Advertised specs for STA-6 and STA-9

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fracs

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Advertised specs for STA-6 and STA-9
« on: 9 Mar 2018, 12:03 pm »
Hi all.

Ref.
  STA-9:  http://www.nuprimeaudio.com/product/sta-9/?v=3e8d115eb4b3
  STA-6:  http://www.nuprimeaudio.com/product/sta-6/?v=3e8d115eb4b3

I'd like to confirm the advertised "gain" values for the STA-6 and STA-9. On the NuPrime website, for example, the STA-9 is quoted with a gain of "x 22". However, they also quote input sensitivity as "232.8 mV rms for 1 W output into 8 Ohms". So to try and reconcile this data I use the following reasoning:

1. NuPrime quote input sensitivity for STA-9 as 232.8 mV rms for 1 W output into 8 Ohms.

2. Using P = V^2 / R, then output voltage is 2.828 V rms.

3. Therefore, voltage gain is 2.828 / 0.2328 = 12.15

4. Convert voltage gain to power gain on logarithmic scale:  20 x log10 ( 12.15 ) = 21.69 dB

5. NuPrime quote that STA-9 gain is “x 22”. Given the above calculation, I think they meant to say “22 dB”.

If my reasoning is correct then does this mean that the gain of the STA-6 is similarly 28 dB and not "x 28" ?

Thanking you all.

rustydoglim

Re: Advertised specs for STA-6 and STA-9
« Reply #1 on: 16 Mar 2018, 06:15 pm »
I think Jye (by the way, he is our senior product manager for audio) has replied to you in email, I will ask him to post here.

Jye

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Re: Advertised specs for STA-6 and STA-9
« Reply #2 on: 19 Mar 2018, 07:34 am »
The gain specs for the amplifiers are in multiplication factor and not in dB. The website is correctly stating a 'x22' gain for STA-9 and a 'x28' gain for STA-6.

fracs

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Re: Advertised specs for STA-6 and STA-9
« Reply #3 on: 19 Mar 2018, 02:24 pm »
Yes, thank you. Jye replied to my email. Jye confirmed that the specified gains are linear.

I was interested because I am doing a "paper exercise" to compare expected behaviour of the NuPrime STA-6 with my former amp, a Yamaha AX-570. The Yamaha amp has a (power) gain of 29 dB, and this worked well with my Roland Digital Piano + JBL speaker combination. I recently sold the Yamaha amp, and have been looking for a suitable replacement. The JBL speakers are ancient, but I still like them.

I have since had another look at my math and I have realised a curious oddity: 28x linear (voltage) gain is approximately equal to 29 dB (power) gain. Ie. the "numbers" work out to be "about the same".

Therefore, I have decided to order the NuPrime STA-6. Destination is Canada.

left channel

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Re: Advertised specs for STA-6 and STA-9
« Reply #4 on: 19 Mar 2018, 03:19 pm »
Gain aside, those two amps have very different sound signatures. The six is cold and the nine is warm. 

fracs

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Re: Advertised specs for STA-6 and STA-9
« Reply #5 on: 6 May 2018, 08:13 pm »
[update]

So I purchased the STA-6, and I am pleased to say that I am extremely satisfied.

My configuration is as follows:

Source:     Roland A-90 EX digital piano
Amp:        Nuprime STA-6
Speakers: JBL TLX 18

I would not class myself as an audiophile. I chose the STA-6 on the basis of its claimed sound quality, simplicity and size. The size is terrific, as it fits neatly on top of one of my speakers. The sound quality is fantastic. The last amp I used in this configuration was a Yamaha AX-570, which I adored and reluctantly sold (moved OS). The STA-6 has filled a big gap for me, and I am very pleased.

Mike