EHX - English Muffin  [schematic]

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Re: EH - English Muffin

Postby gruforevs » 06 Jul 2010, 04:38

So, in the calculator, where it says Zsrc would also be the input. Right?
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Re: EH - English Muffin

Postby DougH » 07 Jul 2010, 20:00

That's correct.
"You have just tubescreamered or fuzzfaced yourself " -polarbearfx
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Re: EH - English Muffin

Postby andregarcia57 » 09 Sep 2010, 14:35

this pedal would be the same as the JCM800 preamp?
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Re: EH - English Muffin

Postby andregarcia57 » 11 Sep 2010, 17:43

possible!
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Re: EH - English Muffin

Postby andregarcia57 » 13 Sep 2010, 18:23

where I find this toroidal transformer for sale?
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Re: EH - English Muffin

Postby Peamiller » 31 Mar 2011, 03:53

Hello,

First post here, although I've been reading a bunch of the circuit dissections, and I'm really digging the site: hope to get some gutshots of a Toadworks Li'l Leo up and do some tracing (SMD eesh).

Anyway, I've been trying a bunch of mods to this English Muff'n, like doubling the treble cap in the tone stack, and getting rid of the treble bleed caps to get rid of some of the harsh brightness, but it's still a bit bright, and when notes tail off, they seem to fizzle out. I noticed that plate voltages are listed on the schem posted earlier from the talkbass link, so I looked up the 12AY7 plate characteristics to figure out how they're being biased. It seems like the plate voltages listed aren't correct. Is it possible that they've biased the tubes too close to being cutoff, so they're fizzling out a little (or maybe just one of the tubes)

The first one has 110k plate resistor, 845R cathode resistor. Looking on the load line, it looks like there's 1.3 mA for plate current and a grid biased -1.1 V below cathode, which would put the plate at about 80 V, rather than the 129V listed on the schematic. This doesn't seem like it's the one too close to cutoff, but would anyone know if that fizzling out is symptomatic of bad biasing? The over-the-top treble I can believe EHX would release, but I'm not sure that they'd bias tubes wrong in a finished product. :scratch

Also, any other ideas about reducing the harsh treble?

Thanks,
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Re: EH - English Muffin

Postby Liquids » 31 Mar 2011, 13:34

I got one used and it came with 12AX7s so I can't compare on that level. Theoretically the AYs should be about half the gain or less, which should in theory help the situation. I think there are a lot of problems in the design but the main issue if I had to pick one is the tone stack. Its inevitably inflexible in its mid scoop, which is redundant and nasty in combination with almost all amps, and makes treble sound very exaggerated by comparison.

The tubes are not biased, so much as they seem thrown together for high gain. But 3 stages of high gain tube stages, and running at 240v or so to boot is a lot of clipping!

Its same old same old though. Grid resistors can stand a huge increase, plate resistors an use a major reduction. High voltage caps in parallel with the plate resistors or from plate to cathode tame highs too. You could even 'jumper' over V1A or parallel it with V1B to reduce gain.

I think a mod to make the tone stack a passive baxandall may be possible and a big help. With the right values, a mid scoop is still available but better control of lows and highs with more control over the mid cut relative to treble and bass is helpful. I just hope I get back to this project at some point. In the end it lead me to sticking to jfets and mosfets at increased voltages and active filtering for the sound i want over tubes, in as far as preamp distortion goes. Easier I'm many ways too.
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Re: EH - English Muffin

Postby Peamiller » 31 Mar 2011, 19:44

I was just playing around with the Tone Stack Calculator (had to put WINE on a mac but it works) and while the values in the Muff'n are different than the standard they give for a Marshall tone stack, they aren't SO far off that they look like they're passing a ton of higher shrill treble. Marshalls don't tend to give this kind of treble anyway. I think what's happening is by running this preamp into an actual amp, it is exaggerating the tone stack. I'm pretty sure you were onto this earlier on in the thread. I use a Vox modeling amp, an AD50VT on the Blackface and AC30 settings clean, so I've got my treble turned up a bit, but also the mids, so I can get a bright enough clean tone. When I roll back some of the treble on the amp, say to about 4/10, I noted that the Muff'n on higher gain settings starts to sound a little muffled, and on lower gain settings, now that I've gotten rid of some of the treble bleed caps, it doesn't have a nice clean treble.

My theory is that some sort of presence/cut control or a fixed cap to ground would help keep the treble knob useful through most of its range while always blocking the shrill, really high content. After all, a lot of Marshalls have one. And in this case, we've got basically stacked preamps & tone stacks. I've noticed that a bunch of Runoffgroove amp-pedals using FETs put either a single or double-pole passive LP filter at the output to get rid of the high stuff.

