Measuring V_pp Of Topping A90 Preamp

[concorde1]

I just attempted to measure V_rms of the AC output from the Topping A90 in preamp mode with no load on it (no power amp). I tried Low Medium High gains. I generated a sine wave with Audacity (amplitude: 1.0) through my PC to Topping D90 to the A90. I multiplied the V_rms by 2*sqrt(2) to get V_pp (peak to peak).

I was expecting 9 V_pp because for this particular test I'm concerned with D90 XLR->A90 unbalanced preamp mode - the specs suggest I should get 9 V_pp for Low gain, and 25 V_pp for Medium and High.

I set the A90 to MAX volume on Low gain for these 3 tests below.

At 50 Hz sine wave, I got only 3.5 V_pp
At 1 kHz I got only 3.276 V_pp
At 10 kHz I got only 2.408 V_pp

I didn't record my findings for Medium and High gains but, medium measured higher than low and high measured higher than medium. This goes against the specs also, which say 25 V_pp for both. Neither gain was equal to 25 V_pp.

I probably tested incorrectly as I didn't get logical results. Voltages should, I believe, be the same at all frequencies. But I thought it was strange that Medium and High gains measured differently.

The purpose of measuring this was, I am worried about turning the preamp higher than line level which would damage the power amp in music (or sine waves) that reach high digital saturation".

My question is, how can I determine where is safe to turn my A90 up on Low gain to not overpower the power amp?

Currently I'm using a temporary Yamaha AV receiver as the power amp; I would also like to know for the amp I'm about to build (Neurochrome Modulus-686), which seems to have an input sensitivity of 2.0 V_rms, or ~2*2.8 = about 5.6 V_pp.

 

[JohnYang1997]

D90 outputs 4Vrms. And use this number and the gain to carry out the expected calculated output.
Low gain 1.3Vrms
Mid gain 4Vrms
High gain 9Vrms

 

[concorde1]

I must note I just realised I did something stupid. I think I left my system-wide headphone EQ on, during the tests. LOL

 

[concorde1]

Not sure if my EQ actually was on or not, will remain a mystery.

D90 outputs 4Vrms. And use this number and the gain to carry out the expected calculated output.
Low gain 1.3Vrms
Mid gain 4Vrms
High gain 9Vrms

Thanks for these numbers. How about for balanced out (which I will be using for the amp I'm building)?

By my calculations from A90 specs:
Low Gain 2.7 V_rms
Mid Gain 8 V_rms
High Gain 24 V_rms

Is that right?

 

[charleski]

The majority of cheap multimeters with an true-RMS function only really work up to around 1kHz, which might affect the results as well. Unfortunately the bandwidth is often buried deep in the specs.

 

[JohnYang1997]

Not sure if my EQ actually was on or not, will remain a mystery.



Thanks for these numbers. How about for balanced out (which I will be using for the amp I'm building)?

By my calculations from A90 specs:
Low Gain 2.7 V_rms
Mid Gain 8 V_rms
High Gain 24 V_rms

Is that right?

You clip ar at high gain so
2.7V
8V
18V
I recommend using Mid gain and turn it down when needed.