DI box with +4dBU balanced Line Level output instead of Mic Level

[Whoops]

have my space echo out signal come directly into my patch bay. so it needs to be converted from instrument level to line level, with a gain control (as OP was looking for above). as it’s going directly into a balanced input, it would ideally be transformer balanced

Buy one of these used,
It sounds fantastic:

 

[PaulSmith]

Thanks so much for pointing that out Whoops - look super cool and exactly the kind of thing I need.

However I neglected to say that probably the main reason I want to build one is that I want to learn more about analog circuits and in this case solidify my knowledge of trafos etc which is why I want to make this a proper DIY situation if at all possible!

Thanks again!

 

[PermO]

https://groupdiy.com/threads/idea-for-a-dedicated-rhodes-preamp-need-help.78018/page-6#post-1103566
Maybe this ?

 

[Whoops]

However I neglected to say that probably the main reason I want to build one is that I want to learn more about analog circuits and in this case solidify my knowledge of trafos etc which is why I want to make this a proper DIY situation if at all possible!

depends a lot on your experience…
If you are not really experienced in DIY electronics then for a DIY route ir would better if you do a project that has already an available PCB that you can buy, has build docs, that many people build it already and you have a support thread around here so you could ask questions and help. As far as I know there’s no project in this forum that does what you need and fills the above criteria.
So in this case it’s better to buy a commercial unit

in the case of the circuit PermO showed, it will work for your duties but more knowledge on DIY electronics and experience is needed.
You need to know how to home etch a PCB, and understand the components and schematic.
Also you need to build a PSU for it as PermO used a battery supply, and for your duties batteries are not a good option it’s better to have a PSU.
It’s doable but not a beginners project for sure

Also for what you want to achieve no transformer is really needed.

If you want to build something with transformers that will be useful tools and great beginners projects search for “NY Dave reamp box” and “Bo Hansen DI”

 

[pucho812]

Check out the the one bottle from NYD. Omit the input transformer, add an output transformer 10k:600, 4:1. It would be tube, it would give you line level output and would have all you need as a Di

 

[Whoops]

Check out the the one bottle from NYD. Omit the input transformer, add an output transformer 10k:600, 4:1. It would be tube, it would give you line level output and would have all you need as a Di

The input would not be Hi-Z, and that seems a requirement for what PaulSmith needs and it's looking for

 

[PaulSmith]

Yes Whoops I do understand - it’s not taking much at the moment for projects to be above my pay-grade - also it’s easy to be overambitious!

And thanks PermO and pucho for your suggestions! Very interesting!

According to the service manual the re301 set to low/impedance output is 0.25kohm so it might not be *so* important to have a hi-z input. Just a healthy gain boost and balancing of the signal is what is required.

As I have a 1:4 mic input transformer lying around I was hoping to build a small project around it. I have quite a serious recording studio so I could make use of pretty much anything haha.

 

[Whoops]

According to the service manual the re301 set to low/impedance output is 0.25kohm so it might not be *so* important to have a hi-z input. Just a healthy gain boost and balancing of the signal is what is required.

If that's the case and you don't need an Hi-Z input, then the tube preamp Pucho recommended might work well.
But in that case (Low-Z input) any Line Amp circuit will work, even any mic preamp circuit so there's many around here to choose from. That's actually quite diferent than the scope of this thread which is about a circuit with Hi-Z input and not Low-Z.

Have in mind that being Tube, IC Based or a transistor discreet circuit you will always need to build a PSU

 

[Philbo King]

Hi,
I have quite a few nice DI boxes already that I use to send instrument signal into different Mic preamps.

Lately I've been having the need to send Instrument signal directly into non-amplified line inputs. (without using any Mic Preamps)

Is there any DIY circuit around or that you know that used the same concept of the DI but with a +4dBU balanced Line Level output instead of Mic Level?

The circuit could be passive or active (it would need it's own PSU)

I'm interested in:
- cheap circuit using Opamps (with output level control)

- more expensive circuit using Discreet circuit or discreet opamp and output transformer (with output level control)

Instrument signal voltage is closer to line level than to a Dynamic Mic output voltage. In a normal DI the instrument level is attenuated to Mic level and them amplified again in the Mic Pre.
It could make sense to not attenuated it and just amplify it one time and enough to achieve +4dBU line level.

I'm not sure of the use case here. If the instrument output is line level already, a DI is not necessarily useful unless you are running the instrument line level output through a 500 foot PA snake back to a mix console (as in an old-school analog PA system). Even then, line level inputs to an input channel on PA console are generally unbalanced.

 

[Whoops]

I'm not sure of the use case here. If the instrument output is line level already, a DI is not necessarily useful unless you are running the instrument line level output through a 500 foot PA snake back to a mix console (as in an old-school analog PA system). Even then, line level inputs to an input channel on PA console are generally unbalanced.

