YOUR fav 5E3 tweaks

[Gee]

It's the 500pf cap that makes the difference by brightening the bright channel, the tone pot & .0047uf is a hi cut for both channels?

So if you wanted to make the bright channel less brighter than the normal channel, would you reduce the 500pF to something like 250pF?

I simply cannot get my head around the 5E3 tone circuit (from an electronic point of view).

[hasserl]

So if you wanted to make the bright channel less brighter than the normal channel, would you reduce the 500pF to something like 250pF?

I simply cannot get my head around the 5E3 tone circuit (from an electronic point of view).

Yes, you could do that.

Re how the tone circuit works: Think of the 500pf cap as a highway bypass around a town. The cap provides a means for the higher freq's to scoot around the Vol pot rather than to get stuck in the traffic going through it. Just as a highway bypass provides a means for traffic to scoot around a town rather than having to go thru town and all the stop lights and other traffic. The lower frequencies can't get thru the cap, so they have to go thru the Vol pot, like trucks going thru town, they get slowed down. This makes the resulting tone brighter, because those hf's are like little cars speeding around the bypass while the lf's are like trucks stuck in the traffic in town. The .005 cap on the other hand dumps some of the highs off to ground. How much is controlled by the pot. When the pot is turned fully clockwise there is 1M resistance between wiper of the pot and the cap, and note that the wiper is connected right to the grid of the next gain stage. In this case the electrons will take the course of least resistance and go straight thru the wiper to the grid of the second gain stage. This is true of both channels. As you turn the control counterclockwise there is less resistance between the wiper and the .005 cap, so some of the highs will be bled off to ground, as you continue turning it counterclockwise more highs are bled off. At the same time you are adding resistance between the 500pf cap and the wiper, slowing down the bypass so those hf's that were speeding around the Vol pot now have to go through it instead of around it. Voilla! The tone becomes darker.

Hope that helps

[stokes]

Hey Stokes!

Are you using a standard 5E3 cabinet? Any clearance problems with the EVM 12L?

-Rick

Rick,sorry I havent replied sooner-been away and havent looked at this post in a while.No I'm not using the standard cab.I built my own,taller and a bit wider.The front is also slanted a bit more as well a bit deeper at the bottom.The chassis hangs the same and the tubes are almost kissing the speaker magnet,so I would guess the EV could be a problem with a standard cab.

[RickyD]

Thanks, Stokes. Thought that might be the case. Not too much room to spare with a Weber alnico Sig 12. Bet that EVM sounds great.

[stokes]

Yeah EV's are great speakers,got a few of them in different amps.I'm a big fan of the Weber's too,got a couple in some amps as well,my favorite is the 15" Californian I use in a cab I built along with a Leslie cab that has one of his 12" Michigans,which is pretty close to the EV.

[Gee]

Yes, you could do that.

Re how the tone circuit works: Think of the 500pf cap as a highway bypass around a town. The cap provides a means for the higher freq's to scoot around the Vol pot rather than to get stuck in the traffic going through it. Just as a highway bypass provides a means for traffic to scoot around a town rather than having to go thru town and all the stop lights and other traffic. The lower frequencies can't get thru the cap, so they have to go thru the Vol pot, like trucks going thru town, they get slowed down. This makes the resulting tone brighter, because those hf's are like little cars speeding around the bypass while the lf's are like trucks stuck in the traffic in town. The .005 cap on the other hand dumps some of the highs off to ground. How much is controlled by the pot. When the pot is turned fully clockwise there is 1M resistance between wiper of the pot and the cap, and note that the wiper is connected right to the grid of the next gain stage. In this case the electrons will take the course of least resistance and go straight thru the wiper to the grid of the second gain stage. This is true of both channels. As you turn the control counterclockwise there is less resistance between the wiper and the .005 cap, so some of the highs will be bled off to ground, as you continue turning it counterclockwise more highs are bled off. At the same time you are adding resistance between the 500pf cap and the wiper, slowing down the bypass so those hf's that were speeding around the Vol pot now have to go through it instead of around it. Voilla! The tone becomes darker.

Hope that helps

Yes that helps and thanks for taking the time to put it all together.

What I struggle with is the overall interactivity of the 3 controls. E.g. how the tone control acts as a gain control and the specific point when one volume is at 12 and the other gets to about 9 and beyond. The whole volume and tone electronic interaction is one big complex equation.

[stokes]

Yes that helps and thanks for taking the time to put it all together.

What I struggle with is the overall interactivity of the 3 controls. E.g. how the tone control acts as a gain control and the specific point when one volume is at 12 and the other gets to about 9 and beyond. The whole volume and tone electronic interaction is one big complex equation.

