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Jensen transformer coupled DIY box?
Old 21st November 2020
  #1
Gear Maniac
Jensen transformer coupled DIY box?

Is there something like the Radial JDI Stereo but without the padding down into mic level? Meaning just pure transformer saturation or would I have to buy a whole new preamp for that? I already have neve clones so I'd like to keep it simple and small, and cheap.

Thanks guys!
Old 21st November 2020
  #2
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dualflip's Avatar
 
🎧 10 years
What is your application? is the input to the DI an instrument with Hi Z that you wish to connect to a preamp or something like that?

A passive DI box uses a transformer, in order to match the impedances from high Z to low Z a step down is necessary, there is no way around it with only transformers. If you don't want that, you need an active DI, there are many out there, the Bo Hansen DI uses an active buffer using discrete transistors with unity gain and the output is coupled into a transformer, that might be what you are looking for.

If you just want to add transformers to a low Z line level signal, such as the output of an EQ or whatever that you wish to connect to your sound interface, then you can use a standard 1:1 transformer, meaning that the output will be the same (or close to in level) as the input signal.

Last edited by dualflip; 21st November 2020 at 06:16 AM..
Old 21st November 2020
  #3
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Radardoug's Avatar
 
🎧 10 years
Jensens aren't cheap so you are already stuck!
Old 21st November 2020
  #5
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jaddie's Avatar
 
🎧 10 years
Quote:
Originally Posted by ChayaFFM View Post
Is there something like the Radial JDI Stereo but without the padding down into mic level? Meaning just pure transformer saturation or would I have to buy a whole new preamp for that? I already have neve clones so I'd like to keep it simple and small, and cheap.

Thanks guys!
Several alternatives have been suggested.

What do you plan to drive these transformers with? It's not exactly easy to saturate a transformer, especially the Jensens. The way it works is, low frequencies saturate first, by a lot. The lower the frequency, the lower the level at which distortion occurs. Varys by transformer design, again by quite a bit. But mid-band and up, you may never hit saturation at all. So to really get down and dirty, you have to be ready to hit these things pretty hard with a lot of level. It's doubtful an instrument alone could actually get there.

For example, an A67j won't hit audible distortion in an normal line-level circuit, though low frequency saturation is measurable. A 111C transformer doesn't even do that, you'd have to drive it to +30dbu to get anything to happen. Jensen DI transformers don't audibly distort until a very hot line level like +21, and even then, anything above 50Hz is audibly still clean. Two graphs below might help with understanding. They are from the Jensen DI transformer data sheet.

You generally can't hear 0.1% distortion.

Old 21st November 2020 | Show parent
  #6
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dualflip's Avatar
 
🎧 10 years
Quote:
Originally Posted by jaddie View Post
Several alternatives have been suggested.

What do you plan to drive these transformers with? It's not exactly easy to saturate a transformer, especially the Jensens. The way it works is, low frequencies saturate first, by a lot. The lower the frequency, the lower the level at which distortion occurs. Varys by transformer design, again by quite a bit. But mid-band and up, you may never hit saturation at all. So to really get down and dirty, you have to be ready to hit these things pretty hard with a lot of level. It's doubtful an instrument alone could actually get there.

For example, an A67j won't hit audible distortion in an normal line-level circuit, though low frequency saturation is measurable. A 111C transformer doesn't even do that, you'd have to drive it to +30dbu to get anything to happen. Jensen DI transformers don't audibly distort until a very hot line level like +21, and even then, anything above 50Hz is audibly still clean. Two graphs below might help with understanding. They are from the Jensen DI transformer data sheet.

You generally can't hear 0.1% distortion.



As you mention, Jensen transformers are not the way to go if you want transformer distortion, thats why you pay the big bucks.

I am not fond of transformer saturation, but my advice to the OP: if you just want a 1:1 transformer to have the signal saturated, the cheaper the better, something like this: Triad transformer

You can even get 10 transformers for less than $3 USD, Cheap Chinese Transformers make sure you drive them from a low impedance.

