Modified Laney VH100R lacks mids

[Emetal]

Voodoo amps modified my Laney VH100R years ago, amp sees very little play about 3 hrs a week so it's still in a great shape, but there is an issue:
the amp seriously LACKS MIDS, so much that I can only use amp if I use EL34's (which are known to have more mids then any other power tubes) with V30 Celestions speakers and MIDS on the amp set to 7.5 or 8 in order to get enough mids in my sound and btw I play Metal where I do not need a lot of mids.
It is impossible to use 6L6 tubes with this amp, the little mids that I have now are then totally gone.
Does anybody knows:
is there a cap I could change back to original value or anything else I could do to get back the mids this amp had before mod?
( I E-mailed Voodooamps but they are not answering)

[J M Fahey]

Maybe, but we don't have either the original schematic (you can google it or ask Laney) but much worse we don't know what's inside your amp *now*.
If you dare to trace its schematic by hand and post it here, then we have something to start with; otherwise .....

[R ski]

sounds like the amp's tone is scooped way to much............most of that timbre is carved out by the tone stack........if you can't get a schematic...trace the wiring from the tone controls is where to focus on.....this process....takes some effort of starting from the treble.....use a pencil and paper....usually I need to redraw the initial drawing to get a better perspective of the circuitry.....once the tone stack is on paper....then you can scan it post it and other members of this community or me could tell you what components will reshape the sound you are after

[Jazz P Bass]

The 'mid cut' mod, if that is indeed what was done, could be at the Master Volume circuit.
C20 may have been substituted with a different value.
You will have to open it up & look.
The schematic is located here: http://music-electronics-forum.com/t16301/

[Emetal]

Well here is schematics again, so I guess I will have to open and see is it the C20 actually 22n (22 nano Farads) as it came from the factory :-(

[Emetal]

Ok this is what I have found out, C20 has not been modified so that is not the direction to go. The modifications I was able to spot are the following:

(These are located on Page 4 in PDF schematics)

C1 has been replaced with 1uF 50v cap
R1 has been replaced with 2.2K
C6 the 2,2nF that is suppose to be there alone now is put into a serial connection with a little circuit consisting of 470K resistor in parallel with a very small brown cap (I cant read the value)
C7 instead of 680nF now there is a serial connection of 47K resistor and 0.47uF 50v
R9 has been replaced with 4,7K
C19 has been replaced with 22uF

(These are located on Page 2 in PDF schematics)

V1 Mods:
-There is an added 22J (I guess that means 22pF) cap between pins 6 and 7 (which is V1B A. and V1B G.)
- 68K that is going from V1A G. to PAD 8 has been replaced with 20K

V2 Mods:
-There is an added 1uF cap between pin 3 (which is V2A K.) and middle pin
-Connection wire that is going from V2A A. to V5A G. has a hidden (shrinkwraped) resistor of unknown value added in serial.
-Connection wire going from pin 2 (which is V2A G.) to PAD 12 also has hidden (shrinkwraped) unknown resistor added in serial.

Following things I believe are not mods but just printing mistakes in schematics:
-PC Board 9078_3 next to PAD 8 says it’s connecting to V3B G. it should say V3A G.
-PC Board 9078_3 next to PAD 18 says it’s connecting to V4B G. it should say V4A G.
- Schematics says that V5B A. is connected to V4B A. via 100K. In reality V5B A. goes to PAD 22. (which does say next to that PAD) and it is V5A A. that is connected to that 100K line from V4B A.

Now can anybody PLEASE figure out which one of these mods is eating my mids :-(

[J M Fahey]

Don't know beforehand, let me go through what you found, maybe something rings a bell.

Ok this is what I have found out, C20 has not been modified so that is not the direction to go. The modifications I was able to spot are the following:

(These are located on Page 4 in PDF schematics)

C1 has been replaced with 1uF 50v cap
R1 has been replaced with 2.2K

Slightly higher C1 lowers deep bass cutoff frequency a tiny bit , slightly lower R1 raises it, these two about cancel out each other, end result is no change. Not here.

C6 the 2,2nF that is suppose to be there alone now is put into a serial connection with a little circuit consisting of 470K resistor in parallel with a very small brown cap (I cant read the value)

Well, here there's both a drawing error and a parts value discrepancy ... plus the "mystery mod".
1) the original drawing is nonsense, it shows C6, 22nF, grounded, which would kill all sound amplified by V1b.
I see this amp basically like a JCM800 in the "normal" setting, to which is added an extra triode stage, V1B for extra drive.
That's what the DPDT relay selects, either a straight connection or passing through V1b.
2) so, to send it back to original (this should add a lot of low mid growl), replace C6 back to original: 22nF (x 400 or 600V) and drop the "padding/brightening" network of 470K//small brown cap which must probably be 470pF , both being the same as what R12//C10 do.
// means in parallel.

C7 instead of 680nF now there is a serial connection of 47K resistor and 0.47uF 50v

47K in series is nonsense, basically puts it out of the circuit.
Are you sure it's 47K and not 4K7 or even 470r?
Anyway, the solution is "back to normal", you know the drill
Meaning, put back what the original schematic shows.

R9 has been replaced with 4,7K

**Back to normal**

C19 has been replaced with 22uF

Leave it, doesn't hurt nor change sound.

(These are located on Page 2 in PDF schematics)

Will continue later, now I'm sleepy

[J M Fahey]

V1 Mods:
-There is an added 22J (I guess that means 22pF) cap between pins 6 and 7 (which is V1B A. and V1B G.)

