I want to try some 400-ish hFE transistors in my wah, but I don't have any. I've got a bunch (2N3904s, 2N2222As, etc) with hFEs under 300. I've got forty 2N5088s, a few 2N5089s, all hFEs over 500.
What's a good part number to look for, so that if I buy 20 or so I have a good chance of getting a few in the 400 to 450 range?
Have a look at the MPSA18 transistor. It may meet your needs.
Also they are used in some of the Crybaby Wahs.
They are just normal BJT devices and not darlington such as the MPSA13.
I have looked at those, they seem to have typical hFEs quite a bit higher than 500.
I started off with a pair of BC109Bs, before I knew about hFE and just how variable transistors were. IIRC the two I have are in the low 300s or maybe even 200s. They sound nice, very glassy, but I would like a little more growl.
I tried 2N5089s in the mid-upper 500s, and that was too much, particularly for Q1. So I have it in my mind that something in between would be right for me. I bought the forty 5088s with the hope of finding some 400-450, but they are all very consistent in the mid-500s. That's okay I needed resupply of those anyway.
I know I can tweak resistor values, but I'd like to try and get the sound I want with the stock values if possible.
Yes, the MPSA18s may be too high in gain for what you want.
I would suggest that you consider BC549B or BC550B series transistors.
The suffix generally indicates approximate gain range.
http://www.mouser.com/ds/2/149/BC550-888526.pdf (http://www.mouser.com/ds/2/149/BC550-888526.pdf)
I agree with BC550B.
Almost every I've used, was in the ~400 hfe range.
Thanks, I'll add those to the list of possibilities. Tayda lists a BC550 for $.03 a pop, but they don't specify a suffix. I could order 200 of those and it will do me no good if they are all As.
Mouser has BC550B for $.15 each, but I'd probably have to buy quite a few to get the hFE range I'm looking for, which is right in the top B or bottom C range.
I'm eyeballing some Telefunken BC108Cs at Small Bear, probably better chance of hitting the desired gain, but too expensive to get a bunch of them. (Though I am a sucker for anything made by Telefunken, Mullard, Amperex, or RCA). Maybe I will buy 4 or 5 and hope for at least one ideal Q1 candidate. Q2 is far less critical for me, but it would be nice get both in that range.
Thanks Plexi, I was typing when you posted. What brand or supplier are you getting those from?
Um... I know I'm a pest about this, but why do they need to be 400-500?
Quote from: R.G. on November 25, 2017, 05:19:39 PM
Um... I know I'm a pest about this, but why do they need to be 400-500?
They don't need to be, in order to work. I'm just trying to zero in on a particular sound, a certain amount of "snarl" (I mistakenly said "growl" earlier, totally different thing). I think it occurs in a pretty specific Q1 hFE range, but I don't really know yet, just experimenting. Going through transistors I have on hand, seems to ba a gap in the range I'm looking for.
However, I've now rendered this thread essentially moot, because I just went full mojo nuts-o and ordered a 5-pack of these:
https://www.ebay.com/itm/222043812064 (https://www.ebay.com/itm/222043812064)
Same as original Thomas Organ "5117" part. Gain range looks nice (fingers crossed). Mouser has new manufacture 2N2925s for less, but they don't look as cool.
OK. Good answer. Carry on.
There was a circuit that showed up once in these pages where the resistor and base junction of the input stage were in parallel with a resistor and diode connected so some of the input current would divert into the diode. The diode junction was in the same direction as the B-E junction of the input transistor and the other end of the diode was connected to the emitter of the input transistor. By juggling resistance values, you could use a very high-gain transistor and tune it down to a lower gain to meet your requirements.
BC549C
2SC2240
mac
Quote from: thermionix on November 25, 2017, 04:46:50 PM
Thanks Plexi, I was typing when you posted. What brand or supplier are you getting those from?
Fairchild!
Take a look closer to the Tayda's description:
Manufacturer: FAIRCHILD
Manufacturer Part No: BC550B
Package / Case: TO-92
RoHS: Yes
Datasheet: Click HereThey're 'B' rated ;)
Another one I would recommend is 2N4401, they're almost that range too
Ah, you're right! They should just say BC550B in the main list then. I'll still look into those in the future to cover that hFE gap in my selection.
But, as we all know, Mojo is just a bit too big to fit into a TO-92 package. So I had to go with the TO-98 style instead.
I'll update in a week or so with a "Best wah ever!" post when I get the 2N2925s installed.
You should look after "B" suffix not "C"
BC549B, BC550B
With more parameter variance and a bit noisier BC548B.
i think the BC183C has around 400 in hfe, also i think the older style BC109 (mine don't have a suffix).
the BC183C is a bit noisy though.
Ivan at diy-tubes.com measured-for-gain some transistors for me recently. he might fix you up with some BC series, or maybe some big-muff types.
[no affiliation.]
These five NOS 2N2925s showed up. The hFE gods did not smile upon me today. They all tested on the low side of, or below, the supposed range. Still, I put the best two (hFEs about 260) in my wah to try them out. They work, no noise problems, don't sound bad per se, but don't get me anywhere closer to my goal. Very clean. I guess I'll order 10 or 20 of the new ones from Mouser, and hopefully get at least one high gainer for Q1. Or maybe just get the BC550Bs from Tayda. I'll leave the NOS type in Q2, I think 260 is fine there. For now, BC109B is going back in for Q1.
Oh well, wasted 9 bucks, not my worst mistake in life.
That's why you never have to believe in mojo haha :-D
Yep, got caught worshipping false idols, and paid the price.
