Re: Marshall JMP-1 Preamp mods?
Posted: 06 May 2013, 17:24
edit..I try in PM...
let's talk jmp-1 mods.
let's talk jmp-1 mods.
tracing pedals since 2007
https://www.freestompboxes.org/
Well Jooshtin, fact is that I have never been able to compare gear before. Neither am I a huge grail-seeker where it comes to tone, or did I try copying sounds from my favourit gitarists (Vai, SRV, Buckethead, Frusciante).Jooshtin wrote:
Cheers Tubetinkerer for sharing your mods and ideas, they have got me thinking, and made me want to have a look at the clean channel sometime (you weren't wrong about the biasing etc earlier either… ). I've just noticed you said your jmp-1 has a lack of range in the tone controls and sparkle in the cleans, usually these have loads of eq available, mine can get way too bright at extreme settings. What amp/speakers are you running it through? Are you using the line outs and not the emulated speaker outs into the amp?
I may try tweaking R142 to reduce the overall gain slightly. However, I find mine sounds superb and gets used loads in the studio, and bizarrely often sounds more "hot-tubey" than some expensive rigs - for clients who want that Marshall sound. Don't underestimate the effect of the power amp/speakers/cabs on the tone. Mine is run through a 9005 all tube power amp (recapped, microphonic ceramic caps in signal path replaced, and biased nicely) into a couple of custom closed back 1x12 cabs (Eminence Wizard & Governor speakers). It gets put in the live room and cranked up loud Also gets used a lot for bi-amping bass too.
IMHO the jmp-1 is the natural progression from the DRP-1, 9001, 9004 preamps - alongside the JCM900. Remember too that when the jmp-1s were designed a lot of UK manufacturers were having a hard time getting decent tubes, so it's no surprise that the OD channel doesn't rely on the tubes for clipping - it does of course add to the tone/mojo and the cathode follower sets the impedance into the OD1 preset marshall tonestack etc.
See graph. Made the simulation in Duncan's Tonestack Calculator with compensation for Bass-LogB-Taper. Didn't check the actual values though, but I didn't find any discrepancies between schematics and actual values yet.Jooshtin wrote: Apologies, in my earlier post by preset tonestack I meant the resistor/cap network between IC12 pins 1 & 3 not the eq later in the chain. This preset tone network is the only difference I can see between OD1 and 2. It looks like a tweaked Marshall tonestack and preset level. It would be interesting to sim the eq shape, also to check the actual values in the unit. If this is the only change it certainly shows the difference a tonestack makes.
all of the drive is from diodes around the IC's, The valves are just for marketing purposes. The Speaker emulator circuit is very good. I have two JMP1's if anyone Is interested 1 of them is for sale.okgb wrote:Yeah, coming back to this [ How to make my JMP-1 more usable ]
no consencous, but if some of the overdrive is derived from the I.C.'a and S.S. where and how ?
I have a few tube preamps, but the the top three get used and the others like the jmp-1 sit
top for me , the CAE 3+ [ desert island only pre, classic not so modern, always usable ]
Mesa Formula pre , great clean & semi grit , worth it for that alone. the od channels in my opinion
don't cut it , just not complex enough with two tubes. Bogner/ Hafler triple giant , voiced different enough
to be not a " me too " often these days running through the latest ADA speaker sim box.
I don't want to sell the Marshall , but it's not cutting it , 10 hundred dollars or best offer , ha !