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Welcome to marriage, the wonderful world of compromise.  

(I mean that in a good way)

Modern tants have a small marking on them to show which is the positive lead, usually.

Aluminums just feel frail and fragile to me.

Sure, if you step on them. 

I try to avoid any polarized caps in the signal path (one less thing to worry about). I go with box caps for everything up through 1µ, and I occasionally use SMD ceramics for up to 10µ. Anything bigger than 1µ is usually either just an AC path to ground (emitter bypass) or a ripple cap on the power rail. I can hear neither frailty nor fragility on a power supply or bypass cap. I also can't hear tonal differences.

But, I'm judging on sound, not feel. So your mileage will certainly vary.

I didn't mean to suggest that the modulation should be removed. I just think it would be cool if it could be controlled or turned off/on. If not, no biggie.

On another note, try probing around the Current Control pins ( 7, 8 ).  I think you'll find the answers to your  initial question.

You mean pins 7/8 on a PT2399?

From the test results graphs I've seen, tants are also noisier than electrolytics (and just about everything else except for the cheapest of cheap ceramic disc caps).

But in real-life tests (that is, with guitars and amps and human ears), I can't hear any difference between tantalum and aluminum. I'm sure it's better for missile guidance systems, but for pedals I can't tell.

Tantalum costs more because the raw material is primarily mined from warn-torn Congo. It is also, in many cases, mined by children and used to finance very unsavory activities.

So enjoy your blood tantalum caps! 

The first pedal I ever modified was my Boss eq; it just couldn't be used in front of an amp, so I modded it with one of the kits and the thing is now dead quiet.

I think the important question is: Did the mod kit change just the part types or was it also the values?

A hissy pedal can often be cured by adding or augmenting some low-pass filtering.

Nice builds!

Who's an English major with two thumbs who can't spell? This guy.

This guy, too. 

I've never played around with the belton, but the pitch modulation effect may come from clock skew between the individual pt2399's on board, meaning the internal oscillators on board drift slightly, and drift relative to each other. this would cause a "chorus" type effect since the delay times will be slightly out of sync.

if the brick were an on-chip solution (ie squeezed into an IC rather than a module), all the clocks would be probably in a phase-locked loop to prevent this from happening.

Aha! Now that is smart thinkin', sir! 

I've always felt that plain jane Pt2399 delays had a bit of natural modulation inherent in the chip.

Interesting. I've never noticed this. And I don't recall hearing it on the old Belton brick that I experimented with. Different ears, I suppose. 

I haven't tried it or really looked into it yet but I'm thinking that the internal pt2399's clocks are modulating the power supply rail as listed in this wonderful doc

Okay, but why doesn't it happen (or why isn't it audible) with a single PT2399? Do you think the effect is cumulative?  (this is more rhetorical than me actually demanding that you answer   )

I'm wondering if using the docs Fig. 2 5V regulation would stop the modulation.

If it really is the internal clock causing the modulation, then I don't see how improving the power supply source would stop it. But it's certainly worth trying out.

Also, Merlin notes that the clock causes noise. He doesn't say it causes pitch modulation. Not sure how much to read into that.

I think a 2N5089 or MPSA18 should work fine in place of the BC tranny.

I found the stereo outputs useless for anything I wanted to do anyways as it's just two mono outs.  

Right, but it does give more overall output (reverb) volume. I hooked it up with a switch so that I could toggle between one output and two outputs bridged mono, and it's quite noticeable.

But surely one of them could be tied into a feedback loop with an opamp stage of some sort.  There isn't enough flow to push it for a dwell loop on its own.  Not sure what the technical term would be, loading effect  

Oh yes, it can be done. I have a working prototype right now with feedback. You can set it for nearly infinite reverb that degrades into noise like a standard 2399 delay with the feedback cranked. It will also do runaway oscillation. Setting it up that way is great for the noise-rock and ambient guys.

I'll post what I have working as soon as I get all the values finalized.

[• Modulation]

I have messed around with the Accutronics / Belton BTDR-2 brick quite a bit now, and I thought I'd post a few simple things I've noticed. This a really cool little device, which allows for a relatively low-cost reverb that can be delivered in a 125B (or maybe smaller) enclosure.

• Modulation
There is a pronounced modulation effect on the output. It's a pitch-bend that is reminiscent of the sound of Rick's Little Angel, but it's more of a pitch dip than a true chorus type sound. Sometimes it sounds like there is a relatively fast LFO speed. The whole modulation sound is rather unpredictable, which is pretty cool and also perplexing.

I sort of wonder if there really is an internal LFO modulating the pre-delay time, or if the internal delay circuits (presumably multiple PT2399-like circuits) are perhaps drawing enough current from the regulator to cause a dip in voltage on the supply pin? I should probably hook up the old volt meter and check that out.

I dig the modulated sound, but it would also be cool if we could figure out how to turn it off.


• Stereo Outputs
The datasheet (which is laughably inadequate) shows both output pins tied together in parallel for mono application. I have confirmed that it will work with just one output connected. However, this knocks down the overall reverb level quite a bit, as you might imagine. But it could be a useful feature in some applications to add a switch to toggle between stereo and bridged mono (or maybe just a more/less reverb switch for mono).

Another use for the second output might be for a secondary feedback loop, although I'm not sure this would be any better/different from just taking the feedback from the bridged outputs.


For reference, here is the first simple circuit I came up with using the brick:
http://www.madbeanpedals.com/forum/index.php?topic=4594.0

This one does not have feedback of any kind, but I'm working on a more complex version that does. And I'm still exploring the benefit of a secondary feedback path.


GTR2 and other who have worked with this brick, I would love to hear your thoughts/input on this nifty little quirky thing. 

The Siliconex usually have a mark to show you which one of the LED-side leads is negative.

Google for the datasheet for the specific part you have to verify which pins are which. It definitely does matter.

If you are having trouble with the opto, I would suggest trying a LED and LDR as separate parts. The up side is that you can if the LED is lighting up properly. And it really doesn't need to be sealed to work.

maybe its just my speakers but I didnt think it was anything special?

I thought it sounded good. But I can still here some hiss in the longer repeats. I know it's pretty much unavoidably with a PT2399 and keeping the repeats bright. But I still would rather have a darker tone with no hiss.

I'm just impressed with the novel approach that Dirk took. He's wicked-smaht! 

Nice!

What's your impression of the pitch-bendy stuff?

Specially since a Windows computer is much cheaper.

With a little planning and some extra work, you can get OS X to run on many non-Apple computers. Check it:
http://wiki.osx86project.org/wiki/index.php/Main_Page