ABY Splitter with isolated out

[stallik]

10 years ago, I built geofex's hum free using a layout by Matt Rabe which included a charge pump. This version includes 2 transformers giving a pair of isolated outputs and a direct if you want it. Link to my original post:

Geofex hum free

This has been a permanent fixture on my board since I built it and while it spent most of that time isolating 2 amps, it's also been very useful isolating 2 effects units that didn't play nicely together. I've since added a 2PDT switch to reverse the polarity of one transformer output

Can't recommend this little box highly enough

[taudio]

I'm looking at charge pumps now.
I guess either one of theses 3 will work fine to power either of theses circuits.. 
LT1054IP
TC1044SCPA
MAX1044CPA (seems a bit tricky to avoid blowing it up because of limited current output? i saw a video from diy guitar pedal on youtube)

I recommend using the TC1044SCPA because it supports a higher maximum input voltage (12V). This will improve the reliability of your design.

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection. This reduces the input voltage a bit but since we're going to be doubling it, the impact is minimal. Depending on how much current your design draws, you may need to adjust R13.

I've attached a better quality image showing only the Super Transformer power supply.

[taudio]

Thanks, there's a lot to read. I'll definetely check it all out.
Where would i get better transformer from Hammond, Jensen and Edcor ?
I would hear a noticeable improvement with them? For guitar signal, i'll have to test again but why did i never notice any sound degradation with the radial aby?
Are they much bigger? How expensive?
Except the 10k:10k impedance, frequency range and 1:1 ratio what other spec is important here in this context?

"Better" depends on what you want. Jensen offers very high performance transformers and they are priced accordingly. Hammond offers a range of products -- from "broadcast quality" to lower end. I'm not that familiar with Edcor, but I took a quick look and they seem to offer good performance at a reasonable price.

Prices range from ~$120 (Jensen JT-11p-1) to ~$23 (Edcor PCW10k/10k or Hammond 107T). Most are going to be a bit bigger than the transformer in the Radial box because they offer wider frequency response (and likely reduced distortion at low frequencies). In this context, there is a (very) rough correlation between size and low frequency performance.

It's difficult to say whether would hear a "significant improvement" because it depends on what you're doing -- the distortion is level and frequency dependent -- take a look at the JT-11p-1 datasheet for an example of this.

You've got the key specs with impedance (10k:10k), frequency response, and turns ratio (1:1). Higher end transformers will also provide data as per the JT-11p-1 datasheet: phase response, and distortion versus level and frequency.

If you're happy with the performance of the Radial box, cloning it using the schematic that RG pointed out is a good option. However, if you want higher performance, you'll need a better transformer or an active design.

Looking at the photos you posted, the Radial box needs a power supply (for the LEDs), so why not go for an active design since you're going to be powering the box anyways? The GEO-FEX design is a good one that has been proven over many years.

For a bit of extra effort, you can use the mixed-feedback "trick" we used in the Super Transformer to reduce distortion at low frequencies. A key point of our design was to see if we could get high end performance from a low cost transformer (the TY-141P) via a clever circuit trick -- the answer is a clear "Yes"

I was hoping to stay under 20-25$ each transformer.

hammond 142A seems fair enough quality?  look at the freq range, it's small and not expensive, what you think?
I can't find the graph of the AEE19-3460 and TY-141P to compare though...
https://www.hammfg.com/files/parts/pdf/142A.pdf?v=1697661931
It also specs phase shift and thd noise, i guess 142A is "better" than the other 2?

I have no problem using active, this is the one you refer to?
http://www.geofex.com/FX_images/TransformerSplitter.pdf
The thing with this one is it needs bipolar power for the IC, how do i achieve that with common easy to find parts?
With this one?
https://www.mouser.ca/ProductDetail/Analog-Devices-Maxim-Integrated/MAX1044CPA%2b?qs=0Y9aZN%252BMVCXfHpZN39Twfg%3D%3D

I found this elsewhere, not sure if its good? see attached image, geofex site does not work so it's kinda hard to find all the info...



