Obsidian- a slight problem

[Alex C]

Hello.  I just got done breadboarding Joe Davisson's Obsidian Overdrive- the 2N5089 transistor version.  It sounds great for single-note leads on the high strings, but from about the open A string down it sounds a bit "dark, thick, and muddy."  I know these descriptions can mean very different things to different people, so I'll try to explain.

On sound clips that I've heard (from Ampage, Runoffgroov, etc.) there seems to be a significant amount of treble even in the low strings, and it seems to "cut through" very well.  That was the sound I was looking for.  Everyone was playing Van Halen-type riffs with lots of palm muting that really stood out well, but my palm mutes sound muddy.  (Yes, I tried adjusting the tone control. ) My guitar is a PRS Swamp Ash Special with a maple neck and fretboard, a relatively "bright" guitar, so I'm pretty sure it's not the instrument.  

I'm fairly inexperienced at "tweaking," so I'm not sure what to try to clear up the lows.  I used ceramic disc caps for the picofarads, poly film for the .01s, and I think ceramics for all other non-electrolytics.  I know that film caps are known to be clearer, but I don't know if that could be it.

I was just thinking, and I have another idea.  Another way to describe the sound of the lows is that it's on the very edge of "sputtering."  A while ago I built a "Multi-Face" or "More Face" or one of those (I think by Jack Orman?) and there was a trimpot to set the bias to accound for differences in transistors.   When it was misbiased, it would "sputter."  My obsidian sounds like it's just on the verge of that.   Could that be it?  Do I need to adjust the collector resistor (that's the one that goes to ground, right? - I still have trouble with the pinouts.)?  I would appreciate any ideas or help or suggestions.  Thanks!

[RDV]

Adjusting collector bias will help, but I think you're still going to have a similar sound going, especially if you run it into a slightly distorted amp. I'm going to unbox mine and use the box for a better circuit. I thought I would get a Heavy-Metalish rythym out of the circuit, but nothing could be farther from the truth. It sucks. Useless 'live' through an amp. I'm not impressed by any of the obsidians.

Regards

RDV

[Marcos - Munky]

Mine works very well. Did you tried the audio probe? Maybe the problem it's in the solder of one tone control caps. Mine looks the opposite of Ricky's obsidian, very heavy-metalish (cool to play death/trash metal) and great live through an amp.

[Jered]

Nobody mention what amps they are using. The obsidian going through an already heavily distorted amp is going to sound awful, gating/clipping sounding like its cutting out almost.  The Obsidian with a cleanish Fender type amp sounds aggresive and heavy but still fairly tight.
   Jered

[RDV]

It doesn't work with my JCM900. I can't use that amp completely clean, it just sounds awful that way. I must have spent a hundred hours debugging the obsidian also, but never finding anything wrong.

Regards

RDV

[WGTP]

I have found that reducing the the bass on the Black Fire makes it much smoother.

Try reducing the 10uf cap in the first stage to 2.2uf or 1uf.  I bet that will smooth it out at a slight loss of drive.  Let me know  

[Alex C]

I'm playing through a 100 watt Carvin MTS 212 tube amp, and for testing I keep the volume low on the clean channel.  

Here's some good news:  while messing around (I'm not sure you could call it "debugging") I noticed that the Tone knob added bass as I turned it clockwise.  I know there are differences in tone controls, with some acting as a filter and cutting bass as it's turned clockwise, and others the other way around (adding bass).

So I switched the points of contact of the  outer lugs of the 100k tone pot.  Nothing changed, just the direction of the bass cut.  But I was moving the wired around and one came loose from the breadboard socket.  I was playing through the circuit at the time and right when that happened, everything cleared up instantly, and it sounded tight and trebly and midrangey and also had solid bass.  I couldn't believe it!  It was perfect!

The one that had come loose was lug 1 when looking at the shaft side with the lugs facing towards you the one on the left (sorry, but I've seen different numberings of pot lugs and can never be sure).   When I reconnected it, it was muddy again, and adjusting the pot didn't help.  So, I'm thinking that if I tried a larger value pot, there would be more resistance when rotated clockwise, and therefore closer to the "disconnected" sound, right?  The only problem is that the original schematic called for a 50k pot for tone, not 100k.  So, using my idea, wouldn't it be even muddier at only 50k?  

Also, when the gain pot is maxed, I get a lot of squealing, but turned down about 5-10%, it stops.  Is this because it's a high-gain circuit layed out on a breadboard (no RF shielding) with long wires?  

I'm glad that this happened, and I hope my hypothesis is correct.  Tell me what you think.

P.S.  -RDV, I would recommend maybe trying something related to this if you haven't already trashed the circuit, because the sounds I'm getting now are great!  


Like Bob Ross says, we don't make mistakes, just happy accidents.

Alex

[Alex C]

ignore this post

[Marcos - Munky]

I don't remember very well, but I think I used a 47K or 50K pot. I will take a look and tell to you. Congrats, you finish a great effect. Mine have this noise when the gain it's on max, and in my effect the gain it's always on max (I didn't used a pot). I think this is because the circuit have high gain, and my guitar teacher said that a noise gate will help alot to take of the noise.

[Marcos - Munky]

I think I used a 47K or 50K pot.

I was wrong. I checked my Obsidian, and I used a 100k B mini-pot.

[RDV]

Without a Hfe tester, putting transistors in a circuit like this one is just shooting around in the dark, strictly a matter of luck if you can cascade the gains upward like we'd all like. I changed out the first 10uF cap with a 2.2uF which seemed to help the low-end response to become smoother, then I replaced the .0033uF I had in the tone control with a .22uF which took some of the high-end super-screech out. It now sounds pretty good through the small amps in the house, but I have yet to try it 'live' through the Marshall. If it still doesn't work , then I'm going to put an eq like in Aron's Smashdrive(3-band) on it & try it again. I really had wanted this circuit to work out for me as I had heard many good things about it, but have been thoroughly frustrated so far. I use this type sound for a part of our show, getting it with the high-gain channel of the JCM900, but had hoped to do it with the Obsidian instead. My disappointment had tempered my previous remarks. Anyone who wants to build this circuit should do it, though I think the transistors should be gain checked and installed from lower to higher gain as you go through the circuit.

Regards

RDV

[Quackzed]

i put a marshal style tonestack on the end of mine (transistor version) and it worked great. i still have to write up a proper build report, just thought i'd chime in... it's still very bassy and i generally keep the bass knob on @ 2 or 3 -just about where the low low bass is barely there, also gets a good scooped sound with the mid knob down and the treble way up and dial in bass for your rig...i just left off the tone section at the end and subbed a "duncan tone stack" marshall style tone cntrl... the volume was still WAY too loud so i'm gonna try out some voltage divider thing and try not to lose the high end...maybee a bypass cap on the top half of the divider ,kinda like you do on guitar volume pots to not lose high end as you roll off the volume...i dig this circuit... lots, LOTS of gain! mine's real quiet as far as noise/gain ratio. ps make that 4.7M resistor at the front 'short' and close to a ground trace/wire. i had it on aligator clips at first and it was NOISY,

[WGTP]

Reducing the input cap or a cap between stages could help.  Try a 10n or 1n to start with.