I'm going to try getting some high voltage caps in there at the end, maybe right after the volume pot, put a cap to ground before the 162k resistor, and another after it. Alternatively, I could try replacing that resistor with, say, two 82k or 56k resistors, each with a cap to ground after to make a steeper LP filter.

It seems like a shame to have to throw out all the usable treble in order to get rid of the unusable. Hopefully this will get rid of deciding between muffled and shrill. I may even put all the treble bleeds back in.

-PM
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Re: EH - English Muffin

Postby Peamiller » 01 Apr 2011, 01:27

So I just put the treble bleed caps back in (almost...didn't have the exact same values and I kind of destroyed one of them), and took out R20. In place of R20, I put a 39k resistor followed by a 1n cap to ground. After that comes another 39k resistor and about 4.3n cap to ground, in parallel with the output resistor to ground, R21. 4.3n is a weird value because it was originally a 1n cap but I decided to push the cutoff to a lil lower frequency, so I placed a 3.3n cap I had in parallel with it. This gives a cutoff of 950 Hz, sloping at 6dB/octave, then slopes steeper to 12dB/octave at 4080 Hz (approx, this is without the input and output loading on these two passive LP filters taken into account.)

It sounds much better, the treble content seems to match the amp a little bit better, and I can put the treble all the way up (it still gets a little rough but only just). The treble knob is basically useful until it's all the way down, if the mid is down as well. Unfortunately, I kind of clooged the soldering job in order to fit all the parts in so it's not the nicest looking, but it's not any noisier so that's good.

-PM
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Re: EH - English Muffin

Postby nap_alfa55 » 13 Apr 2011, 10:56

Hello, someone has developed to the PCB and the layout?
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Re: EH - English Muffin

Postby Liquids » 13 Apr 2011, 14:38

It would be in this thread if so.

If the step up transformer and enclosure issues don't bother you, you could build the circuit point to point on a turret board with built in tube sockets such as antique electronic supply has. But that would be very DIY, and not free. =D
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Re: EH - English Muffin

Postby Liquids » 01 Sep 2011, 17:07

I changed all the values in the preamp to reflect a JCM800 50w model - BUT with none of the bright caps (but all the series/grid resistance).

I also hacked around the EQ board and pots to make it a 'dumble' tone stack, which has a pretty flat midrange if kept high. It actually sounds really good for the JCM800 sound, into my Ampeg run cleanly. It also does a nice edgy breakup sound, and a bluesy neck pickup tone.

That said, I'd like to scrap the PCB and build it from scratch and integrate active filtering. I'm not sure how feasible it is to do so and keep it looking nice...but then I could also modify it to various other preamps on the fly, and work it as a true 'distortion preamp' running into my current clean amp rig. I got the thing cheap and the transformer/power supply/enclosure would probably cost me about as much anyhow. But the case sure is flimsy.
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EHX - English Muff'n torroidal power trans

Postby drewl » 29 Jul 2014, 16:51

Anyone ever replace the internal power transformer in an EH English Muff'n?

It steps up the voltage to ~280v ac for the preamp tube plates.

Waiting to hear back from EH to see if they sell a replacement transformer.

Thanks.
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Re: EH English Muff'n torroidal power trans

Postby drewl » 30 Jul 2014, 15:24

FYI:
Hoffman Amps has a compatible unit the exact size if anyone ever needs to replace one.
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Re: EHX - English Muffin

Postby AuditoryDriving » 17 Nov 2017, 10:13

it s been a long time but... has there been a consensus on useful mods?

Other than the treble, there is this annoying issue with the note decay were notes fade rapidly in a very non-elegant way.. I m using 12ay7s but had not much changed with 12ax7s when i tried. Could it be the biasing of the valves? It s practically the only thing i haven t modded.

It s a shame cause this and the wiggler are my two best pedals in paper, yet they just gather dust...

Many thanks in advance.
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Re: EHX - English Muffin

Postby AuditoryDriving » 26 Nov 2017, 18:02

Just came back to answer my own question

I replaced the left tube with an 12ax7 (mine came stock with 12ay7's) and after extensively testing multiple tubes back and forth, it seems that the problem is gone when there's a 12ax7 instead of a 12ay7 in the left slot. Mind you, I tested many different tubes to exclude the possibility that that specific original tube was bad. I have very little experience with tube designs, but judging by those results alone, i would suspect that the 12ay7 would not bias properly, creating some sort of increasing buzzing(?) sound towards the end of the note and eventually a steep / sudden choke.

The tube in the right slot is not affecting this as far as i could tell (or maybe in a not easily perceivable way). I tested all those by ear in lieu of an oscilloscope. Using a 12ax7 there made the sound slightly less fizzy but the low gain sweetness of the English Muffin was lost for good. So I ended up leaving the stock 12ay7 tube there.

Hope this is helpful for someone in the future :)
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