Last edited by dualflip; 21st November 2020 at 10:59 PM..
Old 24th November 2020
  #7
Gear Maniac
I should clarify I don’t just want jensens for the saturation but for the smoothing out of digital sounds and harshness it seems to do. Jensens have this low pass filter which is quite nifty. I guess I’ll just build my own di stereo box and save a couple bucks. Thanks guys.
Old 24th November 2020 | Show parent
  #8
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Thomas W. Bethe's Avatar
 
1 Review written
🎧 15 years
Quote:
Originally Posted by ChayaFFM View Post
I should clarify I don’t just want jensens for the saturation but for the smoothing out of digital sounds and harshness it seems to do. Jensens have this low pass filter which is quite nifty. I guess I’ll just build my own di stereo box and save a couple bucks. Thanks guys.
If transformers are doing a good job then they should be somewhat transparent and not change the sound passed through them. But as we all know that is not always the case. Maybe look around for a pair of WE 111C transformers (if you can find them).

Best of luck!
Old 24th November 2020 | Show parent
  #9
Gear Maniac
Quote:
Originally Posted by Thomas W. Bethe View Post
If transformers are doing a good job then they should be somewhat transparent and not change the sound passed through them. But as we all know that is not always the case. Maybe look around for a pair of WE 111C transformers (if you can find them).

Best of luck!
Two of those Transformers cost more than a used RNDI Stereo. Are they that good? Would like listening to some samples.
Old 25th November 2020 | Show parent
  #10
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jaddie's Avatar
 
🎧 10 years
Quote:
Originally Posted by ChayaFFM View Post
I should clarify I don’t just want jensens for the saturation but for the smoothing out of digital sounds and harshness it seems to do. Jensens have this low pass filter which is quite nifty. I guess I’ll just build my own di stereo box and save a couple bucks. Thanks guys.
Wow. Please don't be offended, but this is mythology at work.

Here are a couple of points to consider (most right out of Jensen's own data)

1. There's no one thing called a "Jensen" transformer. There are many, many different models made for different purposes. They are not interchangeable.

2. If a transformer is applied as intended, you will not be able to get any saturation. You need to deliberately use a transformer in a way it was not designed for to do that. For example, a JE-115K-E mic input transformer will saturate at line levels at frequencies below 50Hz. But, it's also a 1:10 step-up, so you'll have to deal with 20dB of voltage gain too and a means to work it into a 150K load.

3. There is no "low pass filter" in a Jensen transformer. For example, the JT-11P-1, a line input transformer, has a -3dB down point at 95kHz. The JT-DB-E, a 12:1 DI box transformer has a similar -3dB down point, just a little higher. The JT=115K-E, a mic input transformer, is also down -3dB at 88kHz or so. Sorry, no low pass filter you're ever going to hear. Even other brands do not LPF in the audio band. It's part of good transformer design not to be a LPF.

If you want a low pass filter, make a low pass filter. All it takes is a small handful of cheap parts, a couple of resistors and a capacitor will do it (assuming balanced, single-ended takes one resistor and one cap). Pick your values for the cut-off frequency of your choice, or make the resistor a pot and tune it, whatever. 10K and .001uf will roll you off just above 15kHz, as an example. No transformer worth anything will do anything like that.

Jensen transformers, and really any high quality audio transformer, is designed for transparency. There's literally no point in trying to add "color" or whatever you call lit with one.
Old 25th November 2020 | Show parent
  #11
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jaddie's Avatar
 
🎧 10 years
Quote:
Originally Posted by Thomas W. Bethe View Post
If transformers are doing a good job then they should be somewhat transparent and not change the sound passed through them. But as we all know that is not always the case.
Ever done an ABX/DBT? Those of us that have know, it actually IS the case for a decent audio transformer.
Quote:
Originally Posted by Thomas W. Bethe View Post
Maybe look around for a pair of WE 111C transformers (if you can find them).

Best of luck!
I have two on my bench right now. I've been trying to get them to saturate, in light of this discussion. My test rig won't hit them hard enough no matter what I do. I'm considering building a line driver that can cleanly drive +32dBu into them to find their nasty point. I can't get anywhere near it at +21dBu. Darn good toroidal audio transformers. Very, very transparent. And very ugly.

And you can't afford them.

No, they won't add any saturation or color at all.
Old 26th November 2020 | Show parent
  #12
Gear Maniac
Quote:
Originally Posted by jaddie View Post
Wow. Please don't be offended, but this is mythology at work.

