Boss CE-1 Op Amp Sub

[nickbungus]

Hi Guys

Myself and another forum member, njkmonty (Nick also), have started a collaboration on a Boss CE-1 clone layout.

For reference, heres the schematic.

We've sourced the MN3002's and Nick already has a working clone so we can test chips etc., which is excellent.  We're just looking to make a few tweaks and mods here and there to make it more pedal board friendly (1590bb enclosure, 9v power, guitar impedance, perhaps true bypass).

The first stumbling block is the opamps used in the orginal.  The 7 pin TA7136P is still easy to obtain but very expensive and I was looking for some advice on swapping it out.

The Tonepad Boss DS-1 allows the TA7136P but also allows replacing it with a TL072.


I was looking on advice on how I could changeout the TA7136P's in the Boss CE-1 schematic

Opamp1
---------


OpAmp2
----------


I cant even find a datasheet for the TA7136P.  I did find some discussion on another forum (not the OTHER FORUM) and found the pinout.  Thats about it.

TA7136P pins:
1. frequency comp
2. non-inverting input (+ input)
3. inverting input (- input)
4. V-
5. voltage comp
6. outout
7. V+

Any advice on how to swap these out would be much appreciated by Nick in England and Nick in Australia!

[njkmonty]

http://www.teaser.fr/~amajorel/at203a/ta7136ap.html       what about these?

[njkmonty]

i found this....
http://www.guitarrista.com/phpbbforum/viewtopic.php?f=29&t=24270&start=150


after translation i got this...

I've already looked at the operational and pretty much I've made a scheme. I have based on the information from the tonepad DS-1. In principle I think it should work, although I'm not entirely sure (of theoretical electronics I control quite a bit). So if anyone can take a look, I would be very grateful. The issue is that I do not know if it would get to distort, as does the DS-1


What is on the left is the operational row. On your left what you need, a capacitor and a resistor, so that would have to be removed from the PCB. In exchange we would have to put a new resistance and a diode. In addition, the two circuits of the operational are used, while the original only has one.



1) The damn integrated TA7136AP. As already mentioned, it is an integrated single amplifier, and can be replaced by double commons (TL072, RC4558, etc). The only thing is that I still do not have it very clear.
I have searched for the datasheet and information, and in the end I have found what each pin is for. Specifically this:

TA7136P pins:
1. frequency comp
2. non-inverting input (+ input)
3. inverting input (- input)
4. V-
5. voltage comp
6. outout
7. V +

[alfafalfa]

Could you post a clip , I'm very curious how it sounds.

[nickbungus]

Although I've never played through a CE-1, for me the charm is the little bit of grit it brings.  I've built the tonepad CE-2 and love it but I think theres something special about the CE-1.  Its not true bypass and affects the tone quite a bit even with the effect off.  One clip I saw had a guy comparing the tone using an effects loop, with the pedal off but in the loop compared with it out of the loop.  I'll try and find that clip but in the meantime, heres a clip of the CE-1 vs CE-2.

[nickbungus]

I've created a PDF datasheet for the TA7136AP opamp from the tiff files from the link from njkmonty.

https://drive.google.com/open?id=19gwIDSTC4JEjj02Nl68iTGefkPWkBIB4

[ElectricDruid]

I don't think changing the circuit is difficult. Just drop all the frequency compensation stuff and voltage bias and keep the basic feedback paths.

In terms of replacement op-amp choice, I agree with you nickbungus - a bit of grit is a part of it. For this reason, I'd go with something more old school than a TL072, like a 4558 instead (basically two 741 type amps in the one package). But you could try other stuff from a similar era.

I suppose you could go for 741's themselves (with no advantage in terms of board space) and then you could keep the freq comp capacitor too!

HTH,
Tom

[nickbungus]

Thanks Tom

The 741 would be a great substitute.  Easy to find and cheap.

I suppose you could got for 741's themselves (with no advantage in terms of board space) and then you could keep the freq comp capacitor too!

Ok.  I'm going to do a bit of research now on frequency and voltage compensation.  I need to determine what I need to add, remove and change.  Any pointers would be much appreciated guys.

[yanng45]

We're just looking to make a few tweaks and mods here and there to make it more pedal board friendly (1590bb enclosure, 9v power, guitar impedance, perhaps true bypass).

Great project, it's a truly unique pedal !

I'm curious about that part, i own one and have a played a couple other CE-1 and the whole deal with that pedal to me is dealing with the low input impedance. From my experience with it, let's say you plug your guitar directly in a stock pedal (so 50k input pot) it can sound quite dull with the loading from the pot, you either like it or not. On the other hand, if you replace that pot with a 500k to reduce that loading and get the full signal in, it goes into clipping territory really easily with the pot on full and can sound quite harsh, especially since it doesn't like hot signals / high output pickups.

