Gemini III dual fuzz dissected

[digi2t]

First off, thank you Alex for the info above. I've been so wrapped up with the Ludwig clone of late, that I've just seen your post.

I had some time tonight, so here is a vero for us vero freaks out there;



It is unverified, but I've posted it so that maybe someone else can have a look and proof it. I'll be going over it as well over the next couple of days, but I think it should match up with the schematic. I also added the Millennium Bypass to it, as per the original. Chaosphere left it out, but it would be easy enough to leave out the extra parts to make it true bypass. I figured it's best to have it, and at least present the option. Chaosphere used my schematic to draw his (much cleaner!) schematic, so you can use his, or mine to verifiy the Mill. Bypass layout.

Please note as well, the two gain switches are dp3t center off, and not dpdt.

Cheers,
Dino

[digi2t]

Went over it again today, and found a couple of errors. Missing cut in the Mill. Bypass circuit, and Ge. tone section was incorrect. Now corrected. Everything matches up to the schematic, so if you downloaded the earlier version, discard and use this one.

Cheers,
Dino

[CynicalMan]

Ok, I think I understand the AC128/AC176 section.


The transistors produce a DC voltage over C18, but it drains most of the AC voltage to ground. So it mostly acts as a voltage source, at around 1.5V according to the build doc. That makes the two transistor stages act separately, like a PNP stage with a -1.5V supply followed by a NPN stage with a 7.5V supply.

But any AC signal that does get through will act as positive feedback. Since the capacitor has a higher impedance to bass, some of the bass isn't drained, so there's some positive feedback with the low frequencies. But also, the higher emitter impedance means that the transistors' gain is lowered for the bass. With these two effects combined, the capacitor boosts signals around 100Hz by 3dB compared to an ideal voltage source. I tried tweaking the values of C10, C11, and C18 in LTSpice, and I could get quite a bit of resonance.

I should also mention that the voltages for Q2 and Q3 look wrong in the build doc. Q3's emitter should be lower than its collector and Q2's collector should be lower than its emitter. Maybe the two got swapped?

[Indiefuzz]

I have been following this thread and must have read it 2 dozen times from start to finish. I have a lot of respect and admiration for you guys!

I'd like to challenge myself and give this build a try. I may be in over my head, but wanted to ask if anyone had any advice before I get started?

Is everything correct here? http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=47579&g2_GALLERYSID=ace1fcc31b7d711f6135f011d3090860

Is etching the best way to go? What size enclosure should I be looking to get? What effect does true bypass vs. Millenium bypass have?

I'm really looking forward to hearing your advice!

[Gus]

Alex

As you posted it does looks something like a Harmonic Percolator.  There have been threads about the HP at this site IIRC.

With this type circuit were there is only one DC current path thru both devices the biasing/selection of transistors can be a little tricky.  
The biasing of an grounded emitter transistor stage with one C to B DC bias/AC gain feedback resistor then having two in series from +9 to ground with the two emitters AC coupled to ground by the 47uf adds to the fun by how well it keeps the two gain stages from interacting with each other.

using the schematic from page one of this thread
Q7 bias really? 100K collector resistor with 100K volume control?
Q5 and Q6 1n4148 diodes C to B, why two, they are not AC coupled so how does the 2nd one conduct?

[digi2t]

I have been following this thread and must have read it 2 dozen times from start to finish. I have a lot of respect and admiration for you guys!

I'd like to challenge myself and give this build a try. I may be in over my head, but wanted to ask if anyone had any advice before I get started?

Is everything correct here? http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=47579&g2_GALLERYSID=ace1fcc31b7d711f6135f011d3090860

Is etching the best way to go? What size enclosure should I be looking to get? What effect does true bypass vs. Millenium bypass have?

I'm really looking forward to hearing your advice!

According to Chaosphere, over at the other forum, he's built it, and he claims it as verified.

using the schematic from page one of this thread
Q7 bias really? 100K collector resistor with 100K volume control?
Q5 and Q6 1n4148 diodes C to B, why two, they are not AC coupled so how does the 2nd one conduct?

I can look at it again, but I'm 99.9% sure it's laid out that way. Don't ask me why though, I'm not that smart. 

[digi2t]

Verified diodes, and schematic is as advertised.

[digi2t]

Vero is now VERIFIED!

Here is the updated vero, there were some additional corrections where caps were concerned. Also, I went with Russian Ge trannies on this build. I found that it was easier to find good trannies (read, NOT LEAKY AS ALL HELL), and they gave me a much beefier fuzz than the AC128/AC176 combo. I also teeter-toddered on Q5. I wasn't thrilled with the 2N2222 in this slot, but I found that a 2N3700 sounded better. Then, I tried a BC109B... NIRVANA! Anyway, you can really experiment with different trannies here, sky's the limit.



