L
petejt
Active member
Thanks for this.
blackba
Well-known member
Good Read 
L
LukeCurd
New member
http://www.mrbobo.com/music_JCM800_mods.htm
My modded Marshall 2204 - 50 watt, master volume, JCM800
Marshall 2203/2204 Mods.
Opinions are plenty, regarding the Marshall 2203, 2204 - Here are mine:
Filter Caps: I recapped mine using F&T caps. Many feel these are the best.
Large electrolytics: I used Sprague Atoms. Many feel these are the best.
Audio Signal Caps: For caps in the preamp, that audio signal passes thu - Sozo. This isn't "cork sniffing"- the difference these caps make is plainly audible. I love how they sound. They have a sweetness about the treble that others do not! They are about $2 each. They may not be for everyone ... Orange drops are another popular premium capacitor, and I think they are "tighter sounding". So for example, a high gain amp may benefit from Orange Drops, while medium and low gain amps will benefit from Sozos.
Smaller Audio Caps: Preamps contain some smaller caps that are smaller values than Sozo makes( 470pf, for example). The amps come stock with ceramic caps in these positions. Many on the Metro Amp forum feel that ceramic caps with a higher kV rating sound better (like 1kV or 2kV rating). Another option is Silver Mica caps. I used them on my Marshall. Some feel they are to glassy sounding, I don't know enough to say really.
Resistors: For resistors- the amp comes stock with mostly 1/2 watt Carbon Film. Any resistors that I changed - I used 1 watt Carbon Film. Not so much to make them beefier, or for reliability; but for possibly lower noise. Noise is proportional to the cross sectional area of the resistor, and the 1 watters are physically larger (bigger cross sectional area= lower noise). Noise is also related to the resistor composition (Carbon Composite, Carbon Film, Metal Film) and the resistor value (higher value = more noise). The 1 watters fit in the circuit board just fine.
Tools:
Soldering Iron, about 60 watts. I use a Weller, it must be 20 years old.
DeSoldering Braid: This is what you need to remove the old component.
Solder: I use a silver, Rosin core solder.
Multi-Meter
Tubes: Wow, this is really subjective.
PreAmp Tubes (12AX7) - Tung Sol. I think these are the best sounding, new production tubes. Period. They are slightly bright sounding, but have allot of depth, or "3-D" sound to them. Really. If you have no budget, and limitless time to buy, test, and evaluate tubes - you may find others that compare. But today, I buy Tung Sol 12AX7s , and put in every position of my tube amps.
Power Tubes: Here's what I use
EL-34: Svet, Tung Sol
There is allot written on this amp. Many good resources on the Internet. I also see allot of BS....
Here's some good links:
MetroAmps Forum - These guys know it.
Tube Depot - Besides selling tubes, they sell all the components you'll need
Valve Wizard - A very good tube amp website, some useful free tools
Duncan Tone Stack Calculator - Duncan Amps provides this free tool. Shows the effects of changing
amp tone stack components.
FJA Amp Mods - Jerry knows his shit, many many people give him the highest marks. If you don't know what youre doing,
send your stuf to him. Super nice and helpful guy, he regularly posts over at Rig-Talk, and even has his own section there-
Rig-Talk FJA Amplifier Mods
Amplifiers contain voltages high enough to Kill you!! Even after the amp has been powered Off !!!
If you don't have enough electronic experience to identify and discharge the Filter Capacitors-
which contain these Deadly voltages- take your amp to a Qualified tech.
You Have Been Warned!
Brightness Taming
My JCM800 was the stiffest, brightest "icepick to the forehead" amp ever. Mine is not the exception, most of them are that way. I reccomend this order of mods to address this:
Without changing any componenet values, simply using Sozo capacitors may make your treble sweet enough!
1.
C5 -Preamp volume "bright" cap. Remove this. Seriously. This is a "no brainer".
2.
C4 - change to .0022uf (ala Soldano SLO), decreases brightness, increase mids. Some people remove this entirely, not me.
3.
R22 -Negative Feedback Resistor - decrease value to soften and reduce highs. 8 ohm tap softens more, 16 ohmtap the most soft & least agressive sounding. 100k is stock JCM800 2204; I used 51k. 47k is a common value for many modders.
