Lava Rim 2 - will my changes shorten its lifespan??

[ChrisKelly]

Hi guys

I set up Aron Nelson's Lava Rim 2 on breadboard after I found the schematic on this site. I was looking for a bass fuzz/overdrive to fatten up an analog kickdrum.

As usual, (since I'm a complete noob), I just changed/removed components until it sounded how I wanted it to. I ended up removing the 5k pot/22uF to ground - 'Drive' control altogether,  and just had a 100k resistor between Q1 base and Q2 emitter. And I also removed the 100k trimmer between Q1 collector and the 9V rail. In effect, Q1 collector went straight to 9V and Q1 emitter went to ground with neither having limiting resistors.

Its been working great, but today i realised that Q1 (a 2n3904) was getting really hot. So my questions are:
1) Can the circuit survive much longer like this? Or will Q1 just fail soon without any collector/emitter limiting resistors?
2) Do transistors in this type of circuit often get hot? And is this why Aron recommends they are mounted in sockets (so that you can replace them periodically)?
3) If a limiting resistor IS needed to prevent Q1 from failing, how can I select the smallest value possible (to maximise my output level)?

Thanks
Chris

[PRR]

> Q1 collector went straight to 9V and Q1 emitter went to ground with neither having limiting resistors.

1) Yes, it is frying.

2) Your output is connected to 9V. You shouldn't have ANY sound output. So your description is incomplete.

EDIT!! I am confusing Q1 with Q2.

Text descriptions of circuits are confusing. A crayoned-up schematic would be better.

[antonis]

Let's see what's happening here..
(veeeeery brutally..)

Collector resistor of Q1 shouldn't be considered as "limiting" one (Collector/Emitter current are set by Base current which, in turn, is set by Q2 Emitter voltage & 100k feedback resistor) rather than a tool for getting voltage drop fluctuations across it [+9V - (signal current X h_FE X R_collector)].
Besides the above, its presence IS essential for Collector bias point (a DC voltage level somewhere between power supply rails..) so when signal current alternates on Base, Collector voltage follows it..
(amplified & phase reversed..)

As Paul already told you, you CAN'T get any output from Q1 Collector in the abscense of any Collector resistor 'cause it's permanently tied on +9V supply..
(actually, you could get some voltage fluctuations if only load enough your power supply but that's totally another story toghether with a soon fried transistor..)

So plz remount 100k trimpot and tweak its value to get your desired (a)symmetry of clipping point..
Maximum output level is set by clipping diode pair forward voltage drop in combination with series 5k trim..
(Volume pot only dominates output level..)

edit: I've just realized you've also removed 5k Drive pot, so 100k feddback resistor is actually grounded..!! 
I double Paul's statement.. Your circuit shouldn't work at all..!!
(are you sure your Q1 isn't n-JFET..??)

[ChrisKelly]

Thanks guys

I checked and not only were Q1 and Q2 collectors going straight to the 9V rail, but also Q1 base was too 

Absolute lunacy  No idea how any sound was passing through...

I've added resistors back in as recommended. Thanks for saving me from destroying the circuit!

Cheers
Chris

[ElectricDruid]

I say! It looks like this time the magic smoke stays in!!

[antonis]

I checked and not only were Q1 and Q2 collectors going straight to the 9V rail, but also Q1 base was too 

That said, Q2 base should also be going straight to +9V..

More than interesting..!!