SOLVED Duocast: squeals on 27V, sounds bad on both settings

[DAJE]

No pics just yet, probably later. I'm pretty careful about pre-testing and quadruple-checking parts, so it probably isn't that.

Plus... it sounded pretty good on the test before I boxed it. I turned the trimmers up a bit because it was quiet, below unity even with the knobs up full. The only other thing I did was squirt some IPA on it and scrub the board a bit with a toothbrush.

The squeal is intermittent, but happens more often than not, and mostly on the 27V setting.

Now, the "sounds bad" part may just be Germanium. I swapped the first Ge tranny for a lower output one. Didn't help. The only Ge pedal I have that actually sounds good is my Tone Bender (1.5/2). The other couple I've tried just sound... uninspiring. I also swapped the LT1054 for another, no difference.

Given the rave reviews the Simulcast gets, and the Duocast too, I think something must be wrong. There's no way a well regarded pedal can sound this bad.

Frankly it sounds bad enough I'm considering writing it off and stripping it for parts.

 

[DAJE]

....and I semi-fixed it. I remembered reading something here about someone having a problem with a BC549C having a backwards pinout. I checked the spec sheet from the place I bought mine and sure enough... see pic.

Now, correct me if you know any better, but it looks to me like the PCB sign is backwards. Or it's the right way round and the tranny is backwards. Whatever you want to call it, it's a problem.

I flipped the tranny and the squeal is gone. Oddly, the pedal seems to have returned to the way it was working when I first tested it. In that the GAIN control doesn't do much and the LOW CUT is kind of weird but maybe that's just how it works.

So the remaining problem is that it still sounds a bit harsh on the 9V setting and on 27V it sounds nice but even with the knobs up full it's a pretty subtle effect. I'll try messing with the trimmers again, any advice is welcome as long as it's friendly.

 

[music6000]

....and I semi-fixed it. I remembered reading something here about someone having a problem with a BC549C having a backwards pinout. I checked the spec sheet from the place I bought mine and sure enough... see pic.

Now, correct me if you know any better, but it looks to me like the PCB sign is backwards. Or it's the right way round and the tranny is backwards. Whatever you want to call it, it's a problem.

I flipped the tranny and the squeal is gone. Oddly, the pedal seems to have returned to the way it was working when I first tested it. In that the GAIN control doesn't do much and the LOW CUT is kind of weird but maybe that's just how it works.

So the remaining problem is that it still sounds a bit harsh on the 9V setting and on 27V it sounds nice but even with the knobs up full it's a pretty subtle effect. I'll try messing with the trimmers again, any advice is welcome as long as it's friendly.

I have built both & they are Great sounding Pedals!

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I have to raise this ongoing issue when Members ask for Help with an Issue with their Build. I keep repeating this saying '' Pictures are worth a Thousand Words'' !!! Please supply Pictures of PCB & ALL connections ( Footswitch, Input & Output Jacks, Power Jack ) to it along with a clear...

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[music6000]

You need to get yourself a Tester for Transistors, Diodes, Leds!

 

[DAJE]

You need to get yourself a Tester for Transistors, Diodes, Leds!

Got one. I mentioned

pre-testing and quadruple-checking parts

in the second sentence of the first post.

 

[DAJE]

Here are some pics. There's a bit of IPA residue visible from cleaning the other side of the PCB, I could clean it off but I don't think it's affecting anything.

All electro caps are 50V except C3 & 10 which are 63V.

 

[music6000]

Got one. I mentioned

in the second sentence of the first post.

I used NOS OC71 in both my builds

 

[music6000]

Here are some pics. There's a bit of IPA residue visible from cleaning the other side of the PCB, I could clean it off but I don't think it's affecting anything.

All electro caps are 50V except C3 & 10 which are 63V.

Your Tester should show you C,B, E
From Left to Right with Flat side facing you on Q1, it should be 1 C, 2 B, 3 E
If not, you have a Fake!
Are you putting the Germanium the right way around ????

 

[DAJE]

I used NOS OC71 in both my builds

Cheapo ex-USSR Ge for me.

Your Tester should show you C,B, E
From Left to Right with Flat side facing you on Q1, it should be 1 C, 2 B, 3 E
If not, you have a Fake!
Are you putting the Germanium the right way around ????

OK, the tester shows that the BC549C has the same pinout as shown in both your pic and the one I posted. As they cost me AU$1.28 for ten of them, I really don't think they're likely to be fake. Plus they came from element14 (Farnell) who are pretty unlikely to be selling fake BC549Cs.

