Mysterioso Jr. and Neutrino: Caps in audio path and other sources of noise.

[mudfinger]

I've got a couple of Brian's PCBs on the way, the Mysterioso and Neutrino. I'm also going to build a Ross-type compressor; being a rabid hater of noise in audio circuits, I've been researching components with low noise floors, and it's led to some questions.

First, just to confirm...metal film resistors seem to be a common suggestion for those looking to reduce the noise floor thru component selection. 1/4 watt seems to be the standard recommendation, all reasonable and sensible. How much larger are the 1 watt resistors, and would they not reduce thermal noise?

Second, I've always heard good things about Vishay capacitors, their and their effect on guitar audio circuits. But, they're spendy, and some folks say they're irrelevant outside of the signal path. There's no good reason to just use Vishays throughout? Any good reason NOT to, outside of price?

Third, thermal noise being one of those issues that can only be defeated with blunt force/size...wouldn't 24mm pots be quieter than 16mm pots, all else being equal? I have plenty of room in my enclosures to use the larger pots, any good reason not to?

Thanks for takin the time!

[madbean]

I have heard the larger resistors have a lower noise floor, but it always seemed contrary to common sense. I should really read up on that. Personally, I only use 1/4W resistors. How much noise a metal versus carbon film produces, I don't know. I tend to use metal film in either high gain or non-overdrive applications. For lower to medium gain, I just don't worry about it. I think you would have a very hard time fitting 1W resistors on any of these builds. Even 1/2W ones would be challenging.

With the 24mm pots, I suppose the wafer is larger in size, but both the 16mm and 24mm have the same rating, so I can't say for sure. Common sense tells me 24mm would be more susceptible to noise due to the large metal casings. But, common sense is not always a good indicator when it comes to electronics

As far as caps, I have not used Vishay. I really only use Panasonic Film or (much more frequently) metalized film box caps. For the most part, I find them to be quiet and more importantly, 'toneful'.

There are also many other potential sources for noise, including lead dress, power supply, etc, so it's always a good idea to keep your signal path as clean as possible.

[gtr2]

Would you mind sharing where you purchase your metalized film box caps?

[mudfinger]

That's what I've been reading; the larger resistors...larger anything, really, dissipate heat more effectively due to increased surface area, thus lowering the thermal noise floor. Not all noise is thermal, tho, so there may be other considerations, like component separation, for example.

I'll stick with the 1/4 watt metal film units, and just use those throughout all 3 builds. I'm thinking of going with Vishay for ALL the caps in my compressor build, and get enough to swap in and out of the Mysterioso and Neutrino. Sometimes, "lesser" caps just sound better in a particular circuit.

I'll be using 22ga stranded and solid pushback for the lead dress, and I also have a supply of vintage type braided shield, which I was thinking of putting on the DC power supply to the board. I did not enjoy my experience working with whatever plastic was on the leads in my GGG kit, and I really dislike teflon, as well. Seems to me many pedal designs could benefit from better shielding inside the enclosure, e.g. between the pots and the PCB.

Is there any reason to insist on mylar/mica/etc for particular cap values, or is it just a matter of those materials being common for caps of certain values? From what I've read, film caps are much quieter and more transparent than the other options, no? I can see from the layouts which caps are electrolytic (I think...they're the ones with a defined polarity, right?), but I can't differentiate between any of the other types, which...from what I'm reading, are functionally equivalent? Thanks again for takin the time.

[madbean]

Would you mind sharing where you purchase your metalized film box caps?

I bought a huge number of the AVX brand in every value just before they were obsoleted at Mouser. About 5000 caps, or so.

You can still get WIMA's there. They are a little more expensive, but not too bad.

[jkokura]

I've had very good results with the Topmay caps from Smallbear. Steve has a great range of caps. The Topmays are fairly inexpensive small quantities, especially compared to the Vishays or the Wimas. But the real savings is in bulk - buy a bag of 100 and it will be cheaper than anywhere else I've seen so far. I've priced it out at anywhere I could find, but to buy large quantities of box film caps, Topmays from Smallbear is the cheapest I've found. But then again, maybe someone else could school me on finding cheaper...

Jacob

[mudfinger]

No bulk buys for me; just wanna put my fabrication skills to use on a handful of pedals, then stick to playin. 

