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!
(http://img111.imageshack.us/img111/2771/buffersplitterschematicsx0.png)
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.
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)
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
Quote from: birt on February 04, 2008, 06:07:13 PM
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.
Quote from: Auke Haarsma on February 05, 2008, 01:39:06 AM
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.
Quote from: Auke Haarsma on February 05, 2008, 01:39:06 AM
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!
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.)
QuoteI 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.
Quote from: R.G. on February 19, 2008, 08:10:02 PM
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? :icon_idea:
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?
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.
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.
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):
(http://www.geofex.com/FX_images/humfree2.gif)
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:
(http://img265.imageshack.us/img265/5628/oaspltrph9.gif)
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?
After checking GEO (for something else...) I came across this schematic for a transformer coupled splitter:
(http://geofex.com/FX_images/splitter.gif)
That's pretty much exactly what I'm trying to achieve.
I am very curious how it's going to sound Auke .
You do know the frequencyrange of the small Mouser xformers, I suppose ?
Alf
This circuit will have a freq range of about 60Hz-28Khz according to RG on another forum. Enough for guitar I think.
Quote from: Auke Haarsma on February 26, 2008, 02:39:25 PM
After checking GEO (for something else...) I came across this schematic for a transformer coupled splitter:
(http://geofex.com/FX_images/splitter.gif)
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 :)
yup you are ;)
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.....
(http://img153.imageshack.us/img153/5981/buffsplitver3nh3.png)
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 (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
That would indeed be bad. But I think that the freq range is increased because the xformers are driven by the opamp. As RG says:
Quote from: RGYou might like to use the transformer isolated output of the hum free splitter at GEO (http://www.geofex.com). It uses a $2.50 transformer available from Mouser.com and drives it from an opamp to extend the frequency response to 60Hz-28Khz.
(source: http://www.diyaudio.com/forums/showthread/t-52105.html)
Quote from: alfafalfa on February 27, 2008, 10:57:22 AM
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 !
In my opinion it narrows down the performance too much especially in the low end.
That's a common mistake among people who don't understand transformers and datasheets, alf.
First about datasheets. Datasheets present the numbers that the manufacturer is willing to stand behind, in the sense that if his parts don't do at least that well, he'll give your money back. Some datasheets give min and max values of certain specifications, but many only give either a minimum (or maximum) and a typical value. For "typical" you should understand that the maker is saying "we think most of them are close to this. We hope the ones you get are close too. But we won't give your money back if it's not.
The specifications on bandwidth of transformers in general, and these in particular is a minimum of 300Hz to 3kHz. Why that? That's voice bandwidth on telephones. The actual transformers you get are almost certain to be better than that minimum - but how much? I did the obvious thing and measured it. Right off the shelf, the Xicon transformers I measured were about 150Hz to 22kHz within +/-3db. The manufacturer is obviously not going to go do work to make his products enough worse to make the specs come true, right?
Still, 150Hz is not all that good for guitar. So I used a trick. Transformer bandwidth is tremendously impedance sensitive. To get the best bandwidth in a passive situation, you simply have to drive it from the expected input impedance and load it to the expected output impedance. But I wasn't building a passive box, I was building a box to make the best use of cheap transformers.
So I took note of the fact that the low end of a transformer is limited by the core inductance eating up the input signal before it could be transformed. If you supply a primary from a quite low impedance, it can supply the extra current that the transformer core is trying to eat up, and still supply the signal being transformed too. In effect, the extra power extends the low end response on the secondary side.
In the circuit I set up, I ... measured... 60Hz to 22kHz, which I thought was good enough for rock 'n' roll.
edit: removed because I replied on a msg RG was still editing.
Quote from: Auke Haarsma on February 27, 2008, 02:01:34 PM
1-RG, are you confirming alfafalfa?
No, I'm confirming you. I just accidentally hit the send key before I was ready. Read it again now.
Thanks for your explanation RG!
The PCB can be populated now :icon_mrgreen:
Thanks for the very interesting and clarifying explanation R.G.
