Anti Compression Mod Comparison

Kelster3000

New Member
Joined
Feb 9, 2019
Messages
28
Reaction score
20
Hi All

for the last few years, I have owned a lovely Marshall JVM410H which has had the following mods
4H Choke
Negative Feedback mod 176K resistor
Plexi Cap mod

I generally use OD1 (Orange) with the gain at around 9:00(o'clock) in my originals old school metal band, this appears nice open punchy sound sound not too compressed.

I generally love the sound of the amp and pretty happy with my general tone. However the tinkerer in me keeps me wondering about the anti compression and gain reduction mod, I am just wondering if anyone can point me in the direction of a comparison video/audio of before and after anti compression mod and gain reduction, searched high and low to no avail.
 

jimmyo

Active Member
Joined
Nov 20, 2021
Messages
79
Reaction score
225
Location
California
Try a JJ ECC823 in the first preamp gain position (the one with the metal shield). Lowers the gain and compression and noise for OD amber and red modes only and allows them to balance better with green mode. Doesn’t impact the other modes, and for about $18 a tube is a simple and reversible change that has transformed my JVMs. I use OD2 amber gain on 6 for 80s metal. Less compressed and no squealing or crazy noise, feedback etc, other than the good kind.
 

Tatzmann

Well-Known Member
Joined
Nov 8, 2021
Messages
999
Reaction score
1,409
Lower output pickups.
Still not working out, get a different
amp. Play music or fuss around with
this amp, up to you.

Good luck.
 

spacerocker

Well-Known Member
Joined
Feb 6, 2009
Messages
1,835
Reaction score
1,490
Location
UK
Try a JJ ECC823 in the first preamp gain position (the one with the metal shield). Lowers the gain and compression and noise for OD amber and red modes only and allows them to balance better with green mode. Doesn’t impact the other modes, and for about $18 a tube is a simple and reversible change that has transformed my JVMs. I use OD2 amber gain on 6 for 80s metal. Less compressed and no squealing or crazy noise, feedback etc, other than the good kind.
Not strictly true - it also affects "Clean Red" on the 4-channel amps....but yes it is a good way to reduce gain on OD Orange and Red Modes....
 

pedecamp

Well-Known Member
Joined
Dec 7, 2009
Messages
18,988
Reaction score
20,420
Hi All

for the last few years, I have owned a lovely Marshall JVM410H which has had the following mods
4H Choke
Negative Feedback mod 176K resistor
Plexi Cap mod

I generally use OD1 (Orange) with the gain at around 9:00(o'clock) in my originals old school metal band, this appears nice open punchy sound sound not too compressed.

I generally love the sound of the amp and pretty happy with my general tone. However the tinkerer in me keeps me wondering about the anti compression and gain reduction mod, I am just wondering if anyone can point me in the direction of a comparison video/audio of before and after anti compression mod and gain reduction, searched high and low to no avail.
ECC823 in V1 to reduce gain, KT77 in the power section to reduce compression. EQ in the loop to sculp tone even further.
 

jimmyo

Active Member
Joined
Nov 20, 2021
Messages
79
Reaction score
225
Location
California
Not strictly true - it also affects "Clean Red" on the 4-channel amps....but yes it is a good way to reduce gain on OD Orange and Red Modes....

Yeah you are totally right, clean red also. Was thinking the OD channels. I probably need to spend some more time with clean red again since I changed the preamp tube.

One nice thing I found with changing to the ECC823, it allows you to set the gain higher on amber and red OD1 and OD2 without all the squealing and noise etc. As the gain control also thickens the tone a bit I’ve found I like the OD2 amber and red tones much better now. Gain set on about 6 works for all three modes green thru red. High gain is quieter too and don’t need a noise suppressor as much anymore.
 

spacerocker

Well-Known Member
Joined
Feb 6, 2009
Messages
1,835
Reaction score
1,490
Location
UK
Yeah you are totally right, clean red also. Was thinking the OD channels. I probably need to spend some more time with clean red again since I changed the preamp tube.

One nice thing I found with changing to the ECC823, it allows you to set the gain higher on amber and red OD1 and OD2 without all the squealing and noise etc. As the gain control also thickens the tone a bit I’ve found I like the OD2 amber and red tones much better now. Gain set on about 6 works for all three modes green thru red. High gain is quieter too and don’t need a noise suppressor as much anymore.
I'm glad you like the OD tones better now. I've never tried this valve, as it hadn't been suggested (to my knowledge) when I did the anti-compression mod....It's interesting what you say about the lack of squealing with the 823 though - and is proof that the squealing is due to "too much gain" rather than a fault with the amp (which is what a lot of people assumed back in the early days...) A standard ECC833 has a gain of about 100 each of the separate triodes - but an 823 has a gain of only 10 or 20 on the gain stage which affects OD Orange and Red (and clean red!)....
 


Top