Coloursound Power Boost (fuzzdog kit) - hiss/radio?

bbill335

Put this kit together over the weekend. It's probably the most complicated kit I've done, but it's still just a case of following instructions and getting decent solder joints, right?

Anyway, it's working fine apart from a bad hissing sound when activated, seems to be affected by the gain control and the treble. It does it when the guitar's volume is at zero. 

The problem I have is that, since I've never played another power boost or clone, I have no idea whether it's just a noisy circuit, or whether the tones I'm getting from it are right. With strat single coils, this kit is a beefy clean boost all the way to the end of the gain control where it gets buzzy, fuzzy and compressed.

Schematic can be found in the build doc, but I'm not sure how to diagnose a potential cause of the hiss from looking at that. Can anyone help me out?

thermionic

One thing that caught my attention - does your TC7660 ic have an S suffix?

bbill335

thermionic said:

One thing that caught my attention - does your TC7660 ic have an S suffix?

Yep.

It's less noisy running it off the cioks dc5 (I was using a onespot yesterday, not a daisy chain but just a single 9v mains adaptor) but it was picking up very clear radio. 

thermionic

Clear radio pickup means something is acting as a tuned/resonant circuit somewhere. It's often seen with wah pedals, which have an inductor and a pot to create the resonant circuit. This circuit has no inductor, so I can't suggest anything more I'm afraid.

jonnygreentrees

Have you boxed it up yet? 

I often find circuits are much noisier when I am testing them as opposed to when they are properly boxed up

bbill335

jonnygreentrees said:

Have you boxed it up yet? 

I often find circuits are much noisier when I am testing them as opposed to when they are properly boxed up

Yeah, it got better once boxed up but it's since boxing it up that it's picked up radio.

This picture is (I think) before I fixed the backwards bass pot (  ) and tidied the CLR connection (I always forget not to put that on the main board (  )

I've my best to keep it neat but I didn't want all straight lines and right angles (which I'm aware can lead to noise issues)



What will probably happen is - since I've got a taste of the power boost and liked it - I'll probably try to pick up a fancier version made by someone who knows better about building stuff that doesn't pick up noise and radio signals.

thermionic

Those big loops of red wire coming off the T pot might have some mutual inductance... does it improve if you straighten them out and push them further away from each other.

lasermonkey

Maybe try soldering a small value capacitor (22-100pF) from the input of the circuit to ground. It may well help with the RF interference.

DarnWeight

You could try shielded wire on the inputs (jack-to-footswitch and footswitch-to-pcb).  Also, how does it sound with a buffered pedal in front of it?  I built a Vox Treble Booster which picked up radio very clearly, and sticking a buffer in front pretty much cured it.

bbill335

Thanks for the suggestions, I'll give the buffer a try later. I'm hoping to get the enclosure painted/arty-fied so any significant rewiring will probably get left until then. 

In spite of the radio noise, it actually sounds really really great. It seems a sophisticated circuit (and a refined sound) compared to other boosters/fuzzes from the late 60s.

Matt_McG

I have a noise issue with another Fuzzdog kit.* 

In that case, it sounds very like PSU/switching noise from the charge pump, and nothing I do cures it.

* I've built loads with no issues, no aspersions on Fuzzdog in general.

bbill335

Matt_McG said:

I have a noise issue with another Fuzzdog kit.* 

In that case, it sounds very like PSU/switching noise from the charge pump, and nothing I do cures it.

* I've built loads with no issues, no aspersions on Fuzzdog in general.

Yeah, it's worth saying that the kits are fantastic quality

lasermonkey

Matt_McG said:

I have a noise issue with another Fuzzdog kit.* 

In that case, it sounds very like PSU/switching noise from the charge pump, and nothing I do cures it.

* I've built loads with no issues, no aspersions on Fuzzdog in general.

I assume you mean a high-pitched whine?
If so, chances are you have a fake 7660S. There's a lot of them about. Even the TC1044s from Tayda squeal. Best to get your 7660s from Rapid or the like. They're considerably more expensive, but you do at least get what you're paying for.

Matt_McG

That sounds plausible. Will try that.

lasermonkey

Guess who found out the hard way!

bbill335

Buffer didn't really help. I might go back and fit a toggle for the charge pump as I have a couple of decent 18v sources anyway and it would be good to eliminate the chip as the problem's source. 

One question about the shielded wire idea - I'm guessing you mean the grey stuff you see in D*A*M pedals and stuff? How does the shielding work with those? Does it get grounded at one end?

bbill335

I stuck a 100pf across the input/ground and it's reduced it to manageable levels. You can still hear stuff when things are full whack but that's not a very useful setup for me anyway!

jpfamps

You can get charge pumps to be quiet, however you need to pay care to the layout; for example you should a separate ground for the charge pump and for the audio. These need to be connected together at one point only and you may need chokes to reduce noise.

You also benefit from extra filtering on the power rails, especially if you are using single ended gain stages that don't benefit from the power supply noise rejection properties from op-amps.

Furthermore, as stated above, there are plenty of fake charge pump ICs out there. The most reliable and robust I've come across is the Linear Tech 1054, but make sure you get this from a reputable supplier.

Trying to sort out any power supply filtering / layout issues retrospectively is hard, to say the least.

bbill335

I'm gonna build it again on vero - sans charge pump - and try it with different transistors. I've got a nice, big enclosure from Lee and I'm a bit green with vero as it is and would like to get better. Like I said, I've got clean 18v from a dunlop adapter and from a DC5 so the pump was always a bit of a luxury/convenience.