Lead Dress: OD V2a Grid wire

[Audiodog]

Here is a pic of the clone before I moved the wire. It was touching.

[Audiodog]

Looks like it was pushed firmly together in fact. Looks like some jacket deformation. Maybe that enhanced the vibration coupling? Plus amp is a combo. I had the head on my combo so there was a lot of vibrations.

[martin manning]

Sorry, mis-typed V1a instead of V2a above.

I'm certainly not against keeping those leads separated, and generally avoid parallel routing as a mater of habit. I'm looking for the cause of the problem, which does not appear to be capacitive or inductive coupling if a tiny gap fixes it. If physical contact between the insulators is required, then what is happening? Perhaps some static charge effect? Leaky insulation? Still don't know why that wouldn't show up on the breadboard stage.

Here's a photo from my 124-ish amp. I'd have to open it up to find out what the gap between the green and blue leads is.

[martin manning]

Here is a pic of the clone before I moved the wire. It was touching.

Both leads appear to be above the chassis surface by some amount. Was that the case?

[talbany]

This thread has devolved into bullshit.

I know for a 1000% fact that if your plate and grid wires are physically touching, the amp will absolutely not function correctly. Just try it. Push the V2a grid onto the plate. Touching. Then play the amp loudly. Even the bass control stops working correctly. Terrible abrasive sound. I just last week spent hours troubleshooting a high end clone and the grid and plate wires were touching on V2a. I separated them and the amp kills now. I tried changing the bass cap, the bass pot, the .001 on the bass pot. The control was almost cutting the bass in and out as you turned it! The wires were the cause. No breadboard needed.

Try touching the grid wire. You will hear microphonic noise. Now, imagine the amp vibrations of the grid and plate rubbing, Not open for discussion. It kills the amp sound. Not just a little. I can’t believe we are arguing whether the grid and plate wires actually touching is OK.

A number of years ago I fixed a ceriatone for a friend. The amp had no sustain and the volume was pumping in and out. Turns out Nick bent the V1a grid resistor down and the body was contacting the plate. I bent the resistor back up and voila. Sustain and fatness returned. No pumping in and out.

One other easily noticeable thing. Try pushing the cl2 .05 coupler towards the .002 treble midboost cap. Play. Then move it away. The amp is fatter with some space between them. Always keep out of phase stages away from one another. Ken Fisher would roll in his grave that there are three pages of this…

Who needs a breadboard when you can just do the test on the real amp. It is not subtle. It is a huge and extremely noticeable difference.

Interesting. It definitely made a difference for me (maybe confirmation bias). Charlie W can lend his bat-ears next week and prove me bonkers

I'd love to know why Mr. Dumble looked to be pretty particular about this part of his lead dress.

Running wires down on the chassis will introduce capacitance of about 1pF per inch to ground, which will only affect extremely high frequencies. I would expect similar results running plate and cathode wires close together on the chassis for a couple of inches, which will put a couple of pF between them, and also to ground on each. I can see that in a simulation, it's a loss of about 0.1 dB at 20kHz, but that's going to be too small to see on the scope.

Thanks Martin I was aware that added some capacitance but not aware of how much per inch.

Ian
This has been discussed here quite a bit throughout the years Some people here who have claimed to have heard it makes a difference,others who have said they don't really hear much there.
https://ampgarage.com/forum/viewtopic.p ... 663#p27663
This is not sayin anyone is right or wrong and Martin is the 1st here to actually measure it out on the bench which is always a big help I am a big believer in getting another set of good ears involved with these kinds of things and Charlie's got em!!
Looking forward to your findings

Tony

Scott?? Why are you re-posting me?
I had already addressed the effects of capacitance coupling , positive and degenerative feedback between the plate and grid being too close and even gave him a test to confirm his theory.

BTW? An easy way to prove the capacitance coupling theory on the grid is to take an alligator clip and clip one side to the insulation of the grid wire. Then you can probe around with the other end,attaching it to the insulation of the plate wire see if you get any degenerative feedback there..Plates that are out of phase will kill tone and have a wah like effect on the low end . Plates that are in phase will feedback and squeal .This should test out how noticeable it is on your amp. IMO every amp is different. Dumble seems to run both plates and grid far enough apart V2a to not cause any C.C IMO

Let us know what you find. Ian

This one (with the link) discusses the practice of running the plate V1b and cathode V1a wires next to each other. Not the plate and grid.( Ian inquired about that as well) This is what i was talking about having mixed opinions on? and if it really helps the amp feedback through capacitance coupling or positive feedback.(which Dumble seems more hit or miss on this one)

