Humfree Splitter (from RG's ABY) with questions and schematic

[Auke Haarsma]

I have 'converted' RG's Humfree aby to a humfree splitter. 1 input, 3 outputs.
Goal:
Humfree splitter

Input -> EMG equipped guitar
Output 1 -> Amp
Output 2 -> Amp
Output 3 -> tuner

I did nothing more than combining the 'old' RG aby splitter and the improved hum free aby. Dropped the A/B part, added 1 output. (as shown on the original aby splitter). Below is the schematic. If some1 could look it over for errors I'd be really grateful!



As you see I also dropped in a MAX1044 to get +9V and -9V (also based on RG).

Questions:
-Is it correct that pins 2 and 5 of the transformers are unconnected?
-Will the MAX1044 be able to power the two TL072's?
-Are there any other tricks that I could use in this design to prevent hum?
-do you see any errors or things that could be done better?

Any help  much appreciated.

[Auke Haarsma]

one more question:
-should the input jack be grounded to the enclosure and the ground from the powersupply or should it be grounded as shown above in the schematic (connected to Vr)

[birt]

the transformers are just 1:1 so you can leave the center taps alone.

the output jacks are insulated from the enclosure. if they are not you have ground of all three signals connected and get hum again. teh transformers are there to decouple the outgoing signals.

but the guitar cable going to this box and the box itself are shielding so the need to be grounded to 1 point. that point can be an output that is always in use that has no transformer. that way you have only one ground connection to you amp.

but if your power supply - is connected to that same ground AND the supply is used for other pedals you have once again more than one ground path.

you can also build a small power transformer into this thing to power it. that way you can have everything before this splitter, the input and the enclosure grounded through the mains connection and you can have all outputs insulated. so everything before the splitter and the splitter itself is grounded to mains, everything after the splitter is also grounded to mains through one or more amplifiers.

i might have made some mistakes here, i'm just thinking out loud :p

[Auke Haarsma]

but the guitar cable going to this box and the box itself are shielding so the need to be grounded to 1 point. that point can be an output that is always in use that has no transformer. that way you have only one ground connection to you amp.

but if your power supply - is connected to that same ground AND the supply is used for other pedals you have once again more than one ground path.

Thanks for your reply. So if I understand correclty, if I use a powersupply which only powers the splitter, then I can ground the enclosure to the powersupply?

If I use isolated in- and outputs throughout, there will be no ground connection other than via the splitter/transformers.

[birt]

Thanks for your reply. So if I understand correclty, if I use a powersupply which only powers the splitter, then I can ground the enclosure to the powersupply?

yes. but to the ground connection of that power supply. the negative pole of a power supply is mostly tied to ground and signal ground INSIDE and effect. what you need is a mains ground connection somewhere. that's why i suggested a built-in supply with a 3 prong cord. a 2 prong has no ground connection.

If I use isolated in- and outputs throughout, there will be no ground connection other than via the splitter/transformers.

there will be no ground connection at all. the transformers decouple signal from ground. that's what they are there for. if everything is isolated from mains ground. normally you have signal ground, power supply - shielding of guitar, cable and effects all connected to mains ground through your amp. this means you get signal to your outputs without a problem. but i think it also means that EVERYTHING before those transformers is not shielded anymore.

but i want to repeat this, if someone has more theoretical knowledge than me (a LOT of people here :p) please correct me!

[Auke Haarsma]

sorry for the late reply, but thanks for your reply. I decided to put dipswitch in there which allows you to connect either of all four in/outputs to ground. (connecting to ground was suggested by RG in another thread. I'm using the dipswitch only to be able to connect to ground if necessary.

But, I have another question.

I hate using max1044 (or the equivalent LTC1044). They just die on me like flies on a bloody hot day. And those IC's are to expensive to just mess around with...

Could the humfree splitter also run at 'normal' 9V? What are the downsides of this, other than decreased headroom (4V swing would still be available, which is more than enough in normal situations. The EMG equipped guitar which will be used with this splitter is rated at max output of 1.75V.)

[R.G.]

I hate using max1044 (or the equivalent LTC1044). They just die on me like flies on a bloody hot day. And those IC's are to expensive to just mess around with...

They will die suddenly if you feed them too much input voltage. You simply cannot put more than about 9.5V into them. I've never killed one with any amount of loading. The only two ways to kill them are gross disregard of their power supply needs by either reversing the power supply or feeding them too high an input voltage. Other than that, they're tough. Which means, you're casually doing one or both of these two.

[dxm1]

They will die suddenly if you feed them too much input voltage. You simply cannot put more than about 9.5V into them.

So, maybe a 9.1V Zener across the input of the MAX1044/LT1044 would be a good idea? 

