Re: [Avid-L2] OTish: Audio Level Converter? Pyle Premium Direct Injection Audio Box - 2.36" x 4.09" Passive DI Unit Hum Eliminator w/ Input Attenuator to Connect Guitar & Bass, 1/4'' Impedance Transformer Connector to Balanced & Unbalanced XLR

Nerd alert

Not that it's relevant to your issue but it's worth noting that the XLR pinout 'standard' is anything but. Pin 2 + and Pin 3 - isn't universal, so grounding Pin 3 doesn't always work - sometimes you have to ground Pin 2. Even Shure couldn't make up their minds with an SM58 wired Pin 2 + and the inputs to their little mixer (I'm going back to the 80's here) having Pin 3 hot. 

I made a 4 channel DI box many years ago for a cabaret venue that had a both XLR and 1/4" inputs and outputs for each channel along with 4 audio isolation transformers and a bunch of switches to select which input socket, swap 2&3, short 2 or 3 to 1, ground input to output or keep them isolated. It wasn't for level matching, simply for hum removal. It got frequent use for a number of years. 

/nerd

Tony

Sent by magic over t'interweb

On 10 Oct 2025, at 09:35, John Moore via groups.io <bigfish=pacbell.net@groups.io> wrote:



[Edited Message Follows]

So I tested the Pyle Box which is a bass/guitar direct box and found it does work for my purposes.  I tried going straight out of the M-Track Duo main outs to the PA speaker amp consumer line input and it worked but there was a Hum.  The 1/4 inch to RCA cable was not a TRS 1/4 plug so plugging into the Balanced 1/4 main output on the M-Track shorted pin 1 shield to pin 3 low.  When I ran a TRS 1/4 to XLR cable from the M-Track Main Output to feed the Pyle XLR input/output connection and took Unbalanced instrument input connectors and connected them with the 1/4 unbalanced to RCA cables to feed PA speaker amp consumer line input it worked but depending on the position of the ground lift button the hum would come and go.  The ground lift button shorts pin 1 shield of the XLR connector of the Pyle box to chassis ground which ties it to the sleeve of the unbalance instrument connectors.

 

I found that I got a little more power out of the Headphone jack than the main outputs.  I did some googling around about +4dbu compared to the headphone output of 60mW/ch into 32 ohm and came up with the headphone works out to roughly +5.1 dbu which explains why it's a little louder than the main output.  So far it seems that going the extra mile for a isolation transformer is worth it to eliminate the hum.  I was surprised that I didn't need to use the attenuation switch on the pyle box.  I guess because I'm feeding from volume controlled outputs of the M-Track it wasn't overdriving the consumer line level inputs.

 

Here are the M-Track output specs for the nerds I try my best to emulate  ;-)

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