Yes i will try this option too with the mixed feedback trick, i wonder if they did it on the radial pedal too?

The Hammond 142A looks like a good choice -- decent frequency response and more complete specs. It should work fine. Also, it is not that much more expensive that the TY-141P.

As per RG's earlier comment -- making a PCB layout with different pads so you can try different transformers is a good idea -- just in case. I found that the Hammond 107T and the TY-141P had more or less the same padout. The 142A looks similar, so you may get lucky be able to make a layout where any of them could be installed

[R.G.]

On the history of the geofex transformer coupled splitter: the transformer coupled splitter evolved in features more than performance.

The central idea was a cheaper way to get isolation from a transformer

The first version dates from about 1999, when I was looking at avoiding hum issues caused by powered pedalboards and amplifiers that leaked AC line current into their grounding scheme. Two-wire vintage amps are particularly bad about this.

The central functional module is the opamp driven 10K:10K transformer. This completely resolves the issue of AC mains leakage from the amp. This circuit section can be used alone or with other things added to it. It has largely not changed at all since the first issue.

The opamp needs power. There are single supply opamps, but their sound quality is questionable, so I used a two-supply opamp, the LM833 originally as it has better driving power than most other opamps; but the TL070 series works too. How you provide the power is a question of features. Want single supply? Use a bias voltage resistor string, an input cap and an output cap. Want bigger output than an opamp can do on a single 9V supply? Use two batteries stacked for 18V total; or use two batteries with the center connection now called "ground" for a simple bipolar supply. Don't want two batteries? Use one battery (or today, a single 9Vdc power supply) and a charge pump inverter chip. Don't want batteries at all? use a single 18V supply (for bigger output voltages) or two 9V supplies, or some other bipolar supply that generates +/- voltages up to +/- 15V.

Need more than a single input/single output? The improved version just uses two transformer sections and a wad of A-B-Y switching in front of them as in http://geofex.com/FX_images/humfree2.gif

The Hum Free(er) version uses two transformers running from one beefy opamp, with a similar wad of A-B-Y switching before the transformers. There is really almost no difference in the performance of the transformer isolators here; just one fewer ICs. There's also a provision for taking the opamp output directly for a non-isolated output.

I have trouble coming up with which of these is better. They all use the same core, an opamp driving the transformer, and tinker with the inputs and outputs, and add switching.

The mixed feedback in the version taudio shows is one way of getting rid of some of the inherent distortion that transformers give to low frequencies. I've seen variants which use a feedback winding from a three-winding 1:1:1 transformer to use the opamp feedback remove some of the transformers' native distortion. That seems to be more of a hifi issue than a guitar pedal issue, so I didn't bother to use that.

I get it that circuits can be bewildering at first, and that getting advice on what is better can help. I'm handicapped in giving advice. I've been designing audio/guitar stuff since the 1970s, and I don't see the circuits as whole lumps any more at all. I just see the subsections, how they're put together and switched and controlled. This gets in the way of me seeing whether one whole circuit is better in some way. I see too many possibilities.

[bluelagoon]

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection.

taudio, I were advised that if you have the zener there for overvoltage protection, that it would also provide reverse polarity protection, which nul and voids the necessity for D1 Shotky

[Mat88]

10 years ago, I built geofex's hum free using a layout by Matt Rabe which included a charge pump. This version includes 2 transformers giving a pair of isolated outputs and a direct if you want it. Link to my original post:

Geofex hum free

This has been a permanent fixture on my board since I built it and while it spent most of that time isolating 2 amps, it's also been very useful isolating 2 effects units that didn't play nicely together. I've since added a 2PDT switch to reverse the polarity of one transformer output

Can't recommend this little box highly enough

That's a nice and clean pedal you got there
I think i saw that layout on another thread.
Thanks for sharing

[Mat88]

I'm looking at charge pumps now.
I guess either one of theses 3 will work fine to power either of theses circuits.. 
LT1054IP
TC1044SCPA
MAX1044CPA (seems a bit tricky to avoid blowing it up because of limited current output? i saw a video from diy guitar pedal on youtube)

I recommend using the TC1044SCPA because it supports a higher maximum input voltage (12V). This will improve the reliability of your design.