Here are a couple of points to consider (most right out of Jensen's own data)

1. There's no one thing called a "Jensen" transformer. There are many, many different models made for different purposes. They are not interchangeable.

2. If a transformer is applied as intended, you will not be able to get any saturation. You need to deliberately use a transformer in a way it was not designed for to do that. For example, a JE-115K-E mic input transformer will saturate at line levels at frequencies below 50Hz. But, it's also a 1:10 step-up, so you'll have to deal with 20dB of voltage gain too and a means to work it into a 150K load.

3. There is no "low pass filter" in a Jensen transformer. For example, the JT-11P-1, a line input transformer, has a -3dB down point at 95kHz. The JT-DB-E, a 12:1 DI box transformer has a similar -3dB down point, just a little higher. The JT=115K-E, a mic input transformer, is also down -3dB at 88kHz or so. Sorry, no low pass filter you're ever going to hear. Even other brands do not LPF in the audio band. It's part of good transformer design not to be a LPF.

If you want a low pass filter, make a low pass filter. All it takes is a small handful of cheap parts, a couple of resistors and a capacitor will do it (assuming balanced, single-ended takes one resistor and one cap). Pick your values for the cut-off frequency of your choice, or make the resistor a pot and tune it, whatever. 10K and .001uf will roll you off just above 15kHz, as an example. No transformer worth anything will do anything like that.

Jensen transformers, and really any high quality audio transformer, is designed for transparency. There's literally no point in trying to add "color" or whatever you call lit with one.
Nice post you got there, but I think I'll rely on my own ears. Instruments and Line level running through jensens sound better to me, and definitely are not "transparent" so I'm not sure what to tell you. You can look up Bessel LPF and hypersonic sounds, the latter was discussed by Rupert Neve in a talk he gave. But maybe members with high numbers of posts on gearslutz know it better
Old 26th November 2020 | Show parent
  #13
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jaddie's Avatar
 
🎧 10 years
Quote:
Originally Posted by ChayaFFM View Post
Nice post you got there, but I think I'll rely on my own ears. Instruments and Line level running through jensens sound better to me, and definitely are not "transparent" so I'm not sure what to tell you.
Get expectation bias under control, and we can talk.

Quote:
Originally Posted by ChayaFFM View Post

You can look up Bessel LPF and hypersonic sounds, the latter was discussed by Rupert Neve in a talk he gave. But maybe members with high numbers of posts on gearslutz know it better
Yeah, I understand Bessel filter tuning. What makes you think that’s what’s happening in a specific transformer? And I’m afraid “Hypersonic sounds”, as in the
Oohhashi paper, remains in dispute. If you have a link to Neve’s talk, I’ll take a look.

Dean Jensen did the real work on transformer construction and how to make a real transparent transformer. Jensen knew his stuff, his white papers and app notes are still available. His research was specifically in audio transformers. And his successor took it farther. Even more importantly, his paper regarding “Spectral Contamination” is quite a revelation. But the short story is, once “spectral contamination” occurs, nothing is going to remove it, and Deans transformers do not add it or filter it out either.

If you’d said you could hear a UTC transformer and stated a specific model, we might not be having this discussion.

Expectation bias is very real, and nobody is immune.
Old 26th November 2020 | Show parent
  #14
Gear Maniac
Quote:
Originally Posted by jaddie View Post
Get expectation bias under control, and we can talk.
No offense but if you actually don't hear the colouration of a jensen transformer then maybe engineering isn't for you. Listen to comparison videos on youtube and don't just look at charts and numbers when talking about audio lmao.

The Bessel filter is part of the jensen transformer design.
Old 26th November 2020 | Show parent
  #15
Lives for gear
 
🎧 15 years
Quote:
Originally Posted by jaddie View Post
Dean Jensen did the real work on transformer construction and how to make a real transparent transformer. Jensen knew his stuff, his white papers and app notes are still available. His research was specifically in audio transformers. And his successor took it farther. Even more importantly, his paper regarding “Spectral Contamination” is quite a revelation. But the short story is, once “spectral contamination” occurs, nothing is going to remove it, and Deans transformers do not add it or filter it out either.
really ?
and I suppose Deane hired Ed Reichenbach.
tell us about the peer reviewed white papers on transformer construction.
Old 26th November 2020 | Show parent
  #16
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nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by ChayaFFM View Post
No offense but if you actually don't hear the colouration of a jensen transformer then maybe engineering isn't for you. Listen to comparison videos on youtube and don't just look at charts and numbers when talking about audio lmao.

