Review and Measurements of Benchmark HPA4 Headphone Amp/Pre

[Chester]

Agree, if it was a subtle difference but it’s a big difference. Feels like I have something configured incorrectly.

 

[nagster]

Hey can anyone knowledgeable help me understand what’s happening in my setup right now please.

I have recently got a HPA4 and currently have a Chord Mojo 2 connected via RCA and an RME ADI-PRO 3 FS R BE connected via XLR.

The Chord is set to almost 0db so should be outputting around 4 v rms and the RME is set to +24dbu and 0db so should be outputting around 12 v rms?

When I have them receiving the same source material via Roon and I switch between inputs, the Chord is much much louder than the RME. The HPA4 has the same volume level set for both. No boost is applied to either input.

This is the opposite of what I expected. What am I missing?

I measured the output voltage of the RME ADI-2 PRO FSRBE and Benchmark HPA4. I don't have a Mojo 2.
Doing a similar measurement might solve your mystery.
The HPA4's TRS output seems to activate the protection circuit at about 12 V. In that case the output is muted. Therefore I measured it at Vol: -0.5.

 

[staticV3]

Agree, if it was a subtle difference but it’s a big difference. Feels like I have something configured incorrectly.

And measuring voltages will help you quickly and effectively figure out what is misconfigured.

Much faster than having us guess possible causes.

 

[Chester]

And measuring voltages will help you quickly and effectively figure out what is misconfigured.

Much faster than having us guess possible causes.

Ok thanks for your input.

If anyone else has any suggestions, I’d be very interested.

 

[tomchr]

20*log10(12.171/11.492) = 0.5 dB. Your headphone amp is dialled in to -0.5 dB. That explains the difference. Does this answer your question?

Tom

 

[Chester]

20*log10(12.171/11.492) = 0.5 dB. Your headphone amp is dialled in to -0.5 dB. That explains the difference. Does this answer your question?

Tom

Thank you @tomchr. Rory at Benchmark solved the issue for me. The HPA4 automatically boosts the RCA inputs by 15.8dBu to bring it up to pro level.

 

[Endibol]

Thank you @tomchr. Rory at Benchmark solved the issue for me. The HPA4 automatically boosts the RCA inputs by 15.8dBu to bring it up to pro level.

There is a small mistake. The RCA inputs are boosted by 15.8 dB (not dBu). So the RCA level of 2 Vrms are boosted by a factor of 6.2 to approx 12.3 Vrms. This can be found in the manual.

 

[Chester]

There is a small mistake. The RCA inputs are boosted by 15.8 dB (not dBu). So the RCA level of 2 Vrms are boosted by a factor of 6.2 to approx 12.3 Vrms. This can be found in the manual.

I’m not knowledgeable enough to know who is correct but that was the exact information I was given.