I just want to post here to share my experience with the LXH2 "Marshall" sim I recently built. It is an amazing creature, I've never heard any simulating unit ever coming so close to the original thing, both amp and cab.
If you are interested in these things, please check out my website: http://hem.passagen.se/amps
/Krister
Great clips, convincing.
22 opamps...whew, big monster.
I get the impression the designs are fairly 'new'...?
All the talk of 'hard to soft' clipping seems to be well backed by the tones in the soundclips...
 I'm waiting for the 'boiled down' or 'lite' version...the one fragment of that opamp array ... the part that 'does that'...lol.
Perhaps you can appreciate that I don't fully understand why that number of opamps was chosen [22] for the design.
I'm 'thought drifting' that many of the OA's are to create the 'hard to soft' clipping depending on input levels, but quite a few must be concerned [mostly or partially] with the Eq and resonance sections, all of which of course contribute to the sound of the circuit...
When I opened the page I saw only the first 'row' of the circuit, though ..hmmm, ok, looks like I've seen something like these marks before...then I see the line leading to the second row, and the next and last rows...I started counting and saw the OA's a numbered up to 22...NTSay, 'I've probably seen something like this...' changed instantly to 'what the heck is all this about?' very quickly.
very very nice!! :o :icon_cool:
Ah - surely a cue to take advantage of the TI sample "programme"!!!!
Stephen
Wow, that sounds amazing! ;)
I always wondered what that sounded like, but I didn't want to try before hearing it first, due to the complexity. That LXH2 design has been around for many years.
It is *very*convincing. I love the "ring" of the semi-clean tones too. Sounds like the real thing! I can't believe you did that on perfboard, what a project! :icon_cool:
Thanks for sharing! That's a great job. 8)
Doug
Hmmm .. very interesting ;)
How many filters did you use for the peak/dips and at which centre freqs ?
Looks like this could use 34 opamps with full & adjustable filtering :icon_eek:
Excellent effort.... wow :o
now, what we need is a LXH2 Mesa sim, and i'll be set for life! ;D
(not a fan of the marshall sound, but that is reeeeeally great modeling!)
Thank you!
Actually it's built with 35 op amps ;D and I've implemeted the full MFB filter design as suggested by LXH2, which means the following freq was included:
MFB FILTER FOR PEAKS:
320 HZ
800 HZ
1.2 KHZ
1.8 KHZ
2.5 KHZ
5 KHZ
8 KHZ
11 KHZ
MFB FILTERS FOR DIPS:
600 HZ
1.45 KHZ
2 KHZ
7 KHZ
9 KHZ
Actually I made the thing on a perfboard with 3x1 soldering islands so there where very little need for patching, it wasn't that bad. A Mesa sim would be cool. Some clever person maybe could bleed the Fender and the Marshall sim together and adjust the filters to reflect the tonal quality of it :icon_idea:
There will be new sound clips on my page in some time, I will use my Fender Stratocaster for some shredding stuff and more :icon_razz:
I just love the sounds from it, and it'll be put in a box today :icon_cool:
Wow.... it sounds great!
Right now I am busy experimenting with some speaker sims (from the amps direct out). It sounds really really good!
Very cool sounds, but looking at the schem., I'm not surprised. I mean, it's got it all: pre-EQ (presence control), clipping, post-EQ, ...
The only question I have: What about low-gain sound samples?
Wow, real nice. I'd like to build this myself, but I'm not sure if I'm skilled enough yet. I have only built the beginner project, the ZW-44 vero thingie and modded my JCM 900 a bit this far. Do you think it will do? At least I have acquired a soldering station and basic soldering skills. How about that Elfa parts list? Did you get all parts there? We have Elfa here in Oslo as well, so it would be practical, although I don't like their long shaft pots. :-)
Keep up the good work. The skill level on this forum never stops amazing me.
Lars Erik
Thanks a lot for sharing your Job.
Your information sound like music to my ear.
For a long time i have been waiting and asking for this kind of stuff.
I have done my personal research about tube amp modelling too.
The theory behind LXH2 work is very complete and mature.
A litlle hard to understand for beginners.
