Tone Vendor MK1 transistor options

Song Naga

Song Naga

Member
Hi all,

I've got a Tone Vendor MK1 ready for transistors and I'm wondering if what I've got on hand might work. The BOM calls for an OC75 and a pair of 2G381's. I looked these up and the OC75 seems to have a minimum HFE of 55 and the 2G381's have a minimum of 75.

I've got a bunch of MP39A's and a pair of MA287's on hand, the MP39A's range from 14 to 49 HFE and the MA287's are 70 and 84 HFE. Are these in the ball park and worth trying out, or should I quest for some more appropriate transistors? Thank you for any input!
 
For MkI I've got these notes for hfe ranges:
Q1: 55 - 80
Q2: 65-100
Q3: 100-140

Also, replacing Q2's collector resistor (r5) with a trimmer to bias Q2 correctly can help.

That said, I'd socket the transistors so you can audition them for the best sound.
 
leadfoot said:
Also, replacing Q2's collector resistor (r5) with a trimmer to bias Q2 correctly can help.
Click to expand...
Is there any value in also replacing R7 with a trim to bias Q3 as well? Is there an ideal voltage for the Q2 and Q3 collectors? I'm currently measuring -5.6V at the collector of Q2 and -7.0V at the collector of Q3.

The pedal does sound nice to my ears using the transistors I have on hand: currently I have a MP39A (49.1HFE) in Q1, an MA287 (70.2HFE) in Q2, and an MA287 (84.5HFE) in Q3. I know all these are below the suggested gain ranges so I may replace them soon with higher gain transistor.
 
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