Transformer placement

[warioblast]

Hi,
Last year with the help of some forumites here I successfully turned my DSL 50 into a plexi. I was my first venture into amp building.
I'm about to do mods to it, and I was thinking I could modify the chassis layout too. As you can see I kept the stock laydown transformers, and didn't change their location.
As of today my amp is a bit noisy; could be my heater wiring, could be something else... I have those long wires running from the OT, the preamp tubes close to it so I'm thinking it wouldn't hurt to move the OT, wouldn't it ?

I did some research, but most of the amps I saw didn't use both a laydown PT and a laydown OT. I found a topic here that was relevant but it was old and all the pics were gone. Plus, after all these years, the posters may have more experience.

What do you guys think ? Should I be fine putting the OT close to the PT, simply giving it a 90° turn ? Should I put the OT on brackets and mount it standing up ? ...

[pompeiisneaks]

The fact that those transformers are at opposite ends of the chassis probably avoids any coupling.  Noise can come from a ton of things, bad grounding, heaters etc like you said, I'd try turning the amp on, and chopstick around the grounds, and try moving heater wires a bit first to see if that helps with the noise.  Does the noise change with things like tone pots etc?  Is it still present if you take out some or all of the preamp tubes?  You can try removing one tube at a time to narrow down where it's coming in possibly as well.  I'm not saying it can't be the transformers, but looking at how far apart they are, I doubt it.  You also may want to adjust the OT wire path to ensure it's not too close to signal path somewhere.

~Phil

[PRR]

> amp is a bit noisy

My shoes are messy. Dust? Grease? Flour? Paint? Dog-hair? Different cleaners for different messes.

What is the amp singing? Hiss? Hum? Thunder? Bees? Fiji Radio? WiFi heartbeat??

And yes, it can be mixed-mess. Today my shoes look like dirt and dog-hair. At the limit, most any guitar amp will both hum and hiss. Hum can be eliminated in theory, though your axe always hums (anywhere you can find a wall-plug) so we don't try for dead-zero hum. Hiss happens, inevitably, but some improvement may be found.

[warioblast]

I shouldn't have mentionned that it was noisy.  The reason I didn't describe the noise is because my main concern is the transformer placement. For the record it's hum not hiss.

Lets just say I'm starting to build an amp from scratch and I have laydown PT & OT. How would you arrange them ?

[warioblast]

http://el34world.com/Forum/index.php?topic=9574.msg86897#msg86897

This is the thread that I thought was relevant.

One of my future mods will be to add a tube, so I will make a new metal plate and modify the layout. Ideas on the placement of the choke and can caps are too welcomed I guess. 

[PRR]

> long wires running from the OT, the preamp tubes close to it so I'm thinking it wouldn't hurt to move the OT, wouldn't it?

Well, I just got hurt working on plastic plumbing. Any metalwork scares/scars me.

The OT wires run through the sensitive preamp sections can't be good. Two ways: the main B+ is never pure buzz-free DC so it throws into the preamp. And the plate leads have 300+ V of audio, which the preamp would love to pick-up and re-re-re-amplify as squeal (maybe supersonic).

[pompeiisneaks]

I shouldn't have mentionned that it was noisy.  The reason I didn't describe the noise is because my main concern is the transformer placement. For the record it's hum not hiss.

Lets just say I'm starting to build an amp from scratch and I have laydown PT & OT. How would you arrange them ?

If I looked at the picture you showed of them on opposing sides of the amp, I'd say 'that'.  On the other hand, what you can do, is the headphone trick: http://ax84.rru.com/FAQs/general.html#hp-trick

That helps listen for the optimal location to avoid transformer coupling and hum.

~Phil

[warioblast]

^^ I will give it a try 

[CraigB]

The fact that those transformers are at opposite ends of the chassis probably avoids any coupling.  Noise can come from a ton of things, bad grounding, heaters etc like you said, I'd try turning the amp on, and chopstick around the grounds, and try moving heater wires a bit first to see if that helps with the noise.  Does the noise change with things like tone pots etc?  Is it still present if you take out some or all of the preamp tubes?  You can try removing one tube at a time to narrow down where it's coming in possibly as well.  I'm not saying it can't be the transformers, but looking at how far apart they are, I doubt it.  You also may want to adjust the OT wire path to ensure it's not too close to signal path somewhere.

