"Marshall" sim

[tomwarrior]

i built the preamp section using lm324's. my version sounded terible. i listened to the diffent op amp stages and found i was getting distortion from the first op amp. is this because im using the lm324's? do i need to use tl084's? my version had insane gain and turning down the gain pots(i used a dual 100k) cleaned it up a little but it still didnt sound right. i built mine on a breadboard. yours sounds incredable!!!---tom

[krille2]

lm324, I think it is pin compatible, but the characteristics must match if you want to even get close, a quick glance at the datasheet would be advisable. The clipping characteristics when approaching rail supply voltages needs to match as the op amp makes the hard clipping in this design. Gain factors etc, etc. Personally I don't think it's possible to use lm324 without making appropriate changes to the schematics, maybe (and I say maybe) you could try a tl074 but I think that the design is made for the TL084 chip and of course the results from using other chips could be interesting but also unpredictable, if (of course)  you don't know what you're doing.

A PCB for this would be cool, but you can't get the sound of a hand wired design    Just kidding! 

[petemoore]

  The TL084 is an Integrated Circuit
Quad, Low Noise JFET-Input Operational Amplifier
  ...or standard opamp, just four per package,
  TL082 is the same but packaged as a dual opamp.
  I haven't read the spec sheets on the LM324
  I started building one yesterday using all dual IC sockets...still on the 1rst socket, I hope my approach doesn't turn out to be 'ill-advised'. Plan 'a' is to take it to the output before the speaker cabinet simulator.

[stm]

The LM324 is a somewhat unique OpAmp: it is a low-power op-amp capable of semi rail-to-rail operation     Well, this means both the inputs and outputs can go down to the negative supply (usually GND in 9V baterry powered circuits).  It is great for LFO's and stuff like that, but NOT RECOMMENDED for the audio path because it has high levels of crossover distortion.

Hope this helps.

[petemoore]

  It is great for LFO's and stuff like that, but NOT RECOMMENDED for the audio path because it has high levels of crossover distortion.
  Fortunately you used sockets?...and we have this place.
  A couple 'diff' things I noticed are the *very small resistors [150R and such] between the OA inputs and ground...I haven't quite figured out what's up with that.

[MartyMart]

I built one today using 4X TL072's and 1X TL071
I'm not bothering with the "speaker sim" section , as my Condor is
easily good enough and its about 12 opamps less !!!
I used a bipolar supply from 2X 9v batteries.
It's sounding VERY .... VERY  nice !! 
Mods :
Added in/out caps of 220n, not sure why, they just seemed to be missing.
The 470pf connection to the tone stack :
This sounded awful, WAAY too shrill and dont plug this into an amp, like a regular
pedal, it will sound real bad, needs to be direct to a cab sim.
I've got this 470pf as a 6n8 at the moment ( still tweaking ) and it's working much
better.
From 2n2 to 10n seems useable .... though .....
This could well be due to my Condor's "EQ" setup ...... ??
Great Marshall "Grind" here, but quite a few opamps, so be careful !!

    MM.

[petemoore]

  Marty I did some things too.
  I swapped the .033uf for a .0047uf, redailed the tuners, this tamed the high end nicely.
  I also added a small .0033uf across the diodes, which tamed much of the lots of hiss mine was producing.
  Some type of additional LP Filter enhancement would be beneficial to me, however I'm not well versed here.
  I'm not knowing the term for the LP Filters that mimic speaker freq rolloff as seen on the tail end of amps and amp sims, often a string of 12k or so resistors with small ~2n2 caps to ground.
  But I'm wondering whether something like this might be well implement earlier on, for some possible HF noise reduction...say like on a pot that has signal and a ground right there.
  As far as tunability/tonability it is a real beast.
  I super lucked out and easily just found the right value/taper pots for this thing 
  Some of the noise I'm experiencing could be TL062 related?

[MartyMart]

Thanks Pete, I'll try the parallel cap over the diodes.
I have that 470pf at 2n2 now and that seems about right, those
bass/mid/treble controls are almost "too" interactive, but it offers
lots of "tones"
I agree that a couple of 1n/2n2's to ground here and there would help,
I'm thinking around the dual 100k and single 100k gain stages.
What do you have it "plugged into" ? as it sounds awful into my amps,
need to go direct to the speaker sim, then it "becomes" that correct sound.
For direct normal "stompbox" use, it would need the 10k/2n2ground/10k/2n2ground setup
at the back end, like some of the ROG amp emulations.
Just before final "op amp buffer" woulld be the right place I think .. ?
It has a MIGHTY output level, almost seems a "balanced line" output !!
I have the master volume at around 9 o'clock, that's enough for the condor !

MM.

[petemoore]

I put DC Blockers on In/Out .1uf or so, and "BFC's" from middle of PS to each rail.
  Socketted the first staging cap, the feedback cap, and the treble cap [top of TC on schem].
  68n is in the feedback loop, also in the treble [470pf's] socket.
  I think the staging cap is .022uf 'because for now'.
  I think it's quite the Schnitz [exellent].

[petemoore]

  The amp sim alone does sound 'ampy' but also 'raw'.
  I just tagged on a LP Filter of a couple 12k's 'strung seriesed' w/SP, and a .0047uf and .0039uf to ground [like the ROG speaker filters on amp sims]...for right now, this takes alot of the high end hasinesses, leaves some sparkle.
 

