# Couple of modified BJFs



## HamishR (May 28, 2020)

As the *International Mail Service Disruption *is proving to be very real it's back to vero for me.  I've been quite prolific and in a way having no access to PCBs has been a good thing, as I'm particularly happy with how these two particular pedals sound.

First is a modified Honey Beest, traced by Daeg who is a member here.  Cheers Daeg!  The Honey Beest is a pretty cool overdrive already, but I have discovered that for my use I prefer silicon diodes over LEDs as I like the bark on the low strings.  There will be many who like the LEDs better and I can see why - I just prefer my silicon selection.   

The Honey Beest has a gain, a pregain, a Nature control and volume. I guess the pregain control was made possible by the extra gain stage at the input. The Honey Bee has quite a low output, so I'm guessing this was Bjorn's attempt to increase volume and gain. It works.  But I prefer to have just one gain so replaced the pregain with a resistor in my prefered range of gain and replaced it with a treble pot. So now Nature is two pots, a kind of treble and bass.  I really like how they work in this circuit. It's a cracker.







Then there's the Model G, which i always liked in stock form but felt the C control did next to bugger all and wanted to split the nature into bass and treble again. It works particularly well in this circuit too - it's similar to the Honey Bees but has a leaner midrange and tougher sound.. Again, the LEDs went and silicons stayed. Sounds killer with a Gibson. Loving this pedal! Thanks for the help Chuck!







I'm still coming to terms with the slight crookedness of the board. Screwing the back onto the pedals helps, as does just playing it.


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## music6000 (May 28, 2020)

I see what you mean!
What would you do Chuck?


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## HamishR (May 28, 2020)

It haunts me.


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## SteveF (May 28, 2020)

These look great.


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## Gordo (May 28, 2020)

Fine looking builds, very clean.


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## Barry (May 28, 2020)

Good looking builds


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## steelplayer (May 28, 2020)

Very nice work!


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## Chuck D. Bones (May 28, 2020)

music6000 said:


> I see what you mean!
> What would you do Chuck?



I think I'd take the piss, Mate! That leaning tower of Pisa is not right either.

Hamish, your Veros look a Helluva lot better than a some people's PCB builds!


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## cooder (May 28, 2020)

Sounds very interesting, I'd be keen to see schematics for these with the mods, like bass and treble. Wouldyou be abe to post them or do you have a link?
Thanks so much!


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## HamishR (May 28, 2020)

I can show you a schematic I drew for the Model G mod.  FWIW I call it the Model The G because here in Australia the biggest sporting arena is the Melbourne Cricket Ground, which is known as the MCG or "The G".  I can post the layout too if you want to try vero.  I haven't got around to drawing a schematic of the Honey Beest mod - I call it the Honey Bear.  But I can post a layout.


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## HamishR (May 28, 2020)

"Hamish, your Veros look a Helluva lot better than a some people's PCB builds!"

Thanks Chuck! I just like neat. It makes it easier to troubleshoot for a start. And it's easy.  I may not be the cleverest electronics guy (I still don't really understand how any of this works!) but I can do neat.  And I must admit I think my veros are neater than BJF's PCBs - he could learn a thing or two from the folks here. I guess Bjorn knows rather more than me about how these things work though...


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## Chuck D. Bones (May 29, 2020)

Have you tried using something other than JFETs for the hard clipping diodes?  JFETs are so scarce these days.


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## HamishR (May 29, 2020)

I have tried 1N4001s in the past in a Model G with good results.  I used them because Bjorn has used 1N4007s in the same place - as you can see in the Honey Beest. In fact I intend to build another G with my T+B mods and 1N4001s. From my experience the differences are minimal - you can hear that something is different but it's not huge.  The switch from LEDs to my silicon combo around the Drive pot is much more noticeable.


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## Chuck D. Bones (May 29, 2020)

I think I know why there is a sonic difference between the diode pairs and LEDs.  Take a look at this plot. Ignore the waviness of the red curve, it's an artifact of my curve tracer.  Where the curves are horizontal at the bottom, the diodes are not conducting.  As the curves bend up, the diodes begin conducting.  The steeper the curve, the higher the conductance.  Conductance is the reciprocal (opposite) of impedance.  High conductance = low impedance.