The Bessel filter is part of the jensen transformer design.
All Jensen's I have seen/Used have a frequency response far out of the audio range.
Some of the line outputs are in the 1MHz and above..
Old 27th November 2020 | Show parent
  #17
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jaddie's Avatar
 
🎧 10 years
Quote:
Originally Posted by ChayaFFM View Post
No offense but if you actually don't hear the colouration of a jensen transformer then maybe engineering isn't for you.
That kind of remark is not only uncalled for, but worthy of reporting. I'm considering doing exactly that. This is a technical discussion. Personal attacks are not allowed.
Quote:
Originally Posted by ChayaFFM View Post
Listen to comparison videos on youtube and don't just look at charts and numbers when talking about audio lmao.
1. Post a link so we all know what you're referring to and there can be no mistake.

2. YouTube's audio is all transcoded after upload to compressed, AAC-LC, 44.1, and 320kbps. What exactly do you expect to hear in the "hypersonic" range with that going on?

Quote:
Originally Posted by ChayaFFM View Post
The Bessel filter is part of the jensen transformer design.
Agreed. And the cutoff frequency is way outside of the audio band. It has to be.

Your point?
Old 27th November 2020 | Show parent
  #18
Gear Maniac
Quote:
Originally Posted by nosebleedaudio View Post
All Jensen's I have seen/Used have a frequency response far out of the audio range.
Some of the line outputs are in the 1MHz and above..
Yeah, I guess I should have clarified further. I'm not sure myself what it is that makes certain transformers sound pleasant and frankly makes audio sound better that passes through it. The Bessel filter + saturation is just my guess as to why Jensen's in particular seem to smooth out harsh sounding frequencies and add to a sound. I'm well aware the frequency response itself is flat but as we know with microphones, the frequency response is only a small puzzle piece of a larger sonic picture.

Now as to why people keep giving unwanted, uneducated answers to questions not asked I can say with even less certainty. Especially when they seem to gaslight others into thinking something can't be, when every hot engineer will tell you it just simply sounds good
Old 27th November 2020 | Show parent
  #19
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🎧 10 years
Quote:
Originally Posted by cathode View Post
really ?
and I suppose Deane hired Ed Reichenbach.
It's my understanding (which might be in error) that Jensen needed a company to manufacture his original transformer designs, and initially worked with Reichenbach. Early Jensen cut sheets bear the "by Reichenbach Engineering" statement, which then vanished as the company took manufacture in house. I'm sorry I can't find a reference to prove that. But my initial applications of Deane's transformers were units made by Reichenbach, and in a later conversation with him he off-handedly said something like "oh that's when we were working with Reichebach". But that's a distant memory, and it might have been Whitlock that said that. But yeah, they manufactured product for Deane.
Quote:
Originally Posted by cathode View Post
tell us about the peer reviewed white papers on transformer construction.
I didn't mention any. He studied transformer construction, used computer modeling with software he developed (COMTRAN), and his designs came about that way.
Old 27th November 2020 | Show parent
  #20
Gear Maniac
Quote:
Originally Posted by dualflip View Post
As you mention, Jensen transformers are not the way to go if you want transformer distortion, thats why you pay the big bucks.

