Buzzaround build....

[digi2t]

Yes, GE, in this case, stands for germanium (not General Electric).

Don't get TOO hung up on the model number. Different models generally have different maximum voltage characteristics, but the important thing here is the forward voltage of a germanium diode, which is lower than silicon. As a clipping diode it clips less harshly than silicon, giving a bit more of a rounder fuzz, and less signal loss. The edges of the clip are rounder, and the Buzzaround is already.... buzzy?, enough, so using a silicon diode might make things a bit too harsh. Unless that's what you what. Test both, and use what your ears like.

Insofar as which model Ge diode is concerned, I doubt you'll hear a difference between a 1N60, 1N34, 1N270,....... (insert Ge model number here). Use something that looks the part.

[mcknib]

As digi2t says it's doubtful you'd hear any difference one of the things to watch out for with diodes is the wattage, higher wattage usually means thicker legs.

I was taking it, it was the look you were going for although I don't believe most of the hype about mojo I too always go for NOS parts on tag board builds sad man that I am! I got some of those 4148's too just because the light blue ones look a bit different and at 20p each, why not?.

You should of course always check the datasheet for dimensions if you're not sure or it's not indicated you can always e-mail the vendor.

If you watched the video you can see from the o scope images how the GE signal clipping is more rounded

[PorkyPrimeCut]

As you both so clearly put it, it's the look of a pedal that makes it sound better, right?

The joke of itis that there's every chance that the priciest "mojo" part (The NKTs) might not be suitable. I received a new DMM this lunchtime & it has an HFE reader. Once I've butchered a 9v battery from another pedal I'll see just where I'm at with all this.

I'm chomping at the bit now. Other than WIMA caps coming from Poland, everything else is good to go. Oh, there's some fancy knob dial plates but they were through Aliexpress (yes, I know) so I'll no doubt get them in about 6 months, if ever.

[mcknib]

DMM hFE's aren't accurate they don't take leakage into account so I wouldn't worry about that it's all about how they sound if you got them as a matched set at the recommended hFE's you should be cookin' and you can always use digi2t's link to his build to adjust certain components till you like what you hear.

or go to geofex.com and make up the little testing circuit under - fx skills / how to's and then  -selecting germanium transistors for leakage and gain for your fuzz face clone.

[PorkyPrimeCut]

DMM hFE's aren't accurate they don't take leakage into account so I wouldn't worry about that it's all about how they sound if you got them as a matched set at the recommended hFE's you should be cookin' and you can always use digi2t's link to his build to adjust certain components till you like what you hear.

or go to geofex.com and make up the little testing circuit under - fx skills / how to's and then  -selecting germanium transistors for leakage and gain for your fuzz face clone.

Damn cheap-ass DMMs!! The HFE tester doesn't even work.

It turns out I've already got a transistor socket, red & black croc-clip leads, a battery snap & a mini switch so I'm heading down my local Maplin tomorrow (I usually avoid them) to pick up some resistors, then I'll make that testing rig.

I'm curious, if these NKTs end up being a matching set & have low leakage will they be usable. Similarly, if the HFE for each is level & below the desired amounts, is it really worth using them?

[mcknib]

Yeah they'll be useable maybe not ideal but look at digi2t s link there's lots of good pointers in there, lucifers trip is one of the fuzz guru's on here and perhaps use SIL sockets to experiment you can change resistors and wot not to compensate for hFE / leakage sometimes Q3 I think it was works better with a little leakage perhaps electric warrior will come in and advise too

[digi2t]

Take Billy's advice, and go with the Geofex method; http://www.geofex.com/article_folders/ffselect.htm

Or, if you're lazy (like me), get one of these;



It does jfets, mosfets, silicon/germanium transistors, and diodes too. Made in the UK.

Here are the final gains/leakages of my build, along with the voltages. As Billy points out, this circuit works best with some leakage on Q3. As you can see below, my Q3 had twice the leakage of my Q1 or Q2;


MP16B's for Q1 and Q2, with a nice phat GT402B in the Q3 slot.

Measured with a Peak DCA55 meter, room temperature (20 deg. C) the transistor gains/leakage re as follows;
Q1 - 61 / 0.04mA
Q2 - 64 / 0.06mA
Q3 - 112 / 0.12mA

My final voltages are as follows. Guitar plugged in, with guitars volume at zero, pedal plugged into the amp, all pedal controls at maximum;

Supply voltage = 9.08v

Q1
E - 1.472v
B - 1.535v
C - 4.90v

Q2
E - 1.366v
B - 1.472v
C - 4.90v

Q3
E - 0.0mV
B - 26.3mV
C - 2.265v


Like Billy mentioned, solder some SIP sockets onto the lugs of your board. Then, sort out all your transistors into the three categories (Q1, Q2, Q3's). Record all the gains and leakages, and arrange into lowest gain/leakage to highest gain leakage. I tend to find when dealing with the same type of transistor that gain tends to climb with leakage. Once you have them all in order, you plug them into the sockets, and start auditioning them in your circuit. Lowest gain/leakage in Q1. Same or SLIGHTLY higher gain/leakage in Q2, and the highest gain/leakage transistors in Q3. The emphasis for Q3 is on the leakage. I found that about double the leakage of Q1 or Q2 works nicely, but not so much leakage that it's noisy, farty, hissy, or just plain sounds like crap.

Not very scientific, I know, but it does provide for hours for fuzzy fun.

[PorkyPrimeCut]

Seeing as Maplin sell SIL strip I'm going to rig up a kind of Q1, Q2 & Q3 tester by marking out the strip into 3 sections & attaching jumpers to the corresponding sockets on the tagboard.

something like this....