~Phil

^
Some gut shots might be helpful...Doubt it's placement of transformer coupling hum issue.  Those guys are miles from each other.  Do you still have the DSL PCB?  That might give you an idea where the filament traces run in relation to audio signal path and also the route of the OT primary wires in relation.  Might be mistaken, but the filament supply on the DSL 50 is probably filtered DC, which isn't a bad idea on a higher gain beast.

[warioblast]

Some gut shots might be helpful...Doubt it's placement of transformer coupling hum issue.  Those guys are miles from each other.  Do you still have the DSL PCB?  That might give you an idea where the filament traces run in relation to audio signal path and also the route of the OT primary wires in relation.  Might be mistaken, but the filament supply on the DSL 50 is probably filtered DC, which isn't a bad idea on a higher gain beast.

Well I have just tore the amp apart this afternoon. 
1st pic shows how it looked like when I finished it. It was a JTM 50. Months later I turned it into a 1987 JMP 50 and did a "Larry" grounding.

The DSL had DC heater indeed. I still have the PCBs so I'll have a look at them. I took several pictures before I gutted it off. You can see those long wires coming from the OT. It was a pretty quiet though. And that's why I didn't feel the need to change the OT location. I will give the DC heater a thought  , one of my order is still pending.

[ac427v]

I notice the orange signal leads on preamp tubes are parallel and close to the blue leads carrying 200+ volts DC. Can you lift them with a chopstick to create a different orientation? or rewire/shield them to get some separation? That may reduce hum without rerouting the OT wiring. Or do both;-)
--Craig

[CraigB]

I notice the orange signal leads on preamp tubes are parallel and close to the blue leads carrying 200+ volts DC. Can you lift them with a chopstick to create a different orientation? or rewire/shield them to get some separation? That may reduce hum without rerouting the OT wiring. Or do both;-)
--Craig

Yes, you don't want those running close and parallel to one another.  See attached.  You may consider moving grid wire to pin 7 of V1 to something like that.  That would help with the first stage.  On V2, try to either get the plate and grid leads either as far apart as possible or cross perpendicularly.

[warioblast]

Like I mentionned earlier the amp is tore apart now. But it's something I will keep in mind when I'll wire it back, so thanks for the heads-up.


About the wires coming from the OT; does it matter if they are close to the heater wiring ?


I tried the headphone trick.
Turning the OT 90° noticeably reduces the hum.    5 / 10 more degrees and it's pretty quiet.
I tried the OT close to the PT. I find a few spots were the hum was more or less as loud as it was in the first place.
I find quiet spots in the middle of the chassis but that means I would have to redo the entire layout, board and all so that's a no go.
So I'll keep it on the opposite end of the PT.


I think I could also move the speaker jacks and the output selector closer to the OT 

[sluckey]

You're not gonna have a problem with hum being coupled from the PT. But you could very well have feedback or hum issues with the OT being so close to your preamp tubes. I would not do it the way you have it now.

Sunn did a similar layout with their tube amps but they put the preamp tube sockets very close to the input jacks which kept the sensitive circuit away from the high current, noisy OT. Maybe that is an option for you. Look at these pics to see what I mean...

     http://sluckeyamps.com/sunn/sunn.htm

[warioblast]

I totally see what you mean. Last night when looking for infos about heater I stumbled on this thread http://el34world.com/Forum/index.php?topic=9400.msg85304#msg85304 and saw this
I have to take some measurements, but if I'm going down this road, that most definitely means I would have to make a new smaller board.

[warioblast]

I got a couple more questions.

In the case I would be putting the preamp tubes close to the input and using my existant board, I would have to fly a dozen wires from the back of the board over the tubes and to the controls. (see 1st pic) Would this be a concern ? I'm guessing yes.

2nd scenario, I'm keeping the preamp tubes close to the OT.
Does the orientation of the OT matter to the preamp tubes ? I'm guessing not... I looked at many recent Marshall amps, JCM 900, JVM, VM, YJM... and they have different transformers placement with laydown PT & OT on opposite ends. Most of them have the 1st preamp tube close to the input but also close to the OT.

2nd pic is the original layout of the DSL50.
3rd pic is a rough, modified version of my layout.

I hope you'll dig my MS paint skills. 

