the heater supply. This would limit the inrush current. There would then be a simple capacitor timer to operate a relay which would short out the heater resistor and give them full power. An even slower delay relay would then switch on the HT!

I modified a large number of AC30s like this, and was pleasantly surprised to see a well-known guitarist using one of mine a few weeks ago. The old "standby" HT switch was used instead for simple input muting as the application of HT was automatic.
"Why is it humming?" "Because it doesn't know the words!"

User avatar
lolbou
Old Solderhand
Information
Posts: 2757
Joined: 18 Nov 2008, 21:38
Has thanked: 295 times
Been thanked: 192 times

Post by lolbou »

mictester wrote:a well-known guitarist
with a well-known Red Special? :?:
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

Post Reply