All i'm saying is that since that pedal was not made to work with a guitar signal, just raising the input impedance can pose other problems with the (stock) circuit. It's something to keep in mind.

But there's a sweet spot with a stock pedal placed after a low output impedance pedal, it has that great chorus sound and can have that "edge of breakup" sound when you strum harder, it's amazing to play that way. That bit of grit is definitely part of its sound as you guys mentioned.

[ElectricDruid]

I've been comparing "equivalent circuit diagram"s from the TA7136 and other old op-amps, and while 741 is not bad, LM709 gets you even closer.
In fact, pins 1,2,3,4,6,7 look basically identical. That only leaves pin 5 on the original device! That's a voltage bias pin on the 7136 and a output frequency compensation on the '709, according to the data sheets. I don't understand op-amp internal schematics well enough to say if that's all there is to it.

Tom

[PRR]

Note that '709 is NOT short-proof. (Poof!)

'741/558 sure is, and the '7136 will resist AC shorts (may pop with screwdriver from Out to ground).

'7136 is "unique" in that it is all class A. I can't see why that matters; class AB can be clean enough for anything.

The '7136 "compensation" is simple. Take the 50p and 10p shown in Fig 2, connect just like that, and leave it alone. It will be fine. Stability analysis like this is far above everyone's pay-grade. (I've done it, and quit.)

[reddesert]

I don't think changing the circuit is difficult. Just drop all the frequency compensation stuff and voltage bias and keep the basic feedback paths.

In terms of replacement op-amp choice, I agree with you nickbungus - a bit of grit is a part of it. For this reason, I'd go with something more old school than a TL072, like a 4558 instead (basically two 741 type amps in the one package). But you could try other stuff from a similar era.

I suppose you could go for 741's themselves (with no advantage in terms of board space) and then you could keep the freq comp capacitor too!

The 741 is internally compensated and doesn't need or use an external frequency compensation capacitor - you may be thinking of the LM308, which does. One approach might be to keep the two small caps connected from the op-amp output to ground, just don't connect them to the (non-existent on a 741) op-amp frequency comp pin.

I am not sure why Tonepad used a dual op-amp to sub for the single in the DS-1, or the purpose of the diode they added from ground to the +input, unless it's some kind of static protection. The diode seems like it would only conduct if the +input swings below the negative supply, and I don't see how it could.

[nickbungus]

Thanks for all the help guys.  Its much appreciated.

Nick (njkmonty) found a stash of 741's in his ultra organised (judging by the photos) parts box.

He's going to give it a whirl so hopefully one of us will report back with some positive results.

We've also been in deep discussions about the power supply (Getting the +14v, -14v, +13v, -13v from a 9v supply) and we've got some great ideas.

The poor lad, hes got a working and great sounding CE-1 clone, and I'm hell bent on trying to blow it up with my, 'try this.... try that'.  Good job hes on the other side of the world.

[NFX]

The whole circuit will be fine on +/-14V forget the 13V. It's only on that first opamp which I'm sure was done like that due to some noise produced by the old chip so the more modern opamp setup will be fine on the 14V.

[njkmonty]

crude  but i think it works

[Kipper4]

Plug and play op amp swaps? Wow.
Daring.....l

[njkmonty]

Due to Many complaints from various Poms irritated by their National Teams Performance , here is some more accurate tests of the 2 different opamps in a more controlled environment!
"Come on Cook!  score some runs!"    I need something to silence channel 9..

If you Know who Ezekiel Elliot is, then there is a good chance you dont know what the hell I was dribbling on about!

52 Doors!!!

Im fine thankyou Susan.

Space Corp Directive 34124   No officer with false teeth should attempt oral sex in zero gravity.

[NFX]

Wow I really like the 741 in it

[njkmonty]

here is the MN3002 replaced by a MN3007 chip, the only pin i was unsure about was Pin 1, (whether I leave it the same or connect it to  GND (Pin 7)
It sounds ok just the rate/warble seems more extreme, so thanks to advice of NFX   i change the clock capacitors c18,c19,c20,21   to the following
C18 & C19 250pf change to 120pf
c20 & C21  47pf change to 22pf
results on video 4  below

not sure why very loud lfo ticking after capacitor change??  hmmmm

[willwaush]

here is the MN3002 replaced by a MN3007 chip, the only pin i was unsure about was Pin 1, (whether I leave it the same or connect it to  GND (Pin 7)
It sounds ok just the rate/warble seems more extreme, so thanks to advice of NFX   i change the clock capacitors c18,c19,c20,21   to the following
C18 & C19 250pf change to 120pf
c20 & C21  47pf change to 22pf
results on video 4  below


not sure why very loud lfo ticking after capacitor change??  hmmmm

Have you had any success with this? Why are the videos gone?