5E3 clone - question - anyone know of a good TMB tone stack modification?

tonejunkie99

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I built this amp from parts purchased on ebay. the only modification I made to the circuit is a (pre PI) master volume.
Like I said, I built it from parts on ebay so instead of using a 5E3 chassis, I used a JTM45 chassis left over from building marshall clones...
Everything worked out great and I put the stock tone pot in in the Trebble hole on the JTM45 chassis and the master V in the presance hole.
The only thing is I am OCD and having dummie knobs in the mid and bass holes leaves me wanting to atleast get them all functional.
I like the stock 5E3 tone control, I just want to see it through to the point someone else could plug into the amp and not be confused by having 2 inactive pots...

Does anyone know of a good TMB mod for the 5E3 circuit?
 

Phrygian77

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You're going to have to think about gain, because the 5E3 circuit is is designed around that 12AT7 and a volume/tone control that doesn't attenuate much. The second gain stage is bypassed to make up for the 12AY7. You'll notice a 6G2 has a 12AX7 and an unbypassed second stage.

Trying to inset a TMB into where the the channels mix wouldn't work. Not the way you'd think at least.

You'd be better off essentially making it like a Princeton (blackface). Add a big 25-100k pot for the midrange and that would get you back into tweed land when you want it.
 

loopfinding

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Okay so with only 5E3 stages, you’re going to incur some insertion loss. You also have to split the channels and mix with resistors (take a look at the 6G3 schematic).

Easiest thing to do would be to ditch the MV, convert one channel to a 6G3 control, just build a straight up BF tone stack for the other channel, mix them with resistors, and just use an AB pedal before the inputs to go between tweed/BF. Your tweed channel can be your dirty channel, and the BF stack channel will be like a non-reverb Princeton, pretty clean for a clean channel without the extra stage of a PR.

Alternatively if you want “both” sounds out of the channel with TMB, I would do it but use like a 50k or 100k pot for the mid. That way, at conservative mid settings, you have stock BF stack. But with that high of a resistance, you’re lifting the stack quite a bit and you can get back up near tweed mid/gain territory full on. More authentic BF sounds than tweed though.

In my 5E3 I stuck an inline bass control (like the G&L legacy PTB) after the first coupling cap, before the tone/vol, to blend a series cap in for cut. You lose a minimal amount of gain, but my intent was to cut bass for humbuckers, which are higher output anyway. You could also implement a switch or pot that adds/subtracts capacitors for the cathode bypass cap on the first stage for another low loss solution. And both would allow you to return to stock.

But what will you do with that extra hole if you only add a bass control? Well the most common mod (look at rob robinette’s site) would be the NFB mod. You can stick the switch in that hole. Or you can stick the switch elsewhere and can add a presence knob to it easily. I would recommend a presence knob with the NFB mod, at the very least a fixed value presence filter, because the NFB can kill some of the sparkle. But to be honest, I love the simple removal of the bypass cap more than NFB, and I usually use my 5E3 with the center off position in most scenarios.

Alternatively, you can get a rotary switch and build something like the Orange/matamp FAC switch. The OR preamp and the 5E3 are like distant cousins. Put it between the second gain stage and the PI gain stage. “Pre bass” on one channel and FAC on both could give you a really versatile amp that still does the 5E3 thing when controls are at stock.

Both of those could be really good options for your needs. Don’t listen to the naysayers, this tailoring is the most fun part of building an amp. Putting your spin on it is way more gratifying than emulating authenticity. More importantly, there are hardly any amps out there with these types of minimal/barebone solutions between 50s spartan and 60s bells and whistles anyway, so you’d have to DIY it to keep the aspects you desire.
 
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Phrygian77

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I'm not a naysayer. I just want people to understand that certain changes have unforseen consequences. A good example would be @gabasa removing some of the caps in the bass channel on his BF Bassman, which resulted in excess noise.

Sometimes things work out great, other times not so much. Gain is just something people need to consider when they start piecing part of one design into another. Edit: impedance is another that gets overlooked.
 

printer2

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Here is one idea. I will get a little more creative when I get back in, I have a lot of snow to blow.

GZvOLeL.png


I'm not a naysayer. I just want people to understand that certain changes have unforseen consequences. A good example would be @gabasa removing some of the caps in the bass channel on his BF Bassman, which resulted in excess noise.

Sometimes things work out great, other times not so much. Gain is just something people need to consider when they start piecing part of one design into another.
Excessive noise by removing caps in bass channel? Somehow that does not sound right.
 

gabasa

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I'm not a naysayer. I just want people to understand that certain changes have unforseen consequences. A good example would be @gabasa removing some of the caps in the bass channel on his BF Bassman, which resulted in excess noise.

Sometimes things work out great, other times not so much. Gain is just something people need to consider when they start piecing part of one design into another. Edit: impedance is another that gets overlooked.
And thank goodness we have the support of the community here when things don't exactly work out as planned!
 

printer2

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A four pole switch to change the volume and tone control to a normal V/T control, also to switch around the volume pot to the Tweed configuration into a BF tone stack/volume. Ignore the NFB on another switch.