That's good news Auke , let me know how it works . I have a couple of theose xformers as well.
Alf
Quote from: alfafalfa on February 28, 2008, 10:59:40 AM
Thanks for the very interesting and clarifying explanation R.G.
That's good news Auke , let me know how it works . I have a couple of those xformers as well.
Alf
Sorry , I thought it was the modify button !!
Auke what about the distortion level of those xformers ? Do you have any info on that ?
Alf
I have no other info available about those statistics.
I've put it on my testbank right now. It seems to output has a bit more volume than the input. A couple of questions, it's not humfree yet:
-On the scope I see that the output of the opamp is higher than the input signal. Am I correct in thinking that the 11k resistor sets the opamp gain? Can I lower it to, say 10k, to make it unity gain?
-I didn't have a 2.2uF NP cap. I used two 1uF NP in parallel instead. This is OK, right? (what is the function of this 2.2uF cap btw?)
-Should the enclosure be connected to GND or to VR? I'd say for shielding purposes I can connect it to GND.
Alf, could you mail me your layout please? It's still not available at the DIY Layout creator page, and I'd love to have a look. My email: aukehaarsma at gmail dot com. Thnx!
also:
-into the ltc1044 goes 7.97, but it puts out: +7.97 and -7.76. Shouldn't this be +7.97 and -7.97? Now there's a 0.2V gap. Can this cause problems/hum?
-also, the hum (with the vox ac30 at max volume btw) does respond to the volume knob on my guitars. The intensity of the hum changes (not the frequency). When I plug the guitars directly into the Vox there's no hum (or very very little). This id tested with 1 amp (the vox) on the direct out, and another (Epi Valve Jr) on the isolated out. Removing either amp from the splitter doesn't make a difference.
Quote from: alfafalfa on February 29, 2008, 06:42:06 AM
Auke what about the distortion level of those xformers ? Do you have any info on that ?
The distortion of a transformer depends heavily on how hard and at what frequency it's driven.
The only distortion mechanisms transformers have are B-H nonlinearity and nonlinear core dissipation.
B-H nonlinearity is a low frequency issue, as it takes the product of voltage and time to move the core across a large part of its BH curve. So at high frequencies distortion decreases and core distortion is only an issue at the lowest end of the frequency range for all practical purposes. Nonlinear core dissipation can happen at all frequencies, but it's most severe at the top end. The cure for that is to use thinner iron. However, it's rare that iron nonlinearity is an issue at audio.
Bottom line - for small signals like less than audio line, the transformers in question should be quite good.
Quote from: Auke Haarsma on February 29, 2008, 08:03:34 AM
-On the scope I see that the output of the opamp is higher than the input signal. Am I correct in thinking that the 11k resistor sets the opamp gain? Can I lower it to, say 10k, to make it unity gain?
The gain as drawn is 1+11K/10K or about two. However, the audible difference at such low gains is almost undetectable. It seems to be more "clarity" than more level to most listeners. If you want unity gain, leave the 2.2uF NP cap out.
Quote from: Auke Haarsma on February 29, 2008, 08:03:34 AM
-I didn't have a 2.2uF NP cap. I used two 1uF NP in parallel instead. This is OK, right? (what is the function of this 2.2uF cap btw?)
It's OK. It's also OK to leave it out, as above. It's purpose is to give unity DC gain but allow a gain of about two in the buffer.
Quote from: Auke Haarsma on February 29, 2008, 08:03:34 AM
-Should the enclosure be connected to GND or to VR? I'd say for shielding purposes I can connect it to GND.
Sorry, I didn't dig through your circuit in detail until now. Why are you constructing a "Vr" different from ground? Use ground everywhere you have Vr now, and leave out those Vr parts. You don't need them and things may be quieter. Connect the input jack sleeve to the enclosure, and the direct output. Isolate the two transformer coupled jacks from the enclosure to start with. Depending on the local AC hum field situation, you ... may... need 100 ohm resistors from the transformer secondaries to the splitter local ground. Hum is hard to defeat totally. Oh, yeah. Use a steel, not aluminum box or your isolating transformers can actually pick up hum.
