Gain Settings of Amplifier (Purifi) with preamp

[Rantenti]

Hello dear ASR friends, I have a Holo Audio Serene Preamp and an Audiophonics HPA-S400et Amp on order for their excellent measurements and versatility. I have only used integrated amps before so I have no experience with amp- preamp matching.

I have read that for the Purifi module in the amp, there are 3 configurations for the gain (1, 2 or Bypass).

Set Gain & Bypass on Purifi Amplifier module - Audiophonics Blog

Find the blog of Audiophonics!

www.audiophonics.fr

It states that the bypass mode is relevant in cases where the Purifi amplifier is used with a strong preamplifier supporting a load of 2 to 4kOhm with a voltage ~ 10V RMS.

Here is what I can find about the Holo Audio Serene preamp:

Input: RCA: Max 12Vpp (4.2Vrms) 6800 ohms; XLR Max 24 Vpp (8.48Vrms) 13600 ohms

Output: RCA: 8.5 Vrms 20 ohms; XLR 1: 17 Vrms 3ohms; XLR 2: 17 Vrms 40 ohms

I wonder what gain settings in the amp should I set to get the best performance (dynamic range/ lowest noise/ crosstalk, best SNR/ SINAD etc) when using the Holo Serene preamp? My room is about 25m² and I use 86dB sensitivity speakers listening at a distance of 8 feet.

Thank you for your advice!

 

[AnalogSteph]

It states that the bypass mode is relevant in cases where the Purifi amplifier is used with a strong preamplifier supporting a load of 2 to 4kOhm with a voltage ~ 10V RMS.

Looks like your preamp is exactly the kind they're talking about. You should definitely not need more than Configuration 1 (20 dB total gain).

I would set things up the way they ship and see which volume setting on the preamp you arrive at for normal playback volume (volume normalization enabled in source). Chances are you'll end up at -40 to -45 dB, in which case you could definitely reduce gain a bit. Around -30 dB would be a pretty sensible region.

If you don't have volume normalization, check with unusually quiet / dynamic material. If you end up maxing out the volume before going "this is as loud as it'll ever need to go", pick the next higher gain setting.

 

[Rantenti]

Looks like your preamp is exactly the kind they're talking about. You should definitely not need more than Configuration 1 (20 dB total gain).

I would set things up the way they ship and see which volume setting on the preamp you arrive at for normal playback volume (volume normalization enabled in source). Chances are you'll end up at -40 to -45 dB, in which case you could definitely reduce gain a bit. Around -30 dB would be a pretty sensible region.

If you don't have volume normalization, check with unusually quiet / dynamic material. If you end up maxing out the volume before going "this is as loud as it'll ever need to go", pick the next higher gain setting.

Thanks for your reply!

Sorry for my ignorance, just want to clarify a few concepts about the phrase "a strong preamplifier supporting a load of 2 to 4kOhm with a voltage ~ 10V RMS."

1. a load of 2-4 kOhm: is this talking about the input impedance of the amplifier that the preamp is commected to? The Audiophonics amp in bypass mode coincidentally has an input impedance of 2.2kohms (RCA) and 4.4kohms (XLR)

2. My preamp gives a balanced output of 17 Vrms. Does this value change with load? I mean, how do I know my preamp can output 10 Vrms specifically "AT A LOAD OF 2 TO 4 Kohms"?

3. There are two pairs of balanced outputs on my preamp. Both output 17 Vrms, but one has an output impedance of 3 ohms while the other 40 ohms. Will there be any theoretical difference in sound when connected to the amp?

Thanks!

 

[AnalogSteph]

1. a load of 2-4 kOhm: is this talking about the input impedance of the amplifier that the preamp is commected to?

Si!

2. My preamp gives a balanced output of 17 Vrms. Does this value change with load? I mean, how do I know my preamp can output 10 Vrms specifically "AT A LOAD OF 2 TO 4 Kohms"?

Well, in this case XLR1 is apparently strong enough to drive headphones, they say 3 W into 32 ohms = 9.8 Vrms, presumably current limited at this level, so anything ca. 64 ohm and higher should allow for basically a full 17 Vrms out. The output should be quite bored when driving 4.4 kOhms. That being said, I bet even XLR2 has plenty of oomph behind it.

I did finally find the preamp gain spec that I was looking for yesterday:

Each step corresponds to 1dB over a range of -78dB to +6dB.

What sort of DAC are you using, more specifically what output level does it provide? 6 dB is not exactly a ton of gain. When used with a balanced DAC with ~4Vrms worth of output you should still be getting a good amount of output level, but the Bypass setting may be cutting it close. Just try it and see like I suggested earlier, I guess.

 

[Rantenti]

Hi AnalogSteph,
Thanks for your explanation and your efforts in finding the relevant specs. I looked at the specs but had no idea what information to extract to deduce the answers I need and your explanation was a great help!

My main DAC is the the Holo Audio Spring 3 KTE (5.8Vrms balanced, output impedance 200 ohms) and I've also got a Gustard X26 Pro (5Vrms, output impedance 100 ohms).

I also have two choices of preamps, either the Holo Audio Serene with +6dB gain, or the Topping A90 in preamp mode, which can ouput +6dB in the recommended medium gain mode and 15.5dB in maximum high gain, similar to the maximum gain of the Topping Pre90. But I guess I won't push the preamp to +15dB.

Apparently, both the Holo Audio Serene and the Topping Pre90/ A90 are OK matches with the Audiophonics S400 amplifier. I'll try your recommendations to find the optimal gain settings on the amp. Thanks a lot!

 

[Rantenti]

What sort of DAC are you using, more specifically what output level does it provide? 6 dB is not exactly a ton of gain. When used with a balanced DAC with ~4Vrms worth of output you should still be getting a good amount of output level, but the Bypass setting may be cutting it close. Just try it and see like I suggested earlier, I guess.

Many thanks for your explanation! I'm starting to understand this better.

My main DAC is the the Holo Audio Spring 3 KTE (5.8Vrms XLR) and I've also got a Gustard X26 Pro (5Vrms).

I have two preamps, the Holo Audio Serene with +6dB gain, and the Topping A90 in preamp mode, also +6dB in medium gain.

Since my DAC output voltage is only ~70% of maximum input sensitivity of my preamp, I guess the preamp will pump out only ~70% of its max voltage (17 x 0.7= 11.9 Vrms). And I won't turn the preamp volume knob all the way to -0 dB. So the actual output voltage from the preamp will be even smaller. So it will likely be lower than the 10Vrms mark which is recommended for the Purifi amp bypass mode.

So I'll follow your recommendation and start with the default factory gain setting first. Thanks a lot!

P.S. Holo Audio says the Serene's 3 ohms XLR1 is indeed designed for optional use with headphones.

 

[fourdogslong]

Usually it's best to have the volume control closer to it's maximum rather than turned down significantly. That way with an analog (relay type) volume control you get finer adjustment and less resistance in the path and with digital volume control you keep more resolution, in both cases the signal to noise ratio usually stays better that way too.

So I'd recommend trying the different gain stages on the amp and use the one that keeps your volume control in it's sweet spot.