Sea Urchin issues & PT2399 silly question

[zedsnotdead]

Hi all,

so I just built a Sea Urchin delay. it sounds very, very nice. The only problems are:
1- with the delay set above 75%, I start hearing somekind of "motorboating" noise. Starts subtle, increasing in volume if I turn the delay knob after that 75%, and at 100% it's definetly there.
2- with the "mix" pot also above ~80%, the output starts to distort, like if the signal was going through a overdrive pedal.

Is this normal?

About PT2399, I heard a local DIY pedal builder that bought a original Mad Prof. DBD.
When he was asked why didn't he build one for himself, he said that the original used a "special" kind of IC that makes the original pedal sound much, much better than any clone out there.
Well, I never heard about any "mojo" PT2399 IC's, or about TL072 IC's...
What was he talking about?

[midwayfair]

"Special IC". LOL. Someone posted recently that they played around with the op amp, and they said the "original" one sounded like crap. A good op amp is a good op amp, and these aren't being abused, so it really doesn't matter much what you use.

The motorboating is just something PT2399s do at high delay times, above about 400mS. It's pretty much there for the same reason the harmonic distortion and "shh" sounds are. The newer version of the DBD apparently caps the delay at 450mS rather than attempt to do anything about the noise. You can more aggressively band-pass the repeats to deal with the noise (see the Hamlet, the De Profundis, and perhaps a few other designs with tone controls).

Try swapping the PT2399. If you buy a pile of them, sometimes you'll get a good one.

[GermanCdn]

Sounds like your feedback knob is cranked up into the oscillation range (would give the same sound as your describing, and eventually get out of control if you dimed it), try pulling it back to less than 50% and then crank your delay all the way up.  If it's still doing what you're describing, my diagnosis is wrong, and I'll have to return my mail order doctor's certificate .

As to the second, PT2399s in the Sea Build are highly susceptible to distorting if you've got higher output pickups feeding them.  I build one which was fine with a Strat, but was a pile of mud with a LP.  Again, it will vary with your chip, so if you've got other PT2399 and you socketted it, you can swap them out and see if it makes a difference.

A common upgrade in PT2399 circuits is to use a OP275 opamp as opposed to TL072, which is probably the "mojo" your local guy is talking about.  Typically OP275 are a couple of bucks as opposed to $0.25 for a 72.  I know think Josh uses some in his Multiplex builds, I haven't A/B'd any of mine.  Don't know if it would make a huge difference, it's probably a mix of a small difference + "phantom" difference that you convince yourself because you used a more expensive part.

[zedsnotdead]

"Special IC". LOL. Someone posted recently that they played around with the op amp, and they said the "original" one sounded like crap. A good op amp is a good op amp, and these aren't being abused, so it really doesn't matter much what you use.

And about PT2399, so there are no such thing as a "special mojo thing" going right?

The motorboating is just something PT2399s do at high delay times, above about 400mS. It's pretty much there for the same reason the harmonic distortion and "shh" sounds are. The newer version of the DBD apparently caps the delay at 450mS rather than attempt to do anything about the noise. You can more aggressively band-pass the repeats to deal with the noise (see the Hamlet, the De Profundis, and perhaps a few other designs with tone controls).

If I understood correctily, the "motorboating" is normal above 450ms.
But what about the distortion sound it gets? It is not about the delay time knob, but the "mix" knob. If it gets above 80%, it gets "louder" mixing and starts to distort....

Try swapping the PT2399. If you buy a pile of them, sometimes you'll get a good one.

Why should the PT2399 be a bad one? If there is no "special mojo" about them? Or are you saying that different PT2399 (different batches perhaps?) could yeld different "noises"? Or even eliminate them?

Thank you so much for your reply!

[GrindCustoms]

The OP275 and AD712 wich are suppose to be what is found in production HW of the DBD can't decrease or help with the noise issue, big cork sniffing to me... the app of those IC at the beggining is for AD -» DA converter, nothing sounds more sterile than those.

If you don't want to go into intense filtering modifications of delay section i'd go per Jon insight about the newer DBD and limit the available delay time.

I also agree with GermanCdn about the Feedback control, these can get oscillating quite easily.

[GermanCdn]

The point behind trying different 2399s is that the overall experience with them, regardless of who you bought them from, is that they vary widely for noise, so if you have a pile, you might find that certain ones sound better than others.

[zedsnotdead]

Sounds like your feedback knob is cranked up into the oscillation range (would give the same sound as your describing, and eventually get out of control if you dimed it), try pulling it back to less than 50% and then crank your delay all the way up.  If it's still doing what you're describing, my diagnosis is wrong, and I'll have to return my mail order doctor's certificate .

As to the second, PT2399s in the Sea Build are highly susceptible to distorting if you've got higher output pickups feeding them.  I build one which was fine with a Strat, but was a pile of mud with a LP.  Again, it will vary with your chip, so if you've got other PT2399 and you socketted it, you can swap them out and see if it makes a difference.

A common upgrade in PT2399 circuits is to use a OP275 opamp as opposed to TL072, which is probably the "mojo" your local guy is talking about.  Typically OP275 are a couple of bucks as opposed to $0.25 for a 72.  I know think Josh uses some in his Multiplex builds, I haven't A/B'd any of mine.  Don't know if it would make a huge difference, it's probably a mix of a small difference + "phantom" difference that you convince yourself because you used a more expensive part.

Oh, and I answered midwayfair before I read your post.
Thank so much. Ill try that feedback/delay knob test and post the results as soon as possible.

About the distortion, is there anything I could do beside trying a different PT2399? Something to "tame" the input level? I tried it with single-coils (ceramic, but higher output than the usual alnico SCs) and distorts with the "Mix" above 80%. Shoudn't this pedal work OK whatever pickup/input level we feed to it? Does this means that Mad Professor checks all PT2399 and only uses those who give better results?

edit:

If you don't want to go into intense filtering modifications of delay section i'd go per Jon insight about the newer DBD and limit the available delay time.

The point behind trying different 2399s is that the overall experience with them, regardless of who you bought them from, is that they vary widely for noise, so if you have a pile, you might find that certain ones sound better than others.

Ok, so.... Mad Professor reduced the delay time from 600ms to 450ms, and thus it gets almost any PT2399 to sound good and noiseless?

[GermanCdn]

Part of the "distortion" your getting as you crank the mix up is the noise from the PT2399, because the wetter your signal gets, the more you're going to hear any noise that's going on with it.  Like Jon said, if you swap out the chips, you may find this lessens.  As far as limiting the input signal, there are designs out there that have implemented measures to deal with noise/distortion (CJ's noise control which Jacob uses on his delays, Jon used a different approach on the original Hamlet, etc), but it's probably more cost effective to buy one of those boards as opposed to trying a whole bunch of mods to a DBD.

As far as MP/BJFE testing their 2399s, I would certainly hope so if you're charging $160+ for the pedal.

[midwayfair]

As far as MP/BJFE testing their 2399s, I would certainly hope so if you're charging $160+ for the pedal.

That's so cute. 

The fact that they limited the delay to 450mS to avoid the problem altogether implies that they had little interest in testing the chips to ensure a better product. No need for that kind of quality control if you can just limit the functionality of your design and call it a feature, right? "Look how easy it is to dial in clear-sounding slapback!" ... that's great; a DD-7 can do that range perfectly and also do 6 seconds with tap tempo and it's $40 cheaper.