I personally question if we could get tube amp distortion from solid state.
I wait for somebody that could show a blind comparation between the real thing and the
"amp sim".
The effect of distortion explained by LXH2 can be misunderstood.
I have made the block of distortion of the project (marshall amp sim) and it is simple but effective.
The idea of soft clipping before hard clipping is very important. Pay atenttion to this.
Thanks again. Good Luck
I personally question if we could get tube amp distortion from solid state.
Listening to the sound, I begin to question if you can get solid state dist from tube !!
Also at that level of performance it begins to matter less.
I think I will start with just the marshal sim as my lite version and maybe add the rest once its up and running and I get really hooked. If I can get close to that tone I would be happy. Nice build and really cool sounds ;)
The guitar playing is excelent.
Sometimes we can bet we hear steve vai sound.
The question here is about complexity.
The circuit is too much complex and the ideas behind it are complex too.
Links of Samples of fender simulator can be obtained from the LXH2 site.
Thanks.
very grrat project
Thank you, it's always nice to have a positive response :icon_biggrin:
* Well, ok. I will add low gain sound clips in some days. Please notify me if you want me to record other particular sound examples!
* Lars Erik - I bought all stuff from ELFA, except for the casing (an old external SUN UltraSCSI box) and I will update the page with the complete part list, please revisit the page and you will find out in some days. It is typically long shafted pots except for the dual gang pot witch is also a very small one. Personally I think one must at least have some degrees of patience and soldering experience to be able to succeed with the project, maybe it's a good idea to solder one IC at a time including all lines and listen to the outputs of each op amp to see if it is working. The components and cables are small in comparison to a tube amp and I would say that you need a slightly less powerful soldering iron (ex 15W). Well, I actually got the PSU for free!
* Bernardduur, can you tell more about your cab sim projects?
* I didn't implement the "just preamp out", maybe I'll do that this week and include some sound clips of it for you guys, if you're interested.
Right then.
Who's gonna work up the PCB for this monster?
RDV
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
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 ;D ;D Just kidding! :icon_wink:
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.
The LM324 is a somewhat unique OpAmp: it is a low-power op-amp capable of semi rail-to-rail operation :icon_question: 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.
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.
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 !! :icon_twisted:
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 !!
:D :D MM.
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 ;D
Some of the noise I'm experiencing could be TL062 related?
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.
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].
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.
Quote from: krille2 on January 02, 2006, 07:05:09 AM
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 ;D ;D Just kidding! :icon_wink:
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
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 :D
It's a great circuit
MM.
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. :icon_cool:
That's starting to look a *little* like a guvnor... ;D
Doug
Well, do you have any sound clips? It would be nice to hear what it's like in that form :icon_eek:
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?
Quote from: krille2 on January 05, 2006, 03:24:28 AM
Well, do you have any sound clips? It would be nice to hear what it's like in that form :icon_eek:
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.
Might try a .001uf cap or larger in parallel with the diodes for reduced high's. :icon_cool:
I'm not sure the buffer before the tone stack is essential. That's 3. :icon_biggrin:
If I remove the tone stack and buffers, I'm down to 2 op amps. :icon_twisted:
http://aronnelson.com/gallery/WGTP/Marshall_Sim_001?full=1
..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
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.
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. :icon_cool:
Brehumbaggertz.
I wired about half of the 'plurality' filters...all day basically, up to the 5khz peak filter.
i shudda made the pot wires shorter
I Should Have Gotten A PCB...maybe, seems kinda hummy.
These filters are slow going as far as something to wire up and try out...I just wanted to get some of them going, then try and see if it works, it works but I have ALOT more work to Do.
Alot of work and the hum is bothering me. I wonder how much of this noise I can get rid of and how much more hum that'd be than a commercial unit, not boxed but still I'm concerned with the hum...seems pretty strong.
One slow process, building many of these resistors, digging up all these caps...it took me pretty much all dern day [including trip for parts, after 'longsearches'] to just wire up 3 dual OA's, for a total of 6 of the 13 'plurality' of MFB Stages.
