Is there a Better 10K:10K Audio Transformer than...

[Paul Marossy]

the Mouser 42TM018? I'm looking for something the same physical size, but with a higher bandwidth. The frequency response for the 42TM018 specified on the data sheet is +/-3dB, 300-3.4kHz @ 1kHz 0dB. I know Jensen makes nice audio transformers, with their 10K:10K transformer having a 100kHz bandwidth, but they are like $100 a pop! There must be something else out there. I'd be happy with 10-20 kHz bandwidth. Any suggestions? 

[Peter Snowberg]

Another direction to consider is the use of pre-emphasis and de-emphasis.

Normally, pre-emphasis is simply a gain stage with a high pass filter in front of a process which is then followed by a similar amount of low-pass filtering on the output. In things like DSP and tape recording that will give you better resolution (higher S/N ratio) in the higher frequencies because high frequency signals are generally much weaker than low frequency signals. Boosting the high lowers the noise in that range, but it also limits dynamic range by a value inversely proportional to the level of boost.

Here the transformer is already acting like the low-pass output filter, so if you can place a boost with the opposite frequency response in front, you'll get higher bandwidth.

It's a kludge at best, but what's new?

Is it a situation where you just need to break the ground loop? Could it work with capacitive coupling?

[aron]

What about the Hammond 146E (lousy bass (150Hz) but goes up to 15K) for $13?

I don't know if the 141H is too small.

[Paul Marossy]

Sorry, I meant 10K:10K... 

Is it a situation where you just need to break the ground loop?

Yep.

What about the Hammond 146E (lousy bass (150Hz) but goes up to 15K) for $13?

I don't know if the 141H is too small

Hmm... I don't know. I'd like to keep the bottom end if I can. How large is it physically? The 42TM018 is pretty small - it's like a 5/8" cube...

[Joe Kramer]

Hey Paul,

You might look into these guys:

http://www.edcorusa.com/

I'm using the Edcor PC10K/10K for a small re-amping box based on the Jensen re-amp circuit.  The Edcors are not as small as the Mousers, but low enough profile to fit in a 1590 box.  The frequency response is quite good and the price is definitely right!

Joe

[nelson]

Hey Paul,

You might look into these guys:

http://www.edcorusa.com/

I'm using the Edcor PC10K/10K for a small re-amping box based on the Jensen re-amp circuit.  The Edcors are not as small as the Mousers, but low enough profile to fit in a 1590 box.  The frequency response is quite good and the price is definitely right!

Joe

I am building a hum free A/B/Y box. Perfect! Will even be able to use it with my bass!
Now, if I can just figure out how to order....

[toneman]

Hey Joe,
Where U goin' with that transformer in your hand?

>>>http://www.edcorusa.com/

nice link!!!!
I like the 600:600 units---10bucks..
Much! more expensive than the Mouser xfmrs   
But, super!! freq response!!
I recently bought several types of sm xfmrs from Mouser,
for use in a RingModulator project...   
Looks like easy 2 order......
afn
T

[nelson]

Hey Joe,
Where U goin' with that transformer in your hand?

>>>http://www.edcorusa.com/

nice link!!!!
I like the 600:600 units---10bucks..
Much! more expensive than the Mouser xfmrs   
But, super!! freq response!!
I recently bought several types of sm xfmrs from Mouser,
for use in a RingModulator project...   
Looks like easy 2 order......
afn
T

Hi Toneman

I am in the UK. Phoning an order is annoying. They dont have a list of online dealers up. No online ordering facility. Not easy to order.
That ringer stinger is tempting.....but my to build list is soooooo long.

[toneman]

Hey Nelson,

The www.edcorusa.com guys do paypal, and CreditCards.
Don't see it that difficult 2 ship to UK(?)
U will probably have to pay VAT since it's new stuff.
But, the freq response will B worth it   
RingerStinger Indeed !!!     
Bout' ready 2 pwr up first pcb!!
afn
T

[Paul Marossy]

Thanks Joe! Now we're talkin'. The price isn't too bad, either. It would take up more real estate than I would like it to, but I can work around that for the improved frequency response. 

[Paul Marossy]

Well, that Edcor transformer would work. It forces me to use a Hammond 1590BB instead of a 1590B, but it's not the end of the world. But I am designing something that I plan on selling more than a few of, so I would like to keep the enclosure small because I think it would be a good selling point - nice and compact, but very effective is the idea.  I still am not satisfied that there maybe isn't something smaller than that Edcor audio transformer, though... 

[Plectrum]

Hi Toneman

I am in the UK. Phoning an order is annoying. They dont have a list of online dealers up. No online ordering facility. Not easy to order.
That ringer stinger is tempting.....but my to build list is soooooo long.

Have you looked at the Sowter (UK) site? They're not cheap, but reputedly build some of the best transformers.

Grant.