Excellent explanation by hasserl on the workings of the tone control,but I think I see where you are getting confused,Gee.The tone control isnt actually working as a gain control,but when you turn the tone control up,or more trebly,it isnt actually increasing your treble,it is just letting all the frequencies pass,when you turn it down it is actually blocking the highs,or as hasserl pointed out,dumping the highs to ground, so it seems you are cutting the gain,and to some degree you are since less of the total signal passes,turning it up allows them all to pass more easily,effectively giving you a "bigger" signal for the next stage to amplify.The interaction is actually between the 2 volume controls,to try to put it simply the volume control for the channel you arent plugged into becomes a mid scoop,kind of like when you set a graphic EQ in the classic "V" shape.As you turn that volume control up,it scoops out your mids or cuts them.The reason for this is actually contained in hasserls explanation,that volume control becomes part of your tone circuit,and affects certain frequencies,mostly your mids.Hope that helped and didnt just cloud things up further.

[petemoore]

I bought a kit [1 kit] online, two arrived, built both.
The first came with 250k pots worked first time, sounded great.
When I opened and began building the second one, I saw 3 x 1meg pots, changed the first one to 1 meg.
Built the second one, which sounded even better, then changed the first ones pots back again to 250k from 1 meg. I preferred the 250k's in that one, that's what's in both now.
I use HB's. I started with the first cap on the board, all the pre-amp coupling caps have been reduced in value at least once, IIRC I was settling around .022's mostly.
I added a grid shunt pot, for one output tube operation @ ~7.5w, up to near 15w, then defeat switch restores original grid resistor values.
most of the other mods involve speakers and cabinets, tube brand/types.
Did zener voltage drop and..cathode bypass cap tweeks [original values chosen IIRC], but you said favorite mods.
I'm liking the second one, I think the first one needs another cap value reduction, the main thing for me was getting the bass whooob out of it so note definition could take place and distortion wasnt' a mud-smudge, once the range was moved up from the very low register a bit [my amps always bassed or trebled out anyway]...it's like this amp, 15w musta been big at the time I guess, was voiced for bass guitar tone [which you can get to sound good but very low volume] and full guitar voicing [again not distorting heavily].
Of course it was made with SC Fender guitars in mind, still gets bassy quite easily. I have the normal channel about like the bright.
What we're mostly using it for is distorting, and for that, just a touch too much bass can easily turn tone to mud. Does a great job as-is once volume is turned down, or the bass is tamed and it's cranked.
#1 [the Light One]: EH 12au7, tung-sol's best 12ax7, EH 6v6GT's in the one.
#2 [the Dark One]: EH / RCA / JJ's. and Sovtek 5y3's.
Speaker...'everything amp' sounds through the speaker...how's it doing is a firsty question for tone seekers.

[cminor9]

switchable feedback loop?

Anyone ever try a switchable feedback loop? It is an easy mod, I was thinking about trying it. It is like on a princeton, with a 56K resistor between the output and the 1st cathode on V2 (phase splitter). Anyone have any experience with that or something similar?

I don't think I'd use it all the time, but it sounds like it would add some headroom if it was needed.

[Don]

Anyone ever try a switchable feedback loop? It is an easy mod, I was thinking about trying it. It is like on a princeton, with a 56K resistor between the output and the 1st cathode on V2 (phase splitter). Anyone have any experience with that or something similar?

I don't think I'd use it all the time, but it sounds like it would add some headroom if it was needed.

I just put one in my GA-5 just to help me decide if i want the NFB loop or not. I just used a simple on/off switch, a little wire, a resistor and some heat shrink tubing to make sure nothing would short.

I put the switch on a little panel that I trapped between the chassis and the cabinet.

I also installed a switch to remove the 12AX7's bias bypass cap. That reduces gain too, though not as much as the NFB.

Theses switches will be removed from the amp when I decide how I like it (I like it best with the bias bypass cap and NFB loop).

[Bruce / Mission Amps]

Anyone ever try a switchable feedback loop? It is an easy mod, I was thinking about trying it. It is like on a princeton, with a 56K resistor between the output and the 1st cathode on V2 (phase splitter). Anyone have any experience with that or something similar?

I don't think I'd use it all the time, but it sounds like it would add some headroom if it was needed.

To Don, Nope, I think you are hearing things.
This will not work unless you also remove the cathode bypass capacitor because the capacitor will shunt ALL the NFB voltage right to ground and the cathode will never see it.