[CraigB]

I wouldn't try and locate your preamp tubes near input side with existing board.  It's like exchanging one problem for another in a different direction  I've never played an actual handwired plexi Marshall from the day, but I did own a reissue PCB board Marshall 1987x.  It was noisy in a white noise kinda way, but not in the hum department.  I'd be looking at grounding scheme and lead dress.  Look at how this layout makes the grid and plate connections either as far apart as possible, or if they must cross, make it at a 90 degree criss-cross.  I've used this type of layout (like yours) and Hoffman style layout on my own builds, and hum was never an issue.  I also like to move the first stage grid resistors to right at V1's socket on a terminal strip with shielded wire running back to input jacks, or since this circuit isn't super high gain flamethrower status, you can get away with a Fender BF style arrangement with the grid resistors at the input, but unlike Fender, I like to utilize shielded wire to go from input to socket. 

https://www.tedweber.com/media/kits/6m45p_layout.jpg

[jojokeo]

Looking at your amp's picture you had many sources and probabilities for hum being wires next to each other that shouldn't be ran near each other and places as has been mentioned. But your grounding scheme was equally abysmal. You do not use the chassis as a grounding plane. Signal ground is not chassis ground and you do not ground anywhere and everywhere as you did. A properly conceived and implemented ground plan has only a single ground point to the chassis. Before proceeding you would be well served to do some reading and learning about this important factor starting with Merlin Blencowe and Randall Aiken's detailed methods. It will take several readings of each to begin to fully digest it all.


You see, reading and learning this discipline is not "fun" for most. I will use sailing as an analogy. People just want to get out of the harbor and go right? But what about learning the rules of the waterway? What about learning how to properly anchor? This is analogous to learning about grounding and lead dress for amp building. The time devoted may not be the "fun" part but it's essential to getting to your destination safely, staying and exploring there safely, and returning to home port safely making for an exhilarating trip. If you want an exhilarating amp building experience again and again then you need to take the time to learn and know these things.


Your amp "looked great" but now you know looks don't mean much if the form isn't correct?
Just trying to help, good luck!

[purpletele]

Warioblast,

Nice looking detail work.

I have been taking grounding advice for a few years and now my amps are built very similarly from a grounding scheme perspective.  The result has been very satisfying.

I see the two Cap cans being grounded to the chassis in different spots and I see the power tubes grounded to the chassis. 

Those are two things that I would certainly consider studying for alternative methods.

I bet Jojokeo's Agent 86 layout shows his grounding methods very clearly. 

Also those are is interesting results on the transformer placement.

Looking forward to finding out what works.

[warioblast]

I also like to move the first stage grid resistors to right at V1's socket on a terminal strip with shielded wire running back to input jacks.

That was my intention. 

your grounding sucks

Hey I'm here to learn. 
The pic shows how my board looked like when I just finished the amp. My logic here was I'm going to keep the wires short. It turns out it's not the way to do it with grounding. Before I dismantled it, the amp had a Larry grounding, which I think is a proven wiring.

In the mean time I got Merlin's 'Designing Tube Preamps For Guitar and Bass" book.


Right now I'm trying to see if turning my board into turret strips could be an option if I were to put the preamp tubes close to the input.

[jojokeo]

your grounding sucks

Hey I'm here to learn. 
The pic shows how my board looked like when I just finished the amp. My logic here was I'm going to keep the wires short. It turns out it's not the way to do it with grounding. Before I dismantled it, the amp had a Larry grounding, which I think is a proven wiring.

In the mean time I got Merlin's 'Designing Tube Preamps For Guitar and Bass" book.

That's not exactly what I said, but I figured you were here to learn - picking up Merlin's book is a great start and well worth the investment. Grounding is something that when done right it may not be the cure all you're looking for and depending on overall amp gain and/or gain stages used, etc. but when done wrong it can be hard to recover. The big three "to do's" for least hum and other related issues (oscillations) is component selection and placements, lead dress, and proper grounding scheme.

I've never heard of "Larry grounding" but it may as well be "Barney grounding" i.e. - don't be a Barney.    https://www.youtube.com/watch?v=YW5qaRMWUA4

[purpletele]

Warioblast,

I have not seen the MV hookup that you have in the gut shot above.

I am not fishing for a joke, but what is the name of that configuration?

[warioblast]

purpletele,
that's a Lar/Mar PPIMV

[purpletele]

purpletele,
that's a Lar/Mar PPIMV

Indeed it is, I was turned around and it looked foreign for a moment.


I need to go back and re-read to see what you are up to.  I think you said you demo'd the amp and are rebuilding. 

