Equinox: Easy PT2399 Reverb

[JFace]

Don't quote me on this, but when you're working with mixed mode (part analog, part digital) circuits it's generally best to keep digital parts separate from the analog parts. What I mean  is having separate grounds, supplies and such is a good idea. This is why the PT2399 has an analog ground pin and a digital ground pin. If you have common grounds etc. you'll find that noise from the digital parts of the circuit will creep into the analog parts. So yes, there is a reason why you shouldn't use the 5V as the bias. Also, what's the point? How much will 2 resistors and a capacitor cost?

In general I agree about the cost and space concern for components, but I try to keep things as small as possible to fit the circuit in a small box. In a small build, 2 resistors and a capacitor cost a lot of valuable real estate. But more importantly is that two voltage traces becoming one greatly simplifies the layout. When you have traces for ground, signal, 4.5V, 5V, and 9V things can get hairy, especially in a single sided tight layout.

I see what you are saying about keeping analog and digital references separate. However it is reported that the analog and digital pins for the PT2399 should both be connected to analog ground. You can read this on Merlin's site (Small Time description and the PT2399 notes). I don't see how using a 5V regulated reference as a bias is any different than taking a 9V regulated reference, dividing the potential and using it as a bias.

[merlinb]

Is there any reason not to use the 5V as the bias supply.

Yes, it will be very noisy with digital-induced hash. I don't recommend it.

[psychedelicfish]

However it is reported that the analog and digital pins for the PT2399 should both be connected to analog ground.

I read somewhere (on this forum, I forget where) that it's actually better to connect the digital ground to the main circuit ground through a small choke, which filters out the nasty digital crap from your normal ground.

[merlinb]

I am in the process of finishing a slightly streamlined version of the Equinox. It dispenses with the bright/fat switch and delay trim pot, as they weren't very useful. Here are the build docs so far:
http://valvewizard.co.uk/equinoxII.PDF

[Harold]

I am in the process of finishing a slightly streamlined version of the Equinox.

Nice! This was on my build list already ... I'll try to make it into a vero! 

[chobot123]

Hi Merlin,
I'm building a 15W DC-30 amp clone and I thought to include a serial/parallel effects loop from your book just to experiment and learn.
If I wanted to use the Equinox II in a parallel loop, I have to kill the dry signal.
How would you do it? Is it enough to put  SPST switch between R4 and U1A pin2? Switch closed means normal operation, switch open kills the dry and there's just the wet suitable for parallel loops...

Or do you have any other idea?
I thought also to build the Equinox inside the amp but I don't know how to connect it as DC-30 uses both legs of the PI to mix the channels and I would like to have the reverb on both channels. That's why I started to look at loops ..
Thanks
stefan

[merlinb]

Is it enough to put  SPST switch between R4 and U1A pin2? Switch closed means normal operation, switch open kills the dry and there's just the wet suitable for parallel loops...

Yes, that would be fine.

[Wguitar]

Question about the most recent PDF posted.  That circuit diagram works correct?  I was a little bit confused about whether that was a work in progress or if that was finished.  I am looking to make this reverb unit and I really would like to use that circuit diagram within the most recently posted PDF.

[merlinb]

Question about the most recent PDF posted.  That circuit diagram works correct?  I was a little bit confused about whether that was a work in progress or if that was finished. 

It is finished except for painting the box! Circuit/PCB are both proven.

[Wguitar]

Planning to build it with the FAT switch and instead of the one PT2399 having a set resistor value I'm going to vary both PT2399s, will allow for more variability of the sound and that's what I'm looking for.  Thanks for the diagrams!

[GoranP]

Merlin, I'd like to do this in smd but I'm having problems finding mmbfj112 or sst112 on   bay.
Would J201 or J310 work in here?

[GoranP]

Bumpity bump?

Anyone?

[armdnrdy]

Man must not rely on ebay alone! 

http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/MMBFJ112/?qs=ljbEvF4DwOPc5qOoeoX%252bEQ==

[GoranP]

Well I'd love nothing more than to be able to order from Mouser but over here in Yurp it costs an arm and a leg to get things from there...

Like it or not,   bay is where I need to look most. Places like Banzai or Musikding are reachable but they have virtually no smd components.

[armdnrdy]

When I'm faced with high shipping charges but still need items from a certain source, I put together an order for things that they stock at a good price, and things that aren't readily available from local suppliers.

This is truly the only way to offset the cost of shipping. Two SMD transistors ship for the same price as a semi small order of assorted items.

[GoranP]

Very true. But as my stash grows, it's getting increasingly more difficult to offset $30 shipping cost. And if I get up to $100 to qualify for free shipping, my customs office is sure to have a field day with me.

So I either turn to ebay or look for substitutes. So, any other J's that would fit in here?

[armdnrdy]

I didn't see any on ebay but...check the data sheet for MMBF5457 against the mmbfj112.

The 5457 is a general purpose JFET good for switching.

The J112 in the schematic is used as a switch. 

I don't know if you can source the MMBF5457 in Europe.

[merlinb]

I finally got around to packaging my Equinox II! (Jeez I'm slow...) Eventually I gave up on the idea of doing a 'professional' finish, and just painted the box with random acrylic colours. And like a fool I managed to write the word 'reverb' at the funny angle  

Anyway, I have created an official page for it, with all the files, here:
http://valvewizard.co.uk/equinox.html

[bluebunny]

Nice one, Merlin.  I've worked up a perf layout (cos I enjoy the intellectual challenge!).  I'll try to get time over the Crimbo break to build and verify.  Or it might be Easter.  Or ...   

[Canucker]

Ok so someone is probably gonna slap me for this but since you guys know stuff at the drop of a hat I thought I'd ask before I read through all the pages of responses on this one.... the parts list shows C10 and C32 as NP (non polar) but the blue/black/pink layout clearly shows + symbol for each of those pieces...so who do I believe? The schematic doesn't quite clear it up for me either (though they are my weak point for sure).