4.
C18 - Phase Inverter plate "fizz" cap - increase to 100-150pf to remove very high freq. Do not remove; I used 100pf Silver Mica
5. C4 - this can be removed also.
Voicing:
These mods are similar to the brightness mods. Mosat of them add some gain as well. Mainly what's happening is that we are increasing gain, for specific frequencies.
6. add a .68uf bypass cap to R9. This increases gain, but only in the mids and highs. I liked this sound allot.
C1 - Change to 1 uf. controls frequency gain applies to. Lower value boosts only highs; Soldano SLO and 5150 use higher value 1 uf here (boosts more mids as well as highs)
7. Input Resistor R3- Lower to 10k. Some high gain amps (Cobra) use no R3 at all. Change will be slight; somehwat better pick sensitivity, possibly lower noise. The purpose of this resistor is to interact with the tubes input capacitance and form an RC filter that blocks radio frequency interference.
Tone Stack: see Duncan Tone Stack Calculator for effect of this. Raising R15 Slope resistor does not “boost the mids” like read on the internet (common myth I see repeated over and over). I liked a 39k slope resistor.
Phase Inverter coupling caps (C14,C16 Higher values allow more bass. Soldano SLO, Peavey 5150 use .047uf
Marshall SuperBass uses .1 uf. I have enough bass with the stock value of .022uf. Replcing just these 2 capacitors with Sozo's will make a difference.
Gain
8. I found that raising gain on V1 has side effects. Most amps with allot of gain in V1 use 500k or 250k preamp pots. To fight excessive grid current: add a 2m resistor- from the PreAmp pot. wiper to ground.
Lower C3 to .01 uf, and C7 coupling cap to .0047 (to reduce excessive bass) and blocking current disatortion. Lowering R1 to 1.8k and increasing R4 to 220k is generally considered max gain for this stage.
9. Goose the input to V2a: Eliminate the 470k + 470k voltage divider; use R 330k to ground and R 220k grid.
Schematics
Stock Marshall 2204
My Marshall 2204, as described above
Even after all these mods, my 2204 still Sounds like a Marshall!!
My modded Marshall 2204 - 50 watt, master volume, JCM800
Marshall 2203/2204 Mods.
Opinions are plenty, regarding the Marshall 2203, 2204 - Here are mine:
Filter Caps: I recapped mine using F&T caps. Many feel these are the best.
Large electrolytics: I used Sprague Atoms. Many feel these are the best.
Audio Signal Caps: For caps in the preamp, that audio signal passes thu - Sozo. This isn't "cork sniffing"- the difference these caps make is plainly audible. I love how they sound. They have a sweetness about the treble that others do not! They are about $2 each. They may not be for everyone ... Orange drops are another popular premium capacitor, and I think they are "tighter sounding". So for example, a high gain amp may benefit from Orange Drops, while medium and low gain amps will benefit from Sozos.
Smaller Audio Caps: Preamps contain some smaller caps that are smaller values than Sozo makes( 470pf, for example). The amps come stock with ceramic caps in these positions. Many on the Metro Amp forum feel that ceramic caps with a higher kV rating sound better (like 1kV or 2kV rating). Another option is Silver Mica caps. I used them on my Marshall. Some feel they are to glassy sounding, I don't know enough to say really.
Resistors: For resistors- the amp comes stock with mostly 1/2 watt Carbon Film. Any resistors that I changed - I used 1 watt Carbon Film. Not so much to make them beefier, or for reliability; but for possibly lower noise. Noise is proportional to the cross sectional area of the resistor, and the 1 watters are physically larger (bigger cross sectional area= lower noise). Noise is also related to the resistor composition (Carbon Composite, Carbon Film, Metal Film) and the resistor value (higher value = more noise). The 1 watters fit in the circuit board just fine.
Tools:
Soldering Iron, about 60 watts. I use a Weller, it must be 20 years old.
DeSoldering Braid: This is what you need to remove the old component.
Solder: I use a silver, Rosin core solder.
Multi-Meter
Tubes: Wow, this is really subjective.
