TUTORIAL Amentum Boost

MBFX said:
Oh yeah, I forgot why I posted this in the first place! I had the transistor the other way around, but nothing was happening. Faint sound would come through the amplifier, but nothing much. Turning down the volume pot all the way gave me some signal back. Flipping the transistor around in frustration made things louder. Not quite unity gain, but nearly. I meant to flip it back around and try it again but life got in the way.

Based on what I described, do you think it could be something else? The transistor orientation is the only thing I have changed with the circuit
Click to expand...
Let's take the volume knob out of the equation for now. Jumper the power section to the collector pin and also jumper from the collector pin to C3 (10n). What voltage are you getting with your DMM with respect to ground? You should be close to 9v. Chuck asked you earlier.
 
BuddytheReow said:
Let's take the volume knob out of the equation for now. Jumper the power section to the collector pin and also jumper from the collector pin to C3 (10n). What voltage are you getting with your DMM with respect to ground? You should be close to 9v. Chuck asked you earlier.
Click to expand...
Just checking, I need to measure voltage from collector to ground after removing the pot and adding jumpers?
 
MBFX said:
Just checking, I need to measure voltage from collector to ground after removing the pot and adding jumpers?
Click to expand...
Either do the jumper thing like I said or have the LEVEL pot fully cranked, which should act as a jumper from the power section to your transistor. Measure with your DMM the voltage on the collector pin (see above pinout). The black lead of your DMM should be attached to ground.
 
BuddytheReow said:
Either do the jumper thing like I said or have the LEVEL pot fully cranked, which should act as a jumper from the power section to your transistor. Measure with your DMM the voltage on the collector pin (see above pinout). The black lead of your DMM should be attached to ground.
Click to expand...

Thank you! I flipped the transistor around, then connected the battery. Then I measured the battery while connected to the circuit, and got 9.45VDC. Then I cranked the pot and measured as you said, collector to ground, and got 7.69VDC. Emitter to ground was 0.192VDC. Vce = 5.76VDC, Vbc = 3.69VDC, Vbe = 0.581VDC

I double checked my pot (Mammoth B10K), and it is definitely labeled correctly, so I unhooked it and measured it: 0.01ohm one way, 10.05kohm the other way. When the pot is fully CCW, the voltage between 1 and 2 is 0.00VDC, the voltage 2 and 3 is 3.131VDC, and the voltage between 1 and 3 is 3.130VDC. Fully CW, 1 and 2 is 3.129VDC, 2 and 3 are 0.00VDC, and 1 and 3 are 3.125VDC
 
MBFX said:
Thank you! I flipped the transistor around, then connected the battery. Then I measured the battery while connected to the circuit, and got 9.45VDC. Then I cranked the pot and measured as you said, collector to ground, and got 7.69VDC. Emitter to ground was 0.192VDC. Vce = 5.76VDC, Vbc = 3.69VDC, Vbe = 0.581VDC

I double checked my pot (Mammoth B10K), and it is definitely labeled correctly, so I unhooked it and measured it: 0.01ohm one way, 10.05kohm the other way. When the pot is fully CCW, the voltage between 1 and 2 is 0.00VDC, the voltage 2 and 3 is 3.131VDC, and the voltage between 1 and 3 is 3.130VDC. Fully CW, 1 and 2 is 3.129VDC, 2 and 3 are 0.00VDC, and 1 and 3 are 3.125VDC
Click to expand...
High level these seem ok. is the circuit working now? if not, probe the signal going to base pin and on the output. Are they different volumes?
 
It's still quiet. I don't know what's wrong.... Maybe I should remove the Auditorium board from the equation, solder some leads to some TS jacks, and attach those. I doubt it's the Auditorium, but who knows? I'll build an audio probe and keep trying when I have a free evening
 
MBFX said:
It's still quiet. I don't know what's wrong.... Maybe I should remove the Auditorium board from the equation, solder some leads to some TS jacks, and attach those. I doubt it's the Auditorium, but who knows? I'll build an audio probe and keep trying when I have a free evening
Click to expand...
your probe can just be the output wire
 
The collector current is too low. Ideally, we want the collector current (Ic) to be around 400μA in this circuit for the best balance between gain & headroom. Ic in your circuit is 148μA. You can increase the collector current by reducing R3. Try 4.7M. R2 limits the gain of this circuit to 18dB (7.7x). Lowering R2 will increase the gain and not upset the biasing. Try 680Ω and see if that helps.

Don't try to measure Vbc directly. Your DMM input impedance is 10M and you're putting that in parallel with R3. If we subtract Vbe from Vce, we get Vcb = 5.172V, which makes more sense.
 
I learn more every time I come to this forum, usually from you two and Bean. Thank you! I just got a box of stuff from StompBoxParts including some Soviet Ge transistors so I'm feeling pretty motivated to fix this issue and clear up my breadboard for Fuzz Face adventures. I'll try reducing the R3 value to 4.7M, and R2 to 680R. If that doesn't do anything, I will just depopulate the board, remeasure my components and label them, and reassemble.
 
I have seen that once or twice. I just really like the way the Arrows sounds. What's wrong with this particular circuit?
 
Rimshot from the peanut gallery, if it's not on a board from Bean, Rob or these 2 guys from EQD, I don't look at it. it's not much different than an LBP-1 or Fa-1.
 
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If it does what you want, then that's all that matters.

Have you compared it to any other one-transistor booster like the MXR LPB, Zvex SHO, Keeley Java, Catalinbread Naga Viper or Lovepedal COT?
 
Based on the DC measurements above, I believe his 2N5089 is in spec. The Arrows's biasing scheme depends on HFE and like any high-gain transistor, there is a fairly large spread on the 2N5089's HFE spec. As a result, each 2N5089 will bias a little differently.
 
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