March 5, 2019 at 7:54 pm #4570
Started on my third pedal this week, the EA Tremolo. Was successful with the American Fuzz and the Emerald Ring (that effect made my other pedals so much better!) so thought I would be a little more ambitious. So far I can’t get any signal through the effect. After tinkering around, this is what I’ve come to:
-LEDs light and/or flash as they should, and the speed of flashing is coordinated with the potentiometer setting
-Bypass works fine
-using an audio tester I can only trace the signal through the first few components, however…
-using a multimeter I can find the oscillating voltage at various sites in the circuit
Any suggestions on where to look at voltage or obvious issues with my wiring (it’s a little ragged now after tampering and redoing it in so many places, however the switches are working at least as evidenced by the LEDs and bypass functions).
Thanks.March 5, 2019 at 8:30 pm #4571
Where your audio stops is usually your problem area
What is the last component where you have audio going in but not coming out?
The first thing I would do is reflow your solder joints where you lose audio this would normally indicate a dry solder joint causing a poor connectionMarch 5, 2019 at 9:09 pm #4573
Just heat the joint for around 3 to 4 seconds until the solder melts and reflows heat the solder pad and component leg at the same time to get a good electrical connection, just for info the audio path is highlighted here in blue
Where is it you actually lose audio? The only part of the circuit you should get audio is in the aptly named ‘audio’ section in purple below
Here are the voltages you should be looking for.
Power Supply 9V
G +0.5V to -4V
C 0V – 7V
E 0VMarch 5, 2019 at 10:35 pm #4575
With the neg probe to ground, my readings are:
Q1: 3.48, 2.32, 10.53
Q2: 10.46, 1.99, 1.68
Q3: 1 to -0.3 (continuously changing), -0.53-(-0.18), -0.17
Q4: 6 to 2 (changing), 0.67-0.63, 0.0March 6, 2019 at 7:44 am #4578
That’s correct place your black probe to ground and touch each transistor pin with your red probe with your meter set to 20V DC
So you’re not getting signal into the Gate of Q1 is that correct the pin with the arrowhead on it in the schematic?
I’m assuming you’re using an unregulated power supply with over 10v that would affect the voltage going into the JFET 2N5457 Q1 and Q3 these are voltage controlled devices
If you don’t have audio going into Q1 then your problem lies prior to it C1, R2, R3
R2 and 3 form a voltage divider giving you half the power supply 4.5v
Here’s the transistor pinouts you can find this information in the datasheets or by searching 2NXXX pinout which I find easier to do there is some information on page 15 of the beginners guide to components
Q1 and 3 2N5457
Q2 and 4 2N5088March 6, 2019 at 8:20 pm #4600
I have signal from my audio input through both R2, R3, C1 and then the first pin of Q1. My values after reflowing the socket for Q1 are g=3.4, S=2.3, and D=10.4. I thought of a variable that may matter. Mammoth electronics didn’t have 2N5457 transistors and I remembered that trying other transistors was a way to tinker with the sound so I substituted 2N5089 for the two 5457’s. Could that be the root of my voltage and signal issues?March 6, 2019 at 10:54 pm #4607
For this circuit yes 2N5089 is an NPN BJT (bipolar junction transistor) which you could replace the 2N5088 with but the 2N5457 is a JFET (Junction gate field effect transistor) so they work differently
You can use other JFETs I’ve got a 2N5459 in mine but it has to be a JFET type being voltage controlled rather than current controlled as with a BJT transistor
The closest N channel JFETS would be the 2N5458 and 5459March 7, 2019 at 12:46 pm #4611
FWIW I’ve just built the selfsame circuit, but noticed that it doesn’t seem to work if D1 is not connected.
Maybe try this if it still fails to work after you’ve replaced the BJTs with FETs.
