Amp Techs:I want to thicken the mids on my VTM (marshall 2003 circuit)

peaveyT60

peaveyT60

New member
i have a peaveyVTM (marshall 2203) that i would like to thicken up the mids in. i almost have it tweaked just right, but the mids are too high. its like they control the 1.5k - 3k range. the circuit uses a 33k slope resistor. i want a bit more lower mids for meat. i am torn between either dropping the slope resistor down to around 22k or 16k, OR dropping the mid cap in the tone circuit from 22n to 10n.

thoughts? :dunno:
 
I would try a 47k slope resistor, intsant lower mid boost, this is what Soldano uses in the SLO. What value is the treble cap does your amp use? 390pf to about 500pf would probably work pretty good with the 47k. If you really want to tweak the tonestack go over to www.duncanamps.com and download the tonestack calculator. It's really easy to use and you can get a good idea what changes in the tonestack will do before you use your amp as a guinea pig.
 
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peaveyT60":3ee1e said:
i have a peaveyVTM (marshall 2203) that i would like to thicken up the mids in. i almost have it tweaked just right, but the mids are too high. its like they control the 1.5k - 3k range. the circuit uses a 33k slope resistor. i want a bit more lower mids for meat. i am torn between either dropping the slope resistor down to around 22k or 16k, OR dropping the mid cap in the tone circuit from 22n to 10n.

thoughts? :dunno:
Click to expand...





NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!

Ok, here's what you do:
Increase the treble cap in the EQ to 1000pf, and remove any auto-brightness cap off the preamp control if your amp has one.
Try that first. changing the slope resistor isn't going to boost midrange.
 
Changing the slope resistor may not "boost" the mids, maybe that was a bad choice of words on my part. But say if his amp has a 500pf treble cap changing the slope from a 33k to 47k will make the mids sound thicker and meatier. I personally don't like using a 47k because I'm hooked on upper mid crunch but for someone who likes a thicker sound it may do just fine, I've never tried a 1000pf with a 33k but I think for what T60 is looking for a 47k slope may just be the ticket.
 
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RoccaforteAmps":5de19 said:
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NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!

Ok, here's what you do:
Increase the treble cap in the EQ to 1000pf, and remove any auto-brightness cap off the preamp control if your amp has one.
Try that first. changing the slope resistor isn't going to boost midrange.
Click to expand...

i have already removed bright caps from the circuit. the amp is fine as far as highs go, but i want that mid-thickness that comes on at full tilt, but at a lower volume. i don't want to turn it into something boogie sounding, but would like to bump the mids a bit in that direction.
 
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Nigel Tufnel":6c4c1 said:
Changing the slope resistor may not "boost" the mids, maybe that was a bad choice of words on my part. But say if his amp has a 500pf treble cap changing the slope from a 33k to 47k will make the mids sound thicker and meatier. I personally don't like using a 47k because I'm hooked on upper mid crunch but for someone who likes a thicker sound it may do just fine, I've never tried a 1000pf with a 33k but I think for what T60 is looking for a 47k slope may just be the ticket.
Click to expand...

exactly. i am not looking for a boost to the current midrange frequency, but to introduce more lower-mid frequencies to add just a bit of meat to the sound. i guess i should have worded it better.

using the duncan tonestack, it looks like upping the slope resistor causes more brightness? :dunno:
 
What value treble cap is in that amp? 47k slope with a 500pf certainly doesn't sound brighter to me, another good cap value with the 47k slope is a 390pf. But you may not need to mess with the tone stack to get what you desire. There's a couple of tricks that you can try with the output section to fill things out too. If your amp has .022 output coupling caps then you can try replacing them with .047uf, this will add some extra bass and lower mids from the output section but it may be a little loose feeling, you can always lower the value of a preamp coupling cap or two to compensate though, it's a nice combo, tight preamp and an output section that roars. A couple of other things that you can try are adding a .022 cap in series with the negative feedback resistor, you can mount in between the speaker jack and the nfb wire. It works like a fixed resonance control but the .022 is a pretty mild value it's my favorite, just makes things a bit fatter, the lower value you go with this cap the more bass you get, alot of the depth mod talk I've seen they're using .0033 or .0047 but I think that's a bit much. You can try increasing the presence cap value too, changing the .1 to a .68 makes the presence start to effect more mids along with the highs in the feedback loop, you might even go bigger than a .68uf if you want it to dip lower into the mids. I've never tried a bigger value than .68 there because it's just prefect for me but you can go bigger, although I'm sure it will turn ugly sounding if you go too big there. Good luck, lemme know if I can be of any help.
 
Oh I forgot to add that those mods to the feedback loop will have much less of an effect if your amp uses a bigger value negative feedback resistor like a 100k. If it's lower though they should work great.
 