I can see that you are not really experience in Recording and in Live Sound and also that you need to learn more on basic concepts of different audio signals and different impedance in the context of audio engineering.
You should Google concepts like "Instrument Level Vs Line Level" , "Hi-Z vs Low-Z", "uses for a DI box)

To explain everything that is wrong in what you wrote I would have to write a long post here, and this thread is not about a tutorial on those subjects, it's related to the discussion of circuits that could convert "an instrument unbalanced Hi-Z signal into a balanced Line Level (Low-Z) output,
so there's no need to hijack this thread for something that you could and should learn elsewhere.

If you want to do a separate thread for learning these concepts I would gladly post there and help out, but not here. I've been teaching these subjects for 7 years in an Audio Engineering school and have been using them professionally since many years before until the present,
I will for sure write in another thread.

Even then, line level inputs to an input channel on PA console are generally unbalanced.

Again, that couldn't be further from the truth.
Professional Live Sound Stageboxes have mostly MIC INPUTS only, the ones that even have some Line Inputs are an exception, and all inputs are Balanced and use an XLR connector.

 

[Philbo King]

I can see that you are not really experience in Recording and in Live Sound and also that you need to learn more on basic concepts of different audio signals and different impedance in the context of audio engineering.
You should Google concepts like "Instrument Level Vs Line Level" , "Hi-Z vs Low-Z", "uses for a DI box)

To explain everything that is wrong in what you wrote I would have to write a long post here, and this thread is not about a tutorial on those subjects, it's related to the discussion of circuits that could convert "an instrument unbalanced Hi-Z signal into a balanced Line Level (Low-Z) output,
so there's no need to hijack this thread for something that you could and should learn elsewhere.

If you want to do a separate thread for learning these concepts I would gladly post there and help out, but not here. I've been teaching these subjects for 7 years in an Audio Engineering school and have been using them professionally since many years before until the present,
I will for sure write in another thread.



Again, that couldn't be further from the truth.
Professional Live Sound Stageboxes have mostly MIC INPUTS only, the ones that even have some Line Inputs are an exception, and all inputs are Balanced and use an XLR connector.

I'm not here for a dick measurement contest. Have a great day!

 

[Whoops]

I'm not here for a dick measurement contest. Have a great day!

You could at least be here to learn a little bit, but to learn something one needs to be humble and have a will to improve knowledge. By your post you seem to lack both.

I offered to explain in a separate thread all the concepts that could help you understand the questions that you bring in your post and also the wrong assumptions that you made,
My offer still stands in case you change your mind

 

[Philbo King]

Hey, I'm just an engineering tech who worked in aerospace research & development for 30 years, while operating a recording studio parttime for 45 years. I haven't done FOH PA engineer work since the 70s, while working my way through college, so I admit my knowledge on arena & club PAs is about 45 years out of date. Got tired of the road, built a studio.

Humble enough for ya? Que sera sera...

 

[Electrobumps]

Hey, I'm just an engineering tech who worked in aerospace research & development for 30 years, while operating a recording studio parttime for 45 years. I haven't done FOH PA engineer work since the 70s, while working my way through college, so I admit my knowledge on arena & club PAs is about 45 years out of date. Got tired of the road, built a studio.

Humble enough for ya? Que sera sera...

you could have been gracious and said thanks for the offer of help and would have got some help. You might be a bit further away from that now.

 

[Philbo King]

I'll look him up if I ever need more education. But thanks for the offer.

 

[Chandra]

Here is a low cost Instrument to line level pre-amp.
Regards.

 

[Whoops]

Here is a low cost Instrument to line level pre-amp.
Regards.

Thank you,
that's a nice JFET buffer circuit, I remember now that I've seen that article in the past.

From what I gather in the document I guess you could achieve what I was looking after with this kind of arrangement, let me know what you think:



It seems to me that with a Pot at the circuit (JFP gain module) output that there is the need for a buffer after the Pot in order to drive the transformer? is this correct.

Thank you

 

[Chandra]

I feel, you may not need a buffer in between. This is because of the low output impedance drive capability of the output stage (40 ma) But you can add one anytime you want it. See the attached buffer drawing from Pioneer Spec 1 preamp as a reference which you can modify for 24 volts supply. Make sure the transistors are biased to class A.
Regards.

 

[john12ax7]

Transformers generally like to be driven from a low impedance. Having a pot feed a transformer is not a good idea unless you are intentionally looking for increased distortion.

 

[Whoops]

Transformers generally like to be driven from a low impedance. Having a pot feed a transformer is not a good idea unless you are intentionally looking for increased distortion.

Yes, that was what I though.

That should also be one of the reasons that in the Mic Preamp Schematic Scott added a second "JFP" circuit




As far as I can see the second JFP stage will amplify more 26db's while also being a buffer to drive the transformer after the Pot. For a Mic Preamp that works great as you need the extra Gain. But for a a DI box with Line Level out, that extra 26db's will be too much are not needed at all, so probably a simpler buffer with unity gain will be better for this duty