Op Amps

[amz-fx]

Even 741 IC can sound good in certain effect pedals

It certainly can but in those circuits it is probably acting as a defacto lowpass filter... you will get better performance by using a more modern chip (like a TL071) and tweaking the frequency response of the R-C components to your taste.

The distortion measurements certainly have meaning especially when micro-differences in components are being compared.

I did a test a few years ago where I made a TS-9 clone using cheap ceramic capacitors and another using all expensive metal film and polypropylene capacitors... in blind A/B tests, none of the guitarists who played the pedals could detect any difference between them.

http://www.muzique.com/editor.htm#caps

🙂 best regards, Jack

 

[skyraider]

Hi Jack,

Do you hear any major differences between TS-808 and TS-9? I have built the 808, and wondering if its worth the effort to build the TS-9.

What opamp do you use for your clone? From my tests, I found LM833 is the sweetest. (I couldnt get my hands on NOS JRC4558)

 

[troystg]

What I understand is that you want to build a test bed to experiment with different opamp sounds? I dont think its a good idea, because the opamp might sound good in the testbed, but as a complete guitar circuit, it might sound bad. Why dont you just replace the opamp in your amp with a socket and try different opamps for comparison?

Hi Skyraider-

Actually I need to build just a buffer circuit for a guitar and not replace an opamp in a device.

I am currently hoping to build the buffer around the BB OPA134 but since I need this buffer to be as transparent as possible I was going to build a test circuit to evaluate as many opamps as possible.

I need a gain of 1-2 but mostly need the impedance of the guitar pickup to be changed and be able to drive a LONG cord with low noise.

 

[amz-fx]

I don't hear any MAJOR differences between the TS9 and TS808... the reason I made the TS9 pedals was because I had an original TS9 to compare with... I used old RC4558 chips in the clones.

If you want a good buffer chip, try something like the OPA2604 which is high input Z and can drive long lines easily.

Or go hog-wild and get one of these chip replacements: http://www.lcaudio.dk/com/ad8065.htm

😀

regards, Jack

 

[troystg]

Hi amz-fx-

Funny you should mention that, I was looking at this:

http://www.partsconnexion.com/econnexion/econnex_v2n7/econnex_v2n7.html

Scroll down to the section after the caps.


And yes, I am looking for a hi-z input, low-z output op amp that has output current ability.

 

[amz-fx]

Here are some chip adapters for d-i-y:

http://cimarrontechnology.com/

regards, Jack

 

[troystg]

Hey amz-fx-

So after looking at that I have to ask, are they paralleling two opamps?

Is there no decoupling resistors or anything?

Can you parallel two opamps like that with direct connections?

 

[skyraider]

You can try this buffer circuit, I took it from ampage website sometime before.

You dont need to parallel two opamps, there is nothing you can gain from doing it. If it is a dual opamp package, you can just ignore the other channel.

 

[amz-fx]

Can you parallel two opamps like that with direct connections?

You can parallel two opamps.... what you get out of it is increased current drive. Typically, a small value resistor, 10 - 50 ohms is inserted on the output of each opamp before they are combined to the signal output. This insures that the opamps share the drive more equally.

regards, Jack

 

[troystg]

Great!. That was what I was looking for regarding the parallel opamps..

I will try a single first, but then if needed go parallel..

 

[skyraider]

Parallel opamps has no advantages to the buffer in this application. Sure you get more current, but it is unecessary. Furthermore, you increase the noise level which would be amplified few hundred times later in the amp.

Something worth tweaking, try biasing the opamp into class A. It has been done successfully with audio circuits, and I believe it could do some miracles for guitar buffer too.

 

[troystg]

Well I grabbed a 741 OPAMP from radioshack to play with until the OPA627 arrives.

I did not see any method of biasing the opamp..

Any suggestions?

Can the OPA627 be biased class A?

What OPAMP would you recommend as a buffer biased class A?

And sorry for the questions, but does an opamp biased into calss A require a heat sink? I could glue on to the top of the package maybe...

 

[skyraider]

Try this link for more information:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=38984&highlight=

Basically you connect a resistor between the -ve supply to the opamp output. The preffered bias current is between 5-10mA. Lets say your -ve supply is -4.5volts, and you want to bias it to 10mA. Just use R=V/I, you get the resistor value of 450 ohms(470 preferred value)

It works sometimes with certain chips, but Ive not tried it with guitar buffers yet.

 

[amz-fx]

Parallel opamps has no advantages to the buffer in this application. Sure you get more current, but it is unecessary. Furthermore, you increase the noise level which would be amplified few hundred times later in the amp.

Using a pair of opamps in parallel will actually decrease the noise by about 3dB due to random cancellations... four opamps in parallel would reduce it even further but that's about the practical limit.

I don't see any reason to try to force the opamp into class A operation since this cuts the available clean headroom in half... though it certainly is a point for experimentation. 🙂

rabstg, there are some practical examples of buffers on my site at:

http://www.muzique.com/lab/buffers.htm

regards, Jack

 

[troystg]

Hey Jack-

Thanks for the info.

As the signature states, I'm from Lafayette.

I'm part of the economic displacement program we routinely run in LA.

Mind me asking what area you live in, and what bands your currently playing with?

 

[skyraider]

Using a pair of opamps in parallel will actually decrease the noise by about 3dB due to random cancellations... four opamps in parallel would reduce it even further but that's about the practical limit.

I didnt know that
😱 😕 😱

But i never see this idea implemented in any circuits before.. I guess I can try it with my noisy JRC's

 

[skyraider]

A bit sidetrack,

Jack,
Im going to try one of your distortions some day. The shaka Bradah looks very appealing

 

[MrGuitardeath]

Slap one of those buffers in there while you're at it!

I just recently built a JFET buffer very similar to the ones on Jack's site.

Talk about no noise and a richer tone!!!!

I made some simple mods.....DOn't really know what I'm doing but they worked.

Here's the one I built:
http://www.till.com/articles/GuitarPreamp/

On the voltage bleed section, I used a 20 k trim pot which I keep wide open for optimum output.
I also eliminated the output cap and resistor, and swapped the 6.8k resistor with a 15 k.
The horrendous treble drop off is no longer an issue.

Dead silence and quite honestly it seems to be giving me a little extra sustain. Hate to say it but this circuit performed rather poorly untly I made those simple changes......don't even know exactly what some of them did other than the 20 k trimmer.

Is it possible to use this buffer POST high gain to clean up the sound???

 

[amz-fx]

Is it possible to use this buffer POST high gain to clean up the sound???

Once you get noise or distortion in a signal it is quite hard to remove, so it isn't going to do that, but it might sound good in that position for other reasons.

The shaka Bradah looks very appealing

It sounds like no other overdrive on the market; you should try it!

Mind me asking what area you live in, and what bands your currently playing with?

I live in Baton Rouge, but am currently retired from playing live. I played in bands for many years but gave it up after I moved to Louisiana a few years ago.

Regards, Jack

 

[MrGuitardeath]

post gain

Yeah I noticed using the buffer post gain seemed to give me a richer or denser tone.
Seemed very tube like to me and it actually did reduce noise.