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection. This reduces the input voltage a bit but since we're going to be doubling it, the impact is minimal. Depending on how much current your design draws, you may need to adjust R13.

I've attached a better quality image showing only the Super Transformer power supply.

Thanks
But hmm, i think LT1054 is even higher max input voltage at 15v isnt it?
https://www.mouser.ca/ProductDetail/Texas-Instruments/LT1054IP
Also LT1054 seems to have 100mA output current compared to 20mA on the 1044scpa.
I think there's an error on the mouser page about the output voltage it says -5v...
Not that i want to use LT1054 but i like looking at options.
1044 is cheaper though and probably just fine i saw it multiple times on pedalpcb.com layouts.

What are the multiple PWR_FLAG in your schematic?

 

[Mat88]

The Hammond 142A looks like a good choice -- decent frequency response and more complete specs. It should work fine. Also, it is not that much more expensive that the TY-141P.

As per RG's earlier comment -- making a PCB layout with different pads so you can try different transformers is a good idea -- just in case. I found that the Hammond 107T and the TY-141P had more or less the same padout. The 142A looks similar, so you may get lucky be able to make a layout where any of them could be installed

Yeah i will try to make a pcb that fits the 3 transformers we talked about here, hoping they have similar pinouts layout, but i think i will try the passive basic version first in a cheap enclosure and see how it goes, then do the fully featured active one in a nice enclosure with fancy artworks

[taudio]

I'm looking at charge pumps now.
I guess either one of theses 3 will work fine to power either of theses circuits.. 
LT1054IP
TC1044SCPA
MAX1044CPA (seems a bit tricky to avoid blowing it up because of limited current output? i saw a video from diy guitar pedal on youtube)

I recommend using the TC1044SCPA because it supports a higher maximum input voltage (12V). This will improve the reliability of your design.

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection. This reduces the input voltage a bit but since we're going to be doubling it, the impact is minimal. Depending on how much current your design draws, you may need to adjust R13.

I've attached a better quality image showing only the Super Transformer power supply.

Thanks
But hmm, i think LT1054 is even higher max input voltage at 15v isnt it?
https://www.mouser.ca/ProductDetail/Texas-Instruments/LT1054IP
Also LT1054 seems to have 100mA output current compared to 20mA on the 1044scpa.
I think there's an error on the mouser page about the output voltage it says -5v...
Not that i want to use LT1054 but i like looking at options.
1044 is cheaper though and probably just fine i saw it multiple times on pedalpcb.com layouts.

What are the multiple PWR_FLAG in your schematic?

 

You're right!

I misread it as LT1044 -- the LT1054 would work fine too. However, as you note, it is *much* more expensive.

They are pin compatible so you could start with the TC1044 and see how it works.

The PWR_FLAGs are there to keep KiCad happy. You can safely ignore them.

[Mat88]

I'm looking at charge pumps now.
I guess either one of theses 3 will work fine to power either of theses circuits.. 
LT1054IP
TC1044SCPA
MAX1044CPA (seems a bit tricky to avoid blowing it up because of limited current output? i saw a video from diy guitar pedal on youtube)

I recommend using the TC1044SCPA because it supports a higher maximum input voltage (12V). This will improve the reliability of your design.

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection. This reduces the input voltage a bit but since we're going to be doubling it, the impact is minimal. Depending on how much current your design draws, you may need to adjust R13.

I've attached a better quality image showing only the Super Transformer power supply.