I am not fond of transformer saturation, but my advice to the OP: if you just want a 1:1 transformer to have the signal saturated, the cheaper the better, something like this: Triad transformer

You can even get 10 transformers for less than $3 USD, Cheap Chinese Transformers make sure you drive them from a low impedance.
Could you please clarify your last point? I heard this before from some engineer who designed equipment but for some reason lower impedance is better for driving transformers and higher ones are less desirable?
Old 27th November 2020 | Show parent
  #21
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jaddie's Avatar
 
🎧 10 years
Quote:
Originally Posted by ChayaFFM View Post
Yeah, I guess I should have clarified further. I'm not sure myself what it is that makes certain transformers sound pleasant and frankly makes audio sound better that passes through it. The Bessel filter is just my guess as to why Jensen's in particular seem to smooth out harsh sounding frequencies and add to a sound. I'm well aware the frequency response itself is flat but as we know with microphones, the frequency response is only a small puzzle piece of a larger sonic picture.
Let me clarify further. The explanation you're reaching for is contained in the understanding of "Spectral Contamination", which is a measurement technique that quantifies high frequency intermodulation distortion caused by ultrasonic signals being fed through an amplifier or device that is nonlinear in the ultrasonic range. When signals of any kind hit a device that is nonlinear in their range, distortion results, in particular, intermodulation distortion which places new product signals above and below the originals, as sum/difference components. These often land in the audio band as undefinable grit that isn't harmonically related to any audio signal.

The Bessel filter in a Jensen transformer, if placed before the offending nonlinear amplifier, filter off the ultrasonic out of band signals, keeping them out of the nonlinear range of that amplifier, and thereby reducing or eliminating spectral contamination. However, once the contamination intermodulation products have been generated, and occur in-band, and are complex, non-harmonically related components that cannot be filtered out after the fact.

Merely placing a Bessel filter in a circuit doesn't accomplish anything audible unless there are two things going on first:
1. Significant energy, usually at the very upper edge of the audio band like the top half octave and above

2. An audio system that is nonlinear in the range of those signals.

The result is intermod products thrown down into the audible band.

This means that if filtering has already occurred, like with 44.1kHz quantization, where the filter is far, far below the Bessel filter cutoff, then the Bessel characteristic accomplishes nothing.

If, however, signals with ultrasonic content are passed through a Bessel filter prior to being fed to a nonlinear system, then yes, the spectral contamination will be reduced or eliminated, and that audio will sound better.
Quote:
Originally Posted by ChayaFFM View Post
Now as to why people keep giving unwanted, uneducated answers to questions not asked I can say with even less certainty.
Perhaps it is because in a forum like this, where participants have limited time to engage and write everything in ultimate detail, full understanding is neither recognized nor accepted because the whole discussion is incomplete.

It's worth pointing out that Jensen's process of Spectral Contamination measurement has been well out of reach for most mortals for several decades. The equipment required is complex and difficult to manage, not to mention expensive. However, the most recent updates of REW now contain the ability to general the test signal that Jensen used a programmable waveform generator to create, and required special filtering in those days. Now, REW generates the multi-tone signal, and modern high performance soundcards can both produce and analyze that signal without introducing incidental spectral contamination of their own.

The tools are now available to everyone for free. This is a very significant thing, as having the tools was the barrier to entry into the world of spectral contamination measurement and understanding.
Old 27th November 2020 | Show parent
  #22
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dualflip's Avatar
 
🎧 10 years
Quote:
Originally Posted by ChayaFFM View Post
Could you please clarify your last point? I heard this before from some engineer who designed equipment but for some reason lower impedance is better for driving transformers and higher ones are less desirable?
The reflected secondary resistance (to the primary) in parallel with the source resistance forms a high pass filter with the transformer primary inductance, the higher the resistance, the higher the cut-off frequency, so you start losing bass. With good quality transformers the inductance will be such that this cut off frequency is well below 20Hz for a certain range of source resistances, with cheap transformers like the chinese I mentioned, the primary inductance is quite low and even small amounts of source resistance will make you loose some low's.

However, transformer distortion increases with higher source resistance, so if you want more transformer saturation, which is what you are asking for, you may want to increase the source resistance. As you can see, its a double edged sword, more resistance = more distortion but potentially less lows, pick your poison.

The engineer who gave you that advice was correct, if you want to have the cleanest signal from a transformer, you should keep the source resistance low.

Last century there was quite a lot of research on how to make a transformer and the circuits surrounding them in such a way that the transformer non-idealities became less significant, someone should've told them that decades later people would want exactly the opposite...
Old 27th November 2020
  #23
Lives for gear
 
🎧 5 years
Dean Jensen passed away over three decades ago. Isn't a little late to rewind the Reichenbach, Jensen stories?
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