Having no real clue how 'critical' for instance the '202k' resistor value is, I made all the 'funny' values, and all values of R very close if not exactly 'on' value...something like .5 % tolerance...because why not...I figured all that work to make a 'comb' [probably wrong term but] that has 'bent teeth'...no, I decided to make the filters as close to the 'target' freqs as possible.
Are ya using 2 batteries, or did you build a dual supply? If it's the latter some extra filtering might help.
RDV
Re-update
This noise hum stuff is the guitar, I turned the vol down on that [ ] and the noise dropped at least 90% right there, didn't have loudness going on but the noise with guitar off is super low.
I've thus far included the 8Khz peak filter, thinking strongly about leaving off the 11khz as there is plenty of [what sounds like very high end] hash for all without the highest freq peak filter in...Sounds pretty good... :icon_lol:
After the 3rd or 4rth filter speed of building increased alot, following the value charts, schematic and board took a bit of getting used to, hitting target resistor values takes time also.
I decided to use some brownie caps [in sockets of course lol], for some of the filters, to get more AMP MOJO...2x/lol.
Its a long process, but I'm building of this beast, piece by piece, I still have the speaker damping and bass boost to go also, that alone will certainly change the Freq Response.
I'm using 2x longboard [rectangular] with 'end stock' so that I can screw 'sub boards' right to that and connect PS and in/out wiring.
It's looking like the 'box' will end up being a pan.
Quote from: petemoore on January 06, 2006, 11:40:01 AM
Re-update
This noise hum stuff is the guitar, I turned the vol down on that [ ] and the noise dropped at least 90% right there, didn't have loudness going on but the noise with guitar off is super low.
Pete, 95% of the times I've experienced hum in the way you describe is because I've connected the input or output jack with the wires crossed (i.e. shield as signal and vice-versa).
i built the preamp section of this omiting the tonestack and opamp 8. the thing that gets me is it is way too bright going into the preamp of the clean channel on my amp(valvestate) and way too bassy going directly to the poweramp. it sounds awsome going into my npn boosted ruby amp with the amp set for a clean sound. can anybody explain why? thanks in advance.---tom
Quote from: tomwarrior on January 06, 2006, 02:34:45 PM
i built the preamp section of this omiting the tonestack and opamp 8. the thing that gets me is it is way too bright going into the preamp of the clean channel on my amp(valvestate) and way too bassy going directly to the poweramp. it sounds awsome going into my npn boosted ruby amp with the amp set for a clean sound. can anybody explain why? thanks in advance.---tom
Yeah, you left too much of it out...
Seriously... You guys are building bits & pieces of the thing, which was designed to function as a whole in a complete system, and then coming back and asking why it doesn't sound right. (?!?) LXH2 has some pretty detailed explanations on his site as to how it works, what ea stage/section contributes, and etc. Go there for clues.
As to why it sounds good with the npn/ruby, you would have to put it on a scope to see what those other pieces are contributing.
Doug
this is the complete preamp schematic;
http://img257.imageshack.us/my.php?image=marshprb1hi.png
i got it from the LXH2 websight.
looks like a bunch of hipass filtering with no lowpass filtering if im correct.
Seriously... You guys are building bits & pieces of the thing, which was designed to function as a whole in a complete system, and then coming back and asking why it doesn't sound right. (?!?)
[>I didn't ask why it doesn't sound 'right']. I know why it sounds like it does [sometimes] hopefully by dissecting it or building it piece by piece I'll be able to discover even more of what makes it tick, and possibly even understand it, we pick every other unit apart and dissect the fragments...why not this one...?...I'd guess because a lot of thought went into the design in the first place, and mods are ... more or less 'moot'....pick the Fender or Marshall and go to town !!!
No need for a pre-boost. No need for a [ ] or EQ. It is complex, widely variable etc. and stands alone quite strongly...I guess...soon maybe I'll hear the whole completed unit's sound.
I was merely doing it piece by piece, on perf, sampling each section and testing as I go...to see IF it works, and HOW it works.
As far as mods for more gain, treble, etc. dial the knobs....there is plenty 'o controls, huge gain available.