This has been discussed here quite a bit throughout the years Some people here who have claimed to have heard it makes a difference,others who have said they don't really hear much there.
https://ampgarage.com/forum/viewtopic.p ... 663#p27663
This is not sayin anyone is right or wrong and Martin is the 1st here to actually measure it out on the bench which is always a big help I am a big believer in getting another set of good ears involved with these kinds of things and Charlie's got em!!
Looking forward to your findings

Tony

[talbany]

BTW.Here is an old piece that Gil Ayan wrote on lead dress he sent me a few days ago. IMO it's a timeless piece and everyone should have a copy.

Since I know some of you do engage in amp customization, I thought
I'd pass on to you some of the things I have learned about lead dress
in an amplifier, which is probably one of the hardest things to do
correctly. Although most typically a problem when high-gain stages
are present, even Fender had its share of trouble with lead dress
starting with the second generation Silverface amps, and these amps
can be hardly considered high gain. Most Fender fans will say that
Fenders were always less prone to oscillations that Marshalls, making
it sound as if there is something superior about the design. While
it's true that Marshalls almost always behaved worse, it warrants
pointing out that Marshalls typically run at higher levels of gain,
so it's the old apples and oranges stuff.

Most people read about this subject, and know a few things, such that
grid leads "should be" short, etc. But, the shortest path between
two given points is not necessarily the best for tone's sake. In the
specific case of Fender amps, there is a grid lead that goes from the
rightmost volume control to the 2nd stage of the "vibrato" input.
This is the single longest lead in the hole amp, and the one that can
give you a tremendous headache if you're building additional gain
stages within the amp. No pain, no "gain" though (yes, pun
intended). [Also, even if you're not considering customizing any
amp, you can always improve the stability of your later Silverface
amp by tweaking the lead dress and getting read of the tone-eating
caps at the power tubes]

I found that moving that wire around could do one of three things:
give a good sound, make the amp break into oscillation (whether you
can HEAR the oscillation or just "feel" it -- the old parasitic
type), or result in a very nasal sound. You can do the lead dress
by trial and error, and maybe you'll get there, but there is a way a
found to be more effective and it does work indeed.

Use a long wire, temporarily of course, to make the connection whose
lead dress you want to optimize. If you pull that wire away from the
rest of the circuit, you will hear the tone is unfettered, even
across all frequencies and without any unwanted side effects --
well, you will most likely find this anyway. Get a cable with
alligator clips on both ends; wrap a portion of that wire around the
grid lead. Leave one end of the alligator wire not touching
anything (you can clip it to the insulation of the cable so that is
doesn't move around), and with the other end, start probing the
entire circuitry. When touching plate connections, remember you're
dealing with 200+ volts, so... be cautious.

What's going on here is that now you're capacitance coupling your
grid lead wire to all other points of the circuit via that alligator
clip patch wire, which is similar to what would happen if you lay
your wired back into the circuit. As expected, plate leads from
stages which are in phase with the grid wire in question will make
your amp squeal like a pig when you touch them with the alligator
clip, so you'll want to stay far from those wires. Conversely, plate
leads out of phase with the grid lead will KILL TONE big time, again
keep your distance. In some extreme cases, you may lose almost all
your output, but even if that doesn't happen, you will think there is
a wah-wah stuck on the bass side of the throw because of the
degenerative feedback that's taking place. Additionally, there are
several points within the circuit that will also affect the sound,
although maybe not as severely. Also, bear in mind there is some
stuff going on underneath the chassis as well, so if you're probing
around open areas of the chassis and find that, although it should
"all be ground," there is a still change in tone, well... it could be
your reverb transformer, the filter capacitor can, etc.

What to do? Map out the areas of the circuit where it is "safe" to
run your lead dress, based upon your experimentation as described
above, and you will end up with an optimum path for the grid wire.
In most cases, this will not be a straight line -- which is
obviously the shortest distance, belying the rule suggesting to use
the shortest possible lead for grid connections. If you HAVE to go
across another wire which you've determined to be an offender with
the probing exercise, cross it perpendicularly; this will minimize
capacitance coupling and the tone will be most likely preserved.