Thanks
But hmm, i think LT1054 is even higher max input voltage at 15v isnt it?
https://www.mouser.ca/ProductDetail/Texas-Instruments/LT1054IP
Also LT1054 seems to have 100mA output current compared to 20mA on the 1044scpa.
I think there's an error on the mouser page about the output voltage it says -5v...
Not that i want to use LT1054 but i like looking at options.
1044 is cheaper though and probably just fine i saw it multiple times on pedalpcb.com layouts.

What are the multiple PWR_FLAG in your schematic?

 

You're right!

I misread it as LT1044 -- the LT1054 would work fine too. However, as you note, it is *much* more expensive.

They are pin compatible so you could start with the TC1044 and see how it works.

The PWR_FLAGs are there to keep KiCad happy. You can safely ignore them.

Ah ok great thanks again

[Mat88]

On the history of the geofex transformer coupled splitter: the transformer coupled splitter evolved in features more than performance.

The central idea was a cheaper way to get isolation from a transformer

The first version dates from about 1999, when I was looking at avoiding hum issues caused by powered pedalboards and amplifiers that leaked AC line current into their grounding scheme. Two-wire vintage amps are particularly bad about this.

The central functional module is the opamp driven 10K:10K transformer. This completely resolves the issue of AC mains leakage from the amp. This circuit section can be used alone or with other things added to it. It has largely not changed at all since the first issue.

The opamp needs power. There are single supply opamps, but their sound quality is questionable, so I used a two-supply opamp, the LM833 originally as it has better driving power than most other opamps; but the TL070 series works too. How you provide the power is a question of features. Want single supply? Use a bias voltage resistor string, an input cap and an output cap. Want bigger output than an opamp can do on a single 9V supply? Use two batteries stacked for 18V total; or use two batteries with the center connection now called "ground" for a simple bipolar supply. Don't want two batteries? Use one battery (or today, a single 9Vdc power supply) and a charge pump inverter chip. Don't want batteries at all? use a single 18V supply (for bigger output voltages) or two 9V supplies, or some other bipolar supply that generates +/- voltages up to +/- 15V.

Need more than a single input/single output? The improved version just uses two transformer sections and a wad of A-B-Y switching in front of them as in http://geofex.com/FX_images/humfree2.gif

The Hum Free(er) version uses two transformers running from one beefy opamp, with a similar wad of A-B-Y switching before the transformers. There is really almost no difference in the performance of the transformer isolators here; just one fewer ICs. There's also a provision for taking the opamp output directly for a non-isolated output.

I have trouble coming up with which of these is better. They all use the same core, an opamp driving the transformer, and tinker with the inputs and outputs, and add switching.

The mixed feedback in the version taudio shows is one way of getting rid of some of the inherent distortion that transformers give to low frequencies. I've seen variants which use a feedback winding from a three-winding 1:1:1 transformer to use the opamp feedback remove some of the transformers' native distortion. That seems to be more of a hifi issue than a guitar pedal issue, so I didn't bother to use that.

I get it that circuits can be bewildering at first, and that getting advice on what is better can help. I'm handicapped in giving advice. I've been designing audio/guitar stuff since the 1970s, and I don't see the circuits as whole lumps any more at all. I just see the subsections, how they're put together and switched and controlled. This gets in the way of me seeing whether one whole circuit is better in some way. I see too many possibilities.

Thanks 
You say the fist version made about 1999, which one is it?

I think what is confusing me is that on the hum-free(er) it says:
It's hard for me to believe that it's been over twelve years since I first posted this one. But times move on, and with the feedback from people who have built it, I have come up with some improvements
And the fact that this is explained:
What makes this possible is the advent of cheap 3PDTs. These things were once hugely expensive, but today, they're
only a few dollars each. The extra set of contacts in SW1 lets me add a switchable ground connection for the "off"
primary, and lift that for the "both" setting. I've shown SW2 as a 3PDT, which you may want for cosmetic consistency,
but a DPDT works just as well, as you can see that one section of SW2 is unused.