Or more simple.

Ur91wXH.png


A four pole switch with converting to 5E3 V-VT from VTB-VT
EYmvDux.png

Think this is the right schematic.

IQmEfrh.png



Could always just use a two pole and only switch the tone stack channel and leave the tone/volume as normal.
 

King Fan

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All good ideas here. Even tho this'll sound dull, even dumb, after Printer's great post, I'm in tune with those who say "let it be... a 5E3".

My reasoning is partly cuz I hear you saying it's mostly the two unemployed pots (or empty holes) that bother you, not the actual desire to have bass and mid control. Of course, if you actually *want* more tone control, the ideas above to create switchable preamps (6G3 v. 5E3) are appealing from a sound / function point of view. Or (with a labeler or custom faceplate), Rob's 5e3 mods page has both a Framus (Mid) option and a Baxandall / James option. I haven't looked into the net gain in pots, but they'd have the advantage they're (I assume) a tested solution.

If it's really mostly OCD, the custom faceplate idea is great. Or get an old Dymo labeler and make little plastic labels to 'customize' the dummy pots. Call one Presence, the other Dwell, or Sag, or Lead, or High Pass... then point out to your friends their amazing (tho subtle) effect on the tone. :)
 

Phrygian77

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How about just turn it into a JTM45 circuit with 6V6 output tubes and a 5Y3 rectifier? You can even cathode bias it like the 5E3. This is a circuit I played for years and it sounded awesome.

That's s cool idea actually. May have to try that my self at some point. Despite what people sometimes say, a 5Y3 can usually handle a 40uF input filter too.
 

gabasa

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That's s cool idea actually. May have to try that my self at some point. Despite what people sometimes say, a 5Y3 can usually handle a 40uF input filter too.
Lol, here's the proof. I turned an old Traynor Bass Mate head into a mini Bassman/Plexi in 2003 after punching a couple of holes in the chassis to add a couple of extra tubes. This circuit works really well and it was a wicked amp for me at the time! The power amp is all 5E3, the rest was Bassman/Plexi.

Picture 048.jpg
 

Phrygian77

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Excessive noise by removing caps in bass channel? Somehow that does not sound right.

There are 3 gains stages there in the bass channel, before the extra gain in the PI. The caps I was referring to would normally filter out hiss that would be apparently from the extra gain. I'm not sure why that doesn't sound right to you. There was a whole thread about it. Did you read it?
 

Phrygian77

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@printer2

 

printer2

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There are 3 gains stages there in the bass channel, before the extra gain in the PI. The caps I was referring to would normally filter out hiss that would be apparently from the extra gain. I'm not sure why that doesn't sound right to you. There was a whole thread about it. Did you read it?
No, can't be everywhere. I expected the others on the forum would be able to help there. I did not look at it as you did not supply a link. Just read the thread and the only things I can see a capacitor that could reduce hiss are the reduction of the grid stopper on the input with a capacitor across the input to roll off radio frequencies and the cathode resistor bypass capacitor. It does not seem either route was taken. In Fender amps the bypassed plate resistor with a capacitor is normally done with a value that gets rid of oscilations and is not used to get rid of hiss. That is why I I was confused. Other amps, particularly high gain amps use capacitors across the plate resistor to bleed off highs. As a side benefit it would reduce hiss. But at the cost of high frequencies, one thing that I do not see Fender doing with this date of amps. In the end the OP of the other thread went to reducing gain rather than changing the cap value, although I might have missed it, the thread did not entice me at the time and I just skimmed it today.
 

gabasa

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No, can't be everywhere. I expected the others on the forum would be able to help there. I did not look at it as you did not supply a link. Just read the thread and the only things I can see a capacitor that could reduce hiss are the reduction of the grid stopper on the input with a capacitor across the input to roll off radio frequencies and the cathode resistor bypass capacitor. It does not seem either route was taken. In Fender amps the bypassed plate resistor with a capacitor is normally done with a value that gets rid of oscilations and is not used to get rid of hiss. That is why I I was confused. Other amps, particularly high gain amps use capacitors across the plate resistor to bleed off highs. As a side benefit it would reduce hiss. But at the cost of high frequencies, one thing that I do not see Fender doing with this date of amps. In the end the OP of the other thread went to reducing gain rather than changing the cap value, although I might have missed it, the thread did not entice me at the time and I just skimmed it today.
I basically changed the tone stack in the Bass channel to standard blackface, then clipped out the two caps circled in red. Those two caps filtered out a lot of hiss, and I had to up the value of the cathode resistor in that third gain stage in order to get things nicely under contol. The amp is great now, and @Phrygian77 helped me with it by suggesting a Ken Fischer value for that resistor.

I guess the overall point to the OP is that if you stray from a known circuit, there may be issues that pop up, which can hopefully be dealt with successfully afterwards.

bassmanaa864.gif
 




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