[Ardric]

I just built a stereo line-level isolator into a 1590B for a buddy.  I used the 553-TY144P transformers from Mouser, which are 15K:15K, about 3/4" wide and less than $4.

Three of the four RCA's were isolated from the box, and I tried to be careful about grounding.  I also added a ferrite bead on the input side of each channel, and an 18k-470p across the output side as a compensation network.  Got the idea from the Jensen Transformers web site application notes, which seem like a great source of info on this stuff.

I was pleased with how pretty it all turned out, and it totally eliminated the hum/buzz problem he was having.  Quite amazing, really.  Not the slightest bit of it left, even with his stereo reciever cranked to max gain.

The downside?  When they say 200-15KHz bandwidth, they're not kidding.  The low bass is mangled.  Loud kick drums come out as an ugly "braap".

I'm going to have to rebuild it with decent transformers.  The Edcore sounds like a good next try, but it won't fit in the box.

Don't do what I did!

[R.G.]

Wow - those transformers look great for under $6.00. I'd probably not have done the thing with the Mouser transformers if I could have found those.

However;
The Mouser 10K:10K transformers will get down to an actual, measured -3db at 60Hz in the active driver circuit I used. They are flat out to 20Khz but do have a peak above that. So if you can use down to 60Hz, they work fine. I suspect the Edcar ones would do subaudio with the same drive setup.

Active drive of the primary of an audio transformer can extend the low end a lot, without precompensation.

[Paul Marossy]

Well, what I am trying to accomplish in my Parker Fly Splitter box is to have one output from the piezos go thru an FET piezo buffer circuit to an output and the magnetic pickup output is currently going thru the 42TM018 transformer with no other circuitry. The problem is that the transformer really whacks the sparkle from the sound when it is switched in the signal path and it seems to be because of the bandwidth of the transformer. Since the magentic pickups have a lower bandwidth than the piezo pickups, I want them to go thru the isolation transformer to avoid ground loops when two different amplifers are being used simultaneously. Is there some sort of circuit that I could build to prevent that? An FET buffer or something like that? I was going to look at the old GEO Hum Free A/B Box for ideas, but it's apparently nowhere to be found now... 

[R.G.]

I was going to look at the old GEO Hum Free A/B Box for ideas, but it's apparently nowhere to be found now...

It's the fourth item down in "New At Geo".

Well, what I am trying to accomplish in my Parker Fly Splitter box is to have one output from the piezos go thru an FET piezo buffer circuit to an output and the magnetic pickup output is currently going thru the 42TM018 transformer with no other circuitry. The problem is that the transformer really whacks the sparkle from the sound when it is switched in the signal path and it seems to be because of the bandwidth of the transformer. Since the magentic pickups have a lower bandwidth than the piezo pickups, I want them to go thru the isolation transformer to avoid ground loops when two different amplifers are being used simultaneously. Is there some sort of circuit that I could build to prevent that? An FET buffer or something like that?

That sounds like an OK thing to do. By itelf, yes, the transformer will kill the higher end. You'll need a higher impedance shown to the pickup. You could do that with a JFET buffer or an opamp on board. The only drawback to that is the need to replace batteries. An opamp or JFET driving a 42TM018 should restore the sparkle.

[Paul Marossy]

It's the fourth item down in "New At Geo".

Yeah, but that's not the original one, which is what I was referring to.  Anyhow, I see what you've done there.

That sounds like an OK thing to do. By itelf, yes, the transformer will kill the higher end. You'll need a higher impedance shown to the pickup. You could do that with a JFET buffer or an opamp on board. The only drawback to that is the need to replace batteries. An opamp or JFET driving a 42TM018 should restore the sparkle.

Thanks RG, I'm on it!

EDIT: Uh, one more question. If both of these FET circuits are sharing the same power supply, can hum somehow find its way into the audio path even though there is the inductor in series with one of the outputs?

[R.G.]

If both of these FET circuits are sharing the same power supply, can hum somehow find its way into the audio path even though there is the inductor in series with one of the outputs?

It should not be a problem if you use the transformer output isolated from the ground from the piezo buffer. Although the primary of the transformer shares a ground with the piezo buffer, the secondary does not. You may have to connect the isolated ground to the other ground through a resistor in some odd hum cases, but in general, the transformer isolation keeps the grounds from interacting.

[Paul Marossy]

It should not be a problem if you use the transformer output isolated from the ground from the piezo buffer. Although the primary of the transformer shares a ground with the piezo buffer, the secondary does not. You may have to connect the isolated ground to the other ground through a resistor in some odd hum cases, but in general, the transformer isolation keeps the grounds from interacting.

Cool, thanks for the help on that. I put a J201 FET in front of it, and now I can't perceive any difference between the guitar going thru the audio transformer and it being bypassed after fiddling with the trimpot on the source of the FET. Now I think I am satisfied with this little box now and feel confident about its performance enough to take a crack at selling a few and seeing how it goes...

[R.G.]

Cool beans. Which transformer did you use?