Help with Variable Impedance Active Direct Box

[dbelousov]

I agree, this Radial looks like an excellent solution.

1M DI in parallel with an amp lowers the impedance enough to produce audible difference. I personally tested it in the presence of 10 people with ENGL E650, sadly, there is no information on its impedance.

 

[Whoops]

1M DI in parallel with an amp lowers the impedance enough to produce audible difference. I personally tested it in the presence of 10 people with ENGL E650, sadly, there is no information on its impedance.

Some DI's have a buffered link output, other it's just a plain passive split

 

[abbey road d enfer]

A lot of piezo pickups have around 1Mega output impedance.

I can't let you say that, sorry. Piezo's are capacitive. Their impedance varies with frequency. A typical undersaddle piezo has a capacitance of about 500pF, which requires a resistive load of 4 Megohms for a good response down to 80 Hz (low-E).
Many other piezo have a larger capacitance. The piezo discs I use for piano and double bass are 2.5nF. Used in singles, they require a load of 1.6Megohm for response down to 40Hz (E on the double bass). Since they are usually used in doubles, a load of 1Megohm is adequate.

From the Radial website:

I know the usual sales blurb. Ovation started it in the early 70's. No matter what, piezo pick-ups are an expedient. They never sound good, but they make acoustic instruments audible in a noisy environment.
The double bass, in particular does not benefit from extended bass response, because it invariably results in VLF feedback and rumble.
The natural acoustic response of the double bass starts to fall at about 55Hz, so most bass players are not concerned about their amplified sound following the same pattern.

 

[Whoops]

I can't let you say that, sorry. Piezo's are capacitive. Their impedance varies with frequency.

Yes that's correct

No matter what, piezo pick-ups are an expedient. They never sound good, but they make acoustic instruments audible in a noisy environment.

I can't agree on that, over the years I worked with musicians that had piezo pick-ups that sounded really good, I also have some piezos that yield an excellent sound. Not the same as a Miced instrument, but excellent nonetheless.
Yamahiko pickups are extraordinary for Piano and the Doublebass system is also great sounding.
I was blown away the first time I used the Piano Yamahiko, I've been using the C-Ducers before (still use a pair) but those are a tool, the Yamahiko sounded pretty natural.

https://www.yamahiko.info/en/

Also for acoustic guitars, the Carlos Juan piezo pickup systems sound better than anything I've heard before.
And it's much more than a tool for live sound, I record and use the DI from those pickups in a studio environment with no problems.
https://carlosjuan.eu/#&panel1-2

Yamahiko advises the Countryman DI for their picukps (10Meg) Carlos Juan advises the Radial SB4 Piezo (5Meg)

From my personal experience, and I've tried that in the past, using a typical 1Mega input DI for those pickups didn't provide a good enough load for the Piezos and the sound was compromised. While using an higher impedance DI brought the best from those pickups and the sound was quite natural and the tone balanced.
I have used 5M to 10M DI with Piezos since then, and as most people I'm quite happy with it.

Piezo Preamp systems from different manufacturers (Shadow, Fishman, LR Bags, K&K) also seem to take that into account, the schematics I've seen and the circuits I fixed had an Impedance of 2M2,4M7, 5M or 10M, but never 1Mega. Normally with a Jfet input.

If you use a 1meg input DI with Piezos I completely understand why you say "They never sound good", it's understandable, and I guess I would feel the same in those circumstances.

 

[abbey road d enfer]

I can't agree on that,

OK, I agree that piezo pickups have made significant progress compared to when I had to use them regularly.
Still, I don't think the elevated input impedance is the reason for this improved quality. IMO it owes much more to the mechanical coupling of the sensor to the instrument. the systems that sound good sense a larger portion of the instrument's soundboard than typical undersaddle types.
I think an enlightening experience would be to use one of these pickups with a VHZ DI and apply different loads. I'm not sure the one with the highest Z wins in a practical situation.
I'm not willing to invest time and money in such an experiment, though.

 

[Whoops]

I think an enlightening experience would be to use one of these pickups with a VHZ DI and apply different loads. I'm not sure the one with the highest Z wins in a practical situation.
I'm not willing to invest time and money in such an experiment, though.

I'm trying to finish the mixing and mastering of a pretty difficult record at the moment,
but when I have the time I can do some recordings using different DIs on different instruments with piezos and we can have a listen.

I have also some Bo Hansen DIs to finish (more projects than free time unfortunately) I will do 2 with the standard 1meg input and other 2 with 10mega. Easy to do one or the other, I can even probably find a way of making it switchable, I can also then record both and share it.

Best Regards

 

[abbey road d enfer]

I'm trying to finish the mixing and mastering of a pretty difficult record at the moment,
but when I have the time I can do some recordings using different DIs on different instruments with piezos and we can have a listen.

I'm not interested in that. Different DI's are bound to sound different.

I have also some Bo Hansen DIs to finish (more projects than free time unfortunately) I will do 2 with the standard 1meg input and other 2 with 10mega. Easy to do one or the other, I can even probably find a way of making it switchable, I can also then record both and share it.

That would be interesting. I don't doubt there would be differences, particularly with low capacitance pickups. The issue is how much these differences affect the perceived quality. You know that quite often, a High Pass Filter improves it.

 

[rp3703]

As I stated in my OP, I am only looking for a DI specifically for recording E-guitar and E-bass direct which will be re-amped. I don’t care about piezo instruments. I just don’t want to pay $800. The MW-1 is designed specifically for recording DI guitars and it’s variable input impedance is controlled with a pot. If as was stated earlier in this thread, guitar pickups need to see an input impedance similar to the input impedance of a guitar amp, then why would you need any value other than 1M?
As far as the thru goes, please continue to discuss. While the thru I am envisioning will only be used for a tuner or cue mix, so I could not care less if it is slightly colored, I do not want the addition of a thru to affect the DI signal being recorded.

 

[Bo Deadly]

If as was stated earlier in this thread, guitar pickups need to see an input impedance similar to the input impedance of a guitar amp, then why would you need any value other than 1M?
As far as the thru goes, please continue to discuss. While the thru I am envisioning will only be used for a tuner or cue mix, so I could not care less if it is slightly colored, I do not want the addition of a thru to affect the DI signal being recorded.

I haven't been reading this thread intently but when I mentioned the through connection, I meant to an amp which if it's 1M will be in parallel with the 1M of your DI and the load on the guitar will be only 500K. Personally I doubt that would have any audible effect on the signal but if you're trying to be as transparent as possible, you would need to use a higher value. Or, if you want to get fancy about it, make it so that the normalling connection of the through jack disconnects something so that the DI input is 10M when something is plugged into the through connection and 1M when something is not.

 

[Whoops]

If as was stated earlier in this thread, guitar pickups need to see an input impedance similar to the input impedance of a guitar amp, then why would you need any value other than 1M?

If you only recording E guitar and E Bass, I personally dont see any reason to go over 1 Mega.
But lower might be nice for bass, reduces hi end, its a cool sound, I consider it a tone/character knob.
But its personal choice its up to you, 1 mega might be the only you need