Why does this XLR adapter cause distortion?

[audiobomber]

My Audiolab 8200CD/DAC/Preamp has RCA and XLR outputs. I wanted to connect a power amp and a headphone amp to these outputs. The Audiolab manual says the RCA and XLR outputs cannot be used simultaneously, therefore I planned to switch whichever amplifier was not in use. I purchased a pair of Hosa RCA Female to XLR Female adapters, which I used for the headphone amp connection. I heard music, but also some buzzy sounding distortion. I tried connecting the power amp to the adapter instead, and same result. Any idea why this plan didn't work?

[lucretius]

10 hours ago, audiobomber said:

After further investigation, I don't think input voltage overload is the issue. I turned my preamp down to -60dB and still heard distortion on the XLR outputs, with a 100kOhm load. I have some new gear on the way which will help with the diagnosis. 

 

Perhaps the Audiolab preamp cannot tolerate having its cold output signal (XLR pin 3) shorted to ground?  It's possible that the distortion might be avoided with a cable/adapter that left XLR pin 3 unconnected (i.e. floating). Or maybe you need one of these:

https://www.jensen-transformers.com/product/pc-2xr/

 

Why not consult with Audiolab?

[bluesman]

I don’t know the Audiolab device, so these are just general comments that probably apply to your problem in some way. Balanced XLR outputs send out of phase signals from pins 2 and 3. Shunting 3 to the shield at the unbalanced end sends the out-of-phase signal to ground, and this can drive some unbalanced line inputs nuts.

 

Transformer coupling is often used in the output stage of balanced devices to power a second (unbalanced) output. You may need an inline coupling transformer for impedance matching between your balanced output and unbalanced input.

 

Also, the signal level is usually hotter from a balanced output. Most devices with balanced inputs have trim pots or switches to attenuate as needed. But devices with unbalanced inputs do not, so you may simply be overdriving your amps.

[lucretius]

It looks like the output voltage on the XLR outs on the Audiolab CDQ are twice that of the RCA outs.  Could it be too hot for the headphone amp?  Also, I assume XLR pin 3 is grounded.

[Speedskater]

If you are going from an XLR output to a RCA input, there can be problems.

There are 3 & 1/2 common types of XLR output stages and no one type of adapter will work with all of them.

[audiobomber]

2 hours ago, lucretius said:

It looks like the output voltage on the XLR outs on the Audiolab CDQ are twice that of the RCA outs.  Could it be too hot for the headphone amp? 

Input overload would explain the harmonic distortion I heard. 

[audiobomber]

After further investigation, I don't think input voltage overload is the issue. I turned my preamp down to -60dB and still heard distortion on the XLR outputs, with a 100kOhm load. I have some new gear on the way which will help with the diagnosis. 

[audiobomber]

39 minutes ago, lucretius said:

 

Perhaps the Audiolab preamp cannot tolerate having its cold output signal (XLR pin 3) shorted to ground?  It's possible that the distortion might be avoided with a cable/adapter that left XLR pin 3 unconnected (i.e. floating). Or maybe you need one of these:

https://www.jensen-transformers.com/product/pc-2xr/

 

Why not consult with Audiolab?

A grounding issue makes sense.

 

My goal with the adapter was to connect the Audiolab preamp via RCA to my power amps and connect to my Asgard 2 headphone amp via XLR. A couple of days ago, I bought a Hafler HA15 headphone amp, which has XLR inputs and an RCA pass-through. I should be able to implement my original scheme. If not, I will use the pass-through. 

[bluesman]

On 5/9/2019 at 11:31 AM, lucretius said:

It looks like the output voltage on the XLR outs on the Audiolab CDQ are twice that of the RCA outs.  Could it be too hot for the headphone amp?  Also, I assume XLR pin 3 is grounded.

Standard XLR pinout uses 1 as ground.

[bluesman]

Another thought - if the output stage of your Audiolab is cross-coupled (aka servo-coupled) and your adapter leaves pin 3 floating, you’ll get the distortion you seem to be describing regardless of output level.

[lucretius]

18 minutes ago, bluesman said:

Standard XLR pinout uses 1 as ground.

 

I know -- but most adapters ground pin 3 by tying it to pin 1.

[lucretius]

8 minutes ago, bluesman said:

Another thought - if the output stage of your Audiolab is cross-coupled (aka servo-coupled) and your adapter leaves pin 3 floating, you’ll get the distortion you seem to be describing regardless of output level.

 

I looked up the adapter the OP was using -- it grounds pin 3, it doesn't leave it floating.

[Speedskater]

Not all balanced output stages are happy about having pin 3 (or pin 2) connected to ground.

[audiobomber]

I found this description of the Hosa GFX 132 adapter online:

• Designed to adapt a phono plug to an XLR input. XLR pin 3 is grounded resulting in an unbalanced signal
• XLR pin #2 connects with the center RCA contact (signal)
• XLR pins #1 and #3 are joined and connected to the RCA sleeve (ground)

I provided the above to Audiolab and asked about compatibility. At this point it's academic, because I received the Hafler HA15 headphone amp, which I'm using with Yorkville DLX XLR cables. My speaker amps are connected to the Audiolab RCA outs. Everything is working great. 

[audiobomber]

Audiolab's advice is to split the unbalanced output with an RCA splitter in lieu of dual outputs.

[lucretius]

3 hours ago, audiobomber said:

Audiolab's advice is to split the unbalanced output with an RCA splitter in lieu of dual outputs.

 

So they don't even want to tackle XLR to RCA?

[audiobomber]

They didn't say so, but I believe that grounding pin #3 is a problem for their design, and no way to avoid that with an XLR/RCA adapter.

[lucretius]

12 minutes ago, audiobomber said:

They didn't say so, but I believe that grounding pin #3 is a problem for their design, and no way to avoid that with an XLR/RCA adapter.

 

Benchmark has a cable XLR -> RCA, with pin 3 floating:

https://benchmarkmedia.com/products/benchmark-xlrfm-to-rca-adapter-cable-pin-3-floating?variant=547648461

 

However, I take it you want to use your own RCA cables?

 

[audiobomber]

14 hours ago, lucretius said:

 

Benchmark has a cable XLR -> RCA, with pin 3 floating:

https://benchmarkmedia.com/products/benchmark-xlrfm-to-rca-adapter-cable-pin-3-floating?variant=547648461

 

However, I take it you want to use your own RCA cables?

 

Good to know, and great price.

 

My preamp has RCA and XLR outputs. The original plan was to connect my power amp via RCA, and connect my headphone amp via XLR-to-RCA, as neither amp had balanced inputs. Shortly after I started this thread, I saw a great sale price on another headphone amp with balanced inputs, and bought one along with a balanced cable. So I no longer need XLR to RCA connection, but at least I know what went wrong should I have a need in the future.

 

I have had no previous experience with balanced cables, I definitely learned something here. My thanks to everyone who participated.