Populated the RR and the Quadrovibe board. The lamp doesn't pulse. Stays lit. The circuit passes the guitar signal. The trimpots seem to do their job. When the toggle switch is set to tremolo the trim volume works. I've checked continuity around the part of the circuit that drives the lamp. Seemingly no solder bridges. I tacked the transistors in their sockets with a little solder. I've double checked transistor orientation. I measured the speed pot resistance and it seems to be functioning properly (although being a 100k pot it only registers 67k).
Is their a part of the circuit I should be focusing my attention on?
Thanks!
(http://img.tapatalk.com/d/14/05/28/ezenesug.jpg)(http://img.tapatalk.com/d/14/05/28/he4ene8e.jpg)
The LFO doesn't seem to be running. Essentially, it's what makes the LED go bright and dark. I would start measuring voltages in there, an Audio Probe is not what you'd use.
Jacob
Voltages on the transistors?
Is that what the lamp specced for this project looks like? Looks more LED-ish, from that angle...
I went with the build document recommendation. It was definitely shaped like a lamp vs LED.
Am I correct in thinking Q4 drives the oscillation? Is that where I need to focus my attention? I pulled up the datasheet on the MPSA13 but I don't know what I'm looking at.
Here are the voltages
Q4: C-9.12V B-7.69V E-16.53V
Q5 (voltages change with the gain trim - this is set about halfway): C-2.59, B-3.7, E-13.08
Quote from: PhiloB on May 28, 2014, 01:24:00 PM
Here are the voltages
Q4: C-9.12V B-7.69V E-16.53V
Q5 (voltages change with the gain trim - this is set about halfway): C-2.59, B-3.7, E-13.08
You have these backwards -- the emitter of Q4 is connected to R19. The collector is connected directly to +18V (or 16.53 in your case). Make sure your transistors are in correctly.
Is your rate LED -- the one connected to R19 -- connected to ground? It won't work without that. Since your emitter voltage is HIGHER than the base votlage on Q4, I suspect not. ;)
I oriented the MPSA13s according to the Layout Diagram. I did I search for pin outs for this transistor so if know how to label the voltages. It could very well be in backwards or I could have labeled them wrong.
Also, I don't have the rate LED attached, didn't realize it would cause a problem:). I'll hook it up tonight and see if the fixes it. If not I'll flip those transistors around (Q 4&5)
Here is the pic of the pin out
Small Bear doesn't list the manufacturer so I'm assuming it is correct.
(http://img.tapatalk.com/d/14/05/28/vu9ujuzu.jpg)
This would have the collector connected to R19 if I'm not mistaken
Did a BING search for MPSA13 pin out and the majority of images were opposite of what I posted above which would make my voltage labeling incorrect.
Thanks very Jon. Insightful as always. Look forward to getting home (late tonight) and hooking up the rate LED. Hope that is all it is.
What kind of lamp is that?
The JKL 560-8099SB
From Small Bear- advertised as 'for the Madbean Vibrato'
It looks red...is that just the lighting?
What color should it be? I have difficulty seeing the color red. It might be?
It seemed white to me;)
Ok, my wife says the bulb is yellow/orange.
More importantly, hooking up the rate LED fixed the issue. My bulb pulses. I have tremolo/vibe!!
Thanks Jon, you nailed it!