The best/quickest/most sure fire way to get a great LHXS sound...buy one. The commercial ones [there Are Commercially produced ones aren't there?] would probly have all the details worked out, and there are lots of them, all the parts work, lots of those, all the wiring is low noise [Probly EZ to get more noise with sloppy layout] and a plethora of other stuff...like a guarantee the thing'll work.
I've been hackin away on this thing for three days straight about. The scheamtic looks big, but when you add in the filters, it nearly doubles.
So far I've read and believe that the bass is rolled off early, then 'built back up' later...among other things.
Doing this thing on perf is a long, meticulous, labor intensive task, I'd get a PCB if I were to do it again....or reconsider and just buy a pre-made unit.
I added a couple more sections and that threw my Bias voltages off...at least I probably wont have to wade through a debug of 30+ opamps, because it's most likely a problem with the most recently added 'sub-board', containing 3 duals.
The first section, past the diodes clipping, is as Doug said, part of a whole system.
I has serious bass rolloff, and is very bright. Part of the design IIUC is to start off this way, then 'build back up' the bass with later stages [there's a knob and oa's labeled "Bass Boost'].
The first section is a dirtbox, basically, a good sounding clipping device, similar to a diode to ground clipper [diodes do shunt signal to ground], but it seems and this is mere speculation/theory or guess...that the OA's before the diodes somehow 'control' the voltage that supercedes the diodes clipping...to produce the 'dynamics' it has. Way too trebley by itself IMO, if you were doing this section for use merely as a dirtbox...I put in some HF rolloff components at the end of this circuit for fun and testing, a couple 12k's strung series with SP, and a couple 2n2's or so going from their junctions to ground [word?].
It took a fairly long short while to do the clipping section, a full day to build half or so of the filters sections...one long build...I felt the need to pre-test and add sections, for debugging simplification, and just to see what they 'do'.
Can't say I recommend this method.
I'm back from point 'Q' to point "A-'.
Having troubles with the opamp bias points after installing the 'additional' boards, also after de-installing them.
Since I took the first section from the schematic, it's kinda funny...I do OK up to inserting the last two opamps I have on my baord, at that point the SUpply Voltage drops about 40%...wierd, used to workk...Daft.
Anyway, Perfing this thing is rediculous.
All the opamps drop voltage when either or both of the last two are dropped in, usually I'ts just one single side that gets thrown off, much easier to debug that.
As it is, one may end up necessarily debugging a rather large number of opamps at the same time.
I don't know what made me think I could or should do this...whatever...I thought it might be fun and rewarding but it's turning out to be a 3 day nightmare, hopefully this time I've learnt my lesson about getting lucky attempting Huge Circuits on perfboard. It's also eatin' juice fast when batteries are connected.
I guess any interest in modding or messing with this type of thing is also 'undesirable', as it is turning out, there is most likely little that DIY-ing on this could achieve.
The clipping section was sounding kind of cool for a minute anyway, I'm not looking foreward to finding a problem among 12 opamps and related components though.
Doing all the regular stuff, isolating and testing V- Gnd and V+, etc.
Got to be something though, DC Blockers I'd think would allow an OA on 'the other side' of it to bias, perhaps I've somehow got some blown OA's.
:icon_evil: :icon_exclaim: :icon_frown: :-\ :-[ >:( :'( ???
Pete, you're a brave man ..... perf !!
I had no problems at all with the "Pre-amp" section and have only made some
changes due to using the "Condor" as my speaker sim section.
I used a large piece of stripboard, about 4 cm by 8
I recommend this 100% as it's a great result.
I took one look at all those opamps and thought .... no no !
4 duals and single for the preamp was enough for me and is also the largest
build I've taken on yet.
My de-bug for that lot was only 10 minutes !! :D
The pre amp with a few small adjustments works very well with the condor, which
is only 2 more opamps ... !
If anyone wants the details, which myself and Pete came up with, PM me.
Marty.
Maybe I'll work on the filter sections some more to blow off steam.
I'd like to get 'em going and try some Fuzz through them, possibley figure out what they need to drive them...that'll be a day or two's wiring right there, compact and not pots means I'll have a potless, fairly compact board for debugging..
