Behringer PP400 Phono Preamp

[RayDunzl]

Ok, I have one of these because it works and it was cheap.

Now $50 on Amazon...

Measurements:

Setup: REW sine generator -41.20dBfs -> USB -> Focusrite 4Pre USB -> Ch3 out ->PP400 in -> PP400 out -> Focusrite Ch7 input -> USB -> REW




Input driven for an estimated 2V output at 1.05kHz.

Most all of those spikes are measurement noise, power spikes from the rats nest and RCA wires and USB at 8 and 16kHz) not the PP400

RCA cable loopback, no signal, no PP400





Hmm...

The same input level at 105Hz clips.

Oh yeah. RIAA...

REW doesn't know about RIAA for a measurement sweep.

Maybe return to all this later.




Using -60dBfs signal giving about 1V output at the lower frequencies, or 6dB lower than CD player output

Green = output for a flat input, red overlay = RIAA curve, red at the bottom, phase

Ok, pretty close for a $25 preamp.




Distortion:

Looks reasonable... Noise (brown) dominates but is reasonably low.





Impulse and Step:

I have no idea what is going on there.

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Conclusion:

So, it works, and the measurements (such as they are) look reasonable, except that completely off-the-wall Impulse.

I've even listened to an LP through it without complaints.

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It was the Chord Review that inspired me to look at this moment...

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Sanity Check:

The two RCA cables used, with a connector so only the two cables create the loopback, to check the Imoulse and Step response. Nothing else changed. Just remove the PP400 from the loop.



Sanity prevails. So why the strangeness as above?

 

[ribosradagast]

I actually have one of these and subjectively think it sounds pretty bad - no bass. I offered to send it to Amir for testing and he said he already has bought one, just needs to get around to actually testing it

 

[RayDunzl]

I don't see "no bass" in the measurements above.

Will do something with an LP and see what happens.

 

[andreasmaaan]

Sanity prevails. So why the strangeness as above?

It's just the minimum phase behaviour you'd expect from the RIAA filter, isn't it?

 

[RayDunzl]

It's just the minimum phase behaviour you'd expect from the RIAA filter, isn't it?

I don't know. Not seen anything like that in my fooling around with the rest of the gear.

I'm new here.

 

[andreasmaaan]

@RayDunzl I'm pretty sure that's what's going on. When I simulate the output of an RIAA filter that's gently bandlimited, I get a step response that looks like this:

Which is pretty similar to your measured step response. So the PP400 doesn't look to be doing anything amiss there IMO.

 

[RayDunzl]

Thank you.

I played around with some "opposite" RIAA-like filter (not well executed() and got an equally ugly opposite Impulse and Step here...

Looping back a flat signal filtered in the chain as if going to the cutting lathe:

Frequency Response:

Step and Impulse

 

[ripmixburn]

Only $19 now on Amazon.