I tried some unusual mods on my Marshall clone

[Code001]

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Here's some things that you can do to tighten the bass.
First you can try lowering the first 2 coupling caps, I find .022's to be too loose under high gain, try .0047's or .0022's, they will tighten the amp quite a bit, the lower you go the less bass you will get early in the preamp.
Also look at what negative feedback resistor value you have, 100k is gainy but it can be too loose 47k might seem a bit smoother and tighter.
Output coupling caps can be lowered to limit bass later in the circuit too, I personally like smaller tighter values around the first stage and bigger values in the pi so the preamp stays tight and you get your thump from the ouput section. For ideas on output coupling caps you can use these comparisons, Superleads used .022, Slo's use .047, and Superbass's used .1, Hope it helps.

Lee Jackson suggests this as well. However, he is someone who believes in increasing the bass. He replaces the 22s with 1s like the Superbasses. He actually said the .0047s would increase midrange and to use those if you don't want a lot of bass.

Another thing you can do is the depth mod which is done on the SLOs and Peavey amps. I don't know how close your circuit is to the real JCM800s, but here's a how-to. I used a 1 meg pot.

http://www.blueguitar.org/new/schem/marshall/modnotes/jcm800res.txt

While it adds bass, it can add another style of bass to it. It's like a presence control, but for the bass. It can tighten things up if you run the depth higher and back down on the bass. For the record, I have my bass at around 3 with the depth at around noon-ish. Also, I have some mods done to my 2204 that might help you if you'd like to know them. I can give you some tips.

 

[philb]

>|<>QBB<

Here's some things that you can do to tighten the bass.
First you can try lowering the first 2 coupling caps, I find .022's to be too loose under high gain, try .0047's or .0022's, they will tighten the amp quite a bit, the lower you go the less bass you will get early in the preamp.
Also look at what negative feedback resistor value you have, 100k is gainy but it can be too loose 47k might seem a bit smoother and tighter.
Output coupling caps can be lowered to limit bass later in the circuit too, I personally like smaller tighter values around the first stage and bigger values in the pi so the preamp stays tight and you get your thump from the ouput section. For ideas on output coupling caps you can use these comparisons, Superleads used .022, Slo's use .047, and Superbass's used .1, Hope it helps.

Thabnks for the info.

I changed the output coupling already from .1 to .022. I'm going to do the resonance mod next. I have .022 caps except the first stage where I have .047 in there. The most dramatic chagne so far has been the supply voltage. I used to be below 200v now, I'm sitting at > 300v

 

[philb]

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Lee Jackson suggests this as well. However, he is someone who believes in increasing the bass. He replaces the 22s with 1s like the Superbasses. He actually said the .0047s would increase midrange and to use those if you don't want a lot of bass.

Another thing you can do is the depth mod which is done on the SLOs and Peavey amps. I don't know how close your circuit is to the real JCM800s, but here's a how-to. I used a 1 meg pot.

http://www.blueguitar.org/new/schem/marshall/modnotes/jcm800res.txt

While it adds bass, it can add another style of bass to it. It's like a presence control, but for the bass. It can tighten things up if you run the depth higher and back down on the bass. For the record, I have my bass at around 3 with the depth at around noon-ish. Also, I have some mods done to my 2204 that might help you if you'd like to know them. I can give you some tips.

Thanks man, I appreciate it. It looks easy to do as I have a free 1M pot now (my amp is only a single channel)

 

[Code001]

Try doing the following:

Replace the 33k slope resistor in the EQ section (R15) with a 47k. This makes the tone a little more fat, but without sounding overly bassy. The SLOs use this.

Replace the midrange pot with a 50k. It'll give you more range on the mid knob.

Increase V1 Plate Resistors from 100k to 150k (more gain)

Increase PI Plate-Loading resistors from 68k/100k to 120k/150k (more gain)

Solder a 220k resistors between the output and the ground on the gain pot (more fullness)

 

[philb]

>|<>QBB<

Try doing the following:

Replace the 33k slope resistor in the EQ section (R15) with a 47k. This makes the tone a little more fat, but without sounding overly bassy. The SLOs use this.

