EHX BMP - Analysis Part 2 - Output Stage - DC Analysis

In Part 2 of the EHX/Sovtek Big Muff Pi Analysis, we examine the Output Stage Circuit from a DC perspective.
00:00 Introduction
00:29 Tracing the Output Stage
03:26 Applying a Signal
04:38 Prototype Pedal Version
05:05 Output Stage - DC Analysis
10:55 Gain Calculation
13:28 Voltage Divider
18:25 Voltage Measurements
20:45 Current Measurements
23:26 hFE Measurement
24:00 Summary
25:00 Coming Up...
25:29 Outro
Kit Rae’s excellent BMP Page:
tinyurl.com/3pv5rd7r
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[@jonnybishop]

More in-depth Big Muff knowledge!! Loving how much information you're giving away!

[@MusicTechknowledgy]

Thanks 🙏. I’m really enjoying making these and I’m also learning so much as I “walk through” the circuit.

[@georgemuff5482]

This is great. I just picked up a black/yellow model over the weekend and am hoping to understand the differences compared to the green models.

[@MusicTechknowledgy]

Thanks. I was just looking at the transistors in the Green and Black/Yellow versions I have. The green Russian has transistors with green (KT3102) and white (E) dots and the black/yellow EHX/Sovtek version has transistors with a white triangle with EN2 (the N2 means February 2001 I believe). My green version should be very similar to my black/yellow version but sound-wise they are slightly different, be interesting to analyse why during this series.

[@rudy5360]

Great video as always! Learning a lot! Do you trust the component tester to measure hfe? I was testing some KT3102, and two out of the four measured super low hfe, around 26, and different pinout! But I breadboarded the input stage, and all four sound fine

[@MusicTechknowledgy]

Only ever as a rough approximation. I edited out for time but the two other meters showed 380 and 372, I believe that's because they use a different set of test parameters. The Common Emitter isn't dependent on hFE (only RC and RE values) so we're all good circuit-wise. I sometimes use a curve tracer if I really want to know specific parameters but remember that heat also affects the hFE. In comparison, all of my KT3102EMs measure a lot higher - from 450 minimum to well over 600 in two cases (their datasheet suggests a range of 400 to 1000), and I checked that on all 2 meters. They're the ones with the triangle and the letters E and P on the front. The green Russian has ones with green (KT3102) and white (E) dots and the black/yellow EHX/Sovtek version has the white triangle with EN2 (the N2 means February 2001 I believe).

[@rudy5360]

@@MusicTechknowledgy Thanks so much! I'll build my pedal as is and follow along with the rest of your series!