DI box for double bass (piezo)

[twotoedsloth]

Has anyone used the Radial J48 for this task? Any other suggestions are welcome.

Thanks.

[ef37a]

Has anyone used the Radial J48 for this task? Any other suggestions are welcome.

Thanks.

Not at all my area of experience (D bass) but the most important question is whether the pickup is active or passive? If active you should not need a DI box at all and can feed the bass into a line input on a mixer or AI.

A passive pickup on the other hand will need AFAIK a very high input impedance if it is to preserve the fundamental notes of the bass (even more than bass guitar where the position of the pups means you get virtually just 2nd harmonic and above). A value of some 5meg Ohms is required I understand and specialist instrument pre amps are quite expensive? I do not know of any guitar or bass guitar active DI box with such a high input Z, most are the "sacred" 1meg but it would be an easy modd' to most boxes I would think to fit a higher input bias resistor.

Found this: http://www.thomann.de/gb/fishman_b_2_acoustic_bass_preamp.htm
Dave.

[Hugh Robjohns]

I don't think the J48 -- excellent though it is as a general purpose active DI -- is the most appropriate for your situation.

Most peizo pickups want to see a very high input impedance of well over 1M ohm, as Dave suggests. The J48 is a relatively modest 220k.

The Fishman preamp that Dave suggests, by contrast has an input impedance of 10M ohms and is specifically designed for piezo pickups.

Hugh

[twotoedsloth]

Would the Audient Mico make a suitable DI for double bass?

[ef37a]

Would the Audient Mico make a suitable DI for double bass?

Maybe our Audient "ghost" will come back with a more detailed specification than I have been able to find but I cannot see a figure for the actual input impedance of the high Z input. If the double bass pickup is a passive peizo device then it will need to see 5-10megOhms. If it is amplified at all then the Mico will be fine since the input has a 20dB pad and could surely take such a level.

Dave.

[shufflebeat]

One of my regular compadres uses one of these:

http://www.dv247.com/studio-equipment/fishman-pro-eq-platinum-bass-preamp-di-for-electric-and-acoustic-bass--43699

We've been through just about every combination over the years and this is the most usable solution he's had.

[ef37a]

One of my regular compadres uses one of these:

http://www.dv247.com/studio-equipment/fishman-pro-eq-platinum-bass-preamp-di-for-electric-and-acoustic-bass--43699

We've been through just about every combination over the years and this is the most usable solution he's had.

That looks to be a very reasonably cost effective solution indeed!

I would aver the Mico could handle the level from that unit tho' I have to say, with respect, it seems far too good a preamp for such a mundane purpose? That Fishman box will surely feed directly into a desk or AI?

Dave.

[twotoedsloth]

Well, I am trying to decide between purchasing a DAV BG1 mic preamp, and the Audient MIco. If the Mico can function as a DI box for bass... I might be able to justify buying both.

[ef37a]

Of COURSE you can justify buying both! Point out to naysayng parties, partner/accountant/bank manager, that you NEED the bells and whistles of the Mico and its DI input but also musthave the super clean characteristics of the DAV! (Then buy that Fishman pre out of petty cash on the qt).

Note from> <a href="/sos/dec03/articles/davelectronicsbg1.htm" target="_blank">http://www.soundonsound.com/sos/dec03/a ... bg1.htm</a>

Hugh points out that the DAV really needs to partner a converter working at "pro", high levels.(Tho' I don't see any problem in using an inline attenuator to feed a lesser converter, at least pro tem?).

Dave.(weird here init? I did not boldly go!)Edit #2 Not bold anymore!Edit #3 And link is not blue anymore!

[Audient Sontronics UK]

Hi,

The MiCO mic input impedance is about 2k and the line input is about 25k.
The instrument input is about 500k.

Hope this helps.

[Martin Walker]

Well, I am trying to decide between purchasing a DAV BG1 mic preamp, and the Audient MIco. If the Mico can function as a DI box for bass... I might be able to justify buying both.

I've just sent a PM to our official Audient poster (Gareth), so hopefully he'll post on this thread sometime in the near future on its suitability for this task.

Somehow I doubt that the input impedance will be any greater than 1 Mohm though.

Martin

[ef37a]

So, the Mico is 500k.

This is about par for the course for many pre amps and AI's.
Now I know it is outside the normal remit of such things but I often wonder the Z is so low? I am guessing here but I would bet the stage uses either a good old TL0 or a discrete FET and thus could just as well have an input resistance of 10meg?

Thought so! My ZED10 has two high Z inputs specc'ed at 10meg and even with a 26dB boost inserted they are still very low noise.

Dave.

