Questions on Mad Prof Deep Blue

[motterpaul]

Okay - so I built this circuit and it does work. I was a little out of practice (have not built anything since last year). But here are my questions.

I built the top version since that was what I saw most people building when I looked at pictures in the comments.  (http://tagboardeffects.blogspot.com/2012/02/mad-professor-deep-blue-delay.html)

Mine sounds like a delay - but nothing like a "pro" delay pedal for various reasons I will enumerate.

The circuit calls for an OP275 or an AD712 - which is a low noise jfet op amp. BUT, since I did not have one of these I searched for a substitute. I saw people saying that the correct sub is the TL072 (82, etc) - and I can see the pinouts are the same. However, with mine I ended up using a TL071 - and it works, while the TL072 does not work.  How could this happen? Isn't that theoretically impossible, or are they close enough that if I made one simple mod (perhaps by mistake) the 071 would work? I did have to troubleshoot this build, and found some continuity between adjacent strips I didn't expect, so I cleaned them up. My question: is it possible for someone to change a circuit to take TL071 instead of TL072 with maybe one simple change to the circuit - or have I lost my mind?

Next - this circuit uses a 78L05 5v voltage regulator, and mine appears to be working (pinouts for the pt2399 all read under 5v). But, here is what I find, the circuit sounds best when the volume is all the way down (CCW) - and if I turn the volume up it gets distorted and flabby sounding, and actually quieter. Now, I know how to wire pots by now - but I OFTEN find myself ending up with pots that want to work in reverse (as just described) and I don;t know why.  In this case, it is possible I am just overloading the gain stage, and hence getting a more distorted but not louder sound?

In this circuit - does the initial gain stage need a jfet IC capable of running at 5v. Or is there another way to design it so the PT2399 only runs at 5V, while the input is running at 9v? I am wondering how critical this input IC selection (OP275) must be? Why does it ask for the relatively rare OP275 or the AD712? Is it because these are supposed to be the "cleanest" op amps, for best fidelity to feed the PT2399, or it is because they run at lower voltages?

Finally - like many, I got a bunch of PT2399 from Tayda, but I am not sure if they are bad. Many bad ones are pictured online, and mine appear to look like the better ones. Or is that misleading? Is it safer to go with a known good supplier and to pay more like $3.00 apiece for a PT2399, or is it possible a mass purchase from a Tayda could still have decent chips?

As I said, my circuit works. It has decent fidelity, and every pot (mix, delay, repeat) works as expected. It sounds like a regular delay pedal as long as the volume pot is turned mostly counter-clockwise (actually, as I turn it up there is one spot where it goes from good to crap, from clean to flubby and lower volume).

The only parts I did not have (other than the OP275) were the 360K R, and the 47pF cap (I used two Rs in series and a 43 pF).

I have the exact parts on order, but I am still wondering how it is the TL072 does NOT work. I also wonder about the input stage - whether the regulator only works on the PT2399, or it if affects the entire circuit? Sorry, but I don;t know enough about regulators to look at the circuit and see what does what.

[Frank_NH]

Schematic:



* A TL071 is a single op amp while the TL072 is a dual.  You must use a dual - TL072 should be the one to use.

* Op amp uses +9 volts as its source, and the input is biased at 4.5 volts, per the schematic.

The rest of your questions should be put on hold until you change back the op amp to a dual.  Does it not work with a TL072??

Post a hi-res picture of your board and perhaps we can crowd-source review it for you.

[motterpaul]

So they recommend a TL072P - is the P different from other chips TL072?

I know this seems crazy and it could be that I just got mixed up, but I was pretty sure I had left it working, and when I looked I saw the 71.  Anyway - thanks for answering my question. I have the original parts coming so I might just build it from scratch.

So, is VB 9v, and VD is 5v?

[Travis]

It doesn't really matter what the suffix on the TL072 is

If it isn't working with a (functional) dual op amp like the TL072 then something is wrong with your build. You could use basically any dual op amp and it should work.

Are you grounding any lug of the volume pot? Did you make the link and cuts under IC1?

The volume pot is controlling the gain of the second op amp channel. It's not a standard voltage divider volume control. If you messed that up or have a bad pot that may explain it. It sounds like your problem is based around the dual op amp somewhere..

[motterpaul]

Yes, I made the cuts and the link under the Opamp (IC1) - on the volume pot I linked lugs 2 & 3, and tied 2 back to the board as the circuit shows (I don't believe it goes to ground). The only thing I did different was I used an audio taper on the volume put, because that was the only 25k I had.

I am guessing I got my op amps confused because I did have this circuit working at one point. You get tired when trying things and sometimes you forget what you have done. Maybe I was trying different op amps and left a 071 in there by mistake. Right now I am so tired I can barely get a different OpAmp mounted.

Did you ever notice that the IC sockets with holes (instead of tabs) may look like they are more solid, but they are actually a lot harder to work with?

[Travis]

Sounds like you need to take a break from the board and look at it with fresh eyes..

To pop the ICs in easily you usually have to bend the legs inwards to a 90 degree angle from the IC body. This can be done by gently "rolling" the legs in on a table top

[Frank_NH]

Yes fresh eyes help a lot!  

