Help for jcm900 emulation circuit

[ubaid88]

Hi,
Iam found circuit of fet 4 tube of jcm900 emulation in some this forum. I want use this circuit preamp only with diy marshall speaker sim.. The guy didnot include the pcb layout so i decided to make my own. But i need to know what does  "to P.I." and 'from T.S" means.

[petemoore]

  PI can be Phase Inverter [creates out of phase signals to drive push pull output amplifier section, not shown or used in the Jfet Emu].
 TS Can be Tone stack
 and that's what they were probably called here
 I'd connect the two.
 That'd make buncha voiced gain stages into a Tone Control, then some gain recovery transistors, into a two pole LP filter [speaker sim], out.

[Ripthorn]

If doing a cab sim, I would play with removing filter just before the output to see if it makes the cab sim seem more realistic.

[ubaid88]

can you suggest me what to do if i only need a preamp and direct connect to speaker sim.

[anchovie]

Leave out R21, R22, C26 & C27. Connect straight from the junction of C24 & C25 to the Master Volume pot.

[Fender3D]

watch out!
in the above schematic you miss the q2 drain resistor, unless c3 should be connected to q2 source.

[ubaid88]

what to do with tone stack and phase invertor. I dont want them. Can directly I connect one TS with PI? Has any one used this before. If not can you suggest any other fet sim for mesa or marshall which can work with non-j201 fets e.g. 2n3819, mpf102 ,2n5457 or 2n5486.
Thanks.

[wavley]

what to do with tone stack and phase invertor. I dont want them. Can directly I connect one TS with PI? Has any one used this before. If not can you suggest any other fet sim for mesa or marshall which can work with non-j201 fets e.g. 2n3819, mpf102 ,2n5457 or 2n5486.
Thanks.

My question is why you would want to emulate a JCM 900 and eliminate the tone stack and Phase inverter?  These two elements are a huge part of the sound of a JCM 900.  That is a Post PI master volume so a good chunk of the distortion you hear in an amp like this is coming from the PI.

.

[ubaid88]

Ok here i got newer version of same project.

[ubaid88]

what to do with tone stack and phase invertor. I dont want them. Can directly I connect one TS with PI? Has any one used this before. If not can you suggest any other fet sim for mesa or marshall which can work with non-j201 fets e.g. 2n3819, mpf102 ,2n5457 or 2n5486.
Thanks.

My question is why you would want to emulate a JCM 900 and eliminate the tone stack and Phase inverter?  These two elements are a huge part of the sound of a JCM 900.  That is a Post PI master volume so a good chunk of the distortion you hear in an amp like this is coming from the PI.

.

Ok if i include them then from where can i get those circuit diy . If they are available then yes i will. I you any of them please tell me.

[petemoore]

can you suggest me what to do if i only need a preamp and direct connect to speaker sim.
  This is what the schematic shows, preamp stages, tone controls, a couple more Jfet stages, a two pole low pass filter [speaker sim], output.
  The phase inverter and output amplifier sections are not shown and do not lend themselves to being 'Jfet-ed'.
  Phase inverters prepare a signal for push-pull output tube amplification, splitting the signal into + and - halfwaves to drive one tube to ''push'' and the other to ''pull'' on the speaker coil [impedance matching output transormer between tubes and coil of course].
  The output section does contribute to the sound of tube amps.

[anchovie]

Ignore the "to PI" and "from TS" labels on the schematic. Just pretend that they're both joined together. They've probably just been taken from the amp schematic that this is based on and in the case of the Phase Inverter this is now irrelevant as this circuit is no longer an amplifier - you'd only need a Phase Inverter if you were building a real tube power amp!

As for the tone stack, again don't let the "from TS" label confuse you - the tone stack is already in this schematic! That's what your bass/middle/treble controls are!

[petemoore]

  The "PI" kinda goes off into...nowhere...er...where the phase inverter probably is, exactly on the amps schematic.
  The TC recovery stages...probably put there? to bring the signal level up after the control attenuates it for TMB controls.
  Speaker sim also added to roll off some upper-highs [I guess].
  To be sure, compare with the amp schematic.

[anti-idiot]

The first schematic was full of mistakes (sorry, my bad).

The second JFET was a source follower (and i used the drain, Fender3D was right), the labels "to PI" and "From TS" should be connected, it was cut because of the limits of space. anchovie is right too.

The second version of the emu omited the 2nd fet (why use a buffer at the beginning of the circuit?), changed a few values and fixed some mistakes. why have two gains? the second gain of the SL-X (i think it was called 'sensitivity') gave no sound at zero. when the pot was at maximun, the total resistance was 500k. I swapped the 1M-pot/1M-resistor for a 470 resistor. The Sl-X should be pretty much like a JCM800 with an extra stage.

I also changed the value of the mid pot (the 1M was a mistake, now i use a 50k, which is more responsive than the typical 25k)

The PI was a "pet name" i gave to the last 2 stages of the emu. They are adaptations of the P.I. (same thing with the Plexizer, Thunderchief, erik's JCM800, etc). The Presence control is pretty useless.

The original amp used a buffer at the beginning, 2 gain pots, starving plates, M5201 for switching volumes, etc.