Messages

After re-reading the RG Keen debugging page, I thought q3 could possibly be a bad transistor, so I changed some things, Q1 stayed 2n3904, Q2 is now a 2n222 and Q3 is 2n3904.
Voltages are now
Q1 E 1.68 B 1.12 E .51
Q2 E 5.20 B 1.68 E 1.20
Q3 E 5.88 B 1.60 E 1.10

Sound is still crackly/splatty, volume when maxed is still only slightly greater than unity. Have I at least eliminated the transistors as the problem for now? Aargh.

Derek

I think the next part I need to focus on is the q3 emitter, it is way higher than the base, which I think means it is saturated if I read the RG Keen debugging page correctly.

My voltages are:
Q1 C 1.58 B 1.04 E 0.5
Q2 C 5.30 B 1.58 E 1.11
Q3 C 5.33 B 1.60 E 4.10

Does that seem like the next logical place to look? Not sure how to decrease the emitter voltage though.

Derek

Changed Q1 and Q2 to 2n3904 transistors, Q3 is still the BC109. Increased R6 to 470K and increased R13 to 150K.
With 9.12 volts in I am getting
Q1 C 1.58 B 1.04 E 0.5
Q2 C 5.30 B 1.58 E 1.11
Q3 C 5.33 B 1.60 E 4.10

R6 and R13 seemed like big increases from the 1k8, does that indicate a problem?
Q3 emitter is still high, how do I bring that down?

Otherwise it is somewhat improved, less fizzy, more volume (but still not much more than unity when maxed).

Thanks Haberdasher and Bean for your help so far, what do I do next?
Derek

I meant larger resistors, that was typed before I had any caffeine.
Derek

Power I measured at 9.12 volts, I will see what larger transistors will do to get the collector voltage down firtst, then maybe look at the C4 mod.
Derek

I rechecked the resistors again with  DMM for R6 and R13 and they both were at 1.78K. What value resistors would be good to try next to get the collector voltage down?
BTW the transistors I am using are 2n2222a for  Q1 and Q2 and a BC109 for Q3.
Derek

Am working on a Cherrybomb, and the sound is fizzy and only comes out when strings of guitar are plucked hard. Wiring, values, and orientation of components seem correct. Only substitution was on C4 I used a 220pF cap instead of the 200pF as listed.

Voltage readings with 9.12 volts in are
Q1 E .63 B 1.19 C 1.73
Q2 E 1.26 B 1.73 C 9.10
Q3 E 5.29 B 1.60 C 9.01

My guess is q3 is the problem because it is misbiased, is this right? But shouldn't the collector voltages also be around 5 volts also?

Where should I be focusing on to get this working correctly? Thanks for any help.
Derek

Just wanted to make sure I read things correctly, but on a TO18 transistor the emitter is marked by a tab, correct? And for Q1 the emitter leg is the one closest to C2 and R2 on the cherrybomb pcb board/layout?
I have a 2n2222a I want to put in Q1 and Q2 and a BC109 for Q3 and want to make sure they go in the right direction.
Thanks for any help, Derek.