An inexpensive audio transformer with DIY projects

[boomertech]

I found this nice transformer a few weeks ago and thought that it could be useful for DIY DI Box or interstage coupler to break ground loops. It has 20-20KHz +/-1dB bandwidth which is really, really good for such an inexpensive tranny ($5 each). The only version Mouser has at this time is the 1Kohm primary and secondary model, but with a healthy primary driver it should work nicely. The data sheet has a nice comparison graph with all of the models.

I haven’t tried this tranny yet, although I plan on getting a few to play around with.

Invalid Link Removed

-Frank

 

[jeffmensch]

Pretty good specs on that one and it's less spendy than the equivalent Hammond. Definitely worth experimenting with.

 

[Downunderwonder]

Correct me if I'm wrong but a 2PDT plus that makes a passive polarity flipping device?

 

[boomertech]

Correct me if I'm wrong but a 2PDT plus that makes a passive polarity flipping device?

Yes, you can flip polarity with a transformer and a 2PDT switch if you want isolation. If you want to pass the input ground to the output you would also need to switch ground positions (3PDT switch) on the secondary output.

But, you need to accommodate for the low primary impedance with a healthy buffer driver on the primary side.

-Frank

 

[Downunderwonder]

What are the odds of XYZ fuzz pedal, that flips its output, having the goods to drive it in its own little loop?

 

[boomertech]

What are the odds of XYZ fuzz pedal, that flips its output, having the goods to drive it in its own little loop?

It would be entirely circuit specific to the fuzz circuit to determine if it has the juice to drive a 1Kohm load. So, I would say the odds are not favorable. The odds would get better with the 10K/10K tranny and even better with the 100K/100K tranny.

Let's say the fuzz pedal has a fixed 1K output impedance (somewhat typical) and it's output driver is stiff enough to handle a 2Kohm load (1K from the fuzz and 1K from the tranny primary). The signal on the primary coil will be -6dB down (1K + 1K voltage divider) plus the -3dB tranny insertion loss will give the tranny output -9dB signal when configured as a 1:1 coupler. If you configure the tranny as a 2:1 coupler for lower output impedance then the output signal will be down somewhere near -15dB.

-Frank

 

[Downunderwonder]

Thanks. Doesn't sound too great for anything less than a phantom powered DI then.

 

[boomertech]

Thanks. Doesn't sound too great for anything less than a phantom powered DI then.

For what you are after, the 100K/100K may work exactly like you want.

Like jeffmensch said above this tranny is $5 and the Hammond 140TEX with very similar specs is close to $70. Any design that would use the Hammond or similar may work very well with this tranny and save the DIYer some cash.

Many people love the sound they get thru a transformer, so this could be a very inexpensive way to get those tones in a DIY circuit.

EDIT: The most basic way I can see to use this would be in an effects loop on your amplifier. Tranny, two jacks and a metal enclosure is all that would be needed. If the 1K load is too much for the effects loop then a simple buffer driver could be installed. Then your SS amp now has transformer coupling!

-Frank

 

[AltGrendel]

Yes, you can flip polarity with a transformer and a 2PDT switch if you want isolation. If you want to pass the input ground to the output you would also need to switch ground positions (3PDT switch) on the secondary output.

But, you need to accommodate for the low primary impedance with a healthy buffer driver on the primary side.

-Frank

I don't understand a word of that, but it sure reads nice.

 

[boomertech]

JohnK and I are working on a GK amp simulator in another thread where we used one of these transformers for an output. I ran some tests to see how it handles shunt attenuation and plotted the results.

TY-250P transformer testing shunt attenuation:

The green trace is the 0dBu reference input signal.

The purple trace is the transformer output without a load connected across its output terminals.

The yellow trace is the output with a 1K ohm load across the output terminals… I was expecting at least a 6dB drop because the secondary impedance on this transformer is 1K ohm. So, it’s only a little bit more than expected.

The orange trace is the output with a 500ohm load across the output terminals.

The blue trace is the output with a 250ohm load across the output terminals.

I am very, very impressed with this $5 transformer. It accepts a shunt attenuator very well and the frequency response is very good and stable with all of these loads.

-Frank

 

[mbelue]

Many people love the sound they get thru a transformer, so this could be a very inexpensive way to get those tones in a DIY circuit.

EDIT: The most basic way I can see to use this would be in an effects loop on your amplifier. Tranny, two jacks and a metal enclosure is all that would be needed. If the 1K load is too much for the effects loop then a simple buffer driver could be installed. Then your SS amp now has transformer coupling!

I've read about this before but really don't know what it is audibly. Would you say this is similar to the "tube feel" discussion?
Something subjective and subtle that might not be noticed by/important to everyone.