*If* it's 22 pF it's killing highest highs/RF , probably added to tame some nasty oscillation.
Try "with" and "without" but shouldn't affect sound much.
Definitely no mid scooping here.

- 68K that is going from V1A G. to PAD 8 has been replaced with 20K

You mean V1B ?
*Probably* adding the 22pF was "too much" so they tamed that added Miller capacitance cutoff with a smaller series R.
I'd go back to original 68K and if any, remove the 22 pF.

V2 Mods:
-There is an added 1uF cap between pin 3 (which is V2A K.) and middle pin

Standard noob "mod".
I assume the center lug is grounded, so it's actually in parallel with R10.
They see that big cathode resistor and think "I'll bypass it and owner will be happy with the added gain" ; "my cost=10 cents".
Yes, gain increases a lot.
Yes, sound loses growl, bite.
Remove that added capacitor.

-Connection wire that is going from V2A A. to V5A G. has a hidden (shrinkwraped) resistor of unknown value added in serial.

Can't find that connection in the schematic.

-Connection wire going from pin 2 (which is V2A G.) to PAD 12 also has hidden (shrinkwraped) unknown resistor added in serial.

Can't fond it either.
Are we looking at the same schematic?
Always indicate what page we are in.

Following things I believe are not mods but just printing mistakes in schematics:
-PC Board 9078_3 next to PAD 8 says it’s connecting to V3B G. it should say V3A G.
-PC Board 9078_3 next to PAD 18 says it’s connecting to V4B G. it should say V4A G.
- Schematics says that V5B A. is connected to V4B A. via 100K. In reality V5B A. goes to PAD 22. (which does say next to that PAD) and it is V5A A. that is connected to that 100K line from V4B A.

Can't comment.
You have the actual amp before you.
I stayed up 5 extra minutes but now I'm definitely getting some sleep.

Now can anybody PLEASE figure out which one of these mods is eating my mids :-(

[Emetal]

Ok I have posted this problem also on another forum:
The Amp Garage :: View topic - Voodoo modified Laney VH100R lacks mids

There is several replies, and yes we have identified mistakes or differences between page 2 and Page 4. Page 2 is one to look at when talking about V1 i V2 mods. It corresponds to reality in the amp. If you can please read the stuff over there so I do not have to repeat all things, but the suggestions are pretty close to what you saying, with few differences..

[J M Fahey]

Well, Aleksander Niemand seems to have given you my exact same suggestions, so I guess he must be a very intelligent man
Basically, "go back to original"

But *please* , decide on what you are trying to correct: here you speak of "lack of mids", there of "nasal" sound, the exact opposite.
Please choose one.

As of the amp being harsh, it's a JCM800!!!, what did you expect?
That "sickness" is easily cured by setting Master Volume above 7 ; preferably on 10.
At low settings (2 or 3) it will be *definitely* buzzy.

[Emetal]

Hmmm I thought that nasal sound is when it lacks some frequencies, OK maybe I can not describe correctly but it was a pinched sound something was missing, anyway, I have changed C6 back to original, got low mid growl (great) then I removed 22pF and sound got even better (got more nice highs), but got microphonics.. So what I am looking for now is how to keep those highs but tame the microphonics, or some middle ground.. Anyway, these changes have opened up my sound and it is a right direction I was looking for whatever that is, I do not dare do describe anymore After I get the parts and after few rehearsals I will fiddle with other things like C7 going back to original or the other thing that was mentioned for C7 (470 Ohm and 1uF)

[Emetal]

Now when I got the sound where it sounds pretty good, could you please tell me what do I do with 10K when 22pF pulled out - should I revert 10k back on 68K, and also is there another way to tame the microphonics that are appearing after 22pF is pulled out? Some guy on the other forum was mentioning putting caps in parallel with R5 or R7 I can't get it straight, is this something you would do or...?
Here is the V1 photo so you can see it in reality...

P.S. please note the following things: Voodoo mod has 22uF in B stage of V1 and 10K grid stopper is in A stage of V1. They are not in the same stage. Further V1A A. is going to PAD 6 and then to R7!!! And V1B A. is going to PAD 5 and R5!!! This is how it is on the PAGE 2 of PDF and in my amp. PAGE 4 is WRONG

[J M Fahey]

I would roll back that 10K to the original 68K.
Try it and post what you hear.
If "microphonics" return (although I think you mean "oscillation", not the same thing) and it's an "inside the amp" situation, not something caused by guitar/cables/whatever external, then we'll se what we can do.
Problem (not only here but in general Elctronics repair) is that paths (theories about what might be wrong) split into smaller paths which also split in .... and so on and on and on, so best is supposing something and agreeing or discarding.
Otherwise your head explodes with "possibilities".
Let's go step by step, which so far has worked fine.
Good luck.

[Emetal]

Ok I am having lot of fun now

Did not have enough time to try everything, I will post all together at ones when finish, gotta have rehearsal between every change to evaluate the sound that way (bedroom levels are not how I wanna reference) One thing is standing up as a rule though if releasing the low-mid furry by reversing C6 and C7 one must definitely remove that extra gain causing 1uF from V2. Otherwise ridicules amount of gain is achived

Ohhh and btw here is a pic of that Voodoo Mod from C7, everybody were saying that has no logic (47K making cap invisible to signal)... well you can see the colors now..

[J M Fahey]

Only explanation is that a cheap hired hand at the bench misread the code as "47 something" , anything from 4K7/470 to 47 ohms.
But it should have been noticed at the final quality inspection