I just tonight fixed a Stone Grey Distortion build, which has a modified layout which uses the CD4049UBE rather than the 4069 and LEDs for clipping.  I finished building it last night, popped it into my trusty test rig and...NOTHING.  The LEDs glowed brightly, which I thought was unusual.  So I set it aside and came back to it tonight.  After looking over my layout, I realized that I had forgotten to make a track cut and 9V was being supplied right to the LEDs (yikes)!  Fixed that and it fired right up.  

I think we can work through your DBD build and get it working.  If you get stuck, go ahead and post some pictures of your board.  Sometimes, it's the little things...

[alltrax74]

I built quite a few DBD, which is a fine pedal, but due to the 2399, you will always have this kind of shhhhh on long time delays when you play clean.
I tested many 2399, and even with the high priced selected ones from dr tweek I got the same results.
But on short time settings it sounds great

[tjdracz]

Agreed about the noise thing. I went through about 15 PT2399's from different sources and some were horrible, some more acceptable. Even with the best one the noise was clearly there. Finally exchanged my DBD + £70 for a Squier Jaguar and Boss DS1. Deal of a lifetime and now I've got bargain Alesis Midiverb and Yamaha SPX handling my delays. So much better!

[Frank_NH]

If you want a nice low-fi (tape-style) delay, check out the 1776 Effects Multiplex Echo Machine and Multiplex Junior projects.  

1776 Effects

I just recently built the Multiplex Junior and it sounds great.  I want to try pairing it with a tremelo circuit to get a Mr. Black Deluxe style trem-echo!

[Chris60601]

I built my DBD some time ago. I love that thing! I use it in a loop with Box of Hall, my Carbon Copy, and the Small Stone when I need to go off into the "Worship" or ambient. It all works really well.
The Trem is something I still need to add to my set (but I really don't have a need for one.

Cheers
Chris

[Muadzin]

I used to think that the DBD would make for an excellent booster, if you dig leads with some echo, on the account of the volume knob mod. Still do, but now I like the Madbean Dirtbaby better.

[rocket88]

I haven't built the dbd, but it's on my list, actually the one with tails, but so far out of all the delays I've played and/or owned my favorite is the danelectro reel-echo. It's stupid big, but it's meant to look like the controls for a tape delay. I know i have a disturbing love for all things danelectro, but it has such nice warm, tape like repeats. I got mine off ebay when the first came out for $50, as the guy mislabeled it and figured the bidding wou,d go higher. My number 2 favorite is the deville dark echo, but I couldn't pony up over $300 for a delay. But, now he's reissued a Mr. Black version, which is like $160, and I'm really itching to get it, as I dont think we'll end up cracking it. The delay is full of warm dark delay goodness.

[alltrax74]

Anyone tried the Madbean zero point  double delay ? ?

[Chris60601]

I have the ZP mini slated for the weekend. Not sure how this will turn out.

Cheers
Chris

[motterpaul]

I do appreciate the feedback guys. I will let you know when I get this working again (when the new parts arrive). I am sure I had it going as designed (with a working op amp)  at one point and it sounded pretty decent - but still not great.

By the way - would you guys consider this a "basic" PT2399 circuit, with near unity gain on the input so basically all you are hearing is the PT2399? If this is not one - could you name one?

Also BTW: There are three different designs here - but not one that mentions "ducking." Ducking is when a delay lowers the volume of the delays when it is getting fresh input - the goal is to eliminate the delays sounding too loud over what you are playing live. To me, a delay without ducking feels more like a gimmick effect than a truly usable effect for playing lead. I do understand there is that "just right" point where this can get close, but having a real "ducking" effect built in would be a real asset. In theory, it is accomplished by having a sidechain compressor triggered by the input signal to lower just the delay.

In my live rig I use a TC Electronics Flashback Delay, and I have it in the loop built into my Tim pedal. It works nice that way since I mostly just use the Tim as a boost for leads. It does have ducking built in.

[inefficiency]

I don't find that I need ducking to keep a delay from "getting in the way".

I use a MXR Carbon Copy and I love it. Because it's an analog delay, the repeats get darker and degrade, so I find that my bright signal never gets overwhelmed by the dark repeats.

[Frank_NH]

In my live rig I use a TC Electronics Flashback Delay, and I have it in the loop built into my Tim pedal. It works nice that way since I mostly just use the Tim as a boost for leads. It does have ducking built in.

Funny you should mention the Flashback as I'm probably going to spring for a Flashback X4 as I move towards a non-multi-fx live pedal board. The X4 allows for three delay presets and has a looper built in.  It will be paired with my DIY dirt pedals and a Visual Sound Liquid Chorus (and maybe a Wah/Volume pedal).

[rocket88]

I've got a flashback too. It's great, I actually one to get another one, the alter echo?, that's sold only though proguitarshop because it had a binson echo mod that isn't available on the normal one or as a toneprint. I love that the flashback has a reverse delay. It's not practical, but fun as hell to get real spacey psych stuff.

[Muadzin]

I use a Flashback in my rig as well, but mostly the Nova Delay. Both have ducking and to be frank I never use that feature. Never found delay to be so overwhelming as to present a problem.