5E3 with Presence control. How?

[MHProd]

How can I implement a Presence control (classic 5K/.1uF) in the 5E3 circuit WITHOUT adding NFB?
Thanks!

[martin manning]

Inasmuch as presence is a frequency shaping of GNFB, you can't.

[MHProd]

Thanks Martin.

The build I have sounds great but the top end is very muffled. Tone pot is on 10. I'm playing in closed back cabs, so that's not helping... I'm wondering how I could add a pot to control the higher frequencies (similar to the Hz impacted by the Presence control). Any unconventional ways of achieving this?

I found this in the Mesa NOMAD amp:

http://i4.photobucket.com/albums/y134/D ... Stack2.png

Maybe that could work... Looks like a pot with a .002uF cap and 10K in series, going out to the PI. Not sure if that would work?

[tictac]

If you converted your 5E3 concertina PI to a Jim Kelly type concertina which is a like a 5E3 with feedback you could use the type of presence control he used. You don't need to do the fixed bias thing he used, (the resistor network on the grid) but some people call it the "Paul C" mod and really like it. It doesnt change your tone much actually. Your amp will sound a bit different but it's completely reversible and I've never heard anyone say Jim Kelly amps had bad tone....

One thing you might have to do if you go this route is reverse the plate wires if you end up with some loud oscillation when you power on.

I like to bring the amp up slowly with a variac to minimize cardiac arrest....

Yes I know it won't be a 5E3 anymore but if you add presence control of any kind it won't be a 5E3 either. You might like it better, who knows?

TT

[MHProd]

The amp sounds "OK" with the Tone on 10 (that's after some tube rolling to maximize the top end response). But I'd like to get more range out of it, maybe by using an extra control. I'm really trying to not implement any NFB circuit. I'm thinking of maybe installing a 100pF or 220pF cap on the volume pot but I'm afraid it's going to affect the wrong frequency.

I guess another option would be to revise the Tone circuit. Maybe a smaller cap on the pot (like 680pF) and a bigger one between tone and volume (2000pf)?

[Cameron]

Are you running the amp volume on or close to 10? if so that would make the top end of the tone control be less effective..also are you sure you have 1meg controls in it? A friend of mine liked to put a 470k with a 500pf over it and a 470k to ground after before the PI.. ..like a Marshall kind of voicing....he liked it with 4x12s cabs.

[martin manning]

The MESA Nomad circuit adds a treble cut at the output of a typical TMB tone stack, and really a presence puts emphasis on treble by cutting bass, as does the so-called treble peaking network (470p//470k and a 470k to ground) seen in Marshall circuits. A Vox cut control is another way to reduce high frequencies. If the frequency content you are looking for isn't there now it won't appear, but it's all relative. You are on the right track looking for ways to increase the treble content, the tube rolling was a good idea. Have you tried playing it through a different speaker?

[Stevem]

And what do you have for a output transformer?
If you pull the signal off of ther input to the PI and pump it into another amp how does it sound?

[MHProd]

It's a big bottle 5E3 with a 6K6 priZ XP OT. Tone on 10, volume on 5. It does sound like a very good 5E3 but no sparkle, no "air"... I'm thinking more and more the lack of "air" is because of the 4x12 with 70s Greenbacks (the amp is in head format). Right now, I don't have an open back to try it in. I didn't think about the Marshall peaking network... I might just try that. Should i put it on the pot or straight to pin 2 V2?

[Cameron]

It's a big bottle 5E3 with a 6K6 priZ XP OT. Tone on 10, volume on 5. It does sound like a very good 5E3 but no sparkle, no "air"... I'm thinking more and more the lack of "air" is because of the 4x12 with 70s Greenbacks (the amp is in head format). Right now, I don't have an open back to try it in. I didn't think about the Marshall peaking network... I might just try that. Should i put it on the pot or straight to pin 2 V2?

It would be very easy to do it on the pot ...to see if it will even work for you. Also is the cab wired for 16 or 4 OHMs ?

[MHProd]

16Ohms. OT has 3 taps so no mismatch.

[tictac]

From your description sounds like what you want is a fixed bias version of a 5E3.....

TT

[MHProd]

I tried the peaker. Works OK. I'm going to try different cap values to hit higher frequency. 500pF is good but not quite there yet.

[MHProd]

I couldn't get the peaker circuit to sound the way I want...

BTW, Chanel 2 is quite different: 2K7/.68uF cathode and .0047uF V1B (split cathode arrangement).

I soldered a 500pF cap on Vol2 pot and it sounds perfect!

I tried to do the same on Vol1 pot but it doesn't seem to affect the sound much at all? I double checked the cap and soldering, all good but it doesn't seem to add much brightness for some reason... Any idea what might be going on?

[tubeswell]

So what does your schematic for this look like now? (with voltages).

You could possibly take the princeton reverb* NFB loop typology (where the NFB is inserted at the cathode of the driver in font of the cathodyne stage), and put a presence control in that NFB loop. If using the 2k7/47R voltage divider that the PR uses, I would start with something like a 250R pot wired as a variable resistor in series with, and on the ground side of, a 10uF cap. Put the pot and cap in parallel with the 47R (with the +ve end of the cap pointing to the cathode). You will probably want to play around with the bypass cap value for the driver stage

Or utilise the PR NFB circuit, but with a stepped treble boost with a variable HF boost control at the cathode of the driver stage. Use something like Rk=1k || [5kA (variable resistor) + 22uF cap] || 100nF

* because a PR has essentially the same type of driver/splitter as a 5E3.


Or possibly you could just use a conventional 6G2 NFB loop and put a variable stepped treble boost at the cathode with a 5k pot wired as a variable resistor in series with a 10uF cap; all in parallel with the 1k5 cathode resistor.