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Re: BJFE - Emerald Green Distortion Machine
Posted: 01 Sep 2018, 07:41
by Manfred
jalmonsalmon wrote:So ...
MP38A's work for this and sound more or less the same as the CV7351's?
Like blind fold comparison test?
I am not sure, since the frequency response is not the same on the low end.
Theres is a diffrence from about 10db @ 10 Hz, that means there is three times less low frequency level using the MP38A below 30Hz,
but I think it is finally not audible.
Next, will omitted more specifically change the capacitor between base and collector, to see the influence on the frequency response.
The next task is the measurement of each FET-stage seperatly.
To the end with, I will build the device, but that is a winter work.
Re: BJFE - Emerald Green Distortion Machine
Posted: 02 Sep 2018, 16:15
by Manfred
As announced, here the frequency responses for differten Caps placed between base and collector.
Re: BJFE - Emerald Green Distortion Machine
Posted: 05 Sep 2018, 02:07
by Manfred
Output curves and frequency responses for different "Voice" potentiometer settings.
On the measurement frequency of 1 kHz, the potentiometer setting has had no influence on the shape of the clipped signal curves.
On the annotation in last columns the "k" is missing, 50 means 50k.
Re: BJFE - Emerald Green Distortion Machine
Posted: 06 Sep 2018, 15:34
by Manfred
I mad further frequency response measurements because nothing has changed significantly for potentiometer resistances greater than 5 Kiloohms.
That corresponds to the half rotation of the "Voice" button, due to the logarithmic potentiometer.
Those values are 1 Kiloohm, 2.2 Kiloohms, 3.3 Kiloohms and 3.9 Kiloohms.
In summary, on Stage 1 the "Voice" button affects the low and low mid frequencies on its lower half rotation,
the mid and high cut frequencies remained largely unaffected.
Re: BJFE - Emerald Green Distortion Machine
Posted: 09 Sep 2018, 05:29
by Manfred
Output curves and frequency responses for different "Voice" potentiometer settings of stage 3.
- OutputSignalsStage3.png (9.32 KiB) Viewed 2558 times
The value of R_pot means the resistance between terminal 2 and terminal 3 of the "Voice" potentiometer, so the right stop corrospondes with 0 Ohms.
Using the 4.7 nF capacitor, the potentiometer setting has not a noticeable influence on the frequency response,
so I using a 47nF capacitor, that gave a marked change, but only up to a resistance of 5.1 Kiloohms.
This gives only a small rotation left away from the left stop.
Maybe this capacitor have been read incorrectly.
Later on, the build circuit make the truth come
Re: BJFE - Emerald Green Distortion Machine
Posted: 10 Sep 2018, 21:46
by Manfred
The final chapter discusses the clipping circuit.
For comparison purposes I also measured the circuit using 1N4148 diodes.
The spectrum shows amplitude peaks on the odd harmonic multiples of the input frequency.
The amplitude amounts of the harmonics are significantly greater using the BY458 diodes.
- Spectrum BY458 & 1N4148 clipping diodes f_in = 1kHz.png (6.1 KiB) Viewed 2531 times
Re: BJFE - Emerald Green Distortion Machine
Posted: 03 Aug 2022, 00:13
by sopapo1
Hello, Im am interested in doing this build as I am built another two bjfe designs (drd and model h) and I am very addicted to his designs, sound great and the responsiveness are huge, I think this pedal live to the hype¡¡
The original version use a bjt in q2, I dont have any germanium to try, so I would like to try a silicon version, which one would be a good candidate? bc549? bc108? somehting with low gain I think. Obviously I will have to play with several resistors to bias it...which biasing?' vcc/2? or lower......
Thanks for all
Best regards
Re: BJFE - Emerald Green Distortion Machine
Posted: 03 Aug 2022, 10:02
by Manfred
sopapo1 wrote: ↑03 Aug 2022, 00:13
Hello, Im am interested in doing this build as I am built another two bjfe designs (drd and model h) and I am very addicted to his designs, sound great and the responsiveness are huge, I think this pedal live to the hype¡¡
The original version use a bjt in q2, I dont have any germanium to try, so I would like to try a silicon version, which one would be a good candidate? bc549? bc108? somehting with low gain I think. Obviously I will have to play with several resistors to bias it...which biasing?' vcc/2? or lower......
Thanks for all
Best regards
Try a BC547A, BC548A or BC549A these are the successors to the BC107A, BC108A or BC109A, the gain group A is important.
Change the values of the resistors from 100k and 22k to 150k and 56k.
Re: BJFE - Emerald Green Distortion Machine
Posted: 24 Aug 2022, 06:10
by sopapo1
Thank you very much Sir¡¡ I will try this. I will report my results¡¡¡
Re: BJFE - Emerald Green Distortion Machine
Posted: 28 Jan 2023, 22:40
by pacealot
I'm curious if anyone has looked at the Emerald Green Overdrive to see exactly how it differs from the EGDM. I'm sure it'd be simple enough just to tweak the stock EGDM for lower gain, but I wonder if the Overdrive version has any bigger secrets to reveal. There don't seem to be any traces of it out there yet...
Re: BJFE - Emerald Green Distortion Machine
Posted: 14 Jun 2023, 15:18
by pacealot
I managed to get a hold of an Emerald Green Overdrive myself, and so I can now answer my own question: the only difference between the two circuits is the value of three resistors and the addition of a fourth. Here's a schematic:
R4 has changed from 14.7K to 12K, R9 from 8.2K to 6.8K, R14 from 8.2K to 12K, and R18 is a new 330Ω resistor between the Q2E bypass cap C8 and ground. Interestingly (and surprisingly to me, especially given the published blurbs about the pedal), no cap values were changed from the EGDM version. On the subject of cap values, the Q2 base-to-collector ceramic disc marked "100K" reads close to 10pF rather than 100pF, so I reflected that in the schematic. Given its role there, I'm guessing it's more a matter of taste and HF noise taming than anything else anyway.
The only thing not shown in the schematic is the LED wiring, which includes what appears to be a Zener in series with a 1K CLR evidently to cause to LED to fade sooner as the battery weakens to indicate that it should be replaced shortly. (Thanks to Chuck D. Bones over at bugg's forum for that insight and countless others regarding this circuit.)
Here are the obligatory gut shots: