Author Topic: Attenuation vs. 'Gain Control'  (Read 3006 times)

Offline Morne Coetzee

  • Trade Count: (+13)
  • AVForums Super Veteran
  • ****
  • Posts: 756
  • Total likes: 15
  • POWER | PRECISION | PURITY
Re: Attenuation vs. 'Gain Control'
« Reply #15 on: May 09, 2018, 02:55:29 PM »
Very interesting read, thank you. I have always wondered about this. I do have a question though.  I noticed that I can set the output voltage of my digital source via dipswitch, the manual reads: "Maximum Output Voltage:
Can be adjusted via internal switches from 0.3V to 4.25V to match system sensitivity." This source is connected via balanced cable to my preamp.

Getting to my preamp (fully balanced dual monoaural) I can again adjust the gain manually between +/- 0-18dB for each channel (supposedly to level match different components) manual reads: " Fully balanced instrumentation amplifiers are used in the gain stages, and each input can be separately adjusted for 0 - 18dB of gain. This allows the volume control to work in its optimum range even with sources of substantially different output levels."Volume control: "The attenuator modules are constructed on their own four-layer Arlon boards, where local power-supply regulation and bypass capacitors make for clean power and optimum isolation. An array of precision resistors provides attenuation in 0.1dB steps down to -57.0dB, at which point the steps increase to 1.0dB. In total, this hardware provides for more than 65,000 steps, allowing the"stepped attenuator" to act—and sound—like a continuously variable control."

My preamp in turn, is connected via balanced cable to my monoblock amplifiers with the following specifications: Rated continuous-power outputs: 150W into 8 ohms (21.8dBW), 300W into 4 ohms (21.8dBW), 600W into 2 ohms (21.8dBW), 1200W into 1 ohm (21.8dBW). Frequency response: 20Hz-20kHz, <0.5% THD. S/N ratio: better than 80dB (ref. 1W), better than 105dB (ref. full output). Input impedance: 100k ohms balanced, 50k ohms unbalanced. Output impedance: <0.05 ohms, 20Hz-20kHz. Damping factor: greater than 800 at 20Hz. Input sensitivity: 130mV for 2.83V output, 1.59V for full-rated output. Voltage gain: 26.8dB. Typical power consumption: 540W ±5% at idle, 210W ±5% in standby. Mains voltages: 100V, 120V, 200V, 210V, 220V, 230V, or 240V AC mains operation at 50 or 60Hz, set at factory.

My question is this, given that I can adjust these settings and having the specs what should my optimum output voltage setting be as well as gain setting for the stated amplification? Should I adjust these settings or just leave it at factory default? I can adjust my volume with 0.1dB resolution, so volume "range" has never really been an issue.

Thanks I appreciate your input  :thinking:
« Last Edit: May 09, 2018, 03:13:51 PM by Morne Coetzee »
There is Always justification for more Amplification!

Offline Morne Coetzee

  • Trade Count: (+13)
  • AVForums Super Veteran
  • ****
  • Posts: 756
  • Total likes: 15
  • POWER | PRECISION | PURITY
Re: Attenuation vs. 'Gain Control'
« Reply #16 on: July 15, 2018, 08:35:32 PM »
Very interesting read, thank you. I have always wondered about this. I do have a question though.  I noticed that I can set the output voltage of my digital source via dipswitch, the manual reads: "Maximum Output Voltage:
Can be adjusted via internal switches from 0.3V to 4.25V to match system sensitivity." This source is connected via balanced cable to my preamp.

Getting to my preamp (fully balanced dual monoaural) I can again adjust the gain manually between +/- 0-18dB for each channel (supposedly to level match different components) manual reads: " Fully balanced instrumentation amplifiers are used in the gain stages, and each input can be separately adjusted for 0 - 18dB of gain. This allows the volume control to work in its optimum range even with sources of substantially different output levels."Volume control: "The attenuator modules are constructed on their own four-layer Arlon boards, where local power-supply regulation and bypass capacitors make for clean power and optimum isolation. An array of precision resistors provides attenuation in 0.1dB steps down to -57.0dB, at which point the steps increase to 1.0dB. In total, this hardware provides for more than 65,000 steps, allowing the"stepped attenuator" to act—and sound—like a continuously variable control."