[Auke Haarsma]

Thanks RG and dxm1. A 9.1V zener is exactly what I'll be using. I ordered that yesterday b/c that seemed to most logical thing to do.

I think most 1044's died when using a Onespot. Despite how much I like the onespot, it does indeed put out something closely to 9.5V.

But could you answer the other question too? Can the humfree splitter be used at 9V instead of 18V? Is it just the headroom that's affected, or are there other things too?

[R.G.]

The 1Spot does put out nearly 9.5V, the voltage of a fresh alkaline battery.

Note that a 9.1V zener may or may not help. You will need to put a resistor in series with it to keep it and the power supply from duelling to the death. If you connect it across a power supply that puts out 9.5V and it's really 9.1V, then the power supply will pump the full output current through it for the few milliseconds of life it has left, then it will burn out. If it opens, the power supply will be applied to the circuit with no zener protection again.

This is prevented by putting a resistor in series with the zener to allow the operating voltage through but limit the maximum current to what the zener can handle. In the case of a 1/2W zener, that's 0.5/9.1 = 55mA. With the 9.5V 1Spot, the resistor value is 9.5-9.1/0.055 = 7.27 ohms. It's tough to do this one right with standard parts.

However, a 1Spot will not kill a 1044 by overvoltage. It's close, but the 1Spot does not go over 9.6V on any we have ever measured, even taking into account manufacturing variation. The rating on a 1044 is 10V. I've used this setup many times and it works fine. Reverse connection will kill it though, and that's the likely culprit.

There exists a higher voltage converter in the LT1054, I think. As I remember it's rated for 15V.

Yes, you can change to 9V only. All you lose is headroom. But now you have to dink with the power supply to get a bias voltage in the middle of the 9V, as well as putting DC blocking and biasing on input and output.

[Gus]

One can build a splitter using 9V.  Make a Vref and use caps between the transformers and opamps and the input to the buffer.

The opamps are set as gain of 2 as drawn(not the input buffer).  One could set them as inverting for a gain of 1
If it is guitar level 9V has enough headroom

I have built splitters with a 9V supply.

[Auke Haarsma]

I use the LTC1044 instead of the MAX1044. It's said the be a substitute. However, after checking the specsheets I noticed one small difference... the max voltage...the MAX1044 has a maxrating of 10.5V and the LTC only 9.5V. I'm pretty sure that's why I got so many defective LTC1044's now.

@RG: Thanks for explaining how to calculate the resistor value. I will try again with the LTC1044 but with a limiting resistor+zener included.

@Gus: I do not intend to have gain other than unity gain. It's a splitter, not a booster.

I copied parts of the schematic by RG (available from GEO):

From this schematic I took the everything but the LEDs and switches. Next I extended the outputs (I need 3 outputs, not 2) in analogy with the other humfree splitter from GEO:

rehosted and resized because the original image is huge

That's how I came to the schematic I posted in the first post in this thread.

Wouldn't this work out as a humfree splitter with three outputs and unity gain?

[Auke Haarsma]

After checking GEO (for something else...) I came across this schematic for a transformer coupled splitter:



That's pretty much exactly what I'm trying to achieve.

[alfafalfa]

I am very curious how it's going to sound Auke .
You do know the frequencyrange of the small Mouser xformers, I suppose ?

Alf

[Auke Haarsma]

This circuit will have a freq range of about 60Hz-28Khz according to RG on another forum. Enough for guitar I think.

[birt]

After checking GEO (for something else...) I came across this schematic for a transformer coupled splitter:



That's pretty much exactly what I'm trying to achieve.

looking at this schem it seems i was right about the shielding and ground concnetions of the output jacks

[Auke Haarsma]

yup you are

[Auke Haarsma]

Here's the schematic transformed to my situation.

Added:
-reverse polarity protection diode
-10 Ohm resistor + 9.1V Zener diode: this prevents overloading the LTC1044. I've tested this on the breadboard and it works nicely, dropping the voltage on the board to just below 9V. This means that also when using a different adapter than the ones I test with (I have a 1Spot and a DIY PS) the LTC is protected.
-dipswitch. This allows the user to bypass the transformer-connection to ground. In other threads I've read RG advised this while trouble shooting. I don't think it's necessary, but I want to make sure this buffer/splitter works this time.




edit: I'll upload the schematic in a minute.....

[Auke Haarsma]

[alfafalfa]

Auke in the datasheet of the Mouser Xformer 42TM018  it says that they have a freqency range of 300 Hz tot  3.4 KHz within 3 db  only !

http://www.mouser.com/catalog/specsheets/XC-600134.pdf

In my opinion it narrows down the performance too much especially in the low end.

Alf