ABY-Box Buffer help

[Vendt]

Hi all,

I'm looking to build a buffered ABY-box with transformer isolation.

Off course I've been looking at this:
http://www.geofex.com/FX_images/TransformerSplitter.pdf

I'm just wondering why is it using 18V?
Would it be possible to use a TL072 with 9V instead of the LM833.
Or are there other/better suggestions?

[stallik]

The way I read it, it's 9v. There are two points on the circuit marked 9v but they are not separate supplies.
I built this some time ago and it's very effective.

[Vendt]

Did you build it with an LM833?

I've prototyped it now with a TL072. It works....no Hum from 2 Tube amps that have enormous hum when not isolated.
The guitar signal seams to have bit too much gain though.

This is the link stating:
Requires 2 9V batteries for headroom.
http://www.geofex.com/FX_images/spltr2.gif

And here is the complete power section:
http://www.geofex.com/FX_images/splitter.gif

[stallik]

This is the layout I used. I built it a couple of years ago and run it on a power supply. That's my excuse for forgetting about the power requirements. The Max1044 gives + & - 9v. As far as I'm able to guage, I'm at about unity gain.
I did run into an issue with it when whacking the open E string. It distorted a bit which was put down to the limitation of the transformers. Not enough of a problem for me to source bigger trannys and irrelevant now as I'm using a passive ABY without hum issues at the moment

[PRR]

You can always question a designer's choice of opamps.

They are interchangeable, as long as you don't need anything "special".

Here the opamp has two primary goals.

1) Guitar is a low level high impedance source. We need an opamp with low hiss current.
2) Transformers are *heavy* loads on opamps. We need an opamp with good output current.

The LM833 was, at the time that was published, very promising. IMHO the hiss current is marginal for guitar, but the output drive is excellent. However it did not catch on and is now hard to find in the usual places (and probably often fake from internet vendors).

'5532 is what the LM833 was trying to copy/improve, and is also a good choice, though sometimes hissy in guitar circuits.

The TL072 is good hiss current but lame output drive for this chore. It would be some better with excess supply voltage. Coming from 9V effects, I too would expect to want 18V supply to cover hot signals dead-clean.

I have no doubt it can work at 9V with TL072 for many-many users. R.G. is a professional designer and his designs cater to working well even in extreme use.

[Elijah-Baley]

I have this project, exactly that layout, "under observation". But now I can't understand the issue of stallik had (in both the case you built it?).
The open E strings distortion is not a good thing, and I can't ingore it, and after how much told PRR, is this issue can be solved changing the IC of the transformer? Or modifing the power section?

Thanks!

[stallik]

As I understand it, RG designed this circuit to overcome some frequency limitations of the small, inexpensive transformers. In another thread I can't find, bass users were hitting these higher limits and fitted larger transformers to overcome the problem.

In my case, a very hard hit on the open, lower E was enough to distort/limit the signal so that it was not as clear as a direct connection to the amp. We're not talking overdrive, just a lack of clarity then an almost gated effect. I considered that my guitar setup wasn't helping as I like a lot of bass. Probably too much.

Others have reported no such issues so I can't rule out a poor build

[Elijah-Baley]

I have to say that I was searching some information about this kind of ABY Box right for a bass player.

So, to build something even more reliable we could replace the 45TM018 transformers with larger transformers?

[Vendt]

Ha,
Thanx for the input.
I will try if the "hard E" problem occurs in my prototype. I love playing hard E's (It's all I can  )
There was some signal that I thought had a little bit too much gain, but I did not check properly yet.
I will try to see what happens if I hook up more silent solid state amps.