P96DI & A72DI - Passive and Active Di Boxes in Business Card Format

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amplexus

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As the designer of the original DI2 and all its successors, I will say I'm not particularly proud of being the subject of "the sincerest form of flattery", particularly by someone that made a butchery of it.
All the points you mention indicate an utter absence of understanding of how it should work from the person who plagiarised it. I pity the people who buy the kit and find themselves with an unusable product.
There are so many mistakes I won't waste my time explaining them and how to fix them.
Caveat emptor.
The number of times I’ve had “custom designs” come across my bench to fix because the builder didn’t understand the circuit they stole or how to troubleshoot it, so the client is on the hook for my repair/modification bill too.

That Kevin has the balls to get all passive aggressive with Whoops with his “figure it out for yourself smart guy!” Comment when he himself so clearly has no idea what he’s doing is rather hilarious tho.
 

abbey road d enfer

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Hi Jean Luc, I didn't know you designed the DI2, is the original the LA Audio or was the original released by another brand?
I designed the original in 1975, whilst at Barclay Studios. It had no pad, no gain, no ground lift and used LM308's, since TL0's were quite a novelty. Only about a dozen were made, since they were for in-house use. Due to the weird phantom arrangement in the API desk, I had to use these low-power opamps.
The first commercial incarnation came in 1978, under the SCV name. Of course it used TL0's and had all the switches.
When SCV acquired the rights to the LA Audio name, all the products were marketed under the new name and manufacturing was delocalised to the UK.
 

Kevin

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In my opinion this forum is for learning and not for bashing other people. Friends let us learn together and give details what you would change and how something can be improved. have a good time!
 

Winston OBoogie

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Kevin,
Although the pcb's for this project are inexpensive, the cost to folks who build it and then have issues is an important consideration.
My advice would be to abandon the sale of these particular pcb's until you figure out the problems.

Here's one problem to be getting on with: Your output impedance pretty much excludes this from working well with any of the existing mic amps on the planet, especially those with a transformer input.

Please read and respect what the original designer of the circuit said in post 18 of this thread.
 
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Kevin

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Hey Jean Luc! Hey New Market! Hey Winston! Hey Amplexus! Hey Whoops!
thanks for all the nice posts ;) i just read them first time yesterday. I never wanted to insult anybody with releasing this schematic and this boards, there also wasn't any "passive agression" anywhere. As I'm also just a human, of course I can't know everything and you are absolutley right that I don't know everything about the original schematic. But you know humans and also sometimes big companies do failures all the time, so I'm really sorry. But I'm totally open to learn, cause I'm still really young and I want to discover the world of audio electronics. I have to be fair, I still don't get everything everybody of you friends posted, since my English seems also not good enough for understanding special phrases. Also I'm a little bit confused at all now about the schematics, you got me to the point I feeling totally dumb now. Maybe someone of you can give me some special training maybe via Skype/Zoom/Google Meet or whatever? I would be really happy to see people in "real" and learn from them!

friends who built it where super happy with the board and the circuit. I got plenty positive reviews by mail. In fact I sold around 4-6 Kits with cases and normally the board is a free giveaway with any order, so most of the boards floating around are free and I don't make money at all with it. On the other hand I don't make big money with these Kits, because the Kits are really close the same price as I pay for it. Cases are super expensive due to special RAL Powder Coating and Individual silkscreen print from a local Screenprinter. The idea just popped up when some friends said they want a professional case instead of just a hammond case. I would be happy with any case idea anybody have ;)
 

Winston OBoogie

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Kevin,
it's obvious you're not getting rich from selling DI pc boards, I think everyone can see that. My reply was more concern for anyone building one.

Regarding the 680 ohms per leg build out resistors you have: This is much too high an impedance to be presenting to a mic pre. 50R, 75R, 100R tops per leg would be where you need to be.
If you need/want RF protection, then a couple of small value caps right at the XLR output from pins 2 & 3 to chassis would be how it's usually done. Not a big honking cap right at the op-amp output.
Look at how it's done in a microphone for hints. After all, you're aiming to present a microphone-like signal from the DI to the mic pre.
 

dyne_engine

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Hello, I build this passive kit fitting it with the Jensen JT-DB-EPC transformer. Everything is soldered right but I have a problem. The signal is clear but I have like a “pad”. For example I have not the same distortion if I connect a guitar directly to an amp or if I use the DI with the thru connection. That should not happen.
Anyone here can give me a suggestion how to fix it? Maybe some resistors to change?
Or does anyone know another diy project that I could use the Jensen transformer with? On the web I found the Jensen JIK-DB1 project, I attach the pdf. I don't know if it can help. Thank you all.
 