That amp that was completed sure looked nice, even the Barney grounding was nice.  I think you are a few grounding connections to a quiet amp.

Please post photos as you progress and live with the results of constructive advice or criticism if you have made a poor choice.

[CraigB]

I also like to move the first stage grid resistors to right at V1's socket on a terminal strip with shielded wire running back to input jacks.

That was my intention. 

your grounding sucks

Hey I'm here to learn. 
The pic shows how my board looked like when I just finished the amp. My logic here was I'm going to keep the wires short. It turns out it's not the way to do it with grounding. Before I dismantled it, the amp had a Larry grounding, which I think is a proven wiring.

In the mean time I got Merlin's 'Designing Tube Preamps For Guitar and Bass" book.


Right now I'm trying to see if turning my board into turret strips could be an option if I were to put the preamp tubes close to the input.

You could do that, but if I may offer my 2 cents, you have a nice board already.  Rebuild the stock circuit and get it working properly, and then if you want to do mods, please consider doing them one at a time.  I believe that would be educational to you in the sense that, say, changing out a cap to a different value, you'll be able to see what effect that one change has made to the tone. 


As far as grounding scheme goes, I've never heard of "Larry", but can tell you I find that splitting grounds to three points works best for me.  Of course your AC power cord "earth" is grounded to the chassis, I usually use the nearest power transformer bolt to where AC enters the chassis.  For power amp ground, PT center tap, bias supply ground, power tube cathodes (or cathode bias resistor if it's cathode biased), power tube plate filter grounds, and power tube screen supply ground all get grounded to the chassis at one of the three remaining PT bolts.  Everything else I consider preamp grounds, those being preamp stage filter grounds, preamp potentiometer and input jack grounds, and all board grounds on the preamp tube side, and those can either be bussed or separately wired to a grounding point on the chassis near the input jacks.  Also, any shielded wire that's used, the shield must be grounded, otherwise, you may as well use regular wire.

[warioblast]

Larry's grounding is a multi-star one, quite popular on the Metropoulos forum.



I'm going to add a tube for a clean channel & make it switchable via relay. The plexi side will have a toggle to switch between JMP 1987 & 2204 JCM 800.
Basically the clean channel of the Bogner Shiva & the blue channel of the Ecstasy. I order a few extra resistors & capacitors to tune the circuit to my ears.
I will start without the Lar-Mar PPIMV.

[purpletele]

Larry's grounding is a multi-star one, quite popular on the Metropoulos forum.



I'm going to add a tube for a clean channel & make it switchable via relay. The plexi side will have a toggle to switch between JMP 1987 & 2204 JCM 800.
Basically the clean channel of the Bogner Shiva & the blue channel of the Ecstasy. I order a few extra resistors & capacitors to tune the circuit to my ears.
I will start without the Lar-Mar PPIMV.

Warioblast

The Larry's grounding diagram and the grounding of the your amp are a little different it seems.

I keeping looking back and forth to the grounding of the Cap Cans again and it doesn't make sense to me to have the two CapCan grounds going to completely different points. One cap ground goes to #5 and One Cap ground goes to #3.

I'm an intermediate student of the game trying to put it all together, so there may proven logic with Larry's grounding that I have not discovered yet. 

Your ne project sounds quite ambitious!

[warioblast]

The metro forum is under maintenance but you'll find all the answers there as Larry explains it in details.

My grounding has nothing to do Larry's. Like I said it was / is my first amp, I winged it and basically I only tried to make the ground wires / paths short.


I decided to locate the preamp tubes close to the input and turn my board into turret strips.
When I desoldered everything I was quite surprised by the amount of wires there was in it.

[warioblast]

I'm racking my brain working on the amp layout.

I thought I was going in the right direction when I realized the phase inverter tube was not far away from the PT (I didn't say close  ) How close is too close ?

I can't seem to find much infos on do's and don'ts of amps layout...

[sluckey]

All you gotta do is just look at some successful commercial amp pics. Marshall and Fender pics are all over the net. How many do you see where "the phase inverter tube was not far away from the PT"?

[warioblast]

All you gotta do is just look at some successful commercial amp pics. Marshall and Fender pics are all over the net. How many do you see where "the phase inverter tube was not far away from the PT"?

I've seen several Hiwatt, Mesa, Bogner, Soldano, Diezel... It should be alright.