[Hugh Robjohns]

The DI input impednace could be almost anything the designer wanted it to be these days. AS you say, the common op-amps make multi-meg impedances pretty easy to achieve.

However, there are practical limits about how high to go -- higher impedances tend to be more susceptible to unwanted RF interference, for example -- and there is a school of thought that says the optimum impedance for most electric guitars is actually between 250k and 500k. A lot of the active Radial DI boxes offer about 250k, for example.

I think the Mico's 500k is born of practical experience on the part of the designer as a good compromise value...

hugh

[ef37a]

500k might be a reasonably compromise but I would suggest it is born of inertia and fashion.

As you say Hugh,electric guitars are not nearly as fussy about the input Z as is often believed (but no guitar amp maker would DARE make it anything other than a nominal* 1meg!)but it would be useful if it were 5-10meg for the piezo pups both on basses and acoustic guitars. If "we" don't point out a need they will not look into changing things.

There is no technical downside that I can see (Fishman and A&H seem to do ok!). The input will always be shunted with a much lower impedance, sometimes R,L and C and in the case of the piezo several hundred puffs, maybe 1nF so noise should be very low.

RF susceptabilty? In my experience low Z high current circuits are far more prone, mic and RIAA stages. In anycase proofing inputs against RF should be done anyway. All the FET input stages of the amps and pedals I dealt with had exemplary filtering and I did not have one single case of RFI trouble in my 2 years.

*Guitar amps with high and low sensitivity jacks have a ~68k input R on the attenuated jack. Nobody has EVER noticed!
Dave.

[twotoedsloth]

All this talk of impedances got me interested to see what my bass pickup is expecting. Much to my surprise, the website ( http://www.wilson-pickups.com/Specifications.htm )states the this pickup doesn't require a preamp at all! I've been using this with a Tech 21 Bass driver for years, the input on the this is 1 megOhm (sic from manual) I assume that this means 1,000,000 ohms, not 1,024 ohms.

Will I notice an appreciable difference if I plug into the Mico, which is 500,000 ohms? And if so, will the difference be good or bad?

Thanks again everyone,

Peter

[zenguitar]

All this talk of impedances got me interested to see what my bass pickup is expecting. Much to my surprise, the website ( http://www.wilson-pickups.com/Specifications.htm )states the this pickup doesn't require a preamp at all!

The phrase 'pre-amp' covers a multitude of sins. It looks like they are saying that when you are plugging into your stage amp you won't need a pre-amp to boost the signal to the required level. However, that stage amp will have it's own pre-amp stages that are in may respects equivalent to a recording pre-amp.

Or, to put it another way. Unlike many piezo pick-ups (which can be very low output) yours is designed to drive an instrument level input without any additional pre-amplification, and therefore should work just fine plugged into any instrument level input whether it is on a backline amp or recording pre-amp.

Andy

[ef37a]

If that pickup is specified for a 1meg input I doubt you will notice any difference going into 500kOhms. Very roughly, the bass turnover frequency, the 3dB point, will be shoved up an octave but even if the rest of your system can reproduce clean bass at 30-40 Hz (unlikely!)the merest touch of boost on an EQ would restore that signal.

Unlike guitar pups which are a horribly complex mix of inductance, capacitance and resistance, a piezo is virtually a pure capacitance, no L so therefore no possibly nasty, peaky resonaces.

Go Mico!

Dave.

[ef37a]

Had this back from A&H (nice peeps!)

The designer of the Zed10 has this to say on the issue

"
It’s more from practical experimentation with electric guitars and acoustics with pickups than anything else and I came to the conclusion that 10M ohms had less effect on the level and (more important) the tone from the instrument.
Interestingly, older Ampeg amps have 5.6Meg input impedance and some of the old Fender amps have 10Meg.
I think 1Meg became the norm because of the biasing requirements of the input triode valves, but we’re using a FET circuit so we’re free from that constraint.

Dave.

[Martin Walker]

Now that's a very helpful reply Dave - well done A&H

Martin

[ef37a]

Now that's a very helpful reply Dave - well done A&H

Martin

Indeed, as I say nice people. A few weeks ago I discovered a problem with the usb system in W7/64 (XP no trouble at at all) and after a few email exchanges this was sorted out satisfactorily. I don't in fact use the usb facility but wanted it "right"!

(The problem turned out to be in the way that W7 sets device levels, all different from XP. Why the buggering H they had to bugger about with the buggering Sound and Audio Devices setup for W7 I really do not know! Buggering worked fine in XP FCS!).

Dave. (I was not happy. Can you tell?)

[Martin Walker]

Dave. (I was not happy. Can you tell?)

No - was it something you said?

Martin