Ampeg - Sub Blaster  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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chicago_mike
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Post by chicago_mike »

Do we know what value the cap lables 317 is?

Oh and what would replace the j175 p fet?
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Post by chicago_mike »

Found the corrected values... :slap:

Should have this testing the octave portion in a few minutes. I will be adding tone controls of sorts to both sections. :)
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Post by audioguy »

I dont suppose anyones made a smaller PCB???

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Post by chicago_mike »

I'm currently debugging mine. :(
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Post by chicago_mike »

Hey how sure are we the Fet is a P channel?

All other octavers I see are J11, J113 or 2SK30..all N channels.

Im going to swap it out for an N channel... see what I get.


Put a J201 in there and now I get output! Im close! :horsey:
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Post by audioguy »

awesome, cant wait to hear/see it~!

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Post by chicago_mike »

Well it IS supposed to be a P channel fet.

However... :mrgreen: :twisted: :block:

I dont have that one and what I DO have are J111 and J201 and 2SK30's. These ARE used in other octavers.

So, my stupid brain says " Hey! Mod the ampeg so you can use an N fet instead!".." And while your at it, add some tone controls to the pedal"... :roll:

So, I'll know later today how it all works out. Soldering in all my bs extra stuff right now.
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Post by audioguy »

sounds cool!

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Post by chicago_mike »

Im getting close!

I lose volume with the BMP tone control and have not made a gain makeup stage. I need to do that.

The J113 has been replaced with a J201 and I altered that section more like the Boss OC-2.

I can test it later today.

Does anybody have a schematic of say a gain recovery stage or can I just steal off the Big muff?
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Post by chicago_mike »

INTERESTING!!!

I can control the pitch slightly with the tone control and volume on the octave channel. :lol: :applause:

At least I know it would work if I didn't fuck with it. :slap:


EDIT : It creates the lower octave even without the signwave input.. :lol:
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Post by audioguy »

Cool man, keep goin!!!

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Post by audioguy »

Any progress over the weekend?

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Post by chicago_mike »

None. I was comparing it to other octaver schematics and found some interesting issues. and It still isnt working like it should.

All other octaver schematics I have use an n channel fet in place where the J175 is. All other octavers have pins 2 and 5 connected ( the CD 4013 ). and couple other things here and there.

Im currently trying my hand on the mutron octave divider. Populating the boards right now.
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Post by mictester »

chicago_mike wrote:None. I was comparing it to other octaver schematics and found some interesting issues. and It still isnt working like it should.

All other octaver schematics I have use an n channel fet in place where the J175 is. All other octavers have pins 2 and 5 connected ( the CD 4013 ). and couple other things here and there.

Im currently trying my hand on the mutron octave divider. Populating the boards right now.
Do you know the pinout of the 4013? Here it is, and I'll describe the function of each pin. There are two S/R bistables in the device, one on each side of the IC.

Pin 1.....Q1..................... Pin 14....positive supply
Pin 2....not Q1.................Pin 13.......Q2
Pin 3.....Ck1....................Pin 12.....not Q2
Pin 4.....R1......................Pin 11.......Ck2
Pin 5.....D1......................Pin 10.......R2
Pin 6.....S1......................Pin 9.........D2
Pin 7.....0V......................Pin 8.........S2

OK. Looking at the left side (bistable 1): "Q" and "not Q" are complements of each other - when one is high, the other is low. These are the outputs from the bistable. Pin 3 is "Ck" ("clock"), which I'll explain in a moment. Pin 4 is "R" ("reset") which overrides clock and other inputs, and sets "Q" low and "not Q" high.

Pin 5 is "D" ("Data"). This is the slightly clever part - The "Q" output will go to the "D" setting on the next pulse applied to "Ck". This means that if "D" is low, the next positive going clock pulse applied to "Ck" will set "Q" to low. Similarly, if "D" is high, the opposite happens. You could consider "D" to be the "preset" pin, and the "Ck" is the "activate" pin.