Replace the midrange pot with a 50k. It'll give you more range on the mid knob.

Increase V1 Plate Resistors from 100k to 150k (more gain)

Increase PI Plate-Loading resistors from 68k/100k to 120k/150k (more gain)

Solder a 220k resistors between the output and the ground on the gain pot (more fullness)

The mid range pot is a great idea. I already have sufficeint gain with the added gain stage so I'm going to do the resonnace mod and probably add a few switches here and there to change component values to switch mode. The bass thing is becoming my obsession

i want the bass to be tight and handle drop d tuning and at a flick of switch go to the normal Marshall tone that we all love

 

[Code001]

If you want to try different midrange frequencies (like, shift the midrange higher or lower), change the 500pF capacitor that's to the right of the V2A Cathode and Plate resistors and to the left of the coupling caps. 220pF will make the mid-range higher, .001uF and bigger will shift the midrange lower. You can even place a rotary switch here and have Lee Jackson's midrange rotary modification thingy.

220pf 1kv
500pf 1kv
.001uf 400v
.0022uf 400v
.0033uf 400v
.0047uf 400v
.01uf 400v

That's actualy 7 and his was a 6 day switch. He would choose between the 220pf and .0047 or 500pf to the .01 depending on what the customer wanted (if they wanted more low mids or high mids).

Mark Cameron has posted something cool on a public forum once. Here is what he said:

"Re: simple mods for
marshalls
3/6/99 10:12 in reply to Niek
Mark Cameron
Everybody has ther tricks to getting the best tone out of a Marshall. So hears
my2cents.
I dont like taking out the caps, thats what makes that Marshall crunch. Try this, lower
the feedback resistor to 27k if its too brite. This takes the icepick treble out, but you
still have that classec sound,Or you could use a 250k pot in place of this
resistor(boogie presence cont.). also play with the presence cap I like the .68 cap over
the .1 cap (this ads more high mids)"

I don't know if he still does this, but it's a simple thing to try. Also, try taking out the 1000pf brite-cap across the gain pot. That, or wire up some 3 way switch to select between stock, a different value and no cap.

 

[philb]

>|<>QBB<

If you want to try different midrange frequencies (like, shift the midrange higher or lower), change the 500pF capacitor that's to the right of the V2A Cathode and Plate resistors and to the left of the coupling caps. 220pF will make the mid-range higher, .001uF and bigger will shift the midrange lower. You can even place a rotary switch here and have Lee Jackson's midrange rotary modification thingy.

220pf 1kv
500pf 1kv
.001uf 400v
.0022uf 400v
.0033uf 400v
.0047uf 400v
.01uf 400v

That's actualy 7 and his was a 6 day switch. He would choose between the 220pf and .0047 or 500pf to the .01 depending on what the customer wanted (if they wanted more low mids or high mids).

Mark Cameron has posted something cool on a public forum once. Here is what he said:

"Re: simple mods for
marshalls
3/6/99 10:12 in reply to Niek
Mark Cameron
Everybody has ther tricks to getting the best tone out of a Marshall. So hears
my2cents.
I dont like taking out the caps, thats what makes that Marshall crunch. Try this, lower
the feedback resistor to 27k if its too brite. This takes the icepick treble out, but you
still have that classec sound,Or you could use a 250k pot in place of this
resistor(boogie presence cont.). also play with the presence cap I like the .68 cap over
the .1 cap (this ads more high mids)"

I don't know if he still does this, but it's a simple thing to try. Also, try taking out the 1000pf brite-cap across the gain pot. That, or wire up some 3 way switch to select between stock, a different value and no cap.

I never installed the bright cap so it's all good.
The rest is interesting. I want to change the input jack and replace them with switches to alter the amp's tone, so probably the input jack, master volume and two switches. One switch to go from high to low gain and the other voicing.