What about using shielded cable? Yes, absolutely, that will help
provided you be sure to ground one end of the shield; other people
recommend you not ground either end and, and instead connect one end
of the shield to the corresponding stage's plate; I have found this
to be another tone killer, and there is the potential hazard of
having a hot shield. It's been my experience that shielded wire is
not bulletproof and might be subject to the same effects I mentioned
earlier, although to a lesser extent if you do things correctly.
Using generic microphone cable is bad, probably even worse than using
no shielding at all if you have cheap wire. It doesn't provide good
protection against cross talk and the copper mesh will be an antenna
attracting all kinds of stray signals to your lead wire. Even if you
ground the shield, you'll be stuck with a signal riding on top of
your grid wire, and there will be some interaction and or modulation.
Foil type shielded cable, although much more expensive, is the only
way to go.

If you've seen MESA/Boogie schematics, you will notice that some
models (the Marks II and above, for instance), have all kinds of
capacitors in their overdrive sections that either shunt to ground or
bypass the plate load resistors. Some writers have said that it
helps control an otherwise extremely buzzy sound, and that it helps
to stabilize the design. Yes, it stabilizes the gain stages, but the
midrange heavy tone which results may not be what you're shooting
for. Regarding the buzzy sound, if you can allow your highs to go
through all the stages unaltered, they will not sound so buzzy
anymore: they will be sweet because they break up easily and give lots
of harmonics, resulting in your amp being extremely touch sensitive
-- one of the keys to the sound of Dumble amplifiers, for example.
If you think you can "control" the treble response throughout the
preamp overdrive stages, a la MESA/Boogie, and then use a presence
control to bring the amp back to life, it won't work even close. The
presence control will sound stiff and flat because the treble it will
let through doesn't have as much harmonic richness since the highs
were stopped at the overdrive stages. I do not like the presence
control on the Mark II and IIIs for this very reason; implement the
same feedback network on a more harmonically rich amp and the
difference is striking. [Since I have had a chance to see the guts
of some very old Boogies, it seems to be that the Boogie midrange
heavy tone may have evolved out of necessity, because the chassis
were very crowded and the amps would have been unstable without
dumping a lot of highs to ground. However, there is no denying
that Boogie came up with a legendary sound, a great sound in many
people's opinion.]

Hope this helps some people out there to save some of the time I had
to spend lead dressing my amp. Some books address various
anti-microphonic techniques (long plate connections, short grid
connections, shielding, etc.), but that alone will sometimes not be
enough. I encourage everyone form staying away from using small
capacitors to get rid of oscillations if you can... yes, that method
does work -- and so does turning off your amp, for that matter -- but
it simply nukes tone. Common tech tips, such as wrapping a loop of
cable around a lead wire and connecting one end of the loop to
whatever quiets down the amp are the same as using capacitors to
combat oscillations, so use them as your last resort if you have to.

Cheers,

Gil

[daniboy79]

I really have to say this ...I have learnt so much from following discussions like these! I really appreciate all the input from those of you with a wealth of knowledge that are willing to pass along to those of us who are hungry for knowledge. Thank you all again!

[talbany]

One last comment about this
I wonder how many 124 style amps out there that have both plate and grid wires running parallel and possibly even touching each other under the board

Look at how close the wiper on the trimmer is to V2a's plate resistor (not far)..Another words if you didn't know to keep these separated under the board and ran them straight up to their respected eyelets there is a good chance they could touch (or come very close)..Just Sayin?

ODS_124071.jpg

ODS_124052.jpg

Tony

[Audiodog]

Close is one thing, touching is another. Btw, did not mean to address you with any attitude earlier. Was speaking in general and happened to reply to your post.

Fact is that one should never ever ever let those two wires touch. Gil agrees too!

One last comment about this
I wonder how many 124 style amps out there that have both plate and grid wires running parallel and possibly even touching each other under the board

Look at how close the wiper on the trimmer is to V2a's plate resistor (not far)..Another words if you didn't know to keep these separated under the board and ran them straight up to their respected eyelets there is a good chance they could touch (or come very close)..Just Sayin?

ODS_124071.jpgODS_124052.jpg

Tony

[martin manning]

I opened mine up and took a close-up photo. They're touching, and it sounds great.

[Audiodog]

Try moving them and compare. I had the clone and my amp on top of one another. Same exact circuit, same type tubes, same NOS parts. It was night and day until I moved that wire. Now they are very similar. Point of reference….

Also, maybe your wire is different as you were not experiencing the strange bass pot action. The clone’s bass pot was not functioning well until the issue was addressed.

I opened mine up and took a close-up photo. They're touching, and it sounds great.

[martin manning]

Try moving them and compare. I had the clone and my amp on top of one another. Same exact circuit, same type tubes, same NOS parts. It was night and day until I moved that wire. Now they are very similar. Point of reference….