Finally, we have pin 6, the "S" ("set") pin, which sets the bistable with "Q" high (and therefore "not Q" low), and a pulse on "R" will switch it back again.

For octave division, we tie the "S" and "R" inputs to ground, because they're unused, and as the IC is CMOS, you don't want to leave them floating or unpredictable things will happen! You connect "not Q" to "D", apply a squarewave to the "Ck" input, and take a half frequency squarewave from the "Q" output.

Because there are two identical bistables in the IC, you can use either or both of them for frequency division (to get one or two octaves down), or as I've seen done in some pedals, use one half for the frequency division and the other for the footswitch!
Last edited by mictester on 03 May 2010, 18:57, edited 4 times in total.
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Post by chicago_mike »

I have a datasheet but havent looked at it yet. :oops:
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Post by mictester »

chicago_mike wrote:I have a datasheet but havent looked at it yet. :oops:
See above! The explanation may seen long, but I tried to make it understandable.
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Post by chicago_mike »

Well you got me thinking now. :slap:

Okay OT for a second..How easy is it to do the footswitch and can it be a true bypass type? Is there enough "legs"????? to do that with a 4007 or a 4013? I have seen relays used as well, but I think I would like to try CMOS switching. I see the 4007 all the time in the dod pedals but I dont see them ever being true bypass. Unless I am missing something glaring at my face. Happens a lot. :oops:

yeah your explanation is cool. :)
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Post by mictester »

chicago_mike wrote:Well you got me thinking now. :slap:

Okay OT for a second..How easy is it to do the footswitch and can it be a true bypass type? Is there enough "legs"????? to do that with a 4007 or a 4013? I have seen relays used as well, but I think I would like to try CMOS switching. I see the 4007 all the time in the dod pedals but I dont see them ever being true bypass. Unless I am missing something glaring at my face. Happens a lot. :oops:

yeah your explanation is cool. :)
OK :horsey:

Rule 1: Repeat after me: "True Bypass is for Boutique Boobs"

Rule 2: Repeat after me: "Properly designed buffers cannot be heard"

Rule 3: Repeat after me: "CMOS switching is silent if biased correctly"

Rule 4: There is no Rule 4...... :slap:

The ICs you're interested in for truly silent switching are the 4013, for the logic part, and the 4066 to route the audio. The 4066 is described as a "quad analogue switch", and is capable of handling several volts of audio before it distorts. In my designs, I also use an input and an output op-amp (usually halves of a dual package), and guarantee that the signal leaving the box is at low impedance whether the effect is on or bypassed. Low impedance means that the signal will drive anything, including long cables, without degradation. Forget all the mojo BS you've been fed - read and repeat the Rules above!

Remember - you're starting off with a pretty poor, high impedance, low level signal from the guitar. If you can get it into a form you can work with before it has gone far (an active buffer inside the guitar is best), you can maintain the basic "sound" of the instrument without losses!

Also remember - most of the mojo is lies.....
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Post by chicago_mike »

Oh I dont believe in any of that mojo.

I already have a preamp (lakland) in my bass(es) and a custom bartolini buffer module. Built for only two people so far. 8) ( Bill the buddha Dickens) Being the other guy. I've been a tube amp tech for MUCH longer than Ive dealt with these little toys. :lol: And I got sucked into working on smd while making these ram testers that look like proton torpedoes. 8) We soldered to gold traces and measured capacitance in cables to .000004 something. The cables were like 6 inches I think. That was in interesting job. And did soldering / wiring for jet fighters...and tank simulators. :horsey: But I digress... :mrgreen:

So back to your rules. :thumbsup

Is there a schematic of a switching system as you describe? I already have quite a few 4013's and 4066's. :)
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Post by chicago_mike »

LADIES AND GERMS!!!!!!

the previous schematics have some incorrect areas.
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