stupid question? JMK Hamlet + 18v?

[duck_arse]

ahh, apologies - I was looking at the original docs from jon, I didn't realise it had been beaned. ignore my C9//R14 reference.

[heathfball20]

Well, I went ahead  and soldered a hard jumper from the c2/c3 to the 3rd output leg. That fixed up the dry and wet signal. Now I need to find the whatever is being grounded. I have that ground noise from the amp. Gonna tackle that after work today.

[midwayfair]

Well, I went ahead  and soldered a hard jumper from the c2/c3 to the 3rd output leg. That fixed up the dry and wet signal. Now I need to find the whatever is being grounded. I have that ground noise from the amp. Gonna tackle that after work today.

Ground sounds like silence. A LACK of ground connection, however, can sound like a hum. First make sure all ground points on the enclosure and jack connections are complete (for instance, if you're not inside an enclosure, is your output jack grounded?). Then do an audio probing ... find out if the hum exists at the input, the collector and/or emitter of Q1, and the gate, drain, and source of the 2N5457 (you should still be able to hear low frequencies at the source). The things to look for will be different depending on where you find it.

Good job finding the missing connection! Those are definitely one of the hardest fixes to identify.

[heathfball20]

Haha, yes a lack of ground is definitely what I meant! Lol, my bad. I promise I know that! Yeah I have that hum sound, I just couldn't think of the word to use. I appreciate you're help! Your telling me to take out q2 and the pt2399 helped me to really understand the schematic. Point to point is how it is. Once that clicked, I went through the the connections and found that break. I'm learning a lot! I'm just glad I learn quick! I do this stuff on Big trucks finding breaks in continuity where thousands of wires are involved. I should have caught on a whole lot quicker but at least I get it now

[heathfball20]

Ok, so here are the pin readings on the transistors.

Q1 2N5088
E=2.06
B=1.83
C=11.77

Q2 2N2457
D=16.67
S=0.72
G=0

Q3 BS170
D=0
G=Fluctuates
S=0 - 0.02

REG 78L05
I=11.02
G=0
O=4.95

[heathfball20]

Does the LED have to be a specific kind? I only had the super bright clear LEDs. Would that affect it?

[heathfball20]

When i touch the drain on Q2 2N5457 to a ground, most of the hum goes away.... but i lose the tails. when i touch the emitter on Q1 2N5088, the guitar signal just gets amplified and distorted.

[heathfball20]

Ok, so. Q2 2N2457 when i ground the source leg, most of the hum goes away. and i still have the tails.

[midwayfair]

I need to know where the hum is introduced.

You can build an audio probe with a cable, some aligator clips, and a capacitor. If you look on the debugging pare for this form, it has an illustration. You'll use that to probe for sound at different places in the audio path.

While it's interesting that grounding the source of Q2 kills the hum, it doesn't really tell me much of what I need to know. (For the record, what that does is max out the gain on Q2 assuming a bias that keeps the FET working.

[heathfball20]

Ok, so what am I to listen for while probing? Do i need to have the signal from the guitar?

[midwayfair]

Ok, so what am I to listen for while probing? Do i need to have the signal from the guitar?

Yes, or a test signal, or just listen to see if there's hum.

[heathfball20]

I guess thats not what im understanding. There is a hum as soon as you apply power. When the output is plugged into the amp, without a guitar signal. Whether the delay is on or off. The delay sounds awesome, i  wondering if i should just get a noise gate. Like the EHX Silencer. Because outside of the hum... when i play with it, the pedal sounds just amazing!

[heathfball20]

I believe the hum is being introduced at the emitter pin on Q1 2N5088? Or at R2 on the R2/R3 leg. Its clear on signal on the other leg of the R2. The Base and Collector legs of Q1 are clear as well

[heathfball20]

FYI. I changed the board. I didn't like all the breaks I found so that was the logical conclusion. The pedal works. Both delay and bypassed. Like I said before, the hum I have now, I believe it is being introduced on the Q1 emitter leg or at the R2/R3. I was able to narrow that down by audio probe.

[midwayfair]

FYI. I changed the board. I didn't like all the breaks I found so that was the logical conclusion. The pedal works. Both delay and bypassed. Like I said before, the hum I have now, I believe it is being introduced on the Q1 emitter leg or at the R2/R3. I was able to narrow that down by audio probe.

(a) Is it there regardless of whether the delay is bypassed?

What are you using for Q1? 2N3904? 2N5088?

Short the 4.7K on the collector and audio probe at the emitter. Is the hum still there?

(b) If you breadboard just Q1 (the input cap and collector, base, and emitter resistors) and audio probe the emitter, do you get the same noise?


It's just an emitter follower, there's really no reason you should hear noise there unless it's also at the input, but I'll try to eliminate every possible source

[heathfball20]

Yes the hum is there when the delay is bypassed and active. I'm using a 2N5088 for Q1. Ive used 2 2N5088's and the result is the same. I'll short the resistor at the collector and audio prob when I get home from work this evening. Thanks.

Yes Q1 is at the input just before the bypass switch

Here is the link to the schematic
http://jmkpcbs.com/wp-content/uploads/2014/03/Hamlet+.pdf

[heathfball20]

Sorry it took so long to reply. Its been pretty busy.

So i breadboarded the Q1 like you said Jon P. Hum at the Emitter is not present.

Im thinking the hum is at the R3 side of R2 because the signal is clean at the C1/R2/Base connection. but on the R3 side of R2 the hum starts.

Could it be coming from VA? im sure this is another stupid question but are all the VA's on the schematic connected? is that supposed to be a layer of connections on the Circuit board so you have VA, VB, VC? Or am I way off?

BTW Jon P. I checked out your band Midway Fair. You guys are pretty good. Not really my style of music to get into, but from a musicians stand point... not bad man.

[midwayfair]

The Vx components on the schematic are all present.

Is there a chance you can figure out the frequency of the hum?

This thingll kill a battery in an hour, but if you power it temporarily with one you can rule out the power supply.

[heathfball20]

I cannot measure the frequency of the hum. It's a kind of deep tone. I'll use a 9 volt and see what that does

[heathfball20]

Jon P!!!! You're the man! All my 9V batteries are dead :/ but I had an old 9V 1300ma power supply from my wife's old breast pump. The shield was ground, and the prong was +, so I had switched that on the power supply circuit board. Plugged into my pedal chain and SILENCE!!!!! My old power supply is apparently bad. But all is well in my world now! I appreciate your help sir.