 

[boomertech]

I've read about this before but really don't know what it is audibly. Would you say this is similar to the "tube feel" discussion?
Something subjective and subtle that might not be noticed by/important to everyone.

The added distortions from transformers are usually very subtle (except with output power transformers), but harmonically pleasing to the ear. Here is a page I just found that goes into some depth on transformer distortions... there is more info near the bottom of the article:

http://www.soundonsound.com/sos/feb10/articles/analoguewarmth.htm#Top

-Frank

 

[boomertech]

I ran tests on the TY250 tranny and here are the results with 20Vp-p, 10Vp-p and 5Vp-p signals feeding the primary. I used a USB sound module as the signal source into my SWR power amp to drive the primary side of the tranny. I used a 10K pot on the secondary coil configured as a standard volume pot. I set the volume level on the secondary pot to make sure that no levels would exceed 2Vp-p to keep the sound module input from clipping. The FFT results are interesting:

You can see how wavy the trace for 20Vp-p is from 20 to 200Hz. This is what signal distortion looks like in an FFT analysis. This transformer only cost $5 and because it is so inexpensive, I believe that the core is made of low cost materials and easily saturates with this level of signal at low frequencies.

The 10Vp-p trace is a bit cleaner, but there is still a little bit of distortion under 200Hz. The 5Vp-p trace is even cleaner.

-Frank

 

[boomertech]

John K just finished the GK power amp simulator that we worked on together (he had the bulk of the work) and said he might be up for another project.

After running tests on this transformer and seeing how the large input signals distort like a pushed output transformer, I came up with this conceptual boost circuit. This will be a much simpler circuit than the GK power amp simulator. In fact, I tried to make all of the components, but a few, all 1’s, 10’s or 100’s. It is not a simulator for any particular amplifier, but it is modeled after the push-pull output of some tube amplifiers. The push-pull driver stage for the transformer also incorporates some soft clipping that tube amplifiers are famous for.

*** IMAGE REMOVED - UPDATED IMAGE LATER IN THREAD***

There are only two controls, DRIVE and LEVEL. The drive control is a dual control that increases the gain of the push-pull amplifiers for soft clipping and transformer saturation, while also decreasing the gain at the output amplifier. The drive control is designed to keep the same volume level throughout its control range because this amp can have approx. 24Vp-p signals in the circuit. The output amp has a gain of approx. 20dB so that a boost can be realized.

-Frank

 

[johnk_10]

that's awesome Frank. I really like this idea.
i'll build it up soon. hopefully tomorrow.

 

[johnk_10]

I take it that you meant to use one TL072 and that pins 6&7 on the TY250 are jumped together?

 

[recnsci]

I believe that the core is made of low cost materials and easily saturates with this level of signal at low frequencies.

Core saturation is determined by maximum flux density for given material, and flux is determined by transformer geometry and current trough windings. If you check table 3. here you'll notice that "expensive" nickel alloys have smaller max flux density than steel (most of audio output transformers are plain silicon steel core, mic/low-level transformers are often nickel alloys because of low level performance). So, IMHO key issue with this transformer is size/geometry, it's most likely made of silicon steel like rest of output/matching transformers, nonscientific rule of the thumb would be smaller transformer -> higher flux density for given current -> lower max current/power.

BTW, Edcor makes great low cost audio transformes (https://www.edcorusa.com/matchers)

 

[boomertech]

I take it that you meant to use one TL072 and that pins 6&7 on the TY250 are jumped together?

Good catch. Updated

-Frank

 

[boomertech]

Core saturation is determined by maximum flux density for given material, and flux is determined by transformer geometry and current trough windings. If you check table 3. here you'll notice that "expensive" nickel alloys have smaller max flux density than steel (most of audio output transformers are plain silicon steel core, mic/low-level transformers are often nickel alloys because of low level performance). So, IMHO key issue with this transformer is size/geometry, it's most likely made of silicon steel like rest of output/matching transformers, nonscientific rule of the thumb would be smaller transformer -> higher flux density for given current -> lower max current/power.

BTW, Edcor makes great low cost audio transformes (https://www.edcorusa.com/matchers)

Those Edcor trannys look nice.

This $5 TY250 transformer looks like it is going be nice for low cost FX projects. We want a transformer that gets a little dirty in the bottom end.

What's funny is that the manufacturer has no info on their website for this guy.

-Frank

 

[recnsci]

What's funny is that the manufacturer has no info on their website for this guy.

-Frank

It is in their catalog http://triadmagnetics.com/pdf/13.pdf

BTW, another option is to drive it with JFET/BJT differential pair, since primary is center tapped (with problem of maintaining balanced idle current without tight matching and temperature coupling of pair). With JFET pair it would sort of be like push-pull tube poweramp , but JFET output characteristic is not the same as pentode, and distortion would not be as dominantly low frequency any more as compared to voltage drive.