Also, maybe your wire is different as you were not experiencing the strange bass pot action. The clone’s bass pot was not functioning well until the issue was addressed.

Next time I'm in it I'll try moving the grid lead so it's not touching the plate lead. It's been that way since it was built. In your case, something wrong with the wire is what I'm left with too.

I don't see how bass pot function could be related to this issue. It's upstream, on the other side of Cl2.

[Audiodog]

The issue was the increased bass that caused more of the inductive feedback. It was directly related, After hours of parts clipping in and other things I tried, the wire was it. Had the same thing with a Ceritone I mentioned. I even notice a change in feel and tone if you push CL2 coupler towards the treble cap. These are well known lead dress issues. Read Gil’s post Tony linked. Not subtle, I am more surprised you feel that your setup is OK and is not effecting the sound. I know for a fact the plate grid lead dress is crucial to the point of multiple amps that I have fixed that were not functioning correctly, The Ceriatone owner was watching and witnessed the fix and was speechless. I moved the V1A grid resistor off the plate wire and wow…. Totally different amp. The volume was really pumping in and out before the fix.

No offense, but how do you know that the amp is performing at 100%? Point of reference is crucial.

Please try moving your OD1 wires while playing loudly and see if things change.

Try moving them and compare. I had the clone and my amp on top of one another. Same exact circuit, same type tubes, same NOS parts. It was night and day until I moved that wire. Now they are very similar. Point of reference….

Also, maybe your wire is different as you were not experiencing the strange bass pot action. The clone’s bass pot was not functioning well until the issue was addressed.

Next time I'm in it I'll try moving the grid lead so it's not touching the plate lead. It's been that way since it was built. In your case, something wrong with the wire is what I'm left with too.

I don't see how bass pot function could be related to this issue. It's upstream, on the other side of Cl2.

[martin manning]

The issue was the increased bass that caused more of the inductive feedback.

Ok, that makes more sense, i.e. the problem got worse when the bass was turned up. I don't think we know what the root cause is, though, and I will stand by my claim that neither inductive nor capacitive coupling between these two leads is enough to produce the result you are describing.

Please try moving your OD1 wires while playing loudly and see if things change.

I had someone come over and play while I poked the grid lead around with a chopstick. I tried both lifting the grid lead and pressing it against the plate lead, and neither of us could hear anything happening. This was done at a variety of control settings, including Drive level, PAB on or off, Mid boost on or off, Bright on or off, Bass up or down, etc. My partner couldn't see what I was doing, and I didn't tell him what I was looking for, other than to listen for some change in the sound.

[ayan]

The issue was the increased bass that caused more of the inductive feedback. It was directly related, After hours of parts clipping in and other things I tried, the wire was it. Had the same thing with a Ceritone I mentioned. I even notice a change in feel and tone if you push CL2 coupler towards the treble cap. These are well known lead dress issues. Read Gil’s post Tony linked. Not subtle, I am more surprised you feel that your setup is OK and is not effecting the sound. I know for a fact the plate grid lead dress is crucial to the point of multiple amps that I have fixed that were not functioning correctly, The Ceriatone owner was watching and witnessed the fix and was speechless. I moved the V1A grid resistor off the plate wire and wow…. Totally different amp. The volume was really pumping in and out before the fix.

No offense, but how do you know that the amp is performing at 100%? Point of reference is crucial.

Please try moving your OD1 wires while playing loudly and see if things change.

Try moving them and compare. I had the clone and my amp on top of one another. Same exact circuit, same type tubes, same NOS parts. It was night and day until I moved that wire. Now they are very similar. Point of reference….

Also, maybe your wire is different as you were not experiencing the strange bass pot action. The clone’s bass pot was not functioning well until the issue was addressed.

Next time I'm in it I'll try moving the grid lead so it's not touching the plate lead. It's been that way since it was built. In your case, something wrong with the wire is what I'm left with too.

I don't see how bass pot function could be related to this issue. It's upstream, on the other side of Cl2.

Hi everyone. Scott, it's been a while, good to see you here again. Just thought I'd mention that paper that Tony included above was originally posted somewhere -- maybe Ampage? I forget -- on May 18th, 1998 according to my records. Just to keep things in perspective! But, for the amp in question that lead wire was crucial. That converted 68 Deluxe Reverb could sound great or terrible depending on where that wire lay. I have to say that I never encountered an effect like than in any of my ODS builds.

G.