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Understanding Low Gain and Preamp / advice on amplifier selection (Benchmark AHB2 or the Apollon Hypex NCx500)

Matze

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I don't fully understand the concept of Low Gain and which devices are needed to implement it. That's why I'd like to hear your opinions and experiences on this matter. Initially, I found the Topping LA90 discrete particularly interesting in Bridged mode as 2 mono blocks, which would provide more power, but after some reports from this forum, it seems to be prone to failures. At that price point, this would be acceptable compared to the other candidates.

So, now I'm interested in the Benchmark AHB2 and the Apollon Hypex NCx500 DM Dual Mono Stereo Amplifier, both offering different designs, namely Class AB vs. Class D. I'm still undecided about which amplifier design I prefer and whether Class D with more power is better or worse. Both amplifiers have received excellent reviews in forum tests.

While reading the reviews, I stumbled upon the topic of Low Gain, which I don't fully understand from a practical perspective. When the amplifier operates in Low Gain mode, it amplifies less and also produces less noise and distortion. However, it requires a higher input voltage of 10V? Am I correct in understanding that a preamplifier is necessary to operate in Low Gain mode? Okay, let's assume the chain: Source --> DAC --> Preamplifier --> Amplifier... where is the optimal place to adjust the volume in practice? I would have assumed that the optimal position is the last link in the chain, and by reducing the volume on the amplifier, you simultaneously reduce the noise, etc. However, why do the two amplifiers listed above not have volume control?

Why do some people use DSP for volume control? For me, the DSP is at the beginning of the chain in the source. I use an RPi4 with Moode Audio and Camilla DSP as a player.

I would greatly appreciate your opinions, advice, and experiences on these amplifiers or others that you can recommend.

Thank you very much in advance!
 

MaxwellsEq

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I don't fully understand the concept of Low Gain and which devices are needed to implement it. That's why I'd like to hear your opinions and experiences on this matter. Initially, I found the Topping LA90 discrete particularly interesting in Bridged mode as 2 mono blocks, which would provide more power, but after some reports from this forum, it seems to be prone to failures. At that price point, this would be acceptable compared to the other candidates.

So, now I'm interested in the Benchmark AHB2 and the Apollon Hypex NCx500 DM Dual Mono Stereo Amplifier, both offering different designs, namely Class AB vs. Class D. I'm still undecided about which amplifier design I prefer and whether Class D with more power is better or worse. Both amplifiers have received excellent reviews in forum tests.

While reading the reviews, I stumbled upon the topic of Low Gain, which I don't fully understand from a practical perspective. When the amplifier operates in Low Gain mode, it amplifies less and also produces less noise and distortion. However, it requires a higher input voltage of 10V? Am I correct in understanding that a preamplifier is necessary to operate in Low Gain mode? Okay, let's assume the chain: Source --> DAC --> Preamplifier --> Amplifier... where is the optimal place to adjust the volume in practice? I would have assumed that the optimal position is the last link in the chain, and by reducing the volume on the amplifier, you simultaneously reduce the noise, etc. However, why do the two amplifiers listed above not have volume control?

Why do some people use DSP for volume control? For me, the DSP is at the beginning of the chain in the source. I use an RPi4 with Moode Audio and Camilla DSP as a player.

I would greatly appreciate your opinions, advice, and experiences on these amplifiers or others that you can recommend.

Thank you very much in advance!
Simple answer: high or perhaps normal gain in the high twenties is fine for normal domestic line level gear. Pro gear often has a higher output, for which low gain is better.

Here is an excellent thread that answers all your other questions:
 
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Matze

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That's a great thread, but it doesn't answer my question as to why there's no volume control on the amplifiers. Because if the amplifier is the weakest link in terms of THD, SNR and SINAD in the chain, then one would need to reduce the volume or gain there. I gather from the thread that it's not necessarily best in terms of THD to set everything in the chain up to the amplifier at full volume. But I'm still not clear on the gain modes:

Let's take the AHB2 as an example:
  • Low-Gain = 22 dBu (9.8 Vrms)
  • Mid-Gain = 14.2 dBu (4 Vrms)
  • High-Gain = 8.2 dBu (2 Vrms)
My DAC (Topping D90 III SABRE) delivers 4V and can be switched to a maximum of 5V. The 5V wouldn't be sufficient for Low-Gain. So, I would need to use a preamplifier. However, if I were to stay with Mid-Gain, then the DAC can be directly connected to the amplifier. Correct?

Then, I also gathered from the thread that regardless, SNR is added by each link in the chain and is amplified by each link in the chain over its course. So, would the chain DAC -> Amplifier in Mid-Gain be preferable over a chain DAC -> Preamplifier -> Low-Gain?
 

DVDdoug

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That's a great thread, but it doesn't answer my question as to why there's no volume control on the amplifiers.
Traditionally, the preamp (or other source) is the control center with the volume control. Sometimes it has a remote control. Some power amps have a volume/gain control but it's (usually) not intended for everyday volume control.

So, I would need to use a preamplifier.
Most of the time a preamp is attenuating. But there is usually some "available gain" if you need it. (Phono preamps and microphone preamps are actually amplifiers.)[/quote]
 

MaxwellsEq

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That's a great thread, but it doesn't answer my question as to why there's no volume control on the amplifiers. Because if the amplifier is the weakest link in terms of THD, SNR and SINAD in the chain, then one would need to reduce the volume or gain there. I gather from the thread that it's not necessarily best in terms of THD to set everything in the chain up to the amplifier at full volume. But I'm still not clear on the gain modes:

Let's take the AHB2 as an example:
  • Low-Gain = 22 dBu (9.8 Vrms)
  • Mid-Gain = 14.2 dBu (4 Vrms)
  • High-Gain = 8.2 dBu (2 Vrms)
My DAC (Topping D90 III SABRE) delivers 4V and can be switched to a maximum of 5V. The 5V wouldn't be sufficient for Low-Gain. So, I would need to use a preamplifier. However, if I were to stay with Mid-Gain, then the DAC can be directly connected to the amplifier. Correct?

Then, I also gathered from the thread that regardless, SNR is added by each link in the chain and is amplified by each link in the chain over its course. So, would the chain DAC -> Amplifier in Mid-Gain be preferable over a chain DAC -> Preamplifier -> Low-Gain?
There's no definitive answer, since it depends on gain and noise behaviours. So let's consider the preamplifier case. Adding a device in series may add noise and distortion, so in theory, a preamplifier will degrade the chain. But, and this is a very big but, most of the time a preamplifier is attenuating the signal, which will normally attenuate upstream noise!

There's a much better reason to add a preamplifier - avoiding software glitches in DACs. By default a DAC should allows be at 100%, but it's possible in some DACs to use DSP for attenuation. But this can, and has, gone wrong destroying speakers and hearing. A preamplifier will stop that happening.
 
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Matze

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Traditionally, the preamp (or other source) is the control center with the volume control.
After carefully reading through the thread, I've come to the conclusion that one definitely shouldn't adjust the volume at the beginning of the chain. So, not in the DSP of the source before the DAC. In my case, using the RPi4 with CamillaDSP. Or should I understand it as adjusting each subsequent device to the sweet spot between good SNR and good THD? If the volume at the end of the hifi chain is too high, then adjust it down at the beginning?

most of the time a preamplifier is attenuating the signal, which will normally attenuate upstream noise!
This seems to apply to analog sources such as a turntable. The source is digital up to the DAC, so there is no noise present until the DAC (I'm excluding noise in the recording). The DAC is already the link in the chain with the best SNR/THD values. Therefore, I see no need for attenuation through a preamplifier here.
 
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