Jump to content

H4n + MixPre + padded cable = I need resistor advice


muntus

Recommended Posts

Hello sound guys! This forum has been a tremendous resource for me as I have attempted to learn more about achieving good sound. I have produced a few low budget projects(shorts) and have never been satisfied with how the sound turned out, which has led me to buy some equipment. I started with a Zoom H4n a number of years ago. Recently, I found a Sound Devices MixPre on ebay for a reasonable price. I know the H4n is not the most ideal portable recorder, but it's what I have and I would like to use it with the MixPre. My understanding is that when used with the proper padded cable and using the 1/4 inputs to bypass the noisy preamps, good results can be had.

 

I have a soldering iron, but need help on choosing resistors.

 

The MixPre has XLR outputs as well as a 3.5mm tape out.

 

XLR output impedance = 120Ω

Tape out impedance = 2.1kΩ

 

If I wanted to make a -25db L-pad, what resistors would I need for R1 and R2? I'm assuming I want to use the XLRs, but it would be nice to have the information in case I wanted to go with the tape out.

 

I'm half nerd on my dad's side, but I have little to no experience with impedance and resistors, so any help on this would be greatly appreciated. Thanks!

Link to comment
Share on other sites

Taking a look at the Zoom specs, it has either a balanced or an unbalanced input.

 

Here are some quick figures for what you requested.  Referencing the L-Pad in Jim's link, and using the unbalanced input:

 

R1 = 9.1k ohms, R2 = 430 ohms.  In this case you don't need an R3.

 

In unbalanced mode the Zoom offers a really high input impedance (480k ohm), so that won't affect the R2 voltage drop much.  Roughly speaking, the ratio of voltage dropped across R1 vs the voltage supplied to the load across R2 should be about 22:1 for about -26dB attenuation. 

 

For a balanced input, the Zoom specs list 1k as the input impedance so that needs to be taken into account when designing the pad.  For a balanced input (the H=pad configuration in Jim's link), you could go with the following:

 

R1 = 4.7k (note: Each R1 is 4.7k), and R2 = 300 ohms.  Again, no R3 is necessary.

 

Roughly speaking, the ratio of voltage dropped across the total of the two R1 resistors vs the voltage supplied to the load across R2 should be about 40:1 for about -32dB attenuation.  For the balanced input, you'd want more gain reduction to allow proper headroom since, internally, the recorder doesn't attenuate this input as it does the unbalanced one.  Since the balanced input has a characteristic impedance of 1k ohm, you need to take into account what the resistance of R2 is in parallel with the input impedance.  

 

I hope this helps without being too confusing.  Good luck.

 

NOTE:  If it explodes don't blame me <g>.

Link to comment
Share on other sites

As John stated, an H-pad for the Zoom's XLR mic level inputs which are (allegedly) balanced. The 1/4" are unbalanced @ -10dB (nominal) or there-abouts... both still go through the POS preamps though.. as with most of the budget recorders. As I and others have previously stated, the Tascam DR-100mkII and DR-40 support +4dB balanced, is a better choice for using with external preamps.

Link to comment
Share on other sites

Thanks for the information guys. Maybe I now have more questions. :)

 

When building a padded cable, and using the calculator referenced above, do I enter the input impedance as what the source is(in this case, the MixPre) and the output impedance as the what the desitnation would be(in this case, the unbalanced 1/4" on the H4n)?

 

As far as I know, the tape out on the MixPre is about 25db too hot when going into the unbalanced 1/4" inputs.

 

There is a cable that a lot of people have bought to achieve the desired results: http://www.sescom.com/product.asp?item=LN2MIC-ZOOMH4N-6 I think I would prefer to make my own cables(to learn how to do it), but I could always go this way with the Sescom cable if I am unable to do it myself.

 

From my research, it is always preferable to use the unbalanced inputs on the H4n over the XLR inputs. However, the tape out on the MixPre is still too hot and you have to knock down the signal. The goal seems to be have the gain settings on the Zoom in the 27-30 range. This seems to be the Goldilocks zone for clean sound using this combination. Here's one guy's approach http://www.danmccomb.com/posts/987/connecting-zoom-h4n-to-sound-devices-mixpre-part-ii/ with many people using his exact approach or similar. I just prefer to roll my own cables.

 

Again, thanks.

Link to comment
Share on other sites

  • 2 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...