Besides the obvious difference in Vf, notice how the Si diodes begin to conduct very gradually, starting around 0.8V and it takes another 360mV (45%) to get up to 1mA.  The LED turns on much more abruptly starting at 1.5V and only takes another 170mV (11%) to get up to 1mA.  Diodes in the feedback loop see lower current than hard clipping diodes.  They usually peak out below 2mA and spend most of the time well below 0.5mA.  What all this means is that the diode pairs will have a smoother, more gradual transition from clean to dirty and less of the harsh high-order harmonics in the dirty region.


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## HamishR (May 30, 2020)

Wow - that's really cool!  I'm surprised at how much difference you can see when it's graphed like that.  The things I like about the Si diode combo is that there is a lot of room between hitting the string hard and hitting gently, and as you can see on the graph that area is smoother than with LEDs. Then there is the sound itself: LEDs give a kind of "blatty" sound; less distinct on the bass strings and rounder on the trebles, which can sound softer and less aggressive. I prefer a crisper sound where I can hear the definition, the twang, on the bass strings. I also find the Si combo to have a more vocal quality when used in these pedals.

One thing I have to admire about these BJF designs is how he has added clipping in different stages which is far more like how an amp distorts. Instead of having all the dirt appear in one place he spreads it out and gives it a different character in the different stages. I guess that's why it sounds more complex and "natural". It's not necessarily better but it is a great sound to have available. The G in particular I can see being used as a foundation sound, especially with a Gibson. I think using the Si combo rather than LEDs actually makes it a more of an "all-round" OD rather than a lead guitar OD.

I play with a pick and fingers style and the extra dynamic range with my mods makes these pedals a lot of fun and very expressive. I can go from clean to quite dirty just by how I pick and it all sounds very natural. The Honey Beest/Bear is a ruder sound with more mids which is fun but the G is a real old school rock'n'roll sound.  Overall I still prefer my modded BB Preamp but these BJFs are seriously cool.


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## cooder (May 30, 2020)

Awesome, thanks for posting schematic (I'm into schematics and see what I can learn from it, I'm personaly not into vero builds, although I admire what you do there. Great stuff.
Any links and postings of schematics is great for me to see, thanks for sharing!


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## HamishR (May 30, 2020)

I have a schematic for the Baby Blue OD as well if you would like that?

Today I built another G with treble and bass knobs, but used 1N4001 diodes where the original uses 2N5952 Jfets as diodes. Comparing them side-by-side has been interesting - so far I don't have a lot of time on them but with my Les Paul the all silicon diode version has more dirt and less volume, meaning that to get it to sound the same as the Jfet clipping version I keep the gain knob lower and the volume higher. They can sound very similar once I have adjusted them. Both sound fantastic! I think the all Si version is also a hair brighter, and that could be the increased high order harmonics I guess.  Actually I have no idea but that sounded good to me.

I suspect that if I can find some diodes with a similar response to the Jfets it would sound more or less the same. I think I'll be keeping each as they are because so far I like both equally. And if you are getting low on 2N5952s rest assured that using 1N4001s will get you pretty close sound-wise and might just get you the extra dirt you desire. I am using gain at around noon on the original and about 10.00 in the new one.

Any suggestions for diodes to simulate Jfets, Chuck?


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## Chuck D. Bones (May 30, 2020)

I'll have to run traces on some JFETs and get back to you.  It's a silicon junction in a JFET, just different geometry.


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## cooder (May 30, 2020)

Awesome and yes I'd be interested in the Baby Blue OD schematic please!
Thanks so much for the in-depth description and observations with clipping diodes and jfets, very cool!


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## Chuck D. Bones (May 30, 2020)

There's a trace on FSB.  

You need to register to view the pics.


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## music6000 (May 30, 2020)

Her's my Baby Blue Build from 2018:


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## HamishR (May 31, 2020)

That construction looks very Menatone.  Except neater!

I drew my own vero layout for the Baby Blue because I didn't like the ones I found online. I have developed my own anal peculiarities about layouts.    I quite like the Baby Blue but only with a Gibson. I think it's extremely ordinary with a Strat, for example. It compresses more than I like but at low gain with a Les Paul it has something I like.


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## cooder (May 31, 2020)

Awesome, thanks again! It is a pretty neat schematic and great to folow through! Cheers!


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## HamishR (Jun 1, 2020)

Hey Music 6000 - how do you like the Baby Blue? Do you use it much?