Here's a video of how it sounds. I'll tell you right now, the Ge side on my clone has quite a bit more fur on it, but you can dial that down a bit with the trimmers. Personally, I like more fur. I have two caps subbed here, since I didn't have them on hand, a 680nF, and a 120nf. The 680nF is 660nF (2 x 330nF's), and a 120nF is a 100nF.

As I mention in the video, the 1nF cap (C1, input to ground) is a Polystyrene in the original unit, and I used one here as well. I was never one to dwell on the mojo hype that one cap sounds better than another blablabla, but in this case, the difference is day and night. Period. I had a metal film brownie here to start, but it sounded dark and bassy. Pop a polystyrene 1nF in here, and wow! BIG difference. Besides, the one I used was from an old Farfisa organ, and it has "DUCATI" marked on it. Now how exotic is that.

Honestly, I like my clone better than the original. I mean, the original is great, but my clone just flat out rips!

Cheers,
D.

[dorrisant]

Great job Digi2t, good to see you verify for the Vero board guys... I will have to try this on my pcb trace... most of the parts are in, just waiting on a couple of caps. Looks like I need to get the right input to ground cap.
Would you let us know where you are sourcing your Russian transistors... I like more fur on tap as well...
Again, great job!!!

Tony

[digi2t]

Great job Digi2t, good to see you verify for the Vero board guys... I will have to try this on my pcb trace... most of the parts are in, just waiting on a couple of caps. Looks like I need to get the right input to ground cap.
Would you let us know where you are sourcing your Russian transistors... I like more fur on tap as well...
Again, great job!!!

Tony

Thanks Tony, I had a lot of fun with this one. It a VERY versatile fuzz. I can`t stress enough about the importance of the input to ground cap. Normally, I`ve never noticed a difference between caps, so I`ve always gone with whatever I`ve had on hand (read: cheapest). But, in this case, hearing is believeing. Lucky for me, that old Farfisa organ I tore down not long ago had a few of them. The difference is day and night. I can`t explain the science behind it, but the difference between the two 1nF caps is almost surreal. I even tested them on my cap meter to be sure, and both registered 1nF. Crazy.

As for the caps, Ebay is my friend here. The best ones I`ve found to date for fuzz are MP20B`s. MP16`s are OK as well, but lower gain. GT402`s are nice, and for NPN`s, GT404`s. As for consistancy, MP20`s are tops. They`re my fav`s in the 70 - 90 hfe range. GT402B (or V I believe) come in second for the 100 - 130 range. The GT404 tends to hover around 90 - 120. Gain ranges are generally fairly good, and leakage low to nil. Likewise for the MP16`s. GT402`s are a bit looser, and GT404`s tend to stray quite a bit. But, compared to what I`ve seen so far with AC128`s, and AC176`s, they`re way ahead of the game. Lots less garbage. They do exhibit more hair though. Fuzzier, with a bit more wooliness to the tone. Check out pinkjimiphoton`s Liberal Komrade, you`ll clearly hear it. Nonetheless, for the price, nothing you can`t deal with, either with a different cap, or the EQ.

[dorrisant]

Digi2t,

I have to ask... Would you be willing to part with one of those caps you found in the old organ? I'm putting together the final parts order for three different pedals and that is one of the few caps left to get.
If you don't want to part with any I can totally understand. PM me if you will.

That said, thanks for doing what you've done for this project. I for one will be hearing what this pedal has to offer very soon.

Cheers,
Tony

[digi2t]

Digi2t,

I have to ask... Would you be willing to part with one of those caps you found in the old organ? I'm putting together the final parts order for three different pedals and that is one of the few caps left to get.
If you don't want to part with any I can totally understand. PM me if you will.

That said, thanks for doing what you've done for this project. I for one will be hearing what this pedal has to offer very soon.

Cheers,
Tony

Sorry Tony. I've only got a couple, and I'm saving them for other projects. A quick search reveals that West Florida Components carries them, 25 cents each. I've dealt with them on several buys, no worries there.

[dorrisant]

Thanks man... I'll look them up!

Tony

[onthetundra]

Hey I put this vero together and I have a couple of questions/issues:

1.  The tone switch as wired does not alter the sound at all.
--I'll try a different switch but Im not getting any change with this the way it is

2.  My silicon switch alters the sound at both ends of the blend.  The germanium switch barely makes any difference at either end of the blend.

3.  Can you please reconfirm the transistor numbers on the vero layout?  I figured it out by looking at the schematic but maybe you could make it clearly labeled.