After doing a preliminary check on prices, I think I will go with Vishay to the extent possible; I'm also really digging Sozo caps, but those are spec'd for use in amps.

I'm seeing that quite a few 1/2 watt and 2 watt Vishay resistors will fit on Brian's PCBs, btw. Actually gonna wait on the PCBs to arrive before I order parts.

What IS the functional purpose of using box/drop caps in certain positions, is there a dissipation factor that I'm missing?

[madbean]

Box caps offer uniformity in size. That's the main advantage for me. And, as I said, they "sound" very good, too.

[mudfinger]

Box caps offer uniformity in size. That's the main advantage for me. And, as I said, they "sound" very good, too.

Ah, gotcha.  Thanks!

Enclosures, meter, and wire are now on hand; I'm thinking that I'll want to snag a few different brands of certain components to hear the differences...what's the best way to setup a particular component for swapping? I've seen turrets and those IC heatsink things, but I have no idea on the merits of one method over another, or if there are other methods that might be even better, what do yall think?

[mudfinger]

Good times, the PCBs arrived yesterday. Really nice work, Brian!



It's funny, for some reason the PDF versions seemed larger, on the same scale as my GGG PCB (yes, I set to 100%  ). 1/4 watt and 1/8 watt resistors it is! I'm going to build the Neutrino according to plan; no funny business for that pedal. But the Mysterioso...I'm good enuff with a soldering iron and diligent enuff in following layouts to build the pedal as is, but I'd rather dispense with one of the knobs...and a switch, too. Can yall help me sort that out? Here's my preliminary questions (should I post a layout on the thread?):

1. I don't want the B/R switch; this will be the first pedal in the chain. Besides the switch, which other components does that eliminate, and will I need to jumper any connections or what have you?

2. Why is there a BOOST and a VOL pot? I know I want the boost on at all times, isn't the volume working against that to begin with? What changes to components and the circuit does eliminating the volume control entail?

Thanks, guys.

[mudfinger]

Mysterioso layout, for reference:

[Boom]

The BOOST isn't normally wired up a pot on the outside of the enclosure, but as a trimpot on the board (set to your liking, and forget about it). You could of course move it to the outside and use a normal pot...

I'm not familiar with this cicrcuit so I can't comment on how it is best used though, sorry.

[madbean]

The Boost is a feature brought over from the original Blackstone circuit. In fact, the Blackstone has TWO internal trimpots for boost! One is a straight boost (more gain) and the other is frequency dependent. For the Mysterioso, I reduced this to one trimpot which has a switch that can be used for full frequency or frequency specific boost. You do not have to have either installed, if you don't want to. Simply leave off the switch, C6 and jumper pads 3&2 of the boost trimpot.

If you don't want to have the 'buffer/reactive" feature, I suggest leaving off the "buffer" part. This means you can leave out C1, R2, Q1, R3 and C4. Also, you will need to jumper pads 1&2 of the "B/R" switch.

[mudfinger]

The Boost is a feature brought over from the original Blackstone circuit. In fact, the Blackstone has TWO internal trimpots for boost! One is a straight boost (more gain) and the other is frequency dependent. For the Mysterioso, I reduced this to one trimpot which has a switch that can be used for full frequency or frequency specific boost. You do not have to have either installed, if you don't want to. Simply leave off the switch, C6 and jumper pads 3&2 of the boost trimpot.

If you don't want to have the 'buffer/reactive" feature, I suggest leaving off the "buffer" part. This means you can leave out C1, R2, Q1, R3 and C4. Also, you will need to jumper pads 1&2 of the "B/R" switch.

Thanks for the replies, Boom and Brian; much obliged. I was planning on wiring the boost to an external pot as shown in the PDF layout; presumably I could then leave off the trimpot, no? I'll be keeping the switch for fullfrequency/mid selection on the boost to see which I like better as time goes on. 

Looks like removing the volume pot from the circuit is just a matter of jumpering the relevant pads, ya?

That's exactly what I needed to know about the B/R switch and related components, thanks!

[Bucksears]

Hmmmm.....I may remove the buffer and boost footswitch from mine and see if that simplifies things for me. I actually shelved it after troubleshooting it again and it's still producing noise; more SOUND this time too, but still noise.