I flipped it round so it matches the PCB again and - for whatever reason - that seems to have improved things again. I was very careful with the Germanium pinout because I've had that problem before, and it is 100% definitely plugged into the sockets correctly. What I think may have been the problem is that both trannys are socketed, it's possible they weren't connecting properly and that was causing the issues.

Anyway, it now seems to be behaving as intended. It's late here but I'll mess around a bit more again tomorrow to confirm it's fixed, then, I guess, post a build report. It looks good on the outside, so that's something.

 

[music6000]

Yep, That is why I don't use sockets for Transistors!

 

[DAJE]

Yep, That is why I don't use sockets for Transistors!

Wise move. The few pedals I've built for other people, I solder the transistors too. Thinking I might do that with this pedal once I've confirmed that the problems are fixed.

 

[fig]

Yep, That is why I don't use sockets for Transistors!

A pet peeve of your I've noticed.

 

[Harry Klippton]

A pet peeve of your I've noticed.

Certified socket haters club

 

[DAJE]

I have soldered the transistors into their sockets and... nope. Still squeals intermittently on 27V, though for some reason only when the high gain footswitch is on. I'm starting to suspect a dodgy transformer. And it still doesn't sound very good. Last night when it decided to work properly it was sounding decent, but today, when I can turn it up louder, there's still a harshness to the drive that's just not pleasant.

I'm ready to write this one off. The drill template had an error (not mine) so I had to stretch the pot prongs to fit the PCB. And now this. I was really intrigued by the descriptions of this pedal but... can't win 'em all. I'm a musician, not an electrician. I really just want nice sounds, I'm never going to grasp how pedals work to the level that many people here do. I can follow instructions and most of the pedals I've made have worked first time, but if they don't, I'm lost.

 

[music6000]

I have soldered the transistors into their sockets and... nope. Still squeals intermittently on 27V, though for some reason only when the high gain footswitch is on. I'm starting to suspect a dodgy transformer. And it still doesn't sound very good. Last night when it decided to work properly it was sounding decent, but today, when I can turn it up louder, there's still a harshness to the drive that's just not pleasant.

I'm ready to write this one off. The drill template had an error (not mine) so I had to stretch the pot prongs to fit the PCB. And now this. I was really intrigued by the descriptions of this pedal but... can't win 'em all. I'm a musician, not an electrician. I really just want nice sounds, I'm never going to grasp how pedals work to the level that many people here do. I can follow instructions and most of the pedals I've made have worked first time, but if they don't, I'm lost.

Have you tried turning the trimmer down on the High side, it's a pretty hot circuit.
I still can't make out your resistor values in the Pic's provided!!!


Edit : I just plugged mine back in & there is a jump in Volume @ 27v & in switched High Gain mode but I couldn't get it to Squeal.
Is your Low Cut around the 9.00 O'clock to 10.00 O'clock position as it can be quite bright at straight up position!

 

[DAJE]

Have you tried turning the trimmer down on the High side, it's a pretty hot circuit.
I still can't make out your resistor values in the Pic's provided!!!


Edit : I just plugged mine back in & there is a jump in Volume @ 27v & in switched High Gain mode but I couldn't get it to Squeal.
Is your Low Cut around the 9.00 O'clock to 10.00 O'clock position as it can be quite bright at straight up position!

I'll give it a try later, I'm just letting it go for now. Got other projects to work on anyway.

 

[fig]

If you swing back around to it sir,

You can probe @ Q2 (signal into Ge) and Q3 (signal after) if you suspect it as the issue.
Maybe also check signal in/out @ the transformer (R14/15 node & pin 3 of LEVEL1).

Just suggestions...may not even be good ones. Hope you get 'er sorted.

 

[DAJE]

OK, I'm going to mark this one "solved". I wound back the trimmers as @music6000 suggested, and that helped. It's not squealing today, even when I tried to make it squeal. There's still some harshness to the sound, which could be a bias issue, but as I have no clue how to fix that I'm just going to make do with it.

It sounds good on some settings, which is better than nothing, and it does look nice. Possibly this is something that works better on a loud high gain valve amp. I'm a bit disappointed but it's not like I don't have 20 other dirt pedals to play with. Or thereabouts. I compared it with the Aft Preamp I made recently (NPN Ge Rangemaster) and I prefer the Aft. The Duocast might get some use or it might go sit with my other less-inspiring pedals.

 

[DAJE]

I still can't make out your resistor values in the Pic's provided!!!

I went over them all, and all of the capacitors too, and confirmed that they are all the right values and in the right places.