Vintage Modern 2266 conversion to 1987/2204 specs

Everything from original vintage Marshalls to reissues.

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HF1600ie
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by HF1600ie » Wed Nov 24, 2010 8:20 am

Anything that can be done to the Body control to move the frequency center and make it work more like a gain control?
The thing is that bofre it starts producing preamp/bass distortion, it pushes the bass frequencies too much. The Detail knob gives mid/highs but it also gives gain.

The Body control above 5 is useless. it could give only gain increase above 5 and let the bass frequencies as they are at that point.

twango
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by twango » Mon Dec 06, 2010 3:00 pm

sorry, was off.......

yes, the mod revoices the "body" channel to the "normal" channel of a JTM/JMP like specs. I like with a strat or tellie for a "woody-lightly-breakup-crunch".
Using the body in higher settings when higain is on it´s more a fuzzy, farty tone like rectifiers, bogners or that kind of amps... :hide:

Actually both controls, detail & body are gain controls! The difference in both in the modded amp is just a 470pF cap bypassing R14 on the detail channel. You can experiment with the values of R8/9 and add a bypass cap to make the body-sound more or less gainy and fatter or sharper.

The mid boost is isolated from circuitry as you mentioned! I didn´t like the original sound. The original circuit switches between " mud" and "more mud"... :mrgreen:
I used the switch to shift the values on the cathode of V2 from 10K (stock 2204) to 4K7 (more gain and bite).

The low gain sound (and modded circuit) is very close to my 1971 JMP50 Bass, the high gain is very close to my old 2204.

There are no bleeder resistors, not self discharging!!!

I try to mark the mods in the schematic and then post it for reference!

twango
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by twango » Wed Dec 08, 2010 4:47 pm

Hi, here´s the schematic.

As you see I ripped the PPIMV too and put in a Master on the treble wiper. The Master is lifted to ground a 470 Ohms and connected to signal ground. If not lifted, there´s a bad groundloop (HUMMMMMM) when turning on the FX loop. That way the Master does not mute the amp fully (but who wants to mute an amp fully :palm: ) and the bad mistake I made with the twisted signal cords to and from the master pot does not even hurt anymore :mrgreen:
Did I tell I ripped the Reverb apart too... cause? yes, reverb sucks! :wink:

Have fun!!!
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HF1600ie
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by HF1600ie » Thu Dec 09, 2010 5:42 pm

Hi Twango!

When you say "I used the switch to shift the values on the cathode of V2 from 10K (stock 2204) to 4K7 (more gain and bite)", I can only see the 10K resistor you have added, not the 4,7K one. Is this resistor a way to control the overall gain of the High Dynamic Range?

I am trying to manipulate the Body control. I´ll start by channging C4 to 3,3uF, so I can push it harder without getting a lot of mud, but also more distortion that compliments the Detail Body.

Also, i´ll change the Mid-boost capacitor C6 to 5nf. Hope it just adds a few more warmth for jazz runs, now.

I am not that experienced doing this. I´ve been reading things and sharing a few ideas at the vintage modern forum. I like the amp a lot, but the Body control the Mid-boost, the reverb are what I like less !!
What does R88 do in there? And C2 and C3? I´d like to understand the basics of the primary filters of the sound, when it goes into the preamp valve, and when it comes out from there! :-) Maybe thats what C1+R4 and R6+C4 do and then C2+R3 and C3+R5 do.

