Gretsch Control Fuzz & 748 Op-Amp

[mansormi]

After ordering my 748 op-amps I was surprised to see only 8 pins coming out of a VERY small chip.  According to the schematic (controfz.gif) I need to make connections at pins 10 and 12 (so I expected a 14 pin op amp). 

Can I still make this work?  I have the pin-out diagram of the op-amps in my possession, but don't know where to make my connections now since the number of pins are different.  I have no formal training in small electronics, so I would appreciate any advice.

-Mike
Go Pistons

[MartyMart]

Its two sides of a normal 8 pin "dual op amp"
So, first section on the left of schem :

Input is pin 3,  "+" input .. ( 4 on schem )
Inverting input connection is pin 2 ( 5 on schem )
6 on schem is pin 4 to ground
10 on schem is pin 1, so 25pf is from pin 3 to pin 1 and 1 is output
to the 10k and 0.1uf ...... next "half of opamp" :

The direct "link" from first to second half connects to pin 5 ( 4 on schem )
The 100k/0.47uf connects to pin 6 ( 5 on schem ) which is the inverting "-" input
The 25pf connects across pins 5 and 7 ( 7 is also the output and is marked as 10 on the schem )
there is no "extra" pin 6 to ground ( as on the schem ) our new pin 4 to ground
is all we need.
So the 330k is connecting across pins 6 and 7
Pin 8 is the 9v + connection  .... 

Hope that helps ??

MM.

[MartyMart]

Oh, by the way, if your chip is "very small" - like less than 1cm long, then its a
"surface mount" chip and not a DIL ( dual in line ) version  !!
That will be almost imposible to wire up and wont "fit" in a standard 8 pin DIL socket  !

MM

[Mark Hammer]

After ordering my 748 op-amps I was surprised to see only 8 pins coming out of a VERY small chip.  According to the schematic (controfz.gif) I need to make connections at pins 10 and 12 (so I expected a 14 pin op amp). 

Can I still make this work?  I have the pin-out diagram of the op-amps in my possession, but don't know where to make my connections now since the number of pins are different.  I have no formal training in small electronics, so I would appreciate any advice.

-Mike
Go Pistons

There was a time when single op-amps (of which the 748 is one) would come in 14-pin packages.  I still have some 14-pin 741's at home.
The key thing to pau attention to are the pin designations, regardless of package and size.  On singleop-amps in an 8-pin package, the compensation loop is usually between pins 1 and 8.  The 748 in the Controfuzz uses this loop.

You actually don't NEED to use the compensation loop or a 748 for that matter.  You could easily make the effect with a 4558 dual op-amp. 

There are 2 key elements of a Controfuzz:

1) The fuzzed signal is REALLY fuzzed.    Enough that it sustains for an ungodly length of time.
2) The fuzzed signal is seriously attenuated.  Enough so that when you pluck a note, the clean signal appears to be louder at first.

The "magic" of the Controfuzz is that the decay on the clean signal will be much faster than that on the fuzz signal.  The illusion this creates is that the note gets fuzzier towards the end, rather than starting out fuzzy and cleaning up over time as is more typical.  That illusion is a product of the relative decay phases of the clean and fuzzed notes and their relative balance.  You don't need to use a 748 to achieve that.

[tiges_ tendres]

it's also really noisy!!  At least mine is.

I wish there was a way to just get the distorted sound, and not bother with the clean, because the fuzz is out of this world.

[MartyMart]

I wish there was a way to just get the distorted sound, and not bother with the clean, because the fuzz is out of this world.

You can Here's how ( with a little help from some nice people here sorry, I forget who ! )

Change first feedback r to a 270k ( was 220k )
Change 100 ohm off pin 2 to a 2k7
Install a 120pf cap across pins 1 & 2
make the 220k off the diodes a 22k
I used a 10k fuzz pot and  50k vol pot, opamp is a TL072cp all else is stock
Now the "clean" is all but gone and its a "fuzz monster"  !!

MM.

[tiges_ tendres]

I wish there was a way to just get the distorted sound, and not bother with the clean, because the fuzz is out of this world.

You can Here's how ( with a little help from some nice people here sorry, I forget who ! )

Change first feedback r to a 270k ( was 220k )
Change 100 ohm off pin 2 to a 2k7
Install a 120pf cap across pins 1 & 2
make the 220k off the diodes a 22k
I used a 10k fuzz pot and  50k vol pot, opamp is a TL072cp all else is stock
Now the "clean" is all but gone and its a "fuzz monster"  !!

MM.

you get a big kiss!!! 

Awesome, thank you!

[mansormi]

I think that will help me, but it also raised a couple new questions.  In your explanation, Marty, would I still be using two op-amps as I see in the schem or just one dual op-amp.  My electronics store had to cross reference the 748s and special order them.  So I couldn't see that they were for suface mounting. 

I should have originally posted the pin-out of my 748 because some of the pin change overs you mentioned don't make sense to me.  I know to pay attention to the pin designations and not get hung up on pin numbers.  My 748 diagram is as follows: 
1-compensation, 2-invert input, 3-non-invert, 4-V(-), 5-Balance, 6-output, 7-V(+), 8-compensation.

I have seen TL072 come up a few times, along with 5534 and 4558, during my research.  I am going to exchange my 748s for some of those.  Thanks for the help.

[MartyMart]

I think that will help me, but it also raised a couple new questions.  In your explanation, Marty, would I still be using two op-amps as I see in the schem or just one dual op-amp.  My electronics store had to cross reference the 748s and special order them.  So I couldn't see that they were for suface mounting. 
I have seen TL072 come up a few times, along with 5534 and 4558, during my research.  I am going to exchange my 748s for some of those.  Thanks for the help.

TL072 - dual opamp
NE5534 - dual opamp
RC4558/4559 - dual opamp

These and many others do have the same pin out, which will work by my description above ( ref to the schem ).
I would recommend the TL072 for this project, it works and sounds great.

http://www.alldatasheet.com/

Use this for checking and downloading the spec sheet for pinout also

Cheers,

Marty.