@billy: 2 questions if I may
- 5459s are fairly easy to obtain here (South Africa), unlike 5457s and 5458s, which are scarcer than hen’s teeth. However they don’t always seem to be a comfortable straight swap. Some (unwanted) distortion creeps in, or so it appears to my ears. Do they behave similarly to 5457s, or should one adjust bias resistors or what have you? BTW I’m not assuming there’s a straightforward answer to this one.
2. For some unknown reason, on my build the rate pot works the other way round (i.e CW gets slower). I’ve double checked the installation and it looks ok. Just wanted to check that this is intended? If so, well and good and I haven’t entirely lost the plot.
Thanks again and hope this doesn’t entirely Muddy the Waters (pun intended). Best, MarcMarch 7, 2019 at 1:39 pm #4614
Yes that’s where I’d start adjusting the bias resistors distortion is more likely to come from Q2 which amplifies the signal from the buffer Q1 that’s not to say a FET wouldn’t cause it best way to suss where it distorts is to audio probe it
And yes the speed pot on mine was the same there are different versions of the pcb simply swap lugs 1 and 3 around at the pot lugs not pcb pads no chance of accidentally lifting solder pads with too much heat desoldering then plus it’s a lot easier to desolder pot lugs just heat and lift away no need for solder braid or sucker or new solder
D1 is part of the circuit if it’s not there then you d have an open circuitMarch 7, 2019 at 2:00 pm #4616
mybud – it appears that the LFO and Ctrl sections get their voltage supply thru D1, so D1 must be connected for the circuit to work properly.March 11, 2019 at 11:23 pm #4706
With the 5457s now in place, I have the following voltage:
Q1 D: 9.7, S:4.9; G: 3.2
Q2 C: 9.7, B: 1.8, E: 1.5
Q3 D: 0.1, S: 0.9, G: -0.03 to 0.04
Q4 C: 4-4.5, B: 0.6, E: 0.0
I can trace the audio all the way through the volume pot. The only other substitution I’ve made was a 330n capacitor for C2 because the part was out of stock.
Any suggestions? I still have no effect on the signal.March 12, 2019 at 8:44 am #4713
Hi : Here are some voltage measurements from my circuit (averaged because they fluctuate quite a bit).
Q1: D S G
8.44 5.72 4.04
Q2: C B E
4.55 2.17 0.97
Q3: D S G
-1.75 0.001 -2.0
Q4: C B E
1.75 0.6 0.0
Perhaps these’ll help, hope so.March 12, 2019 at 10:05 am #4714
If you have tremolo audio OUT at volume lug 2 and not beyond that would suggest a problem with the wiring from the pcb to the 3PDT incorrect wiring or dry solder joint or the kill switch is engaged
We would need a picture looking down on your 3PDT so that we can trace which lugs the pcb IN and OUT ‘T’ pads go to I can’t actually trace it in the photos we have
Volume Lug 2 is the circuit out which goes to the OUT jack tip via the 3PDT it is also very easy when the 3PDT is the wrong way up to wire your IN to your OUT the wrong way round ie wire your IN to the right and OUT to the left the quickest way to check is simply put your IN cable from your guitar into your OUT socket on the pedal and your OUT cable to amp into your IN socket if you get audio you’ve wired it the wrong way round on the 3PDT lugs, note in that scenario you would still get bypassMarch 12, 2019 at 10:18 pm #4741
I tried switching the inputs and it didn’t resolve the issue. I re-flowed all the joints on the PCB. I double and triple checked the wiring to the switches. The audio output at the volume pot is very low, but if I use the audio tester at other points I can detect the tremolo (but only as a beat, not as an audio signal). Should I scrap the project and start over? I feel like the board is correct but I can’t get to the problem. The LEDs respond to the pots, I’ve switched back and forth so I know it isn’t just the kill switch.
My voltages aren’t perfect, but they aren’t far off of mybud’s.March 12, 2019 at 10:33 pm #4744
I can say that something is a miss but I would be looking at everything.
Take voltages with the Speed pot down and the Depth pot full up because of the LFO. I would be curious where your 2N5457s came from because good ones are very difficult to find these days. I agree with what Billy said.
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