Topic: Modify Bass roll off off core sound battery box

[tdg455]

Was wondering if anyone has modified a core sound battery box so the bass roll off would work for line in into an M1/D100. I am using dpa 4061's with the HEB box, bass roll off only works mic in. I asked Len if I could have this modified and he just said "no"

Thanks for any help

Tom

[udovdh]

I don't know teh design of the CS bbox, but if it is a more or less simple bbox (with capacitor and resistor) one could replace the capacitor rather easily?

[cgrooves]

Actually, the bass roll-off works going line-in, it is just not effective because of the high line-in impedance on the m1.
Have you experienced the actual need for bass roll-off when recording line-in?

[tdg455]

You are correct the bass roll off is just not as effective.
    I guess it all depends on what I record. I recorded Judas priest the other night and the bass was pretty high. When I have used the mic in, the bass roll off on this box takes away too much in my opinion. I believe the roll off is at 120 hz, 6db per octave. I was thinking of changing it too around 80 to 90 hz at 6 db per octave.
   I opened it up and it does look pretty simple. just some caps , resistors, wires battery and the switch.

[udovdh]

Mic impedance is 4K7.
Line impedance is 47K on the DAT.
So changing the capacaitor to something 10 times smaller would make sense.
Maybe 11 times or so to get the results you want?

[cgrooves]

"When I have used the mic in, the bass roll off on this box takes away too much in my opinion. I believe the roll off is at 120 hz, 6db per octave."

The reason it takes away too much using mic-in, is that it is actually starting to roll-off at approx. 240 hz on the m1.

Most (all commercially sold?) battery boxes are designed around a 'generic line-in impedance of 10 kohm'.  Since the m1 impedance is 47 kohm mic-in and 4.7 kohm line-in, you have to do the conversion to see what the actual roll-off will be.

Using mic-in on the m1, your battery box starts rolling off at approx. 240 hz (way too much)
Using line-in on the m1, your battery box starts rolling off at approx. 25 hz (not very much)

My battery box (see stealth signature line) has only two settings (32hz & 150hz), so really, I'm just rolling off at 6.8 hz because I ALWAYS use Line-in.  This is basically like running flat, which is what I want anyway.  I'm just using the box to power the mics. (Even though it is a custom box, it was still designed around the 'generic line-in impedance of 10 kohm.)

What you want, is a battery box that has a good selectable range of roll-off values based on running line-in (47 kohm) on your m1.  To my knowledge, there is no box like this on the market even though there is a demand for them. Custom is the only way to go that I know of.

I would suggest doing some searches on this site for both mic-in versus line-in & bass roll-off.  These topics have been covered many times.  I would recommend you running line-in all the time, because the pre in the m1 will easily brickwall.  You can reduce the bass in post if it is too excessive (until you get a custom battery box).

[tdg455]

Yeah when I playback I just turn the bass down for now. But I think the a/d conversion might be better if you cut out a little of the bass. I could be wrong. Does anyone have an answer to that question? Does the a/d convertor work better if some of the bass is rolled off?
   For most music and performances it isnt necessary. But if anyone has been to a Velvet Revovler show recently, and was close to the stage, you know why you sometimes need to lower the bass. I dont understand why the sound guys have the bass jacked up so high. And for VR it really doesnt matter where you are.
    I think I will swap out some caps. Just need to find out what I should get

Thanks for all your help

Tom

[cgrooves]

"Yeah when I playback I just turn the bass down for now."

What I meant by reducing the bass in post, is using the equalizer package provided with most software to reduce the low frequencies prior to tracking & burning to disc.

Good luck on your modification project.

[tdg455]

I primarily listen to dats, so that is why I mentioned using my eq on my stereo to turn down the bass. Or certainly one could eq their recordings to their liking if they listen to cdrs.

[dklein]

The advantage of rolling off in the battery box is that it allows greater dynamic range in your recording.  Since the low end isn't serving up all that power, you'll be able to turn the levels higher. 
If you search around you'll find a bass rolloff calculator (excel spredsheet) that will give you the info you're after regarding impedance, frequency and capacitor values.  Info about cap types is somewhere around here too

[udovdh]

Please post an URL! (could not yet find it)

[zhianosatch]

You are correct the bass roll off is just not as effective.
 I guess it all depends on what I record. I recorded Judas priest the other night and the bass was pretty high. When I have used the mic in, the bass roll off on this box takes away too much in my opinion. I believe the roll off is at 120 hz, 6db per octave. I was thinking of changing it too around 80 to 90 hz at 6 db per octave.
 I opened it up and it does look pretty simple. just some caps , resistors, wires battery and the switch.

i'd go with around 70 Hz... i have a custom mps-6010 with -6dB/octave at 85 Hz and it's usually way too much. now i just turn it off all the time.

[dklein]

Please post an URL! (could not yet find it)

http://taperssection.com/index.php?topic=31681.msg446604

[udovdh]

Please post an URL! (could not yet find it)

http://taperssection.com/index.php?topic=31681.msg446604

Thanks!