3 way passive guitar splitter

[alfafalfa]

Just made a pcb for a 3 way guitar splitter with very high quality transformers.
I used Sowter 3575 transformers and added a possibility to use either single opamps or dual ones.
This is for more experiments.
I'm first going to use a Burr brown OPA627Ap 

The layout was made with DIY layout creator and has been uploaded , may take some time to appear.



I used the Jensen schematic  as014 .


Alf

[Auke Haarsma]

I'm working on something like that. I'm very cursious to see the schematic and/or layout.

Btw, if you use opamps, doesn't it become active (instead of passive)?

[Pushtone]

Btw, if you use opamps, doesn't it become active (instead of passive)?

Sure, active splitter with transformer isolation.

One output is un-buffered and non-isolated (direct out)
so thats your primary path to ground.

The other four are transformer isolated.

The buffer is there to drive the relatively low impedance input of the transformers.
The Jensen x-former is a 13k ohm input with a 10k load.
A far cry from our standard 500k to 1meg input impedance we like to see on pedals and amps.
Without the buffer the x-former would suck the life out of the tone and drop the level by so many dB.

I wonder if there is anything to gain by giving each transformer its own buffer? I see a TL074 in thare schematic.

[Auke Haarsma]

I overlooked the reference to the schematic, but your reply pointed me to it:
http://www.jensen-transformers.com/as/as014.pdf

In RG's splitter he uses an opamp to drive each transformer individually. He also uses 1:1 transformers instead of these 13:10

[alfafalfa]

Hello Auke,

I am not going to use the Jensen  xformers but bought the 3575 xformers from Sowter UK , very good .
Frequency response from 15 Hz to 60 KHz  within 0.25 dB , and expensive as well.





I guess you are right , it is active but with isolation transformers so in a way both .
Anyway I will be able to get rid of the hum when using three amps without  tampering with the safetyground of two of my amps !

I will report how it goes.

Alf

[Auke Haarsma]

Hi Alf,

Wow, those are around 50 pounds a piece (incl VAT). I use xformers of about 4 euro a piece...

Those look amazing, just as the specs. Please do keep us posted on the progress! Good luck!

[alfafalfa]

Auke , I will.

I chose them because I want to use them for acoustic guitar use too.
And  I am going to need the frequency range and the dynamics of an 18 volt powersupply.

Alf

[Auke Haarsma]

The layout is not yet available at the DIY layout creator page, as you said. Any chance you could post an image of the layout here for reference?

[Pushtone]

Hello Auke,

I am not going to use the Jensen  xformers but bought the 3575 xformers from Sowter UK , very good .
Frequency response from 15 Hz to 60 KHz  within 0.25 dB , and expensive as well.

Frequency response is totally overkill for guitar but I appreciate a quality x-former. 
But its their common mode rejection spec that will make your amp quieter than with a "telephone" open frame transformer.
They are magnificently shielded in those massive cans, they look like little burgers.
I wonder if the can is made of Mu-metal like the Jensens?

I work with the Jensen x-formers a lot. Mounting these "can style" x-formers can be tough.
We drill out holes in 3/4" plywood to make cups then epoxy the x-former into the hole. We found this necessary because the x-formers are heavy little bastards and a hard shock can un-mount them and inturn the loose x-former damages other things inside the enclosure.

Photo of an isolation mic snake. See the x-former cans sitting in the wood.

[Paul Marossy]

Yeah, those Jensen audio transformers are expensive, but the performance on them is really good. You get what you pay for. 

[alfafalfa]

Today , I discovered I made a few major mistakes in my pcb .   

So I corrected it and it works like a dream now. No hum , no noise .
First I tested it with a TL071 .



No wires attached yet.

Alf

[Auke Haarsma]

Good to hear Alf!

Could you please post the circuit or pcb layout? I'd like to compare it to the schematic I'm using.

[alfafalfa]

I will , when I 've finished it completely.
The schematic I used is the Jensen  AS014.

http://www.jensen-transformers.com/as/as014.pdf

Alf

[alfafalfa]

I just made a new design with a ground plane.






This one works alright.

Alf

[alfafalfa]

Forgot to add : for xformers you can either use the Jensen JT-11P-1  or the Sowter 3575.
And  as for the opamp , a TL071 works too.

Use a symetric powersupply:  + and - 9 volts , giving you a big headroom. 

Alf

[Auke Haarsma]

Thnx for posting!

Could you explain the function of the 50k resistors (R7, R8)?

[alfafalfa]

Auke,

R7 and R8 are meant to provide a treble roll off  just like the direct out .
You can make them 50 K pots if you like !

This all according to Jensen's infosheet  AS014.

Alf

[Auke Haarsma]

Ah ok, I see it in the datasheet now too. Thanks!

The version by RG doesn't have this treble roll off. Funny thing is that I did 'feel' that the isolated outputs on my splitter where a bit more trebly than the direct out. I wonder why RG left them out. Cool thing is that I now know an easy way to roll off some treble.

[alfafalfa]

Here the finished pcb populated and tested.

It works perfectly now . I tested it on three amps : two set clean in stereo and one with several fx boxes:   a distortion and a rebote 2.5 .
You can get you fav  balance between the clean and overdriven sounds, and both at the same time.
If you use footpedals in between you have complete control.
The sound is very clear not too much treble , and absolutely no hum or noise.
Must try a fourth amp from the other xformer.

I will box it up as soon as possible. A friend of mine will help me to silkscreen the box.


http://www.esnips.com/doc/234333e4-9510-41ca-ab86-f1bf00ec8f4b/IMG_0002-sm



http://www.esnips.com/doc/f9f02bdf-6222-4a4d-b73a-e154e9da8e85/IMG_0006-sm

Alf

[quasimono]

Hi alfafalfa,

i am sorry for warming up such an old topic, but i am currently looking to build a A/B(/C)+Y Splitter box with transformer isolated output(s), and your pcb layout and parts list would be very helpful for me.
All the links to images in this thread are (long) gone, could you or anyone upload your circuit layout again?

This would be awesome, thank you very much!