Echo Base - a new PT2399 delay

[slacker]

Where you're measuring about 2.5 volts when you're expecting about 5 volts is probably caused by your meter, have a look at my post here for a explanation http://www.diystompboxes.com/smfforum/index.php?topic=110128.msg1009145#msg1009145. If the pedal sounds ok and the bypass switching is working then there's probably nothing wrong.
Have you got the LED connected? If you have does it flash when the effect is on or is it just constantly lit? If it's not flashing then the LFO isn't working which is why you have no modulation. There is a known problem with the LFO in that it stops working if the supply voltage is too low but it looks like you have a good 9 volts so that shouldn't be the problem. I would suggest double checking all the component values and connections around the LFO or maybe just rebuild that section in case you've made an error.

[brunob2]

Hello!
and thank you again for your help slacker..
It works!
It took me a closer look to how opamps really work to realize that shorting pins 1 & 2 would cancel the effect..I had the On/Off of the mod wrong.

The mod just started to work when I disconnected the jumper wire going from pin 1 to pin 2 of the TL072.

So thank you again, I just took on electronics a few month ago, this place looks like a great community!

Cheers!
b

[slacker]

Cool, good to hear you got it working.

[bccbass]

Hello everybody!

I'm a little late to the party, but was hoping I might be able to get a little direction in my Echo Base build. I've been going over this thread, and checking and re-checking my work for about a month now. I'm definitely on the novice end of the spectrum, but have built two pedals without incident. Any guidance would be greatly appreciated - thank you!

I'm using the MusicPCB board.

Symptoms:
The effect is always on (bypass switch does nothing). The LED is never lit. I can hear the delay is working - i can get self oscillation and all the pots change the parameters, but no signal passes through the effect. I can hear the clean signal however. Its as though I have both the delay, and the clean signal but it is not passing through the effect.

By accident, I discovered if I bridge pins 13 and 14 of the 4066 or the E and B of 2n5089 the LED turns on (and pulses with the oscillation) and the pedal seems to work properly (although bypass still doesn't work); I can get the signal to pass through the delay and it sounds pretty close to how it should.

Things I have tried so far:
Checking all solder points, reflow solder, checking for bridges
Replaced all IC's with others, from different sources. (PT replaced multiple times with others, but from same source)
Replaced the 2n5089

Here are my voltages:
4066:
1. 4.4
2. 4.4
3. 0
4. 0
5. 0
6. .4
7. 0
8. oscillates between 3.6-8v
9. 0
10. 4.71
11. 4.71
12. 9.38
13. .86
14. 9.59

PT2399
1. 5.05
2. 2.53
3. 0
4. 0
5. 3.09
6. 2.53
7. .62
8. .62
Pins 9-16 are all 2.54

TL072 on the "IN" side of board:
1. 5.06
2. 5.06
3. 4.6
4. 0
5. 5.06
6. 5.06
7. 5.06
8. 9.57

TL072 on "OUT" side of board:
1. 8
2. 3.3
3. 5.07
4. .86
5. oscillates between 4 and 6
6. 5
7. oscillates between 2 and 8
8. 8.7

7805
1. 5
2. 0
3. 9

5089
E 0
B .6
C .84

BC560
1. 2.3
2. 2.9
3. 0

Any and all help would be greatly appreciated. Thank you in advance!!

[duck_arse]

welcome to the forum, bccbass.

can you post some pics of that which you have built, please? board, component and copper side, and off-board parts, so's we don't miss anything.

there is something amiss around the "out" side TL072. pin 4 should be 0V, not some part volts, and pin 1 should be ~4V5. if you fitted the IC's in sockets, pull the IC's out (after powering off), power on and measure the voltages again on the empty IC socket pins.

[bccbass]

Most certainly!

I re-measured the "out" TL072 and got more normal readings:

1. Oscillates between 4-6v
2. 5.06
3. 5.06
4. Changes between .7 and .86
5. Oscillates between 4-6v
6. 5.06
7. Oscillates between 3-8v
8. 8.8

With the IC removed, the sockets read:
1. 1.05
2. 1.05
3. 5.06
4. 0
5. .7 (then slowly reduces)
6. 5.06
7. 1.7 (then slowly reduces)
8. 9.6

My inclination would be to just buy another PCB and start over, but they're sold out. :/

Thank you!!

[duck_arse]

well, now you just have to hope slacker happens along.

[duck_arse]

while we wait for him ....... please be having a look at the resistor next to pin 14 of the 4066. read the colour bands for me, tell me what value you have fitted.

I can't see you led's orientation from the pics, and I'm a bit worried about how many solder blobs and heat melts I can see on the component side. but if it works, carry on.

[bccbass]

Thank you for looking over my work! Yes - you are correct - the resistor by pin 14 is 10ohm, not 10k. I (very stupidly) put all 10k r's in as 10 Ohm. I must have missed that one - I'll fix now.

