Just some Crunch updates

[Goodrat]

I Thought I would post my latest on new thread.

This one has lower resistor values and caps adjusted for same response.
http://www.rickviola.com/images/CrunchLowNoise050212.jpg
http://www.rickviola.com/images/CrunchLayoutNoPres081112.jpg

[Goodrat]

Forget the links, just go direct to the bottom of this page:
http://rickviola.com/electronics.htm
I'm still playing with the clipping LED trying to find the best choice.
There are all kinds of red LED's with various Vf's. Saying a 3mm is not as good as a 5mm is not always true. It depends on the specs. Red however, usually start earlier.
I will probably go with a 3mm that is spec'd at 2mA and Vf of 1.9. (TLLR4401). I measure Vf at 1.7V with a dc supply (not sure why) and it sounds fine.
The LED will never see above 3mA (true rms measured) with the 470 ohm in series after the op amp so an LED with an absolute max spec of 7mA is fine.
I am ordering a 3mm, 20mA, 1.85 Vf to see how that clips at low currents. (mouser 604-WP710A10SRD/D).
I have not found an actual part called out in a parts list for the crunch box. I'd like to see that detail.

With scope at diodes and 1KHz sine wave input with known pat #'s of LED's I have:

Reference Joyo Crunch box: starts to clip at 1.7Vpk.
My circuit with MV5754A,  5mm, spec 2.0 @20ma: starts at 1.7Vpk.
My circuit with TLLR4401, 3mm, spec 1.9V @2mA: starts at 1.6Vpk.
My circuit with MV577C, 3mm, spec 2.0V @20mA: starts at 1.7Vpk.

[aron]

Thanks for sharing this.

[Goodrat]

I edited with added info.

[askwho69]

wow you're goodrat i'm interested about the antennae hahaha i'm gonna make 1

[Goodrat]

The 4-bay works a little better that the Hoverman BTW.

[Goodrat]

It gets hard to tell what sounds better. That Joyo sounds awfully good. So it seems that my goal is whatever red LED clips at 1.7V.
Looks like I have some samples to buy.
But it seems, though further testing, that even though the diode test on digital meters supply only about 0.2mA, what you measure on such a meter will be close to what you will get at 2mA which is present in a Crunch Box circuit. Led's that are rated for 1.9 to 2.0V  forward voltage at 10 or  20mA should give you the desired 1.7V forward voltage at 2mA.
This is important for just the right amount of distortion. It does seem 5mm (T1 3/4 size) meet this requirement more often, but there are 3mm (T1 size) also if you look.

[Goodrat]

After some testing, it looks like I will be doing some changes. I just could not get it to sound as good as the Joyo clone with the simple tone control. It is not the fault of my lower noise values. It is the tone section at fault.
The cap and resistor, (presence) really makes more of a difference than I thought. I have to simulate that and see a graph. What I will do is use the usual tone control connections and add a cap and resistor to simulate the presence turned all the way up, which is where my Joyo is set and the way I bought it which sound very good.

[J0K3RX]

The cap and resistor, (presence) really makes more of a difference than I thought. I have to simulate that and see a graph. What I will do is use the usual tone control connections and add a cap and resistor to simulate the presence turned all the way up, which is where my Joyo is set and the way I bought it which sound very good.

I agree. The presence makes a big difference but I leave the presence all the way up or close to it all the time, so really no need to add an extra pot. On some amps it will sound a little too bright so I turn it back just a little. Kinda curious what is going on inside the "Super CB" http://www.mieffects.com/blog/?p=100

[Goodrat]

Then again, I try it the next day and I do not see a difference. Then I wonder if I had a bad connection.
If you have the presence all the way up, there is no way it has to be there, looking at the schematic.
So then I try the WSTC tone control again. Tone and presence  all the way up (as I like it) should not make a difference if I short out the last two legs, or not short like the WSTC. But there is a slight difference due to the pot not really zero at full up. So, I think I will just short out the two legs like a standard tone. Easier to draw and build anyway because the cap ends up across the volume control.
So I updated my drawings again for this lower noise crunch I'm working on. I bought all the actual parts I called out on my parts list and I will make a Youtube.

[Goodrat]

To add tho that...
I researched and experimented a lot the last few week or so. I'm ok with using the 100K's for the bias divider with a 2.2uF cap. THis will draw less current. There is definitely less hiss with the lower value resistors in the feedback, keeping the same gain and with all the caps raised accordingly for identical frequency response.  The parts just cost slightly more, but I'm not making a production lot. I'm using a 3mm LED that clips at the same point as a 5mm. Just to prove size doesn't matter
Why do I spent $40 to make what I could buy for $30? The challenge I guess.
One thing was interesting... with better op amps that I have than the 833, one side of the wave would clip way before the other. I don't know why that is. Also, the high freq roll off on my lower values is at almost 3K rather than the expected 1.6KHz. That is driving me crazy. Maybe it is the experimenter board because the calculations are correct. The  Joyo rolls off at 1.6KHz at -3db. So my tone control just needs to be turned left a little to get an exact match to the Joyo.

[Goodrat]

Don't you love when people double and triple post ?
I had to just come on and say that dropping the op amp resistors and raising caps accordingly, is probably too much trouble than it is worth.
Even though technically, all should sound identical, I plug in the Joyo clone and I just go ahhhhh, that's the tone.
There is a subtle difference, even though I calculated everything to death.
What I will do is keep the supply mods to the bias and use original circuit values. Updating my web site soon.
Therefore all I can contribute is less current draw, an alternate layout with easily available better parts, some knowledge about a few "what -if"s and fun spending slightly more than a China clone.