4.  My LED doesnt turn off with the millenium bypass wired the way it is. 
---I think I'll just wire it for 3pdt true bypass.

So far I love this thing.  I built it without the ferrite (I ordered some) and it sounds good but I'd like to get the issues figured out before I box it up. 

Excellent work tracing and creating a layout.

[digi2t]

1.  The tone switch as wired does not alter the sound at all.
--I'll try a different switch but Im not getting any change with this the way it is

I assume that your talking about the tone reversing switch. It`s only effective on the Ge side of things. The more you blend towards the Si side the less it effects the tone. When you`re completely on the Si side, it does nothing. This is as per the originals. I`ve verified this.

2.  My silicon switch alters the sound at both ends of the blend.  The germanium switch barely makes any difference at either end of the blend.

Ensure that you`re using 3PDT switches that are ON-OFF-ON. Also verify your wiring between switches, the blend pot, and your vero. Everything works fine on mine.
*EDIT* - When the blend knob is working properly, the Ge gain switch, or Ge side as a whole, should not affect the Si side, and vice versa. For example, if you are completely over to one side, you can pull a tranny out of the other, and you should not hear any difference or drop out.

3.  Can you please reconfirm the transistor numbers on the vero layout?  I figured it out by looking at the schematic but maybe you could make it clearly labeled.

I must admit that the tranny labels in DIY-Creator are a bit weak. I`ll superimpose more visible labels on them, and re-upload the vero.

4.  My LED doesnt turn off with the millenium bypass wired the way it is.  
---I think I'll just wire it for 3pdt true bypass.

I`ve yet to verify this, I haven`t had time to. I`ll test it tonight, and get back to you on that one. It`s my first time using MB myself, so I`m still a virgin here  . You can easily wire it for TB as well. That`s what chaosphere did, and that`s how it`s written up in his build doc. I`m just trying to keep it as per the original.... somewhat  .

On the transistor front, I`ve been playing with the Si side, and I have a new fav combo. BC547B/BC109B/2N3700 sounds amazing. This combo has more bite to it, really making it more distinct from the Ge side. This also adds more spice to the blend knob. The added bonus is that the Si side is much quieter as well at full gain. I don`t know what it is about 2N2222`s, I`ve never had much luck with them.

I`m also going to test an idea tomorrow, to replace the Lo/Med/Hi gain switches with pots. If my idea works, it will be the ultimate in dialing in the perfect fuzz tone. And it won`t take any more room in the box either. Stay tuned.

[digi2t]

AAARRRRRRRGGGGGGHHHHHH!!!!!
Heads up everyone. The diode D4 for the Mill II bypass is the wrong way around on my initial verified version of the vero. I've updated the vero, but anyone that has downloaded the previous version, ensure that the cathode of the diode is going to +9v, AND NOT TO THE GATE OF THE 2N7000.

Not only will it not work, but you will instantly fry the 2N7000 upon application of power. If anyone has already built this, and the LED is staying lit all the time, this is the problem. Turn the diode around, and replace the 2N7000. Upon doing so, my LED works fine now.

Sorry everyone. It was marked correctly on the schematic, but it fell under my radar when I drew up the vero. I've re-uploaded the vero, with the diode facing the right way, so please double check your version. Everything else is fine.

As for my idea of using pots to work the gains, rather than switches, it dawned on me that there is DC flowing here. Any movement of the pot will produce noise in the circuit. I'm not sure if there is a way around that, but I don't feel like doing a redraw here. There's enough to this baby as is, I'm more than happy to live with the switches.

[dorrisant]

To make omlets, you must break some eggs!

[onthetundra]

I fixed the LED issue with turning the diode around and replacing the mosfet.

I fixed the germanium switch issue by putting an npn germ tranny in for Q3.
I messed up and had a pnp in there. 

Now it sounds BADASS!!!!!!!!!!

This is a MUST build for everyone.  One of the coolest fuzzes Ive done in a long long time.
Thanks for the great work tracing and doing the layout.

[digi2t]

I fixed the LED issue with turning the diode around and replacing the mosfet.

I fixed the germanium switch issue by putting an npn germ tranny in for Q3.
I messed up and had a pnp in there. 

Now it sounds BADASS!!!!!!!!!!

This is a MUST build for everyone.  One of the coolest fuzzes Ive done in a long long time.
Thanks for the great work tracing and doing the layout.

No problem. And guess what... I have a WOW Signal fuzz on the way to my work bench. Stay tuned for another layout. Have fun with the Gemini, it really is a "Fuzz for all seasons". Glad you got the bugs worked out. Please try an post a sound or video clip if you can.

Cheers,
Dino

[dorrisant]

You are the Spaceman source! Please PM me when you start the WOW thread!

Tony