New project for harmonica. Beltone brick or PT2399?

[NevynShyne]

Hola!
I'm just starting out building a few pedals for myself and friends. I've found this forum to be IMMENSELY helpful. The sense of community is rare now-a-days. Thank you.

I got a couple of people who are asking me about an 'all in one' box for harmonica. They plan on using the 'traditional' Shure harmonica mic (green bullet or 535?) with the high impedance 1/4" input. In my head I don't see it being much different than a guitar signal, so I have this hair brained idea...Why not build an "all in one" box that suits harmonica and guitar?

The basics are a 2-3 footswitch dealio that will 'drop in' 3 functions : 1) boost that can get gritty, with master volume. It'll likely be 'always on'  2) simple delay 3) simple verb. Each section will be tailored and 'dialed in' for basic functionality but good general sound. In other words, I don't need all the bells and whistles and deep tweakability.  Hi-Fi isn't necessary. A little 'grit' is fine in this context. Ideas?

There are boost circuits available everywhere, so that's not really an issue.

I'm looking at the PT2399 and the Beltone bricks. BUT, I've not used either and not sure if they are applicable at all?!?! I've found a few schems for each to get me started, but honestly...Putting it all together is out of my depth. Can I use the PT2399 as a verb? that may simplify the layout some.

Any recommendations as to simple delay or verb schems or components? Any preference for the PT2399 or Brick? Smallbear has both, so supply isn't an issue.

It's my hope to put something on the bench and tweak it so that the delay and verb sound good 'out of the box' and will only require a knob or two for each circuit. I'm hoping to fit it all in something around a 1590BB size. ish. sorta.

I know. I'm clueless. Please help.


Carl

Edit: If this thing works, I'll post project pics and schems. It could be COOL! maybe cool? sorta cool?

[Hides-His-Eyes]

A PT2399 for delay and a Belton brick for reverb will be PERFECT for what you want. The only alternative for reverb in that convinience is really the Spin FV-1, which is a PITA to solder as it's surface mount!

I think you'll be a happy man with a MOSFET boost (always on) into a Jfet buffer (so the delays don't get overloaded!) into a PT2399 delay into a Belton Brick reverb. They were pretty much made for this.

[NevynShyne]

Hi.
Thanks for the response.

Mosfet boost into Jfet buffer for the delay.  Perfect.


The PT2399 has a basic schem with the datasheet. It seems that most people start with that and tweak what they need. Right? That's a place to start...yay!

The Beltone datasheet also has a schem for the basic application. Hmmmm...

I'm contemplating a fixed delay feedback rate and speed...OR fixing one and putting the other on a pot. Maybe a 'wet' knob? Which makes more sense to have?

And the verb will be fixed with a pot for the 'wet/dry' ratio.

I'm hoping to have 2 knobs for each section, as it needs to be 'user friendly' and the people asking about it are already overwhelmed with their current set-up. 2 knobs for boost, 2 knobs for delay, 2 knobs for verb. Which parameters make the most sense to put on pots?

That's the thought at least.  

Thanks for the input. It takes a HUGE weight off my shoulders knowing I'm not far off the mark...yet.

When it gets done, IF it sounds good...big if...I'll be posting the info, etc for you guys to take a look at and verify.

Carl


Edit: looking at the data sheet for the PT2399, the input has a 100k take down resistor. Would it make sense to match up the boost (mosfet or jfet) in such a way that the output of the boost matches the input of the PT2399 via a 100kmaster volume pot? It may eliminate unnecessary complexity.  Thoughts?

[anchovie]

It's worth noting that both the PT2399 and the Belton brick (which is PT2399-based) run off 5V which limits the headroom of their internal op-amps compared to the 9V we usually use for pedals. Therefore if you're running a 9V boost at the front swinging signal close to the rails it will then get clipped once you engage either of those effects, resulting in more distortion and less volume in comparison. Might be worth using a boost with clippers on the output to limit the overall signal level coming out. Merlin's characterisation of the chip found the input headroom to be approximately 3.5 volts, so if you use an antiparallel pair of red LEDs to ground after the boost you'll get limiting at 3.4V peak-to-peak.

[NevynShyne]

Hola.

I gotta say that is a VERY good idea...Thank you! Thanks for the .pdf also. I'm reading it now.

Carl

[Ronsonic]

A couple thoughts. Harp likes distortion, but not high gain. Big, fat, asymmetric is the way to go, not clipped gained out. That way there be feedback. Not so much highs and not so much lows.

For the rest, I'm sure you're on the right track with simpler = better.

[NevynShyne]

Hi Ron

Thanks for the suggestion on distortion. It was my thought to have a little fattening from the distortion circuit, but not a high gain scenario. Asymmetric? You sure? I hadn't given much thought to which type of distortion to aim for. I'll give that a look.

I figure harmonica would benefit from some bandwidth limiting, but if I hope to use it for guitar also, then I will have to be very careful what bandwidth I limit. I guess that's where tweaking it on the proto-board will come into play. It doesn't HAVE to be dual-purpose, but if it just happens to sound good on guitar too...well...Win/Win!

I'll be sourcing the parts this week and starting the build. If there's any interest, I'll post proto-board pics, lay-out, schem (when I put the 3 different circuits together, that is.), etc. I think this simple idea may sound good, but it's certainly fun. Thanks for the input.

Carl

[Ronsonic]

On the asymmetric distortion, I'm sure. Now harpo's like guitarists are all a bit different, well even more different (okay, downright weird) but what I've seen that works well for harp is stuff that sounds very retro on guitar. Think T-Bone Walker tones. Grid-leak biased input stage, poorly balanced cathode followers, that sort of sound.

Your harmonica player will use an amp anyway, so some of the tone shaping will come from that.

I'm interested in following this and seeing what you come up with.