PreAmp Tubes (12AX7) - Tung Sol. I think these are the best sounding, new production tubes. Period. They are slightly bright sounding, but have allot of depth, or "3-D" sound to them. Really. If you have no budget, and limitless time to buy, test, and evaluate tubes - you may find others that compare. But today, I buy Tung Sol 12AX7s , and put in every position of my tube amps.
Power Tubes: Here's what I use
EL-34: Svet, Tung Sol
There is allot written on this amp. Many good resources on the Internet. I also see allot of BS....
Here's some good links:
MetroAmps Forum - These guys know it.
Tube Depot - Besides selling tubes, they sell all the components you'll need
Valve Wizard - A very good tube amp website, some useful free tools
Duncan Tone Stack Calculator - Duncan Amps provides this free tool. Shows the effects of changing
amp tone stack components.
FJA Amp Mods - Jerry knows his shit, many many people give him the highest marks. If you don't know what youre doing,
send your stuf to him. Super nice and helpful guy, he regularly posts over at Rig-Talk, and even has his own section there-
Rig-Talk FJA Amplifier Mods
Amplifiers contain voltages high enough to Kill you!! Even after the amp has been powered Off !!!
If you don't have enough electronic experience to identify and discharge the Filter Capacitors-
which contain these Deadly voltages- take your amp to a Qualified tech.
You Have Been Warned!
Brightness Taming
My JCM800 was the stiffest, brightest "icepick to the forehead" amp ever. Mine is not the exception, most of them are that way. I reccomend this order of mods to address this:
Without changing any componenet values, simply using Sozo capacitors may make your treble sweet enough!
1.
C5 -Preamp volume "bright" cap. Remove this. Seriously. This is a "no brainer".
2.
C4 - change to .0022uf (ala Soldano SLO), decreases brightness, increase mids. Some people remove this entirely, not me.
3.
R22 -Negative Feedback Resistor - decrease value to soften and reduce highs. 8 ohm tap softens more, 16 ohmtap the most soft & least agressive sounding. 100k is stock JCM800 2204; I used 51k. 47k is a common value for many modders.
4.
C18 - Phase Inverter plate "fizz" cap - increase to 100-150pf to remove very high freq. Do not remove; I used 100pf Silver Mica
5. C4 - this can be removed also.
Voicing:
These mods are similar to the brightness mods. Mosat of them add some gain as well. Mainly what's happening is that we are increasing gain, for specific frequencies.
6. add a .68uf bypass cap to R9. This increases gain, but only in the mids and highs. I liked this sound allot.
C1 - Change to 1 uf. controls frequency gain applies to. Lower value boosts only highs; Soldano SLO and 5150 use higher value 1 uf here (boosts more mids as well as highs)
7. Input Resistor R3- Lower to 10k. Some high gain amps (Cobra) use no R3 at all. Change will be slight; somehwat better pick sensitivity, possibly lower noise. The purpose of this resistor is to interact with the tubes input capacitance and form an RC filter that blocks radio frequency interference.
Tone Stack: see Duncan Tone Stack Calculator for effect of this. Raising R15 Slope resistor does not “boost the mids” like read on the internet (common myth I see repeated over and over). I liked a 39k slope resistor.
Phase Inverter coupling caps (C14,C16
Higher values allow more bass. Soldano SLO, Peavey 5150 use .047ufMarshall SuperBass uses .1 uf. I have enough bass with the stock value of .022uf. Replcing just these 2 capacitors with Sozo's will make a difference.
Gain
8. I found that raising gain on V1 has side effects. Most amps with allot of gain in V1 use 500k or 250k preamp pots. To fight excessive grid current: add a 2m resistor- from the PreAmp pot. wiper to ground.
Lower C3 to .01 uf, and C7 coupling cap to .0047 (to reduce excessive bass) and blocking current disatortion. Lowering R1 to 1.8k and increasing R4 to 220k is generally considered max gain for this stage.
9. Goose the input to V2a: Eliminate the 470k + 470k voltage divider; use R 330k to ground and R 220k grid.
Schematics
Stock Marshall 2204
My Marshall 2204, as described above
Even after all these mods, my 2204 still Sounds like a Marshall!!