Possible DI - Hi Z - input to Mic or Line input ?
- Thread starter r2d2
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Andy Peters
Well-known member
r2d2 said:
Direct box?
-a
pyjaman
Well-known member
Yes, i'd say a DI...
Or missed something?
Or missed something?
Nishmaster
Well-known member
Jensen has about the most basic schematic on the subject.
http://www.jensen-transformers.com/as/as007.pdf
-Matt
http://www.jensen-transformers.com/as/as007.pdf
-Matt
Repost "guitar splitter" 2005:
Rodger Nichols RIP, bummer, just found out while searching for this bass DI.
Nichols hung out with Zappa back in high school, cool.
ok, Bass DI here>
http://www.groupdiy.com/index.php?topic=18631.0
Nichols hung out with Zappa back in high school, cool.
ok, Bass DI here>
http://www.groupdiy.com/index.php?topic=18631.0
ruffrecords
Well-known member
r2d2 said:
The basic problem you have is converting a high impedance instrument source to a low impedance mic input. The obvious way to do this is with an attenuator. You need to present about 150 ohms to the mic pre input so the bottom arm of the pot divider needs to be about 150 ohms. For a 150K ohms input impedance ,for example, the top arm needs to be 150K ohms. This produces an attenuation of 1000 times or 60dB. So even if your guitar produces a signal level close to 0dBu (775mV) your mic pre gain will need to be set to 60dB so your signal to noise ratio is definitely going to suffer. Most guitars like to look into a lot higher impedance than 150K so this method is on a hiding to nothing before it starts. That's why a transformer is a better bet because the impedance ratio is the square of the turns ratio. So a 10:1 transformer gets from 150 ohms to 150K with only a 20dB loss i.e. 40dB (100 times) better than the other solution. If you want a higher input impedance you can use a pad at the input - say 680K with 150K for a total input impedance of 830K. This pad loses another 15dB so now you need to set your mic pre gain to 20+15 = 35dB and you get a decent signal to noise ratio.
Cheers
Ian
pyjaman
Well-known member
from what I understand in your drawing, you might want to add an hi-Z instrument input to a preamp. You can do this either by just using a DI box (active or passive), or adding built-in high Z input to the preamp. It has been done several times here and such circuits are just "add-ons" to the pre, generally powered by the same PSU witch you can purchase for instance Hi-Z plugins from classic-API, DI input modules from JLM audio, Igor's Preamplifier's universal input board, whistlerock audio has a solution too. Basically, what you need is an impedance converter . You can even check Bo Hansen's tech page for inspiration on adding a di input to an API 312, or his simple impedance converter.
Laurent.
Laurent.
mhelin
Well-known member
Couldn't we just float a FET outputs on pins 2 and 3 with a resistor (~ current source, or another FET connected as CS) from pin 3 (-) to ground to get some practical voltage difference between S and D? Add 1M resistor to gng on gate, preceded by a small cap. This circuit could be fitted inside an 1/4" plug.
Edit: Doesn't work well with transformer input pre-amp though...
Edit: Doesn't work well with transformer input pre-amp though...
![[silent:arts]](https://cdn.imagearchive.com/groupdiy/data/avatars/m/0/172.jpg?1620371656){kind=avatar}
[silent:arts]
Well-known member
[silent:arts]
Well-known member
just put it in front of any mic inputr2d2 said:
r2d2 said:
A ""GTR-BASS" Input To Mic Input adapter" is generaly called a DI box , or Direct Box
you should do a search for "DIY DI box"
Newmarket
Well-known member
Whoops said:
OP's query was from 2012 so hopefully sorted by now
Newmarket said:OP's query was from 2012 so hopefully sorted by now
Old threads are still relevant for future readers that might have the same questions or doubts.
I learned a lot from reading old threads and finding answers that prevent me from posting the same questions.
Thanks
Newmarket
Well-known member
Whoops said:
True