Stupid me won't let the board bias OA 8, the + input insists on 1/3v, despite all wiring, voltage, continuity, etc. beep mode checking possibilities, the tone stack, with a direct connect to +input from 1/2v at certain settings brings the voltage near half.
I changed the opamp a few times, got some other wierd voltages, seems to have settled on 1/3v for today at least, even with the opamp out.
Super dangly potted Gangly board is not DIY Debugging friendly.
Suffice it to say I'm not liking it. Much too much for perfboard.
That 1m bias resistor is going directly to 1/2v from +input, not Gnd, V+ or anywhere else on the board, 1/2v only...I think, after clipping the lead there and touching every node/connection on the board. Why it insists on finding itself at 1/3v, with only a direct connection to 1/2v through the tonestack [or 1m connection through the bias resistor], and nowhere else, with no opamp present, is baffling me totally.
I spent all day, ripping it down to the clipper/TS, debugging, and all I have to show is a rant here.
Perfing this thing is pretty rediculous.
Well I figured out I can plug only one dual OA in, otherwise the battery time starts ticking, 9.08, 07, 06, .05 ...Funny thing is these opamps are showing 1/2v on the inputs and outputs, except the defiant one, which didn't change matters when unplugged.
A real puzzler, and, I'm at a standstill as far as disbugging this one, I suppose I should see if a PS can handle the load better for debugging...or...
I've been over and over every conductive surface on the board, mainly looking for how the power supply is loaded so much.
Pete, you're talking about the "preamp" 1M to ground off the tone cap wiper to opamp 8's + input yes ?
All seems right up to that point ..?
Are you powering with 2X batteries on the in/out sockets.
Across both the power lines I have 47uf's and 1N4001's reversed biased to ground rail and
extra 0.1 poly's to ground too for filtering.
All my pin "8's" are 9v and pin "4's" -9 when you say 1/2V you mean 1/2 V is ground right ?
Would seem like a "drain" somewhere around the tonestack or opamp 7 ...
I thought you had this section working fine and just the "Speaker sim" was a problem :icon_eek:
I'm about to try a version as a "9v" circuit, just the preamp section using 9v 4.5v and ground .....
Luck,
Marty.
Uh, troubleshooting isn't always the most rewarding activity, petemoore. I also had problems with the preamp, around op amp 7 or 8. I had to rewire the lot with new components and off we go with a working amp! And man, was I smiling when I first heard the sound of it! The sound is amazing and it was worth every effort I put into it.
There is a lot of discussion regarding the preamp section which I thought of as to be really good. But as I understand it you should plug it into a power amp -> 4x12 if you don't build the cab sim, from there one could judge if it's bright or not. Compared to other units on the market I think this has a really steady, strong and genuine "Marshall" tone much more so than the weak and buzzy units you could buy. The sound when using my Les Paul is so nice, I could dial in for example a ridiculous close Satriani tone just out of the box, or a really convincing AC/DC tone! When using a Stratocaster it is actually a little too bright to my taste (try a real Marshall stack with stock strat singlecoil pickups – it is REALLY ear piercing bright!!!), so I tried the "another-470pF" mod as suggested here and it worked well, I also added a 27k to the GND leg of the 220k treble pot (to get closer to 250k). I have to investigate a little further... I thought of making this mod in the cab sim instead, around the 6db per octave low pass filter to decrease the brightness somewhat, maybe change the 0.1uf to ~0.2uf. Actually a Marshall should be bright and this is a concern only with the Fender as the Gibson (with humbuckers) needs the treble at 10.
http://www.kjell.com/, thanx for the tip!!
Gadzooks hard to debug.
I finally went door to door, point to point, wire to wire, soliciting for errors, I FInally found a wire on wire nonconnect of 1/2v to the last two dual OA's biasing...Youch that took some time 'n effort. ...following the 'wire' train, I noticed a voltage difference along it...One of those wires that din't get pinned to the wire right and the solder just didn't 'set', sure looked 'connectey' at a glance, had to be one, but it was a blob all over both wires, I surmize only actually physically connected to the top one. Big StrongBear Debug. Took many times the time I'd hoped for.