On the upside, the experience seems to have confirmed that it is a specific Q1 hFE range I'm looking for, rather than some other characteristic. These NOS transistors don't sound any different than some similar 2N3904s I tried months ago. The BC109B I put back in tests about 315, and is definitely closer to the sound I'm after.
The Clyde McCoy wah mods page on Fuzz Central suggests BC109B's in I believe the 350-400 hfe range to get the original Clyde sound with the original value components. My BBE Wah has BC547's in it and sounds very close to my old Clyde McCoy Picture Wah I had when I was a kid and stupidly sold for very little money (when wah became a cliche sound at a certain point). I have a number of BC109B's I got that are in the correct range, I bought a bunch from an electronics retailer when they were really cheap and most measured within the range I wanted. I plan on putting them in a couple of other wahs I have, one is a US made (Dunlop) Vox V847 I have slowly been modding to Clyde specs using the Fuzz Central article as a guide.
Al
Why not just increase the gain of that section of the circuit? I seem to remember something about changing out the emitter resistor to up the growl?
Quote from: kaycee on December 01, 2017, 11:00:04 AM
Why not just increase the gain of that section of the circuit? I seem to remember something about changing out the emitter resistor to up the growl?
That makes sense, but for my own goofy reasons I want to try to achieve this sound with the stock component values. Does a smaller Q1e resistor have exactly the same sonic effect as a higher Q1 hFE? Probably so, but I'm basically just experimenting and learning. My wah is built on an eyelet board, so I can swap components 'til the cows come home and not damage any traces, or even move a wire. I've tried most of the common mods out there, mostly just to see what they sound like, and I keep going back to stock values.
One thing that surprised me, and I don't understand, is that different pots seem to have different tones. Most recently I switched from a Chase Tone pot to a Dunlop Hot Potz II, both 100k, both set as far to the treble end as possible without risking physical damage. With the Chase Tone, I had added a 2n2 cap in parallel with the stock 10n sweep cap to get the overall frequency response where I liked it. When I put the Dunlop in, I had to take the 2n2 cap out. No idea why. But I like that it sounds "right" now with the stock sweep cap value. Keep in mind, I'm talking about the tone across the entire sweep, not just the extreme toe-down end of it, it's not just the different tapers.
I'm planning on getting one of the original Hot Pots from Small Bear soon to try that out. My buddy has a nice vintage crybaby with that pot and I like it. His wah is basically the main inspiration behind my experiments. It just sounds classic as all get-out. He has the stack-o-dimes inductor, and I have a Whipple halo, so they'll never be exactly the same, but still I'm chasing it down. No, I haven't pulled his transistors to check hFE, woudn't risk that. But my feeling is that they're right around 400, at least Q1.
I put in a Tayda order last night, including 30 BC550Bs, so I'll check those out when they arrive in a week or so.
> Chase Tone pot to a Dunlop Hot Potz II, both 100k, both set as far to the treble end as possible without risking physical damage. With the Chase Tone, I had added a 2n2 cap in parallel with the stock 10n sweep cap to get .... When I put the Dunlop in, I had to take the 2n2 cap out. No idea why.
Did you measure the pots?
10nFd to 12.2nFd is about 20%. Pot tolerance is around +/-20%. A low-R pot could need more C to hit the same corner. 90K and 110K are both "100K" but could give the difference you found.
Ah, good point.
I'm actually on my third pot, the first was a CTS-made one that came with the Whipple inductor, looks just like the "black bear" that Small Bear sells. I added the 2n2 parallel cap when I was using that pot, kept it for the Chase Tone, then took it out for the Dunlop.
Values (all out of circuit):
CTS: 90.7k
Chase Tone: 98.4k
Dunlop: 104.2k
So the resistances get higher, I don't know the calculations for how that effects the frequency response in the wah circuit. Does it seem to jive, or is it opposite of what you'd expect?
I'm very curious now, if I get one of the old type Hot Pots from Small Bear and it reads a little low, I could add some series resistance on the "heel down" end. If indeed that's what's making the difference.Edit: Dang, re-read your post.
QuoteA low-R pot could need more C to hit the same corner.
Seems that was it.
Got my stuff in. HotPotz I from Small Bear came yesterday. 111k, nice! Installed it without any other mods. I sure do like the taper. Seems a little more spread out, not as extreme of a "hump" as some others. Also very familiar, it's what I grew up with I reckon. Tone was fairly snarly, still a bit too bright and honky.
Today I got the BC550Bs from Tayda, pack of 30. Selected one at approx. 400 hFE for Q1, and one at about 380 for Q2. (I never know precise hFEs because the only thing I have to check with is my RG/ Geofex "FF Select" tester, and I never have a battery that's exactly 9.0v, and it does make a big difference in readings. Someday I'll invest in a decent transistor analyzer.)
Anyway, the new transistors warmed the tone up in a very pleasant way. Thick and syrupy, but not distorted per se. The "honkiness" it had before is smoothed over. Of course I checked it out with a clean amp first, then I ran it into my BMP and I could barely put the guitar down. Very happy with the results, to say the least. I might actually be done (!) messing with this thing, some 20 months after I initially built it, lol.
[One thing I might do, is put a 3PDT toggle inside so I can bypass the FoxRox output buffer. 3-pole so I can cut power to it. That would save a bit of battery when I don't need the buffer, about the only reason to do it. I don't want a little switch lever sticking out of my wah and getting broken off, so I would mount the toggle internally with a bracket, or maybe it can poke through under the treadle and not interfere with operation. If I had thought about it at the time, I would have added three DIP switches when I built the FoxRox.]