You can however, leave the bypass cap across the 1k5 biasing resistor and then raise both from ground with a 100-150 ohm resistor and insert the NFB voltage at their junction.
If you do that, you must drop the 56K and use something like 2700 ohms to 10K ohms... or a 2700 ohm resistor at the junction and a 10k linear trim pot from the speaker jack.

[cminor9]

I just added the switchable feedback loop to my 5E3. After a few days of playing with it, I am not quite sure what I think. It's actually pretty subtle and doesn't have the effect I had imagined. Engaging the NFB takes a bit of the growl out of the tone, sure, but since this is close to how presence controls work, I expected a bit more high end sparkle. But there isn't much that I notice. Again, it just takes out some of the growl, which I should define as a strong midrange response. Don't know if I have much use for that. I might try playing with the resistor value, maybe lowering it to 27k (from 56k). If I do, I'll report back with the results.

[Bruce / Mission Amps]

I just added the switchable feedback loop to my 5E3. After a few days of playing with it, I am not quite sure what I think. It's actually pretty subtle and doesn't have the effect I had imagined. Engaging the NFB takes a bit of the growl out of the tone, sure, but since this is close to how presence controls work, I expected a bit more high end sparkle. But there isn't much that I notice. Again, it just takes out some of the growl, which I should define as a strong midrange response. Don't know if I have much use for that. I might try playing with the resistor value, maybe lowering it to 27k (from 56k). If I do, I'll report back with the results.

OK, again... see my previous post... you can not do this with a bypass cap installed across the cathode biasing resistor... it just doesn't have much effect at all.

You can however, leave the bypass cap across the 1k5 biasing resistor and then raise both from ground with a 100-150 ohm resistor and insert the NFB voltage at their junction.
If you do that, you must drop the 56K and use something like 2700 ohms to 10K ohms... or a 2700 ohm resistor at the junction and a 10k linear trim pot from the speaker jack.

With that mod done correctly, ... for more bite, drop a .22uF to .68uF cap across the 100 ohm to 150 ohm resistor.

[cminor9]

OK, again... see my previous post... you can not do this with a bypass cap installed across the cathode biasing resistor... it just doesn't have much effect at all.
.

I think you have me and the other guy confused. I actually implemented the Ampeg mod (of course, not that you'd know that), so I have no bypass cap in place there. The NFB comes in between the cathode and the resistor. It's done correctly according to the schematics I looked at, just not as drastic as I had expected. I read the other guy's post and actually thought the same thing as you: with a bypass cap the NFB is lost to ground.

Don't need the amp to be brighter. I implemented one of your suggestions elsewhere, replacing the first coupling caps with .022 and that worked beautifully (it made the difference between not using the amp and using it the other night at a gig). I don't need the amp to be any brighter. I was thinking I'd get more of a "hi-fi" sound, more scooped, more presence, and a bit more headroom. Come to think of it, this amp has very nice presence (good pick attack and all) so I don't need more presence. The amp was fine the way it was, actually.

I was just trying to report back my results compared with the expected effect. I raised the question about the feedback loop, I felt it only fair that I share the results. I might take out the feedback loop. Don't know that I have much use for it. Maybe I'll make the Ampeg mod switchable with the switch I installed for the NFB. But I digress...

[Bruce / Mission Amps]

I think you have me and the other guy confused. I actually implemented the Ampeg mod (of course, not that you'd know that), so I have no bypass cap in place there. The NFB comes in between the cathode and the resistor. It's done correctly according to the schematics I looked at, just not as drastic as I had expected. I read the other guy's post and actually thought the same thing as you: with a bypass cap the NFB is lost to ground.

Don't need the amp to be brighter. I implemented one of your suggestions elsewhere, replacing the first coupling caps with .022 and that worked beautifully (it made the difference between not using the amp and using it the other night at a gig). I don't need the amp to be any brighter. I was thinking I'd get more of a "hi-fi" sound, more scooped, more presence, and a bit more headroom. Come to think of it, this amp has very nice presence (good pick attack and all) so I don't need more presence. The amp was fine the way it was, actually.

I was just trying to report back my results compared with the expected effect. I raised the question about the feedback loop, I felt it only fair that I share the results. I might take out the feedback loop. Don't know that I have much use for it. Maybe I'll make the Ampeg mod switchable with the switch I installed for the NFB. But I digress...

yeah, I know you weren't the original poster. Sometimes I reply to the general theme of the thread and not really right to a specific person. Sorry.

Maybe 56K is too large.
Since you do not have the bypass cap across your cathode resistor, you can add a smaller bypass cap to the cathode biasing resistor... keep it small so frequencies of the NFB and the presence you mentioned are bled off and those frequencies get boosted... not all the frequencies.