Combined with the fact that on the "improved hum free aby" schematic the title says improved but it's using dpdt instead of 3pdt. I understand they are different, not better per say but i'm still not sure which one was made first... 

Another question if i choose to build "improved hum free aby":
Any reason why i should not use one TL074 instead of two TL072 as the schematic specify?
There could be cross talk between both sides of the IC ?
I could also use the un-used opamp to buffer an external output for the tuner pedal instead of being a simple pass through like i saw on other schematics online.

[taudio]

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection.

taudio, I were advised that if you have the zener there for overvoltage protection, that it would also provide reverse polarity protection, which nul and voids the necessity for D1 Shotky

You could do that. However, there is a trade-off ...

Imagine you connect a 9 volt supply that is reverse polarity -- a likely case.

The Zener appears as a diode that drops ~0.7 volts. So, the 33 ohm resistor sees 9-0.7 = 8.3 volts

The power dissipation in the 33 ohm resistors will be V^2/R = 2W. So the resistor, which is likely 1/4W (unless you planned for this case) will burn up, becoming a fuse (and the pedal will no longer work).

If someone connects an 18 volt supply that is reverse polarity (less likely but possible), you need a 9W resistor to ensure it doesn't burn up. At some point, you'll also exceed the power dissipation of the Zener and it will also burn up -- this would happen much sooner if you don't have the resistor installed.

You could assume that the power supply that is connected in reverse polarity is current limited, which may save the resistor (and the diode), but this may not always be the case.

With the Schottky in place and a reverse supply connected, nothing happens -- at least up to the reverse breakdown voltage of the Schottky diode.

So, having both the Schottky and the Zener makes the design more robust ... and it only costs $0.20 extra

[Mat88]

I can use TL072 or TL074 instead of LM833 in the hum free(er) ?
I can combine the 3pdt concept of the hum-free(er) switching section, with TL074, and phase reverse at one of the outputs, and transformer isolation on or off (similar to what radial does) all this in one schematic?
I'll try to lay a schematic and post it here today, so you see what i mean.

There is something i don't understand in the improved hum free though...
There is one DPDT at the top and another DPDT near the center of the schematic right?

When the top DPDT is switched down, it connects either A or B outs to ground... how can that make it a both Y outputs working together at the same time?
I guess my question here is how the Y both mode works exactly?

[Mat88]

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection.

taudio, I were advised that if you have the zener there for overvoltage protection, that it would also provide reverse polarity protection, which nul and voids the necessity for D1 Shotky

You could do that. However, there is a trade-off ...

Image you connect a 9 volt supply that is reverse polarity -- a likely case.

The Zener appears as a diode that drops ~0.7 volts. So, the 33 ohm resistor sees 9-0.7 = 8.3 volts

The power dissipation in the 33 ohm resistors will be V^2/R = 2W. So the resistor, which is likely 1/4W (unless you planned for this case) will burn up, becoming a fuse (and the pedal will no longer work).

If someone connects an 18 volt supply that is reverse polarity (less likely but possible), you need a 9W resistor to ensure it doesn't burn up. At some point, you'll also exceed the power dissipation of the Zener and it will also burn up -- this would happen much sooner if you don't have the resistor installed.

You could assume that the power supply that is connected in reverse polarity is current limited, which may save the resistor (and the diode), but this may not always be the case.

With the Schottky in place and a reverse supply connected, nothing happens -- at least up to the reverse breakdown voltage of the Schottky diode.

So, having both the Schottky and the Zener makes the design more robust ... and it only costs $0.20 extra

Great explanation 

[Mat88]

Oh and i'm i correct?
"improved hum free" has 1m input impedance
"hum free(er)" has 2.2m input impedance
Why the difference between the two?

