Measurements of Behringer PP400 Phono Preamp

[Robciak]

Hi,

This is a measurement of the phono preamp Behringer PP400. It is a simple preamp without any switches and costs around US$25-30.

For measurements, I grounded the PP400 through its output to the analyser. Using a dedicated screw caused significant distortion from the power supply. Below is a graph showing the THD+N distortion for both groundings.

All measurements were conducted using the Audio Precision APx525 audio analyzer with the following settings:

Frequency response measurements were conducted using an equalization curve that imitates an inverted RIAA curve.

MEASUREMENTS

RMS Level and Gain
A 5 mV, 1 kHz sine wave was used as the input signal.

Here are the RMS and Gain results within the generator level range. The PP400 begins to clip at input levels above 50 mV.

THD+N and THD
THD+N and THD distortion are not bad for a device in this price class. PP400 gives around 12 bits resolution.

Below is the THD+N ratio for both the generated and the measured signal levels.
The lowest values were:

Signal-to-noise ratio
For SNR, the PP400 achieved nearly 13 bits of resolution.

FFT
Here is the FFT plot for the signal: 5 mV and 1000 Hz. As you can see, there is no major harmonic distortion.

Frequency response
The measurement was carried out with an inverted RIAA curve applied. The ideal response would be a straight 0 dB line. The PP400 increases slightly for frequencies above 1 kHz (0.5 dB for 20k) and drops to -4 dB for 20 Hz. Not very accurate frequency response.

Intermodulation distortion
The SMPTE IMD test involved two sine waves at 60 Hz and 7 kHz with an amplitude ratio of 4:1. Below are the results for both the generated and measured levels.

Summary
As a $25 phono preamp, the Behringer PP400 offers acceptable THD+N performance but falls short in terms of frequency response. Behringer products are known for providing average performance at a budget price, and the PP400 proves this.

 

[AnalogSteph]

Any chance you could take a measurement of input clipping level at 100 Hz and 10 kHz as well (or even the -40 dB threshold as a function of frequency, assuming the AP can be persuaded to automate this)?

 

[Robciak]

Any chance you could take a measurement of input clipping level at 100 Hz and 10 kHz as well (or even the -40 dB threshold as a function of frequency, assuming the AP can be persuaded to automate this)?

Sure, I'll do it on Monday

 

[Robciak]

Any chance you could take a measurement of input clipping level at 100 Hz and 10 kHz as well (or even the -40 dB threshold as a function of frequency, assuming the AP can be persuaded to automate this)?

No RIAA correction was applied to these measurements.

100 Hz - best THD+N for 12 mV input (2,5 V out)

1000 Hz - best THD+N for 41 mV input (2,3 V out)

10000 Hz - best THD+N for 218 mV input (2,6 V out)

 

[AnalogSteph]

As I thought, that's a typical 1-opamp global feedback kind of deal. Probably similar to this although the limited FR accuracy suggests that an even more basic feedback circuit may have been used (or parts with relatively loose tolerances).

RIAA Phono Preamplifier using LF353N

Ah yes, here it is reverse-engineered:

PP400の画像

ameblo.jp

That's a basic old topology not exactly renowned for its accuracy (as you were able to confirm). Minimum output stage loading is 2k at HF, I'd think a 4580 (what else did you think it would be?) should be able to cope with that. No RF input filtering whatsoever, but at least it means you can choose input capacitance freely with external parallel capacitors.

So not the last word on anything, but at least I wouldn't expect it to be overloaded by vinyl crackling (peaks of up to 500 mVp pre-EQ have been sighted), and the capacitors do appear to be film as cheap as they may be.

 

[Michael Fidler]

RIAA response made me wince a bit! It could be modded with a bit of 'skyhooking' to be much better... Everything else is very decent for the price.

Anyone got the schematic?

 

[kemmler3D]

Looks usable and pretty good for the money, but it's going to sound noticeably thin in the bass, and the clipping kind of concerns me. But for $30 I guess who's going to complain?

I personally find Behringer more and more objectionable over time as their business model has shifted to cranking out endless crappy knock-offs of famous synthesizers, but I wouldn't blame someone for putting this thing in a minimum-budget TT setup.