Hi everyone ... I'm having some issues with my Dyna Comp clone build. I've got a schematic built and have it on the breadboard, but I can't get any output from the IC.
I've verified just over 4v at pins 2 and 3 and I get signal into the chip at those pins. However, I get no audio out of pin 6.
The one issue I've definitely found is that for some reason I'm not getting the expected 2.5v from the bias voltage divider after I pass through the filter.
See the GGG schematic here ... http://www.generalguitargadgets.com/pdf ... _dc_sc.pdf
I get 2.5v coming from the voltage divider of R13/R15, but have around 6v at the base of Q5 after passing through R14. It's supposed to be 2.5v - 3.1v depending on the info I'm looking at.
Could this be the reason I'm not getting any output? Any help is appreciated. I know biases are off, and this is the first place I could find where they don't line up, so I assume it's causing issues all down the line.
Dyna Comp clone bias voltage issue
Anyone? I'm at the point of ripping up the entire second half of the board and reassembling with all new components. I just don't know what's happening.
-
Fender3D
- Cap Cooler
I don't know what info you read... but you should set TR1 for 0V across R14.
If you can't get there, maybe your 3080 is fake or dead...
BTW
27K+56K with 9V give ~2.9V @ junction
Check Q4 also.
If you can't get there, maybe your 3080 is fake or dead...
BTW
27K+56K with 9V give ~2.9V @ junction
Check Q4 also.
Okay, You've lost me at 0v across R14. I'm supposed to have 2.5v @ pin 6 through R14 I thought? I've currently got TR1 bypassed and replaced with two 1k resistors for testing. The voltage at pins 2 and 3 are within spec, so the voltage divider at TR1 seems to be set correctly. It's there to adjust for noise, right? And usually stays set at 50%?
I'm feeding my board off of a battery which is just under 9v. I want to says that the top side of R14 is 2.67v.
I've tried two different 3080s, but they are the lower end 3080E ICs. I can try a third I guess.
I did find some odd issues with the other transistors. The emitter isn't at 0v on Q2 or Q3. It's almost like I've got a bad ground between my boards, but continuity checks fine.
I'll check Q4 and note the voltages and post. Thanks!
I'm feeding my board off of a battery which is just under 9v. I want to says that the top side of R14 is 2.67v.
I've tried two different 3080s, but they are the lower end 3080E ICs. I can try a third I guess.
I did find some odd issues with the other transistors. The emitter isn't at 0v on Q2 or Q3. It's almost like I've got a bad ground between my boards, but continuity checks fine.
I'll check Q4 and note the voltages and post. Thanks!
And the info I'm going by ...
http://www.generalguitargadgets.com/pdf ... struct.pdf - Biases are at the end. Pins 2 and 3 are 4.4v (basically a balanced voltage divider) and pin 6 is 3v.
https://www.electrosmash.com/mxr-dyna-comp-analysis - Says pins 2 and 3 are to be balanced to reduce noise, and should be around 4v. Slightly below is states that "Q2" (transistor base off of pin 6 in this schematic) should be 2.5v, and shows the 2.54v source from the power supply entering "R8" (R14 in the GGG schematic).
http://www.generalguitargadgets.com/pdf ... struct.pdf - Biases are at the end. Pins 2 and 3 are 4.4v (basically a balanced voltage divider) and pin 6 is 3v.
https://www.electrosmash.com/mxr-dyna-comp-analysis - Says pins 2 and 3 are to be balanced to reduce noise, and should be around 4v. Slightly below is states that "Q2" (transistor base off of pin 6 in this schematic) should be 2.5v, and shows the 2.54v source from the power supply entering "R8" (R14 in the GGG schematic).
-
Fender3D
- Cap Cooler
I don't know what noise electrosmash is talking about.
Surely not about hiss since we're dealing with one of the noisiest chip ever made
The noise you're going to reduce is a kind of "tock" when gain abruptly changes (or "compressing")
TR1 is there to null 3080's offset voltage.
By costruction each chip is slightly different, even on the same batch; by applying voltage at its inputs you can set it so that its output is balanced edit: centered around chip's optimal working point voltage (aka bias).
If you put DMM's probes on R14 pins you have ideal offset balance when you measure 0Vcc (no signal @ input, of course)
Short Q4's E and C pins: 3080's gain should change, otherwise it's broken or fake...
Surely not about hiss since we're dealing with one of the noisiest chip ever made
The noise you're going to reduce is a kind of "tock" when gain abruptly changes (or "compressing")
TR1 is there to null 3080's offset voltage.
By costruction each chip is slightly different, even on the same batch; by applying voltage at its inputs you can set it so that its output is balanced edit: centered around chip's optimal working point voltage (aka bias).
If you put DMM's probes on R14 pins you have ideal offset balance when you measure 0Vcc (no signal @ input, of course)
Short Q4's E and C pins: 3080's gain should change, otherwise it's broken or fake...
Hmmm, okay. That's helpful.
Tonight I'm going to remove the input buffer since I don't really need it and then work on checking bias like you've said. I've noticed a difference in the schematics as well with the 500k pot controlling the compression. GGG has pin 3 disconnected and Electrosmash has pins 2 and 3 connected. I believe pin 5 on the IC has an impact on the voltage out on pin 6, so maybe that's one of the issues?
The beauty of breadboarding I guess ...
Thanks again for the help!
Tonight I'm going to remove the input buffer since I don't really need it and then work on checking bias like you've said. I've noticed a difference in the schematics as well with the 500k pot controlling the compression. GGG has pin 3 disconnected and Electrosmash has pins 2 and 3 connected. I believe pin 5 on the IC has an impact on the voltage out on pin 6, so maybe that's one of the issues?
The beauty of breadboarding I guess ...
Thanks again for the help!
So last night I went through all of my bias values and got all but one of the transistors properly biased. I did this by moving my bus connections and some jumpers around on my breadboard. I was able to get output from the IC on pin 6, but it was overdriven. Bias voltage to pin 5 was never correct. After some more adjustment It stopped working and would output audio for a moment when plugging in Q1, then it would die. I assume this is the IC cutting out as it moves outside of it's operating range.
So, it seems that my breadboard is the issue and I'm not going to be able to get a decent prototype with my current setup.
So, it seems that my breadboard is the issue and I'm not going to be able to get a decent prototype with my current setup.
Yeah, I'm sorry for any confusion. I maybe should have said prototype board?
Either way, I've got someone waiting on me to supply a board for printing so I'm going to just double check everything I can, finish my layout and send it on. If it doesn't work, I'm only our a few bucks I guess.
I do appreciate all the help and will let you know if it works out.
Either way, I've got someone waiting on me to supply a board for printing so I'm going to just double check everything I can, finish my layout and send it on. If it doesn't work, I'm only our a few bucks I guess.
I do appreciate all the help and will let you know if it works out.