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abbey road d enfer

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Hello, I build this passive kit fitting it with the Jensen JT-DB-EPC transformer. Everything is soldered right but I have a problem. The signal is clear but I have like a “pad”. For example I have not the same distortion if I connect a guitar directly to an amp or if I use the DI with the thru connection. That should not happen.
It does, though.
The reason is quite simple. The signal from the guitar is loaded by the input impedance of the transformer. This impedance is low enough to attenuate the high-impedance signal of the guitar. In addition, this impedance is inductive, which means that the low frequencies are more attenuated than the high frequencies, which translates in a "thinner" sound.
Anyone here can give me a suggestion how to fix it?
Unfortunately no. You have to accept that as a fact of life.
Anyway, a passive-DI'ed guitar will never sound like one connected to a high-impedance input. You have to look at active DI boxes.
Or does anyone know another diy project that I could use the Jensen transformer with? On the web I found the Jensen JIK-DB1 project, I attach the pdf. I don't know if it can help.
Since this DI uses the same transformer in a similar way, there won't be any significant difference.

BTW, the audio samples published by the OP are definitely flawed, because they are taken with a synth as source. A synth has a low inmpedance output, that can drive almost any low-level transformer without alteration.
The two instruments that really demonstrate the performance of a DI are the electric guitar with passive p/u's and the electroacoustic guitar with a passive (no preamp) piezo p/u.
Electric bass is a little more forgiving.
 
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dyne_engine

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It does, though.
The reason is quite simple. The signal from the guitar is loaded by the input impedance of the transformer. This impedance is low enough to attenuate the high-impedance signal of the guitar. In addition, this impedance is inductive, which means that the low frequencies are more attenuated than the high frequencies, which translates in a "thinner" sound.

Unfortunately no. You have to accept that as a fact of life.
Anyway, a passive-DI'ed guitar will never sound like one connected to a high-impedance input. You have to look at active DI boxes.

Since this DI uses the same transformer in a similar way, there won't be any significant difference.
Thanks for your answer. I can say that I'm a really beginner on diy but as sound engineer I used several time for example the Radial JDI and I never had a problem like that. I have not this problem even with a very cheap Palmer stereo passive DI box...
 

abbey road d enfer

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Thanks for your answer. I can say that I'm a really beginner on diy but as sound engineer I used several time for example the Radial JDI and I never had a problem like that. I have not this problem even with a very cheap Palmer stereo passive DI box...
So you mean you have built the OP's kit?
OK. There's a blatant f..k up in his schemo. The pad is always loading the input, making the input impedance about 5kiloohm.
 
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Whoops

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So you mean you have built the OP's kit?
OK. There's a blatant f..k up in his schemo. The pad is always loading the input, making the input impedance about 5kiloohm.

Abbey he is talking about the “passive DI” kit and I think you are referring the “Active DI”.
 
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Whoops

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The signal is clear but I have like a “pad”. For example I have not the same distortion if I connect a guitar directly to an amp or if I use the DI with the thru connection. That should not happen.

You should rephrase this because its impossible to understand the problem you have, your description is confusing
 

dyne_engine

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You should rephrase this because its impossible to understand the problem you have, your description is confusing
Yes, I'll write again. I have two scenarios:

1. guitar signal ---> high gain guitar amp. I have a sound with a certain amount of gain and distortion.

2. guitar signal ---> DI input. Then I use the output thru connection to the same hi gain guitar amp. I should have the same sound/tone (maybe not 100% identical, but almost the same), instead the tone sounds weaker with a different tone. With less gain.

I hope you understood me now. That of course happens with the pad push bottom of the DI in off position. I don't use the pad on the DI.
 
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Whoops

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Yes, I'll write again. I have two scenarios:

1. guitar signal ---> high gain guitar amp. I have a sound with a certain amount of gain and distortion.

2. guitar signal ---> DI input. Then I use the output thru connection to same hi gain guitar amp. I should have the same sound/tone (maybe not 100% identical, but almost the same), instead the tone sound a lot less weak with a different tone. With less gain.

I hope you understood me now. That of course happen with the pad push bottom of the DI in off position. I don't use the pad on the DI.

Yes, it's clear now the problem you had.

Nice that you solved the issue.
 
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