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Nigel Tufnel":4daec said:
What value treble cap is in that amp? 47k slope with a 500pf certainly doesn't sound brighter to me, another good cap value with the 47k slope is a 390pf. But you may not need to mess with the tone stack to get what you desire. There's a couple of tricks that you can try with the output section to fill things out too. If your amp has .022 output coupling caps then you can try replacing them with .047uf, this will add some extra bass and lower mids from the output section but it may be a little loose feeling, you can always lower the value of a preamp coupling cap or two to compensate though, it's a nice combo, tight preamp and an output section that roars. A couple of other things that you can try are adding a .022 cap in series with the negative feedback resistor, you can mount in between the speaker jack and the nfb wire. It works like a fixed resonance control but the .022 is a pretty mild value it's my favorite, just makes things a bit fatter, the lower value you go with this cap the more bass you get, alot of the depth mod talk I've seen they're using .0033 or .0047 but I think that's a bit much. You can try increasing the presence cap value too, changing the .1 to a .68 makes the presence start to effect more mids along with the highs in the feedback loop, you might even go bigger than a .68uf if you want it to dip lower into the mids. I've never tried a bigger value than .68 there because it's just prefect for me but you can go bigger, although I'm sure it will turn ugly sounding if you go too big there. Good luck, lemme know if I can be of any help.
Click to expand...

thanks for the great info.

i changed to a 22k slope resistor instead of the 33k. i like the shift it brought in, but i may need to adjust the bass cap to roll off some of the low end around 100 hz. it has added meat, but i am unsure if i will keep it permanent.

that output section stuff you mentioned sounds interesting. i love the way the amp sounds at full tilt (it thickens up), but it is just too damn loud and i would rather spend $5 on some beefy 3w resistors than $250 for an attenuator. :lol: plus the whole learning experience and whatnot.

also, i am not looking for more bass/balls, but more thickness in the 500-850 hz (approximate) range; to de-emphasize the 1-2k range where the mids in this amp seemed to be voiced at, but not to the point of something boogie-esque. i know... i know......

also, i am running JJ 6L6, GT12AX7 (V1-V3), JJ12AT7 phase inverter. i do like the change the 12AT7 makes in V1. even if i match the gain with the 12AT7 vs 12AX7, the 12AT7 is a bitt less fizzy and thicker. i am guessing it is mostly b/c of the way it biases warmer than a 12AX7 in the same slot. :dunno:
 
But say if his amp has a 500pf treble cap changing the slope from a 33k to 47k will make the mids sound thicker and meatier.

Just as a heads-up, increasing the slope resistor from 33K to 47K will shift the mids upwards, not downwards towards the lower mids. Personally speaking I would not look here to try and get more lower mids but if you feel that's the place I would not go below 22K but to each his own.


For what it's worth
Trace
 
But say if his amp has a 500pf treble cap changing the slope from a 33k to 47k will make the mids sound thicker and meatier.

Just as a heads-up, increasing the slope resistor from 33K to 47K will shift the mids upwards, not downwards towards the lower mids. Personally speaking I would not look here to try and get more lower mids but if you feel that's the place I would not go below 22K but to each his own.


For what it's worth
Trace
 
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peaveyT60":bcf7c said:
:|::QBB:

thanks for the great info.

i changed to a 22k slope resistor instead of the 33k. i like the shift it brought in, but i may need to adjust the bass cap to roll off some of the low end around 100 hz. it has added meat, but i am unsure if i will keep it permanent.

that output section stuff you mentioned sounds interesting. i love the way the amp sounds at full tilt (it thickens up), but it is just too damn loud and i would rather spend $5 on some beefy 3w resistors than $250 for an attenuator. :lol: plus the whole learning experience and whatnot.

also, i am not looking for more bass/balls, but more thickness in the 500-850 hz (approximate) range; to de-emphasize the 1-2k range where the mids in this amp seemed to be voiced at, but not to the point of something boogie-esque. i know... i know......

also, i am running JJ 6L6, GT12AX7 (V1-V3), JJ12AT7 phase inverter. i do like the change the 12AT7 makes in V1. even if i match the gain with the 12AT7 vs 12AX7, the 12AT7 is a bitt less fizzy and thicker. i am guessing it is mostly b/c of the way it biases warmer than a 12AX7 in the same slot. :dunno:
Click to expand...

Try a 27K if the 22K is too much. Where do you keep the mid boost DIP switch set? If you like it on you might try installing a larger cap for that boost.
Jerry
 
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peaveyT60":f23f8 said:
:|::QBB:

thanks for the great info.

i changed to a 22k slope resistor instead of the 33k. i like the shift it brought in, but i may need to adjust the bass cap to roll off some of the low end around 100 hz. it has added meat, but i am unsure if i will keep it permanent.

that output section stuff you mentioned sounds interesting. i love the way the amp sounds at full tilt (it thickens up), but it is just too damn loud and i would rather spend $5 on some beefy 3w resistors than $250 for an attenuator. :lol: plus the whole learning experience and whatnot.

also, i am not looking for more bass/balls, but more thickness in the 500-850 hz (approximate) range; to de-emphasize the 1-2k range where the mids in this amp seemed to be voiced at, but not to the point of something boogie-esque. i know... i know......

also, i am running JJ 6L6, GT12AX7 (V1-V3), JJ12AT7 phase inverter. i do like the change the 12AT7 makes in V1. even if i match the gain with the 12AT7 vs 12AX7, the 12AT7 is a bitt less fizzy and thicker. i am guessing it is mostly b/c of the way it biases warmer than a 12AX7 in the same slot. :dunno:
Click to expand...

Try a 27K if the 22K is too much. Where do you keep the mid boost DIP switch set? If you like it on you might try installing a larger cap for that boost.
Jerry
 
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