And what does R8 and R9 do? Damn... i have so much to learn. I liked the tone you get. Very JCM800. I like the VM stock as well... just looking to (in a very simple way) correct this little aspects that I don´t like. Otherwise it´s a monster :hairband:

Thanks for helping me understand !

twango
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by twango » Sat Dec 11, 2010 1:03 pm

Hi HF,

sorry, you are right, my description is not right! I changed the cathode resistor on V2 to 10K as used on 2204´s. The 2nd 10K is switched to ground via the boost switch. So you have 2x10K in parallel, this is 5K (not 4K7 :oops: ). Lowering the resistance of the cathode resistor changes the bias of the triode stage (cathode biased/self biasing), making it hotter, getting more gain and a different sound. 10K gives nearly unity gain, using the stage as a clipper stage being fed and overdriven by the input stage. 5K gives you a lot more gain and upper mids bite. You can put in a far lower value, adding lots more gain but also noise and decreasing dynamics. I´m old school so it´s enough gain for me, in fact, the older I get the less gain I use :scratch:

To get the reverb out of the circuit completely, just unsolder R43 and R48 on the FX card.

Changing C4 to a lower value is a good start to eliminate mud!

R88 and C6 building a filter cutting the signal frequencies at a defined cutoff, the greater the value of C6 the lower the cutoff, the lower the value of R88 the more gain above the cutoff-frequency is decreased. Sorry, I can´t calculate this, I always tweak and hear, then tweak and hear..... :mrgreen: If you want to learn about it, search for "calculating R/C constants".

The cathode circuitry is a similar phenomenon, defining the bias of the stages and so the gain and some boost/cutoff frequencies, but I´m not able to calculate this too - I use trial and error and solder in what I like to hear.

R8/R9 are just the remaints of the mixer resistor (R10 detail channel) being split to insert the midboost filter, I just replaced this with the 470K mixer resistor.

BTW, there is a VM forum???? I think I have to check this!

HF1600ie
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by HF1600ie » Sat Dec 11, 2010 4:58 pm

Hi Twango,
Yes, there´s a dedicated forum for this amp. I hope the board doesnt mind me telling this. :wink:
Just google it, and it appears immediatly. I´m affraid if I put the link i may get kicked out of here. :mrgreen:

Well, the C4 capacitor usually is high, right? I think some Marshalls use 220uf, but i´m not sure. The Body knob in the VM is cool untill 5 (12 o´clock), just to add warmth. Bot not actually add "gain". Past 5 it adds some undesired mud. The Detail knob adds high-mids, highs and gain. But maybe that´s the nature of the thing. High frequencies distortion is obviously different from low frequencies distortion, but I think there´s room for improvement in the Body knob.

It would be nice if there was a way to brighten the reverb unit. But I think it´s a "computer-like" unit that is not tweakable.

Do you think your mod to r8 and r9 will "spice" the Low dynamic Range, giving it more gain? I think it will affect HDR too.
Or maybe the mod you´ve performed to the mid-boost can give me more gain when needed, and in whatever dynamic range i wish.

I´m looking after to understand the C2+R3 and C3+R5 and C5+R10 and C8+R11. They all look like filters like C1+R4 and C6+R4. Maybe I should start understanding what you mean with R/C constants ?

I will soon change C4. Let´s see what happens. :drool:

Cheers! :rock:

zzidell1959
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by zzidell1959 » Mon Sep 15, 2014 8:07 pm

Hi Twango,

This is my first post here. Thanks for all the awesome information. I'm going at my own VM mods based of your specs but with NOS mustard caps with the same values.

Would you be able to offer any specific advice for removing the fx loop/ppimv master volume. I'm trying to get the amp as as close to a vintage stock jtm45/1987 plexi as I can. I have no need for master volume or an fx loop, but have minimal electronic repair experience. I can solder however, but need to know how to properly remove these components without, altering or cutting off the rest of the amps circuit. Any advice would be very much appreciated! Cheers,

Zach

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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by RVSE01 » Thu Jan 14, 2016 5:11 am

Can I do the preamp mods to a 2466 as you have described?

Dannyz
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by Dannyz » Mon Jun 06, 2016 1:31 pm

Can anyone re-upload the pictures that Twango has posted in this thread? Im about to mod my VM 2266 head and they would be useful.

Thanks!

theundertakermc
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Re: Vintage Modern 2266 conversion to 1987/2204 specs

Post by theundertakermc » Sat Apr 01, 2017 11:05 pm

i need those too ! pls

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