Ross phaser build help!!!!

[Tychobrahe1979]

I just finished testing my newest creation and nothing happened. I hooked everything directly up. No stomp switch. Just the bare necessities. I like keeping it simple when I first fire up a new toy. Anyway the signal is going through fine but it is as if the pedal were not between my amp and guitar at all. I scrutinized my board making sure nothing was touching something that should not be and that all my components were in correctly. I always test my resistors before I put them in ( I did actually find two that were no good doing this ) and my diodes. I then took my multimeter and checked the entire board making sure everything was getting power. I even checked out my IC's. So I am at my wits end with this one. Going over previous topics about the Ross Phaser I was unable to find any helpful ideas. So if anyone has built this and had the same problem can help I would really appreciate it. Oh yeah I used the tonepad schematic and the mods listed there as well.

[Boofhead]

Which one did you build - black or orange?

Check opamps are at mid-supply - which is set by the voltage on the zener in the orange unit.

Make sure your LFO is working connect a 10k resistor in series with an LED and probe the LFO and make sure it flashes.  On the black unit this might not be a simple exercise.

Don't have my schematics with me so - I'll wait 'til we get the black/orange thing sorted out first before we get stuck into the details.

[Tychobrahe1979]

http://www.tonepad.com/getFile.asp?id=47


Thats a link to the schematic I am using. I checked it out good and it doesn't mention if it is the black or orange version.
Let me just say that I have successfully built around ten different pedals but I still am learning on the go so I am not overly knowledgeable with the electronics vocabulary. I understand what you said about testing the LFO out with a LED and 10k resistor and I will be doing that right away. I'm not sure what you mean about checking the opamps to see if they are at mid-supply. I assume you are talking about the 8 pin 4558 IC which is located directly below the diodes in reference to opamp. I am not sure about the other part though.
Believe it or not I will be going to school soon to get into electrical engineering. :lol:  Well I'll get back as soon as I can with my LED test.
Thanks

[Tychobrahe1979]

Grounding the LED to common ground on the board I got the LED with the 10k probing tip to light up at several spots but no blinkers anywhere. If the mid supply means that pins 4 and 8 on the 4558 should read exactly half the voltage as is being supplied to it then it did.

[David]

Grounding the LED to common ground on the board I got the LED with the 10k probing tip to light up at several spots but no blinkers anywhere. If the mid supply means that pins 4 and 8 on the 4558 should read exactly half the voltage as is being supplied to it then it did.

Umm...  I see two problems.  Pin 8 of a dual op-amp should be getting the full supply voltage, not just half.  Pin 4 is to be wired to ground.

[Boofhead]

Just for interest, that's the Black Ross phaser.

With the multimeter -ve lead on ground pin 4 should measure 0V, and pin 8 should measure +9V.  Those are the power pins, if you don't get these voltages there is no chance of the unit working.  Check your power wiring and your ground connections - make sure you have used the correct terminals on your jacks.   To simplify things even further, you could wire the battery directly to the PCB, and connect the multimeter -ve to the board not the case. If the voltages don't look correct check the power and ground wiring like I said.  Also check the OTA.  The LM13600 isn't a normal opamp it's an OTA.  On that device you should get 0V on pin 6 and +9V on pin 11.

As for the mid supply comment:  I mean that pin 1 and pin 7 on IC1 should be at +4.5V (multimeter -ve still on GND).

You will need to take things in small steps and work each problem  through.  Don't assume anything, use the multimeter to prove what you think is right to be actually right.   Once you have worked through a few effects life will be much easier.

[Tychobrahe1979]

I've been busy but I've finally had time to check it out and unfortunately I still could find nothing wrong. I appreciate the help and I will just keep trying to get it right.

[Boofhead]

OK it might help to isolate the part of the circuit involved in the phase-shifter.

I disconnecting the 27k resistor which is marked VIBRATO in the following schematic (don't worry about the FILTER1, FILTER2 stuff).  With this temporary change the signal is passing though the phase shift part only.  You should at least get an unprocessed signal through - if it's dead there's something wrong with LM13600 part of the circuit- IC2 and IC3.

What's the voltage at the outputs if IC2 and IC3 on pins 5 and 12?
What about pins 8 and 9?

If you get signal then it's highly likely there's something wrong with the IC4 part of the circuit.

[Tychobrahe1979]

Hello again. I am glad to hear from ya. Well disconnecting that 27k resistor totally cuts my signal. There is absolutely nothing.

Here is the volatge readings I got.

pin#               IC2                IC3

5                     both fluctuate between 3 and 5.5 volts
12                      ditto
8                     4.32 volts for both
9                     4.36 volts for both


Oh I am not sure whether or not this matters but those readings were taken with the 27k in.

Well I hope this helps you help me. :lol:

[Boofhead]

To show you how we have isolated the problem a bit of a recap,
- Power OK
- IC1 DC measurements show IC1 working.  The fact you can hear signal
 largely confirms there's nothing wrong with clean path of the signal.
 (For most circuits the opamp used for the audio signal path should have
 outputs at  about half the supply)
- Suspect Phase Problem with Phase shift part of the circuit IC2 and IC3.
- Modify circuit to isolate this part of circuit (BTW, there's no side effects
  modding the circuit in this way - modding other circuit may have
  confounding consequences).   No signal confirms likely problem here.

Now,
-  DC measurements on IC2 and IC3 look OK.  I see two possible areas.
1) A wiring error around the regen circuit or pot is shorting the audio,
    you could de solder the wires to the regen pot and see if it comes to
    life.
2) The LFO signal which feeds from IC4 pin 9 to IC2/IC3 pins 1 and 16 could have a problem.   I suggest finding the 10k resistor to IC2/IC3 pins 1 and 16 on the PCB.  Lift the *other end of the resistor* out of the board ie. lift the end which goes to IC4 pin 9, then connect a wire from this lifted end to +9V somewhere.

Try the unit out in this state. If it works you should get a clean sound out.   That means there is a problems around IC4.  This is the LFO part of the circuit.  The LED test before kind of hints at a problem here too.
When you complete this test, remove the added wire and resolder the 10k.

See how you go - good luck.

[Tychobrahe1979]

Greetings,

Desoldering the regen pot did not change anything. Doing the other trick with the 10k gave me the same bypassed sound I am already getting. I thought that was pretty cool though. The trick that is. I am starting to think I must have upset some kind of a devine power. Haha   Thanks for the time you have taken to help me thus far.

[Boofhead]

10k gave me the same bypassed sound I am already getting. I thought that was pretty cool though

That's Great.   I can smelll the blood.  I have little doubt now the problem is around the LFO-IC4.  It's simply not oscillating.  

What to do now is to go through the motions.  You only have to go through the detail with the parts around IC4 - as it is drawn on the schematic.
- (put the lifted 10k back in, leave 27k disconnected for now)
- first check the speed pot is wired correctly
- check all the part values around IC4 (if you have already done it do it again).
- If you have a polarized cap in for the 3.3uF cap make sure it's +ve goes to the +ve supply rail.  This cap around the wrong way will kill it.
- check IC4 is in the correct way around
- check your soldering, maybe touch-up

[edit:  maybe replace the 0.05u cap or check it, a short there would stuff it too]

If you find something sing, dance and be merry.  If not I'll have to think of  some way to isolate the problem in that part of the ckt.

Good luck, and let us know how you get on.

[Tychobrahe1979]

Hey I really appreciate all the help boofhead. Unfortunately I have run out of time to work on debugging this pedal. I've just left for Mich Tech. I will for sure try out your suggestions for finding the prob when I go home for break. So it is not all in vain. Talk to u later.