[Mat88]

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection.

taudio, I were advised that if you have the zener there for overvoltage protection, that it would also provide reverse polarity protection, which nul and voids the necessity for D1 Shotky

You could do that. However, there is a trade-off ...

Image you connect a 9 volt supply that is reverse polarity -- a likely case.

The Zener appears as a diode that drops ~0.7 volts. So, the 33 ohm resistor sees 9-0.7 = 8.3 volts

The power dissipation in the 33 ohm resistors will be V^2/R = 2W. So the resistor, which is likely 1/4W (unless you planned for this case) will burn up, becoming a fuse (and the pedal will no longer work).

If someone connects an 18 volt supply that is reverse polarity (less likely but possible), you need a 9W resistor to ensure it doesn't burn up. At some point, you'll also exceed the power dissipation of the Zener and it will also burn up -- this would happen much sooner if you don't have the resistor installed.

You could assume that the power supply that is connected in reverse polarity is current limited, which may save the resistor (and the diode), but this may not always be the case.

With the Schottky in place and a reverse supply connected, nothing happens -- at least up to the reverse breakdown voltage of the Schottky diode.

So, having both the Schottky and the Zener makes the design more robust ... and it only costs $0.20 extra

That 1n4741a is a 11v zener, how does that work or what does it do in this +-9v circuit?
It's there considering the tc1044scpca is 12v max so 11v is a safe bet to never exceeed that at the 1044 power in pin?

[taudio]

If you take a look at the Super Transformer schematic I posted earlier, you'll see that I used the TC1044 in combination with a zener (D6) / resistor (R13) and a Schottky (D1) to provide over-voltage production and reverse polarity protection.

taudio, I were advised that if you have the zener there for overvoltage protection, that it would also provide reverse polarity protection, which nul and voids the necessity for D1 Shotky

You could do that. However, there is a trade-off ...

Image you connect a 9 volt supply that is reverse polarity -- a likely case.

The Zener appears as a diode that drops ~0.7 volts. So, the 33 ohm resistor sees 9-0.7 = 8.3 volts

The power dissipation in the 33 ohm resistors will be V^2/R = 2W. So the resistor, which is likely 1/4W (unless you planned for this case) will burn up, becoming a fuse (and the pedal will no longer work).

If someone connects an 18 volt supply that is reverse polarity (less likely but possible), you need a 9W resistor to ensure it doesn't burn up. At some point, you'll also exceed the power dissipation of the Zener and it will also burn up -- this would happen much sooner if you don't have the resistor installed.

You could assume that the power supply that is connected in reverse polarity is current limited, which may save the resistor (and the diode), but this may not always be the case.

With the Schottky in place and a reverse supply connected, nothing happens -- at least up to the reverse breakdown voltage of the Schottky diode.

So, having both the Schottky and the Zener makes the design more robust ... and it only costs $0.20 extra

That 1n4741a is a 11v zener, how does that work or what does it do in this +-9v circuit?
It's there considering the tc1044scpca is 12v max so 11v is a safe bet to never exceeed that at the 1044 power in pin?

The zener is on the input, which is nominally 9 volts. It will start to conduct when the input voltage is ~11 volts (or higher), protecting the TC1044 from over voltage.

It never "sees" the -9 volts because this voltage is at the output of the charge pump and the zener is connected at the input.

[Mat88]

I wonder why they used switched or stereo in and out 6.35mm sockets on the radial pedal... Are they switching to ground when nothing is connected?

[Mat88]

The zener is on the input, which is nominally 9 volts. It will start to conduct when the input voltage is ~11 volts (or higher), protecting the TC1044 from over voltage.

It never "sees" the -9 volts because this voltage is at the output of the charge pump and the zener is connected at the input.

Ah yeah that's what i was trying to say, thanks

[Mat88]

Oh and i was wondering, with either schematics shown in this post, using only out A or only out B will not cause any more hum or noise?
I mean if only one out has a jack inserted, they are all still "hum free" ?