dual circuit blending. muddy...

[jethrofloyd67]

Ok I might be completely off, but I want to make 2 drive circuits in parallel and blend between them.
This is basically what I've come up with so far, and I can't figure out why its so muddy and it gets worse with quieter input levels.
Both circuits work fine by themselves, but once I connect the input caps it just goes to mush.
What am I missing?

[thelonious]

Both circuits work fine by themselves, but once I connect the input caps it just goes to mush.
What am I missing?

You will have a lot better results with actively splitting the signal and blending the two circuits, rather than passively blending. When you connect them together in parallel, the combined input impedance is much lower because the guitar (or whatever the source is) sees the input impedance of the two circuits in parallel. The Runoff Groove Splitter/Blend would fix you up, I think, but it would also make your circuit a lot more complicated. That's probably what you'll have to do, though, if you want good results.

[jethrofloyd67]

I would like to keep it simpler than that if possible, but could you explain how splitting to 2 input buffers is better/different than splitting the output of 1 input buffer?
I tried a boost infront of it and was able to get some more normal range tones by adjusting the volume, too high though and it got really thin and harsh.

[GibsonGM]

If you passively split your signals, you're at the mercy of the input impedance of whatever active device you send them to; this is probably why you're noticing mud at lower levels - you're changing your output impedance as well as input.   The mixing that occurs in the device can cause some of the muddiness you're talking about, too.   Phasing issues and such can be at play, if you go thru any caps or RC sections.  You have a complex signal made up of many frequencies...it will *divvy up* unequally in such a situation - you're noticing this with the passive setup, the thin/harsh battling with mud.

Really, the ROG splitter, with 2 buffers, is anticipating 2 'functions' to occur in between the sends and receives.   Imagine 2 sets of tone controls (or active circuits), and then the signals get blended after.      This is a good way to ensure you have 2 separate signals that are ISOLATED from each other, which a passive splitter can't guarantee.  This way, you get 2 near exact copies of your input signal, and guarantee each effect will *see* the real deal.

Worth experimenting with, for sure, but keep in mind that you need 2 very different signals to really hear much of interest in parallel, IMO....like a fuzz and clean....seems like you're on that path anyway, tho.    This is the way to go, for sure, IMHO.

[thelonious]

+1 to everything Mike said. It is possible that with the right two circuits, with effects of the right impedance before and after, you could get them to blend passively in a happy manner... but you're going to be left with an effect that is super sensitive to what you plug into it.

So: If your goal is to have an effect that gives you reliable results in different situations, you should mix the circuits actively. On the other hand, if you're just looking for a one-off that works for you, you might be able to fudge it. If having a boost turned on in front of the circuit makes a difference... I would try putting AMZ's JFET splitter at the beginning of the circuit to see what happens. It might even work with just a single JFET buffer instead. But keep in mind that when you're trying to fudge things, you're going to have to breadboard a lot and prepare to be frustrated. It looks like a more complicated solution to use the ROG Splitter/Blender, but it might be faster and less frustrating than the alternative.

[duck_arse]

+1 for everything said.

but, my first try would be a single transistor buffer, jfet or bjt, and put a resistor from the buffer output (emitter/source) to each of your 100nF input caps. start at 22k each. (it will end up looking like mirror image of the output caps and mix pot.)

why not?

[jethrofloyd67]

I tried a single jfet buffer with 10K resistors off the source to each coupling cap and it works great now.
I suppose if I have more trouble I can try double buffers but right now its sounding just like I wanted it to!
Thanks so much guys!

[GibsonGM]

+1 for everything said.

but, my first try would be a single transistor buffer, jfet or bjt, and put a resistor from the buffer output (emitter/source) to each of your 100nF input caps. start at 22k each. (it will end up looking like mirror image of the output caps and mix pot.)

why not?

^^  The most simple solution.  And most often, that's the one that we want!   Very 'cathode-follower-like', D.A. 

Thelonius hit on an aspect I didn't mention, which is the "you don't know what will get plugged into this" angle....what might be ok with one guitar can sound like &ss if you use another....using active components (buffers) makes your effect PREDICTABLE, so it will behave in a similar manner each time and not be victim to what you plug in.
That's priceless! 

Glad it's working out, Jethro!

[duck_arse]

I surprise myself, sometimes.

I was thinking about this today, I don't know why, and thort "the 2 added input mix resistors could be replaced by the output mix pot, and the output mix done w/ fixed the R's", like arse about. I thort other stuff as well, I won't bore youe wit dat.

carry on, nice to hear it goes good.

[thelonious]

I tried a single jfet buffer with 10K resistors off the source to each coupling cap and it works great now.

[jethrofloyd67]

Thelonius mentioned my exact problem, the original circuit sounded almost perfect with my bass but it has a very hot pickup and everything else sounded like junk or nothing at all. Now it sounds very close to before with the bass but it works with other guitars too.
I had thought about the mix pot at the front, but I imagine that would make a kind of "see-saw" gain effect between the circuits. which could still be cool.
I definitely want to play with the values of the fixed resistors though, and I might turn the buffer into a boost and see what that can do for me.