Lundahls for amp splitter

[thomasdj]

Hi, Could I use Lundahls LL1539, 1540 or 7101 in amp switcher design?

I would like to use two amps for my 7-string guitar with EMG707's

Here are the links to the datasheets:

LL7101
http://www.lundahl.se/pdfs/datash/7101.pdf

LL1539
http://www.lundahl.se/pdfs/datash/1539.pdf

LL1540
http://www.lundahl.se/pdfs/datash/1540.pdf

Best regards

Thomas

[Steve Conner]

LL1540 is the most suitable, but even it has somewhat too low impedance. It should work though, since your guitar has active pickups.

The other two are no good.

[tedmich]

Jensen suggests a JT-11P-1 (10k/10k)for use as a passive guitar splitter, for ~$55, see:
http://www.jensen-transformers.com/as/as013.pdf

tons of good info too:
JENSEN TRANSFORMERS, INC. - APPLICATION PAPERS AND SCHEMATICS
Lundahls a beautiful and they can make whatever you need but something off the shelf may be cheaper and easier to get

some guys at DIYstompboxes.com love this (active) Jensen design:
http://www.jensen-transformers.com/as/as014.pdf

some even use the Sowter 3575 ($$!)

RG has a nice active design at geofex.com which uses $2 Xicon transformers from Mouser

[thomasdj]

LL1540 is the most suitable, but even it has somewhat too low impedance. It should work though, since your guitar has active pickups.

The other two are no good.

Thanks Steve, I guess I'll have to find a 10k:10k transformer

[thomasdj]

Jensen suggests a JT-11P-1 (10k/10k)for use as a passive guitar splitter, for ~$55, see:
http://www.jensen-transformers.com/as/as013.pdf

tons of good info too:
JENSEN TRANSFORMERS, INC. - APPLICATION PAPERS AND SCHEMATICS
Lundahls a beautiful and they can make whatever you need but something off the shelf may be cheaper and easier to get

some guys at DIYstompboxes.com love this (active) Jensen design:
http://www.jensen-transformers.com/as/as014.pdf

some even use the Sowter 3575 ($$!)

RG has a nice active design at geofex.com which uses $2 Xicon transformers from Mouser

Thanks tedmich, I've also read the files at jensen transformers but I live in europe and can't find any european dealers..

I won't use the design at geofex because of the poor low end design..

[tedmich]

Thanks tedmich, I've also read the files at jensen transformers but I live in europe and can't find any european dealers..

I won't use the design at geofex because of the poor low end design..

this is cheap, good low end and shipping isn't too bad (a Sowter down the street would be +3x more!)

EDCOR - WSM10K/10K

Intnl. shipping:
sales@edcorusa.com

[R.G.]

I won't use the design at geofex because of the poor low end design..

Hi. Can you expound on that statement please?

Did you mean "poor low end response" or "poor low end design"?

I'll go along with you on the first, within reason; it only gets down to 60Hz, 20Hz below guitar cutoff in normal tuning of 82Hz. However, it took some decent design work to do that.

I disagree with you on the second version. The design work was not of low quality. It enabled people to have a usable amp splitter with a $2 transformer instead of a $50 transformer or a $200 transformer. It also states exactly what you get.

So, can you clarify which of these you mean?

As an aside, the design principles used there can make *any* audio transformer pass more bass, not just that one. So it is extensible to improving low end for your transformers in general. So maybe you meant "that design doesn't go as low in bass as I wanted," and a simple transformer replacement would get you more low end.

However, the active buffer on the front end driving an isolation transformer has proven to work well at quite a low cost. And I should mention that using an active driver in front of the transformer gives you the option to use lower impedance transformers than the 10K/10K I used. An active driver can provide for the needs of both the input impedance the guitar has to have and the low impedance drive the transformer needs for good response.

[Steve Conner]

Let me try to explain this a bit more.

It's EXTREMELY difficult to make a transformer that will work on a passive guitar signal without messing it up. The impedance of a guitar with passive pickups is over 100k, and it's almost impossible to make a transformer that won't stifle the bass and treble at that impedance level. Maybe it can be done, but it needs some heavy transformer wizardry with the kind of price tag you would expect.

RG's design cleverly uses an op-amp buffer to drive the transformer, so it can run at a lower impedance level without loading the guitar down. You can now use any 1:1 transformer designed for a 10k impedance, and these are quite common. I imagine that the rolloff in RG's design is just because he used a really cheap transformer, and by changing the transformer for something more hi-fi you could get the low end down to any frequency you wanted.

The last time I needed 10k 1:1 audio transformers, I bought some Oxford Electronic Products ones at £10 each, and they made it down below 20Hz fine. They had a nasty resonant peak of several dB just above 20kHz, though, but I damped that out, and they're now the input transformers of the tube amp in my main stereo system. (If you think they suck, you should see the output transformers )

The low B on a 7-string is what, 60Hz?

[thomasdj]

Hi. Can you expound on that statement please?

Did you mean "poor low end response" or "poor low end design"?

I'll go along with you on the first, within reason; it only gets down to 60Hz, 20Hz below guitar cutoff in normal tuning of 82Hz. However, it took some decent design work to do that.

I disagree with you on the second version. The design work was not of low quality. It enabled people to have a usable amp splitter with a $2 transformer instead of a $50 transformer or a $200 transformer. It also states exactly what you get.

So, can you clarify which of these you mean?

As an aside, the design principles used there can make *any* audio transformer pass more bass, not just that one. So it is extensible to improving low end for your transformers in general. So maybe you meant "that design doesn't go as low in bass as I wanted," and a simple transformer replacement would get you more low end.

However, the active buffer on the front end driving an isolation transformer has proven to work well at quite a low cost. And I should mention that using an active driver in front of the transformer gives you the option to use lower impedance transformers than the 10K/10K I used. An active driver can provide for the needs of both the input impedance the guitar has to have and the low impedance drive the transformer needs for good response.

Hi R.G., Sorry for that one.. I did mean low end response, not quality!

Best regards

Thomas