I just altered the schematic for the Model G because I had a 4K7 on the output instead of 47K. It's correct now.  And just for the record, here is the 1N4001 version. I'm finding this one even better now, and it saves the 2N5952s.  This overdrive suits me very well - it's amazing.


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## cooder (Jun 1, 2020)

Awesome again, thanks for the update!


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## Chuck D. Bones (Jun 1, 2020)

I ran some traces of three JFETs, a BJT & three Si diodes, then plotted them for comparison.  The MPSA18 was tested two ways, just the emitter-base junction and with the base & collector tied together. Vf for the JFET gate junction was fairly high.  Note that JFETs are not designed to work this way, but as long as the gate current is not too high, they'll survive.  I have seen JFETs used as ultra-low leakage diodes in precision circuits. The JFETs, MPSA18 E-B junction & the BA283 PIN diode have the highest Vf.  I think the high Vf is what drives some pedal designers to use them as diodes.  The BA283 or MPSA18 would both make good substitutes.  As always, let your ears make the final decision.


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## cooder (Jun 1, 2020)

Oh man guys thanks for all these mad scientists insights... ! Very cool!


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## cooder (Jun 1, 2020)

Chuck, how do you actually plot that? Is that from a scope?


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## Chuck D. Bones (Jun 1, 2020)

I use this: 
https://forum.pedalpcb.com/threads/my-transistor-diode-test-station.1609/

I export the I-V data as a CSV file, import it into EXCEL, do some filtering and offset correction, then plot it.  The wiggle in the traces are quantization error.  I need to mod the curve tracer or put a preamp between the curve tracer and scope to boost the signal and get better resolution.


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## HamishR (Jun 1, 2020)

Wow... (head exploding quietly)... So it looks like in some ways a BA283#2 could be a good replacement. Except Mouser calls them obsolete! Oh well, I have plenty of MPSA18s.

Thanks Chuck - this is really interesting. Do you think the Vf is the main characteristic here? Could the lower Vf of the 1N400x be why it dirties up faster and has less volume?  I'm also wondering if the lower Vf of the 1N400x - if responsible for more and earlier clipping - is why it sounds a bit brighter and raspier? And I don't mean raspy in a bad way.  It's slightly less smooth and that can sound good too. I suspect the version with the 1N400x diodes would stand out in a mix slightly better. Mind you, we're talking quite subtle differences here. Audible, but subtle.

So when you show "MPSA18 B-E" you mean use just the base and emitter legs?


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## Chuck D. Bones (Jun 1, 2020)

Vf influences into how much clean headroom is available before the dirt takes over and the max volume.  The shape of the curve has some effect too, although they're all pretty similar in that regard.  The CA3130 can swing the output right up to the rails, so the peak diode current in the hard clipper is roughly (Vcc-Vref-Vf)/1K = 3.8mA.  I say roughly because the 1uF cap has some impedance and a little bit of the current sneaks around the diodes thru the 10K and 12K resistors.  If Vf is larger, then the peak diode current is lower. 

Yes, MPSA18 B-E means the curve tracer is measuring the current and voltage between base and emitter.  The collector lead is not connected to anything.

The BA283's are hard to find, but they're out there.  I have some BA482's, I should run curves on them too.


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## HamishR (Jun 2, 2020)

Well despite my best efforts I am actually learning something here. Honestly mate, I have learnt more from you in the last few months than I have ever learnt in my life about electronics. Chuck, you should work in electronics.  

Another thing I learnt today is that the G works incredibly well with my silicon Red Rooster. Well most ODs do, but it seems to mesh particularly well with the RR.

As it happens I am liking the 1N4001 G more than ever, and there is one last thing I'd like to address... What I am calling the bass knob is not really a true bass knob.  It seems to affect low mids and never gets rid of the low end completely. I'm thinking that if I reduce the lowest of the lows before clipping I can get a clearer sound on the bass strings. Right now I can clean up the bass strings pretty well by keeping "bass" below noon but there is still a little noise there. I tried making the 4u7 at Bass 3 smaller but it didn't have the effect I was chasing.  What about the 220nF cap to Vref there? What would happen if I reduced it to 47 or 100nF?  Maybe it's the 1µF at pin 6 I should be looking at?  I love the full range sound of the pedal so I'm reluctant to mess with it much further!


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## phi1 (Jun 2, 2020)

I’ve been enjoying following this thread and admiring your clean vero work.