And yes, I agree, my board looks like its been in the wars - between the resistor debacle and me replacing transistors and trying to fix everything its taken a beating. I very well might try to source a new pcb and start over.

The LED is oriented correctly, I believe, because when I bridge those two aforementioned points it comes on pulses with the LFO speed.

Again - thank you kindly for taking the time to look over my shoddy work!

[bccbass]

Resistor has been replaced - and is still performing as before except:

The bridge between 13 and 14 on the 4066 no longer makes it work, but the bridge between E and B of the 2n5089 does still make it work correctly.

[duck_arse]

well, that point to your bypass switch being bad, cause it's meant to short the 5089 base and emitter to pull the collector low, taking 4066 pin 6 with, and whichever of pins 12 and 13 is selected by the tails/boss switch.

but slacker will be able to clear all this up, I bet.

[duck_arse]

in fakt, looking at what I can see of your switch wiring, it appears you have connected to a lug of both poles, instead of a lug and the common of one pole [if that is a dpdt X-wing switch]. pick one wire, move it from where it is to the middle lug of the other switch half, report back.

[bccbass]

Its actually a spdt switch - sorry for the unclear picture!

I agree - I think there is a problem somewhere in the switching section, but I think its more than just a wiring issue as the switch does nothing, and the delay is always on - its when I short that transistor that the audio signal is able to pass through the delay and be effected.

[duck_arse]

I have to admit that the more I walk around thinking about that transistor, the less I understand the working of it. you say shorting the transistor base to ground makes it work, but the switch action doesn't? also, I was wondering about that TL072 pin 4 that wasn't reading 0V. can you check continuity with ground on that IC?

[duck_arse]

I put the bypass transistor section on the bb to see what is. (I also saw on the circuit diagram the resistor to pin 4 from the TL072, so now that makes sense.)

with the switch on/short/closed/connecting, the transistor turns OFF, so there is no current in the collector resistor, and the collector then sits about 8V6. this pulls all those resistors hanging off it high/on/1.

when the switch is off/open, the c-b resistor provides base bias, the transistor turns ON, pulling the collector down to near ground/0V, I measured around 0V8, which SHOULD be low enough for the stuff following to think 0/off/low.

so - if you measure the collector voltage with the switch open, and then push the switch, does it swing? if no - does it swing when you short across the switch lugs?

geeze, I hope the problem really is that transistor ......

[Sanguinicus]

Hi all. Been a while since i posted here. Loving the echo base... excespt for one small bug.

Basically sometimes it loses volume. This happens when the effect is engaged or not engaged. Obviously the effect is always "on" because it's not true bypass, so it can happen in both instances. It's pretty annoying. Doesn't happen often and I don't know how to recreate the fault. Basically this stops it from being gig-worthy.

I have some other PT2399's lying around that i might try in the mean time. Anyone got any ideas?

[thermionix]

Sounds like a bad connection.  While listening with signal going through, gently wiggle wires around a bit, see if you can make it happen.  Lightly prod the components on the board with a chopstick or similar.  Could also be a bad footswitch, internally intermittant.

[Cenzoru]

Hi,

I'm trying to make the V2 scheme in a PCB board in Eagle. I need some help:
1.  Vref terminals. What are they and whether they should be connected to each other?
2. Why is the color changed (green and red) around the 4066, U4A and U4D ?
3. A/B ?? What should continue to "A/B".
4. Pin 3 and 4 from 4066 are not connected ?

I attached the scheme with some highlights on this questions.

Thank you,

[Oolooloo]

Hi Cenzoru,

Firstly, I should mention that I am not familiar with this particular schematic, but I have built the full version, with delay time modulation, so I may be of help.

1. Vref is short for voltage reference, in this case it provides DC bias for the two op-amp stages (U3A and U3B). Yes, you should tie every point labeled Vref together, they are all the same circuit node. It's the same as if there were wires connecting them, but instead they're labeled to keep the schematic neat and readable. The same happens with +9V and ground.

2. This one I can't answer. My guess is that someone highlighted those parts to illustrate their point in a discussion.

3. Connect "A/B" to "A" to get delay tails. Connect "A/B" to "B" to get Boss style delay (no tails, delayed signal is chopped off abruptly when effect is bypassed). This feature is explained in the original post of this thread. In the full feature schematic, node "A/B" is wired to an SPDT toggle switch so you can have both modes.

4. Yes, they are not connected to anything. The 4th switch on the CD4066 is not required and so it's left unused.

Hope it helps.

[garcho]

^ yes, no need to look at that schematic, look at the original:

http://www.musicpcb.com/documentation/

find the Echo Base link at the bottom of the list and you'll open a PDF with not just the original V2 schematic but also the BOM, some mods etc.