There's every chance I'm going to be swapping at least one resistor out at some point but I want to keep everything as compact as possible. When I start having wires all over the place I start making stupid mistakes. I understand the use of breadboarding but it looks like a nightmare to me.

EDIT - Looks like I posted & missed your lost comments, digi2t.

Those numbers you've listed & the info will be really useful, thanks.

If you look back through this thread you'll see I already soldered SIL sockets to the lugs. I doubt I'll ever fully solder transistors to a board again. Maybe a tiny dot of solder on one leg to stop it falling out over time.

[digi2t]

Your SIP sockets on jumpers looks good. Great idea.

[PRR]

1N191 and 1N192 are listed in G.E. 1964 as Germanium point-contact computer diodes.

1N193 is not in there, and another source says it is Silicon. If I find my other books I might look.

[PorkyPrimeCut]

1N191 and 1N192 are listed in G.E. 1964 as Germanium point-contact computer diodes.

1N193 is not in there, and another source says it is Silicon. If I find my other books I might look.

Yeah, I looked over that same datasheet &, while I'll admit to not understanding much of it, the word "military" made me think it'd be silicon (reliable & consistent*).

Ah well, as it was listed as GE, I'll see if he'll swap it for another one that I can use. The parts are posted already so I'll try'n meet him half way with the return & exchange postage.





* Not words I'd usually associate with the military!

[PRR]

> not understanding much of it, the word "military"

Military/High-Rel :  N
Semiconductor Material :  Silicon

I read that as not Mil-spec, Silicon.

The military used tons of Ge diodes.

[PorkyPrimeCut]

> not understanding much of it, the word "military"

Military/High-Rel :  N
Semiconductor Material :  Silicon

I read that as not Mil-spec, Silicon.

The military used tons of Ge diodes.

Yeah, definitely silicon.

I hadn't clicked on the N meaning. Well spotted

[PorkyPrimeCut]

Still waiting on the WIMA caps so there's nothing new with the actual build.

I did follow advice & put this together though....



Unfortunately, my local Maplin messed up my order & gave me the wrong transistor. What was supposed to be 2.2M ended up no where near than. Worse still, I walked all the way back to the store again, braving Siberian London temperatures (not really), only to find that they don't actually stock the part & it was mis-listed on their website. Grrrrrr! The other transistor is 2.43k, so only 0.04k away from the recommended, bang-on, super accurate value that shouldn't really make any difference in the grand scheme of things.

I've ordered a 2.2M resistor for 3 times the Maplin price online & should get it in a day or so. Then the transistor testing fun begins. Oh joy!!!

[digi2t]

Nice. You'll find that the time and effort invested on this during your "downtime" will be well worth it.

[PorkyPrimeCut]

Nice. You'll find that the time and effort invested on this during your "downtime" will be well worth it.

Hopefully.

I found an "idiots" explanation of that GeoFex tutorial that I reckon will come in handy. The one thing I'm curious about now though is the supposedly all-important 2.473k resistor. I bought a 10 pack of 2.4k resistors & the closest I got was 2.43k (I think I'm repeating myself here). Will it being out by 0.04k really matter much in the long run?
Also, are there any other readings I could be taking while I wait for the 2.2m resistor to show up? I checked that the NKTs were alive & noted down the readings for stuff like B to E, C to E, all that jazz. I don't know if there was any need, I'm just bored 

[PorkyPrimeCut]

Also, I just got some interesting (and pleasing) info through about my diodes.....

"these are 1950's SIGNAL DIODE 1N193 and test as germanium on the Atlas DCA. not the Remakes 1N193 that are High-Speed/Fast Recovery Diodes Type for TV"

I was going to send them back but i'll keep them now.

[PRR]

> supposedly all-important 2.473k resistor.
> Will it being out by 0.04k really matter

No.

It is a 2% "error".

We NEVER know hFE to 2% precision.

There's other minor errors of circuit/method contributing more % error.

The test circuit is 200% or more away from many actual circuits, and hFE varies some with actual in-circuit current.

Every hFE tester does it different, and this can give quite different answers. Older Ge is especially prone to hFE fall-off at low or high current. If current is not stated, you don't know what you have tested.

"2.473k" is the computed "exact" value. 20% "off" in hFE "should not matter" in a good circuit. Some fuzzes are not "good" (in that sense) and may need 5% targets.

Anything 2.35K to 2.6K will be fine.

And if you insist, you can correct your reading by the known deviation of resistance. Of course you could use semi-arbitrary resistor values and apply arithmetic (euw!). If you can't longhand, WalMart has a perfectly good calculator for $0.99(!).

[digi2t]

Also, I just got some interesting (and pleasing) info through about my diodes.....

"these are 1950's SIGNAL DIODE 1N193 and test as germanium on the Atlas DCA. not the Remakes 1N193 that are High-Speed/Fast Recovery Diodes Type for TV"

I was going to send them back but i'll keep them now.

Uh... sorry, I have a problem with this.

I have an Atlas DCA, and it does not tell me if a diode is silicon, or germanium. Only that it is a diode, it's polarity, and it's forward voltage. Now, if I unknowingly test a schottky diode, I could interpret the low forward voltage as it being a germanium diode, but that would be wrong. Just because a diode tests at between .2 to .4 vF does not make it a germanium diode.

To be sure, I did the test with my DCA this morning. While it will display whether a transistoris germanium or silicon, it does not for diodes.

The seller's claim sounds fishy to me....

[mcknib]

I have an Atlas DCA, and it does not tell me if a diode is silicon, or germanium.

I think it does now you can get it upgraded to the latest firmware it detects whether a semiconductor is GE or SI  R 2.3 in the software versions PDF below

http://www.peakelec.co.uk/acatalog/dca_support.html
http://www.peakelec.co.uk/downloads/dca_software_versions.pdf

I keep meaning to get mine done