The other 'input re-wire' error was much easier to find, being as I wasn't relying on something I'd taken for granted that wasn't there.
For right now, I'm rewarding my extensive efforts, having a good 'ol time just using the BMF's with 'something' cooking distortion to get the inputs drive up, and a Mosfet Boost for recovery. The fact that all OA's are 'active' with source guitar or even 'thumbuzz' [touching the -input of each stage is cool, each stages 'frequency specific emphasis' can be heard]...I may choose to tune the output levels [EQ] using these sounds as a guide].
Anyway I'm just peached that I got this part of the circuit working, especially since it is the most foreign to me, even though the difficulties I encountered were not.
It's said: if it isn't broken, don't fix it, which maybe is true. Anyway, I took apart mine yesterday just to get rid of the 470pF cap, and bring it back to original state once more, I swapped the 1N4148 for 1N914 and added a 27k to the GND leg of treble pot 220k to match a 250k more closely and it sounds good too, not really much of a difference actually. Maybe, maybe the distortion is a little smoother with 1N914, but it sure is subtle. I like the brightness of the amp, without the added 470pF which to my ears hides some of the Marshall specific overtones. I think one should attenuate the highs in the cab sim instead if it bothers which it might do if you're using single coils and want a "smoother" sound.
Well, the unit sounds terrific in its original form; I know this from trying out different mods which actually don't seem to bring in any sonic improvements ::). I have tried different tone stack configurations, lots of capacitance changes, symmetrical/asymmetrical diode configs (with odd and even number of diodes) and more. But still, the original is the best so far. And yes, it's not the favorite unit to experiment on as petermoore said, new problems might arise if one's doing it on perf :icon_confused:
:icon_wink:
Quote from: krille2 on January 11, 2006, 04:49:56 AM
Well, the unit sounds terrific in its original form; I know this from trying out different mods which actually don't seem to bring in any sonic improvements ::). I have tried different tone stack configurations, lots of capacitance changes, symmetrical/asymmetrical diode configs (with odd and even number of diodes) and more. But still, the original is the best so far. And yes, it's not the favorite unit to experiment on as petermoore said, new problems might arise if one's doing it on perf :icon_confused:
:icon_wink:
Krille, I'm sure that you're correct - when used with the specificly voiced "cab sim" that it sounds "right".
I have only adjusted the preamp to use with my condor sim, which I'm now very happy with :D
I just needed to get rid of some high shrill content, but have not removed TOO much, there's still plenty
with the tone pot at 50% and above ...
My only other change is 2X 1N4148's by 1X 1N4148 for a bit of assym distortion, which I like better.
Great tones now, in particular from a HB pup gtr :D
MM.
Would love to here a sound clip (or two) from that one!
If i use a quad opamp, does it matter how do i use the discrete opamps in it?
I mean if i use 2 of 4 for the low level (guitar level) signal (near input) and 2 of 4
for the high gain (near output) signal will this cause any problems?
I am giving in to the temptation of building one of these - after I have tested it with two 9v
batteries which power supply should I use - a bipolar 9v or a bipolar 12v?
/Taz
you could build a variable voltage power supply. thats my plan. im hoping it will act simular to a tube amp with a variac. right now im using two 9 volt batteries. i only built up to opamp 13(non-cab out)and it sounds friggin' awsome going into the clean channel of my valvestate halfstack(1960a cab).perfect joe walsh and evh tones.
before you build, i suggest using a stripboard?(the ones for wiring up ic's). i got all my stuff from radioshack- i used seven tl082's and had to use multiple caps in paralel to get certain values.---tom
http://(http://img33.imageshack.us/img33/9494/jan15059ox.th.jpg) (http://img33.imageshack.us/my.php?image=jan15059ox.jpg)(http://img33.imageshack.us/img33/3382/jan15069fo.th.jpg) (http://img33.imageshack.us/my.php?image=jan15069fo.jpg)
Actually I've tried values from 9v -> 12v and I can say that there is not a big difference in sound as far as I can hear. If you go for 12v you may need to add another diode pair to GND. Go for a dual regulated psu.