[Doug_H]

lm324, I think it is pin compatible, but the characteristics must match if you want to even get close, a quick glance at the datasheet would be advisable. The clipping characteristics when approaching rail supply voltages needs to match as the op amp makes the hard clipping in this design. Gain factors etc, etc. Personally I don't think it's possible to use lm324 without making appropriate changes to the schematics, maybe (and I say maybe) you could try a tl074 but I think that the design is made for the TL084 chip and of course the results from using other chips could be interesting but also unpredictable, if (of course)  you don't know what you're doing.

A PCB for this would be cool, but you can't get the sound of a hand wired design    Just kidding! 

I haven't been to the LXH2 site in a while but he used to have a note to the effect that you had to use the TL08* op amp, since the simulator was designed with the particular characteristics of that device in mind.


Doug

[MartyMart]

For anyone building this, I strongly recommend using TLC2262 op amps.
I've just used them and there is a huge increase of quality, more depth, clearer
more gtr personality retained and less noise, even at very high gains 

It's a great circuit

MM.

[WGTP]

http://aronnelson.com/gallery/WGTP/Marshall_Sim

Couldn't help hacking it down to 4 op amps.  May have lost the "character" but much easier to get onto a breadboard now.   

[Doug_H]

That's starting to look a *little* like a guvnor...

Doug

[krille2]

Well, do you have any sound clips? It would be nice to hear what it's like in that form 

I have posted a low gain clip (and a shredding clip) recorded with a strat on the web page if anybody is curious what it sounds like... http://hem.passagen.se/amps/

Actually I have run into some wonders regarding the brightness of the amp when using a Stratocaster with single coils. For the high gain clip I had to back off the treble to 0. That seems radical to me... Any ideas?

[MartyMart]

Well, do you have any sound clips? It would be nice to hear what it's like in that form 

I have posted a low gain clip (and a shredding clip) recorded with a strat on the web page if anybody is curious what it sounds like... http://hem.passagen.se/amps/

Actually I have run into some wonders regarding the brightness of the amp when using a Stratocaster with single coils. For the high gain clip I had to back off the treble to 0. That seems radical to me... Any ideas?

Try doubling the tone stack 470pf to a 1n or so
I have mine at about 2n9 now and it seems much better.
Also Pete added a cap across the diodes, 2n2 helped here also.
MM.

[WGTP]

Might try a .001uf cap or larger in parallel with the diodes for reduced high's.   

I'm not sure the buffer before the tone stack is essential.  That's 3.   

If I remove the tone stack and buffers, I'm down to 2 op amps.   

http://aronnelson.com/gallery/WGTP/Marshall_Sim_001?full=1

[Johan]

..hey Krille..
..since we are both in sweden..I saw that you buy everything from ELFA..they are great, but check out Kjell&co too..( www.kjell.com )..you can really save a lot on their bags with caps and on their stripboards..also has great little LDR's for easyvibe and for optical compressors..and hammond type boxes..or how about 60 IC-sockets for 19SEK (2euro ) ?

..the clips sounds great, by the way..

johan

[petemoore]

  I socketted [like I do] some of the 'early' caps, and diodes.
  The Feedback cap on the M Sim is a good one to socket, as is the 'treble knob' cap, also I have a .0033uf in with the diodes.
  I put a 2x  12k string at the output, and have a .0047uf [probably a little big], and a .0022uf, going to ground after each 12k...[I think that's called a multipole filter].
  At any rate I found the noncab Ampsim to be 'heavy on the treble' as shown.
  I kind of figured that the feedback cap and 10k's must 'do' the treble filtering, being as I see no diodes to ground, LP filters, Caps across diodes etc.
  I might just take it a little farther...past the speaker damping and Bass Boost sections, perhaps the high end is tamed more after going through those sections, and doesn't 'need to be trimmed like I did earlier on...
  Pretty amazing circuit in my recent Exp. Not sure what's REALLY going on...perhaps allowing what seems like 'unruly amounts' of HF content to get to the later sections is part of [what appears to be] a very well thought out 'plan'.
  I plan to work on the 'pre-MFB' sections, box that, then build the MFB [quite a batch of parts to populate there] sections to be placed...later.

[WGTP]

Ok, the bass is being rolled off below 500Hz and the treble is boosted.  Later stages reverse the frequencies cut and boost.  This is frequently discussed as a means of providing "smooth" distortion.  The treble boost seems to be the most unique aspect I can identify.  Other designs use Marshall tone stacks and report good results.

The diodes to ground are "soft" clipping (isn't that usually labled hard clipping around here) and the op amp before the diodes is doing the "hard" clipping when it is pushed.  Ok, the bass is being rolled off below 500Hz and the treble is boosted.  Later stages reverse the frequencies cut and boost.  This is frequently discussed as a means of providing "smooth" distortion.  The treble boost seems to be the most unique aspect I can identify.  Other designs use Marshall tone stacks and report good results.

The diodes to ground are "soft" clipping (isn't that usually labled hard clipping around here) and the op amp before the diodes is doing the "hard" clipping when it is pushed. 

I'm not sure what typical Marshall JCM 800 tone control setting are, but on the Seymour Duncan pickup sampling CD the amp is set with - Bass 10, Midrange 4, Treble 4, Presence 5.5, which would imply a bass boost.