# Dung Beetle hfe gain



## debrad (Jun 10, 2022)

Hi everyone!


I just dropped four 2N5088s into my completed Dung Beetle PCB to make sure it worked before boxing everything up...and it did (YAY!)...but I thought that I would ask if there was a consensus on hfe values for the Dung Beetle.

Looks like the four I chose measure around 235 hfe but I have some closer to 220 hfe and some more in the 400 hfe range.  Does anyone recommend high gain versus low gain or is the circuit a little more forgiving than other fuzzes?  Any specific transistor that might prefer a certain range of hfe?


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## Big Monk (Jun 10, 2022)

debrad said:


> Hi everyone!
> 
> 
> I just dropped four 2N5088s into my completed Dung Beetle PCB to make sure it worked before boxing everything up...and it did (YAY!)...but I thought that I would ask if there was a consensus on hfe values for the Dung Beetle.
> ...



The Scarab was more or less a straight lift of the basic Si MK II by Ricky Don Vance floating around on the web years and years ago (although the Hot Silicon circuit is also a candidate) with an amalgamation of other Fuzz Face and MK II/III mods added in. 

I’ve never seen any dedicated gains quoted for this circuit or the RDV Si MK II but the original had 2N4401 in Q1 and Q2 and a 2N5089 in Q3. 

Judging by the larger emitter resistor on Q3 in the Scarab, the BA folks likely had higher gain 2N5088 when they cribbed the basic structure as a base for the Scarab. 

The 2N4401 I have are either in the 400-420 hFE range or around 280-300 hFE so those have fairly tight buckets. 

It’s hard to know exactly what gains BA chose or if they even cared.

You probably can’t go wrong with lower gain 2N5088 in Q2 and Q4 and a higher gain one in Q1 and Q3, judging by the values that are used for the local feedback emitter resistors in the first three stages.


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## spi (Jun 10, 2022)

I read on madbeans forum where someone recommended 2n3904 for Q1 and Q2, 2n2222a for Q3, and 2n5088 for Q4.
I happened to record this in my notes because I plan to build the Dung Beetle and will try this combination.


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## ADAOCE (Jun 10, 2022)

I’m interested in this because I just sent her with the first 5088s I found and it sounds fantastic


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## debrad (Jun 11, 2022)

Thanks everyone!

I hadn't found any discussion of Dung Beetle or Scarab Deluxe hfe so I figured the circuit must sound pretty good with a wide range of gain.

Thankfully there are folks like @Big Monk who understand the circuit in ways that I hope to some day and I will definitely take his advice to test drive a few different gains in the Q2/Q4 and Q1/Q3 positions.  I will also do a little more reading online to see if there are additional tips on sites like diystompboxes, madbeans, tagboardeffects, etc., etc.

The good news is that this build is already sounding great!


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## Big Monk (Jun 11, 2022)

debrad said:


> Thanks everyone!
> 
> I hadn't found any discussion of Dung Beetle or Scarab Deluxe hfe so I figured the circuit must sound pretty good with a wide range of gain.
> 
> ...



That’s just my best guess based on working on Silicon MK II circuits on the breadboard. 

Definitely try a few out and report back.


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## jjjimi84 (Jun 11, 2022)

I have tried a number of iterations of transistors and found just 2n5088s to sound the best to my ears.


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## Big Monk (Jun 11, 2022)

jjjimi84 said:


> I have tried a number of iterations of transistors and found just 2n5088s to sound the best to my ears.



I’m sure how important hFE is in this circuit.

2N5088 is pretty right around 350-450 hFE.


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## debrad (Jun 12, 2022)

Still test driving different transistors to see if I can find THE combination.  Right now it has a group of 2N5088s that increase in hfe from Q1 (~220) to Q2 (~235) to Q3 (~380) to Q4 (~405) but, if I can be perfectly honest, I haven't heard much difference as I swap them in and out.  I also had pretty high expectations based on all of the reviews I've read but, with the exception of the Dung Beetle's awesome bias control, I feel like I'm still happier overall with my recent Marigold build.

Here are a couple of photos...


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## Big Monk (Jun 12, 2022)

debrad said:


> Still test driving different transistors to see if I can find THE combination.  Right now it has a group of 2N5088s that increase in hfe from Q1 (~220) to Q2 (~235) to Q3 (~380) to Q4 (~405) but, if I can be perfectly honest, I haven't heard much difference as I swap them in and out.  I also had pretty high expectations based on all of the reviews I've read but, with the exception of the Dung Beetle's awesome bias control, I feel like I'm still happier overall with my recent Marigold build.



I personally dig a more straightforward Silicon Tonebender MK II with a Pre-Gain control.


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## Chuck D. Bones (Jun 21, 2022)

This circuit should be pretty insensitive to hFE, provided the hFE isn't so low (<20?) that the circuit won't function.
Q1's hFE doesn't matter.  R4 & R5 set the gain for Q1; R2 dominates the input impedance.
Q2's hFE influences the bias, however the BIAS pot can dial out any bias difference cause by Q2's hFE.
Q3 is fed by a fairly low-impedance source (R7), so its hFE is immaterial.
Q4 is an emitter follower, so its hFE doesn't matter.

YMMV


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## debrad (Jun 21, 2022)

Thanks @Chuck D. Bones!  This is not only a huge help for me in this specific instance but, as I hinted at with @Big Monk above, it's also TOTALLY inspirational in terms of where I hope to get with my comprehension for pedal circuits!


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## Big Monk (Jun 21, 2022)

debrad said:


> Thanks @Chuck D. Bones!  This is not only a huge help for me in this specific instance but, as I hinted at with @Big Monk above, it's also TOTALLY inspirational in terms of where I hope to get with my comprehension for pedal circuits!



I’ll take being mentioned with @Chuck D. Bones anytime. 

He’s forgotten more about circuits than I know.


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