My preamp in turn, is connected via balanced cable to my monoblock amplifiers with the following specifications: Rated continuous-power outputs: 150W into 8 ohms (21.8dBW), 300W into 4 ohms (21.8dBW), 600W into 2 ohms (21.8dBW), 1200W into 1 ohm (21.8dBW). Frequency response: 20Hz-20kHz, <0.5% THD. S/N ratio: better than 80dB (ref. 1W), better than 105dB (ref. full output). Input impedance: 100k ohms balanced, 50k ohms unbalanced. Output impedance: <0.05 ohms, 20Hz-20kHz. Damping factor: greater than 800 at 20Hz. Input sensitivity: 130mV for 2.83V output, 1.59V for full-rated output. Voltage gain: 26.8dB. Typical power consumption: 540W ±5% at idle, 210W ±5% in standby. Mains voltages: 100V, 120V, 200V, 210V, 220V, 230V, or 240V AC mains operation at 50 or 60Hz, set at factory.

My question is this, given that I can adjust these settings and having the specs what should my optimum output voltage setting be as well as gain setting for the stated amplification? Should I adjust these settings or just leave it at factory default? I can adjust my volume with 0.1dB resolution, so volume "range" has never really been an issue.

Thanks I appreciate your input  :thinking:

Does anyone with the technical expertise have any thoughts on the settings that I should be using?
There is Always justification for more Amplification!

Offline Hi-Phibian

  • Commercial Member
  • Trade Count: (+44)
  • *****
  • Posts: 12,007
  • Total likes: 66
  • I really prefer email, see my banner for address..
    • Croak Audio Exploration
Re: Attenuation vs. 'Gain Control'
« Reply #17 on: July 15, 2018, 08:47:17 PM »
Logic tells me to reduce dac output if you want to drop the signal level/match it for good volume control range rather than trimming it on the pre.  Why create it and then waste it...







[Anyone who thinks that wealth is measured in money is blind and narrow minded.  Wealth is obviously measured in turntables and records.]
Proprietor of Croak Audio Exploration.
Fair, not crazy, cash paid for turntables and tonearms from Rega, Linn and Thorens.          http://www.croak.co.za

Offline Steerpike

Re: Attenuation vs. 'Gain Control'
« Reply #18 on: July 15, 2018, 11:03:53 PM »
The volume knob on the AX-5's front panel controls a pair of enormous, motor-driven, Shallco silver-contact rotary switches, each of which contains dozens of hand-selected, low-noise resistors. Every volume-level adjustment made by the user has the effect of switching into the AX-5's input-stage circuit a different set of resistors, the values of which alter the transconductance of those JFETs—

^^^ There's where the mumbo-jumbo enters.

Variable transconductance amplifiers are REALLY old hat... Leon Theremin was using them in his musical instruments in the 1920s. And vari-u valves have been used in just about every AM radio since the start of time.

The way a transconductance amplifier's gain is changed is by varying a fixed DC bias current through a specific transistor (or valve) configuration. To this end, the "quality" of that control signal is irrelevant (as long as it isn't seriously noisy). You don't need a magically high-end rotary switch with resistors touched by the Pope, because that is only valid if you are putting the actual audio signal through such  components: in this case they claim to be putting only the control signal through the Holy Rotary Switch of Antioch.

Variable transconductance amplifiers are less linear than an equivalent circuit with fixed transconductance, so they are not the ultimate in audio building blocks - they just solve one specific requirement, at the expense of some others.

Offline El Sid

Re: Attenuation vs. 'Gain Control'
« Reply #19 on: July 17, 2018, 08:43:26 AM »
"the Holy Rotary Switch of Antioch"

:ROFLMAO: :ROFLMAO:

Offline Nidri

Re: Attenuation vs. 'Gain Control'
« Reply #20 on: July 25, 2018, 10:04:33 PM »
This is Sugden's take:

"The DAP-800’s analogue stage features what Sugden calls a ‘VCV’ (Voltage Controlled Volume) circuit, which first featured in its Masterclass amps, and is seen here in its latest and most developed form. This circuit has a high impedance input section and a current gain stage, which drives a folded cascode stage into a Class A output stage. The folded cascode circuit facilitates a wide bandwidth with maximum dynamics and low capacitive connectivity. The volume control does not attenuate the signal; instead it ‘informs’ the current gain stage of the correct volume level. This means the tonal balance is constant irrespective of the output level, as opposed to most potentiometers and even ladder resistor array active volume controls."

http://www.hifiplus.com/articles/sugden-sapphire-dap800-preamp-and-fba-800-power-amplifier/
https://www.sugdenaudio.com/dap-800-digital-analogue-pre-amplifier