For the bass, one thing you could try is increasing the value of the bass pot. 10k may not be enough to completely take it away with the knob at minimum, though I’m not sure if that’s your problem.

Yes reducing the 220n like you mentioned would reduce some low-mid content. The 1k and 220n determine the cutoff frequency of the high pass filter (F=1/(2piRC) = 723Hz). So reducing the cap would raise this frequency. Reducing the 1k also has the same impact on frequency, although it also adjusts the gain range. For the cap, I’d probably start with 150n (1000Hz) and Experiment from there. You could also try a trimmer where the 1k goes to help you dial in the cutoff frequency exactly (like how the voice knob works on a zendrive).

One more thought based on your description, maybe your happy with the cutoff at 723Hz, you just want a steeper roll off. (It’s currently a 1 pole high pass which can have a shallow effect). I think by reducing the 22n on the input, you could have 2 separate HPF around 723Hz. Using the 470k to Vr as the “R” for the calculation, I get that 470p would put that filter at 720Hz (Not sure if that’s close Enough, do I need to consider the impedance of the op amp for the calculation, chuck?). The problem with this method is it permanently removes some bass. So with the bass knob down you’d get 2 pole HPF, with the bass knob up you’d have 1 pole high pass. (Please correct me if I’m thinking of it wrong). Of course you could also put those caps on a switch to have all the options.

reduicing 1uF at pin 6 could also work. I just thought since there is some soft clipping in the op amp feedback loop, maybe you’d want  to cut bass before that.


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## HamishR (Jun 2, 2020)

Thanks for the suggestions.  It helps because it makes me feel that finally I am getting some of this stuff!  I'll try your ideas one at a time and see what happens.

Anyway, the main reason I am enjoying the G so much is that it is almost all there - it has a complex, natural and quite amp-like sound, it's full and responsive, sounds like a great old small-box plexi with chords, warts and all. It has some imperfection like any great old amp does. As much as I like a clear low-end I worry that if I achieve it I might lose what I like about the G.  But I will have to try it and see.


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## Chuck D. Bones (Jun 3, 2020)

The opamp's input impedance is HUGE, so we don't need to consider it in the calculation.  I agree with all of Phi1's ideas.  I don't think I'd dial down the input cap that far, and I'd only do it as a last resort because as Phi1 says, it's non-adjustable.  You should be able to get the BASS control to do what you want by reducing the 220nF.  To find out if the BASS pot is big enough or not, disconnect one of the leads and see how much of the bass goes away.  If it's still too bassy, then increasing the BASS pot won't get help.  Where are you setting the GAIN pot?

How about adding reference designators to your schematic?


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## HamishR (Jun 3, 2020)

Sorry about the lack of reference designators.  Drawing schematics is still quite new to me.  I will do so now! Actually I was worried in case I had made some rookie schematic mistake, having never been schooled in the art. It appears I have!

And yeah, I was reluctant to decrease the input cap value. I'll try a few things and report back.


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## HamishR (Jun 3, 2020)

Is this better?


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## Chuck D. Bones (Jun 3, 2020)

Yeah, you're gettin' there.  Don't forget the semiconductors.


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## HamishR (Jun 3, 2020)

Cool!    I have tried a few things as discussed - swapping C2 (as shown conveniently numbered above) to 100nF and it did clean things up but made it a little sterile and kinda scooped mids more than extreme lows.  So that's back at 220n.

What seems to be working is using a 470nF for C5.  Maybe it's because it's limiting the lows a little before the hard clippers? I dunno. But it sounds really good and I think is an improvement on the overall punch and clarity. I'm keeping the first G with the 2N5952 diodes-as-clippers as per the first schematic shown here and just modifying the 1N4001 version. And i think I will leave it with the 470nF at C5 for now.  It seems to be doing everything I wanted. There's still plenty of thump if I crank the bass knob - too much really. So I keep it around the noon mark mostly.

Thanks for the help guys! This forum is amazing.


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## Chuck D. Bones (Jun 4, 2020)

HamishR said:


> What seems to be working is using a 470nF for C5.  Maybe it's because it's limiting the lows a little before the hard clippers?



I was gonna suggest that next.  That's exactly what it's doing.  C5 doesn't have much effect on the soft clipping, but it keeps some of the lows out of the hard clipper.


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## HamishR (Jun 4, 2020)

Oh no!  I'm learning stuff!


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