Crowther Hotcake Clone issues

[facon]

Hey guys, a little embarrassing, but I could use some help with a Crowther Hotcake clone. I've built 8 pedals in a row with zero problems and it's strange that I'm having issues with (by far) the simplest circuit. I swear I'm not incompetent.

I'm using the Tagboard Effects vero layout: http://tagboardeffects.blogspot.com/2012/02/crowther-hotcake.html

There are a few small modifications from the original circuit. The 56n capacitor is 47n and the 82n capacitor is two capacitors wired in series for 77n (100n and 330n). I also added an led resistor on the board and cut a trace under the top right 220 resistor to do so. This allowed me to wire the red led lead directly below Presence 3.

Problem: The pedal is very quiet and no gain is present. Volume knob does function (even though all the way on is very quiet). Tone knob also seems to work. Gain knob is not working correctly. When all the way off (left), the volume seems to swell upward quickly until there is a slightly popping sound. Then the volume goes back down. Gain knob all the way up (right) is just the quiet volume. On the gain pot, I have 1 and 2 (from top mounted view, 3 - 2 - 1) wired together with a jumper and 2 is sent to the input sleeve. I have the grounds from the board wired to the input sleeve and center lug on the switch.

Edit:  The volume is now back to normal when the gain is all the way down. When I start turned the gain up (around half way), I get strange swells that end with a pop (almost like a tremolo that sounds like a heartbeat). The swells get faster and pops get louder as I move the pot up. I've gone over the solder joints on lugs 1 and 2 multiple times with no luck. The pot seems to work though because the resistance when reading from input, output and switch ground connections all correlate with the pot's position. I noticed that the gain starts throbbing at around half way. Under that, it seems fine. However, if its under the normal throbbing point and I unplug the input jack, it will start making very loud oscillations or strange noises.

I've gone through all of the ground points on my board with a multimeter and I measure 0 ohms from every component lead on ground from input sleeve, output sleeve and center pin on switch.

Pics:





IC (TL071CP)
P1 141 mv
P2 1.9 to 2 v (jumps around, hard to measure)
P3 2.0 to 2.1 v (jumps around, hard to measure)
P4 0
P5 133 mv
P6 1.9 to 2.6 v (jumps around, hard to measure)
P7 8.24 v
P8 5.65 v (slowly lowers)

Z1 Zener
A 0 v
C 8.24 v

Electrolytic
1 (left) Positive 2.57 v
Negative 84 mv
2 (right) Positive 4.35 v
Negative 0 v

[facon]

Also, if anybody has any links on how to verify IC voltage is correct that would be appreciated.

[jbgron]

I had a similar problem with the Hotcake, lug 1 and 2 of the Gain pot need to go to ground.  I hope this fixes your issue.

[facon]

Lug 1 and 2 are jumped. From 2 I have it wired to the ground at the input sleeve.

[facon]

Okay, I went back over all of the solder joints associated with the gain pot. The volume is now back to normal when the gain is all the way down. When I start turned the gain up, I get strange swells that end with a pop (almost like a tremolo that sounds like a heartbeat). The swells get faster and pops get louder as I move the pot up. I've gone over the solder joints on lugs 1 and 2 multiple times with no luck. The pot seems to work though because the resistance when reading from input, output and switch ground connections all correlate with the pot's position.

[facon]

Looks like I'm giving in for the night. I noticed that the gain starts throbbing at around half way. Under that, it seems fine. However, if its under the normal throbbing point and I unplug the input jack, it will start making very loud oscillations or strange noises.

[facon]

Original post edited to show recent updates. Does it look like I have a bad chip? Is my grounding incorrect? Is my gain pot bad? Any other suggestions?

[kupervaser]

I built this pedal from the following layout:
https://dl.dropbox.com/u/3131065/Pedalen/Crowther%20Hotcake/Pancake%20Project2.pdf

It sounds very nice, however i notice that when the notes decay it doesn't sound very smooth.
Has anyone experienced this?

Here is a sample I recorded:

https://soundcloud.com/jeff-tsyvyan/crowther-hotcake

Looking forwards to some of you guys reply.

[aron]

Sounds like a bias problem. What is that oscillation at the beginning of the clip? That could point to something as well. I haven't used the Hot Cake in a long time, but I don't remember the decay problem.

[kupervaser]

You heard it correctly, it oscillates in bypass, but this is my test rig, so I don;t think the input is grounded in bypass.
I measured the voltages on the IC (TL071CN), they look good to me:

Pin1:0,18V
Pin2:4,8V
Pin3:4,4V
Pin4:0V
Pin5:0,18V
Pin6:4,8V
Pin7:8,8V
Pin8:0V

[kupervaser]

I forgot to mention that I did not have a 8,2V zener at home and I put a 1N4007 diode insted.
Maybe this could be the issue?