Here is a quickie. The right pot on the proto in the simple tone control from my first link with no presence. The left pot is gain. The Joyo Crunch box has the presence full so it is basically not in the circuit anyway. Sorry, I never know what to play in these vids. I'll do a better one when I have an 833 chip which may be brighter. This has a TL072.
Got a schematic of it? I put led's in the feedback of this one which is all original:
Oh, and I tried swapping the 100K bias resistors for 22K like the original Crunch. No difference in noise or sound. Maybe the 833 chip doesn't like it. I receive those tomorrow. Why would they want to drain more battery I wonder? Maybe habit from 741 op amp days, or if the voltage gets low.
« Last Edit: April 24, 2012, 07:52:00 PM by Goodrat »
After looking at how the Joyo does the bypass, I thought I would also kill the op amp input in bypass. I also decided I like the simple tone version. I did not receive the 833 so I don't know if I'll need any changes for it.
BTW, don't ignore the capacitance of any LED's you experiment with. Back to back 3mm are about 25pF and I think 5mm are 100Pf.
« Last Edit: April 26, 2012, 03:33:34 PM by Goodrat »
Thanks for the heads up on the JOYO version. Just got it in the mail and it sounds very good. Much like the lead channel of my tube amp. According to LT Spice sims, the Tone and Presence control sum together in resistance and capacitance, rather than creating a sharper/different roll off. You may want to leave off the Presence and change the Tone cap to .01-.033uF depending on issues. C8 can also be raised or lowered for more or less Treble.
Putting the LED's in the FBL of the second op amp has a smoother rounder tone IIRC. Instead of both the op amp and LED's clipping, it is just the LED's. Nice tone.
A hum I was trying to squelch was just the way I was grounding. You have to be suspicious of these experimentor boards. I wasn't crazy about the resistor though on the 9V input, even though it works very well. So I am back to a Schottky in series and put C1 back to 100uF. C2 can stay at 1uF. The 5819 schottky has a low Vf at these low currents. About 0.2V and I have a big bag of them. Some may want to use them when experimenting with germanium diodes. I'll play with the feedback cap C8. 100pF does seem high. The LM855 came today and yes, it has less hiss at full volume. All else looks fine. At this point it needs to go in a box. The drawing are updated again and dated 4-27-12.
Yeah, I find myself running to Radio Shack from time to time. Those caps are pretty good just expensive and they only have certain/limited values in the store..
I get most of my stuff from here. http://www.thaishine.com/servlet/StoreFront Sometimes they have my orders at my door in 3 days, no more than 4 days and shipping is always free! They don't carry some special stuff but they have just about all you need and they are here in the US.
Mouser took Sunday night order, to Friday on Priority mail. I thought that was slow. I just put the two on the a scope with a signal gen. Perfect! Both have the same response. The Joyo tone CCW cut the lows a little bit more but that is good. I get more play on the high end with mine. I think it is interesting how they control the gain to both stages with the same pot. When I saw the schematic I wondered why they did that. I think the Crunch box does a good job of keeping the character of the guitar without a lot of bad inter-modulation when playing chords. I think the presence control is not needed. So, this was fun. The design is a keeper.
I retrack what I said about the Tone and Presence controls summing. They have slightly different overlapping action. Looking at the original Matsumin version, The Tone control is similar to a Rat and rolls off the highs at 6db/oct. The Presence control is more of a shelving control that lowers mids and treble, but leaves the bass. I'll sim tomorrow and report back some more. Going to Rock On at the Norman Music Festival at the Midnight Hour.
I still think something is different here. It is not the bias resistors or supply caps. I tried substituting and even simulated the presence full up like in my Joyo. The only variation now is whatever LED's they used.
Yeah man, I looked at it real quick seems to look good! I will tell you what I have done differently from the original - 500k for the gain pot and either 2 red 5mm LED's or 1 yellow 5mm and 1 red 5mm LED. I didn't really like the 2 yellows but that just maybe the cheap radio shack LED's I don't know? In any case it sounds excellent...! I really like the 500k for the gain and I use that all the time now when I build one of these.. I have built 5 of them now, killer pedal!
Simmed the tonestack with LT Spice and the Tone and Presence interact a lot. The Tone control has the greatest effect with the Presence altering the roll off slop. For the least mid-range, try the Presence trim pot about midway. Might increase the cap in the presence control, to 47n for more action. The 220n cap can go up or down for more or less bass and gain. The 100pf cap in the first FBL could go down to 1n or more to reduce some highs and further smooth things out.
Might suggest a single 2N7000 or BS170 for clipping diodes.
Might try the diodes in the FBL in the second op amp.
I'll look into that. Down to 1N? Don't you mean up? (1000pF). I hate the nano farad thing. It makes me do math. OK, I know the difference now. The "Stupidly wonderful tone control" extra resistance was somehow cutting my highs slightly. Which doesn't make much sense since the volume control, if not at max, would do the same thing. It is a very slight difference. I can hear my higher strings slightly better. So this is a mystery, but in any case I changed my drawing to a typical tone control by shorting the wiper to the cw leg (or moving one wire). Now you have to tweak the volume if you change the tone, but it sounds better. Ever so slightly, but better. Update: Nope, I can't do it. Maybe it was my imagination. Maybe it's the orange paint
« Last Edit: April 28, 2012, 10:41:33 PM by Goodrat »