Quote from: Auke Haarsma on February 29, 2008, 09:25:43 AM
-into the ltc1044 goes 7.97, but it puts out: +7.97 and -7.76. Shouldn't this be +7.97 and -7.97? Now there's a 0.2V gap. Can this cause problems/hum?
No, and you can simply ignore it. The LTC1044 and all other charge pumps actually put out slightly less than their input. The gap will be ignored by modern opamps, which will work fine with powre supplies that are not perfectly mirror imaged.
Quote from: Auke Haarsma on February 29, 2008, 08:03:34 AM
-also, the hum (with the vox ac30 at max volume btw) does respond to the volume knob on my guitars. The intensity of the hum changes (not the frequency). When I plug the guitars directly into the Vox there's no hum (or very very little). This id tested with 1 amp (the vox) on the direct out, and another (Epi Valve Jr) on the isolated out. Removing either amp from the splitter doesn't make a difference.
I believe that this is the hum from the guitar and cord being buffered into the splitter. If it responds to the guitar volume, it has to be on the input side of the splitter, right? I think that your guitar volume is changing the loading on the input cord wiring and this changes the input hum. The splitter can't fix what comes in on its input. How long are the cables and what kind of guitar do you use?
What the splitter ... should... do is make the hum into two amps no bigger than the hum into one amp.
Thanks for your detailed response!
I'll check all the things you said, but I'll reply now on the guitar part:
-I'm using a '96 Gibson LP Standard with stock pups, and a PRC-clone with Golden 50's humbuckers.
-There's a pretty short (10ft) cable going to my Vox
-There's a bit longer (20ft) cable from my guitar to the splitter
-and another 20ft (old) cable from the splitter to the Epi Valve Jr Head.
As RG suggested I made Vr the same as GND. I also removed R14 and R15 (the 10k's from the ps-section) and got a nice stable splitter now!
I also removed the 2.2 uF since I had too much gain. Right now it's (close to) unity gain.
I've compared the direct output with the isolated output and they sound very much alike. I think I'll record and loop a phrase and then record my vox onto my pc. While recording (and looping) I'll swith from direct to isolated output. Seems to me a good way to compare the output. Ears can be deceiving.
Finalized this week. I used the 'improved quick n dirty oscillator' and my oscilloscope to finetune it. Added a 50k trimpot between the xformer and the first isolated-output. This allows for some treble roll off.
Pics are coming up anytime soon.
And here are the pics. Outside:
(http://img99.imageshack.us/img99/8845/p1010161ti4.jpg)
And of more interest, the inside:
(http://img166.imageshack.us/img166/892/p1010164we7.jpg)
Hopefully it stays humfree! Thanks for all the help!
Yo All,
This has to do with the performance the transformers specified for R.G. Keen's Hum free splitter.
As explained by RG in previous posts, the Xicon 42TM018-RC transformers, available from Mouser, gives a 3dB range of approx. 30-20kHz when driven with a low impedance output such as an opamp.
What has not been mentioned yet, is that there can be significant noise induced when the transformer shows some leakage between primary and secondary windings, indicated by a resistance of 1-3 Mohms between primary and secondary leads.
Of 3 pieces obtained from Mouser, 2 showed this small amount of continuity between the windings. The effect on the signal is such that it shows a thicker trace on an oscilloscope than a circuit with a transformer that has no measureable continuity.
In short, I would measure any transformer before installing into the design, and look for any measureable resistance between the primary and secondary.
QuoteAuke 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 !
In my opinion it narrows down the performance too much especially in the low end.
That's a common mistake among people who don't understand transformers and datasheets, alf.
I only just read this today !
Thanks for the info R.G. ! I wish I had known this before , could saved some money because I bought two special xformers from Sowter. They do a great job but are quite expensive.
(http://i291.photobucket.com/albums/ll291/snofal/splitterpcbs.jpg)
(http://i291.photobucket.com/albums/ll291/snofal/spilt.jpg)
Alf