Directo matic question

[Kipper4]

Is there a good reason why one couldn't build the stompbox cookbook directo matic using a TL074 in place of the LM837?
Although the book states the lm837 delivers studio qaulity spec and can drive 600ohms
I wondered if the TL074 would be a more modern replacement. Also it's a lot cheaper.
Thanks
Rich

[NakedApe]

I think the LM837 is a bipolar transistor input opamp, where the TLO74 is a FET input opamp.  This changes the input impedance for the opamps, Ithink this is why it wouldn´t work. 

[samhay]

A couple of NE5532s are largely equivalent to an LM837.

[R.G.]

It's not so much that the input of the TL07x series is different, it's the output. The LM833 and its ilk were designed with a very robust output stage that can drive 600 ohm loads to near full voltage. The TL07x series can only drive loads of down to about 2K ohms to full output. They're good amps, but designed for a different purpose.

[Kipper4]

R.G the LM833 looks like a totally differant beast on the data sheet comparaison to the lm387.
However the NE5532 does compare quite well unless I'm missing something.
Thanks for any further help on this

[samhay]

833 is the dual of the 837 (quad) isn't it?

[R.G.]

The LM387 was an uber-low-noise chip much earlier than the LM83x series. It was current back in my college days in the early 70s.

The LM833 was designed explicitly for pro-audio work. The LM837 (not LM387) was a quad version. If you are looking for an 837 and can't find one, use two LM833s and dead-bug them in place if you need to for pinout matching.

...oops, simulpost.

[Kipper4]

Super thanks guys I have lots of LM833s somewhere.
I'll put it on the list. Sorry about the typo sometimes I get too excited.
Note to self drink less coffee.
Cheers

[Kipper4]

I can't find thn data sheet for the qaud LM387 so I am assuming its standard qaud configuration.

Is It right that the non inverting input of the second inverting op amp stage goes to ground?

Sorry I cant post the schematic as It's not on the net but I'm sure some of you will have a copy of Boscarelli's Stompbox Cookbook or may even remeber the circuit.
Thanks for any clarification.
Rich

[R.G.]

I can't find thn data sheet for the qaud LM387 so I am assuming its standard qaud configuration.
...
Thanks for any clarification.

We need to be very clear here: is it an LM837 or an LM387 you're looking for. They are wildly different animals, just confusingly named.

The LM837 is a quad opamp. The LM387 is a dual, special purpose preamp chip, not a general purpose opamp.

[samhay]

The 837 has the same pinout as the TL074.
It is standard practice to DC-couple (i.e. ground, perhaps via resistor) the non-inverting input when using the inverting input AND when using a bipolar supply as is spec'd for that project. What are you planning on powering this with?

Edit - looks like RG scooped me this time.

[Kipper4]

I cant believe I did the same typo twice. It's been a long one.
Also was thinking of making a single channel as opposed to two.
I intend to use the a dual LM833 and power it via +9v single supply.
Or do I need to use a bipolar power supply.

[samhay]

You could build a single channel version with an 833 or 5532. You will need to modify it a bit for single supply operation - either by setting up a half-supply Vref (and halving your headroom), or by using a charge pump to create a bipolar supply.

[Kipper4]

I did wonder thanks Sam I'll draw up something in eagle and get back.

[Kipper4]

I didn't find much information that I could get my head around when researching charge pumps except of course GeoFx.
So I'm going with this for my power supply

http://www.geofex.com/circuits/+9_to_-9.htm
Only difference is I'll be using the ICL7660cpa chip which has the same pinout.
Anyone see any problem with this or any suggestions for improvements?

[samhay]

That's fine, but you will need use the 7660S. This version has the 'boost' function that you need to keep the oscillator frequency out of the audio band.

[Kipper4]

I'm guessing from what i remeber in the data sheet then that would mean tying pin7 the osc to ground with a series 100uf cap right?

[samhay]

Nope - pretty sure you want to tie pins 1 and 8 together.

[Kipper4]

Thanks Sam
Just like RG's then at the top of the page here cheers




http://www.geofex.com/circuits/+9_to_-9.htm

[Kipper4]

Necro post.
I finally managed to scratch this off the list.
Its super clean at low gain. Turn that sucker up and it will clip in cubase.
It's always handy to have gain on tap though.
features; ground lift, fx/guitar switch, and polarity swap
I'm really happy with this.
Thanks to everyone that helped out especially Sam.
Cant wait for the xlr barrel to arrive now.
Rich