Phase 45 build, no sound

[Supernaut_]

Hello,

I have a problem with my Musikding 45er Phaser build (MXR Phase 45 clone). Bypass works but there's no sound when the effect is engaged. I've checked the wiring and the solder joints, they all look good to me.

https://www.musikding.de/The-45er-Phaser-kit

I've measured the following voltages on a DMM (referenced to ground):

BAT 8.96

Q1 G: 0.33 - 0.49 (changes constantly)
Q1 S: 0.25
Q1 D: 0.25

Q2 G: 0.36 - 0.52 (changes constantly)
Q2 S: 0.25
Q2 D: 0.25

IC1:
Pin 1: 1.50
Pin 2: 1.07
Pin 3: 0.90
Pin 4: 0.00
Pin 5: 0.79
Pin 6: 4.70
Pin 7: 4.34
Pin 8: 8.88

IC2:
Pin 1: 5.06
Pin 2: 2.67
Pin 3: 1.18 (doesn't vary with speed control)
Pin 4: 0.00
Pin 5: 3.23 - 5.39 (changes constantly)
Pin 6: 3.69 - 5.55 (changes constantly)
Pin 7: 1.23 - 8.23 (changes constantly)
Pin 8: 8.88

C11, R16 & R21: around 8.84

So it looks like electricity is flowing through the circuit but the transistor values seem way too low and the IC values are incoherent. Does anybody know how to fix this?

[11-90-an]

Pictures...?

Checked your pinouts? Tried replacing the ICs?

[ElectricDruid]

Start at the front - the voltages on IC1a are too low. Until that's fixed it's hard to know what's going on with the rest of it. The 1N5230 zener diode means we should see 4.7V or something close to it on pins 2 and 3, but currently it's nothing like that. Maybe a short on C7 or C8?

Schematic:
https://www.musikding.de/docs/musikding/45er/45erschalt.pdf

[duck_arse]

like 11-90 always sez - pictures, please.

odd, one pin of each of the fets is connected hard-to a non-invert pin on an IC, according to the circuit dia, yet no IC pin voltage matches any of the jfet pin voltages. summink ain't rite.

[ElectricDruid]

odd, one pin of each of the fets is connected hard-to a non-invert pin on an IC, according to the circuit dia, yet no IC pin voltage matches any of the jfet pin voltages. summink ain't rite.

Good point. This is *very* odd. Please check the measurements.

[Supernaut_]

Hi guys, thanks for the replies!

I soldered every component again to make sure there weren't any cold joints, but still no cigar. When I strum my guitar very loudly there's a weak distorted signal getting through.

I tried swapping out the ICs for a pair of RC4558s. This resulted in a stronger but a nastily distorted signal way above unity gain. So I'm guessing the original TL072s should be okay. I also swapped the transistors for a non-matched 2N5457 pair but this had no effect whatsoever, so the FETs should be fine.

I also measured again, getting similar results, except for the following changes:
IC1 pin 5 now 0.24
IC1 pin 7 now 7.90
IC2 pin 1 now 7.89
IC2 pin 2 now 7.85
IC2 pin 3 now 0.24 (still doesn't vary with the speed pot)

I agree it's really odd about the non-matching voltages. I'm really at a loss here.

Here's a couple of pics, the additional switch is an "Univibe-switch" wired to C2 and C3 according to this GGG layout:
http://www.generalguitargadgets.com/pdf/ggg_p45_mods_lo.pdf

[11-90-an]

Hmm... I don't think pin 7 of IC1 and  pin 1 of IC2 should reach 7v....

However, pin 5 of IC1 and pin 3 of IC2 are starting to match with the JFET voltages....

Strange...

Have you tried tweaking the trimpot?

[ElectricDruid]

So we've still got the following on IC1a, the input amp?:

IC1:
Pin 1: 1.50
Pin 2: 1.07
Pin 3: 0.90

I still think we need to deal with this before everything else. Unless the signal can get past that first amp, it'll never even reach the phase shift stages, so we'll never know if they're working.

Can you check the voltage across the zener diode please?


Also can you check the value of R24? It should be 7K5, but looks more like 75K.

[Supernaut_]

I checked R24 and it is indeed 75k. I didn't bother to go through the resistor values before, since they came labelled in the kit and I just assumed they were ok. I've now checked all the resistors and the other values seem correct. Could this wrong R24 resistance explain the problem?

The voltage across the zener diode is 0.24 when measured with the Vdc setting on the DMM. Tweaking the trimpot had no effect on sound or function when I tried it earlier.

[mcknib]

If it was a kit I hope you checked all values etc

I hate to say it but there's been a few mistakes with musikding kits recently on here and other forums

1M resistors labelled as 1K came up a few times and a 100R trimmer labelled as 100K

Klaus has always been good with me so I emailed him to give him the heads up after I'd seen about 6 posts which ended up being incorrect values causing build errors

[11-90-an]

I guess you have to get all the values of each resistor to check...

[duck_arse]

R25 wrong will mess wth the osc speed range, but won't stop the werkings. power off, set meter to ohms and measure the resistance between the D1//R16 junction and ground, if you would be so kind. do this measure twice, once with black probe to ground, once with red probe to ground.

[Supernaut_]

Just did the requested measurement: power off, DMM set to ohms (20k), resistance between D1/R16 junction. Black probe to gnd and red probe to gnd yields the exact same result; 0.26.

[duck_arse]

0.26? that would suggest 260 ohms, and that ain't right. either the diode is wrong or cack, or the trimpot value is wrong, or there is a short of some description somewhere. you could try and lift one end of that "zener" diode, and see if the voltage there climbs to nearer 8V. or lift the trimpot, and see if the diode voltage comes up to the specced value.

[Supernaut_]

I actually took a closer look at the trimpot now. It should be a 250k but on the side there's only "250" printed. So I'm guessing they sent me a 250R trimpot instead of the correct 250k?

[mcknib]

Yeah 254 is 250K, 25 and 4 zeros

Not to sure on those blue ones though never use them but I'd imagine the codes the same

[duck_arse]

I'd be removing the trimpot, see if the zener voltage comes up to specced volts - the fets won't sweep without it, but you'll at least have the problem found. do you have any other trimpots about, the value is not critical, just needs to be high. well, higher than 250R for shure.

[Supernaut_]

Klaus is sending me a 250k trimpot and a 7k5 resistor to replace the incorrect ones. Unfortunately I don't have any extras laying about, so it'll take a while for me to get the parts. It would seem pretty logical that the trimpot is causing the voltage issues, maybe I'll remove it tomorrow and do the measurements again.

[Supernaut_]

Okay, so I've now removed the trimpot and done the measurements again. Now the IC and JFET voltages seem logical, it would indeed seem that the trimpot was the root cause.

However, while removing the trimpot, one of the PCB contact point copper coils came out of the board. I'm now afraid that the new trimmer won't work because of this...

[Slowpoke101]

Don't panic.
I don't see any circuit board traces on the component side of the board so the "copper coil thing" is not actually needed. There should be enough left of the solder pad on the solder side of the board for you to be able to solder in a replacement trim-pot. The "copper coil thing" is actually a plate-through connection that usually allows a connection through from one side of a circuit board to the other - double sided boards or sub-layers in multi-layer boards. In a board such as what you have these plated-through holes can make soldering an absolute joy and can help minimise "dry joints" or poor quality joints, but they are not really needed.

Further to your problem with your phaser - about 6 months ago a similar problem occurred with a Phase 90 clone. It's problem was a trim-pot that was supposed to 250K but a 250 Ohm unit was installed.