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Old 13th February 2012, 11:59 PM   #371
Wolfsin is offline Wolfsin  United States
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Perhaps what ticknpop meant was that measuring noise with no signal would be as good as under resistive load. Please, if that is the case then let me know so I can skip ahead, build the whole thing and measure later.
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Old 14th February 2012, 03:20 AM   #372
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Default JC-80 gain adjustments

Here's some info on the gain of JC-80 board

"The default gain of JC-80 is around 14. The gain can be adjusted by altering the feedback resistors R17 to R20 simultaneously as JC-80 has a symmetry structure. Basically it is a ratio of R18/R30 but there is constraint since when R30 is changed the operating current will be changed too."

This can surely be useful for all of us using this board
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Old 14th February 2012, 10:38 AM   #373
AndrewT is offline AndrewT  Scotland
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I would expect the noise output of a power amplifier to be
Quote:
"Noise : <0.1mV"
i.e. <100uVac, over the 20Hz to 20kHz bandwidth.

The noise from a source component should be at least 12dB and preferably more than 24dB quieter than that, over the same bandwidth, i.e. <25uVac and preferably <6uVac.
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Old 14th February 2012, 12:02 PM   #374
Wolfsin is offline Wolfsin  United States
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Default Is Kubota quiet enough?

Thank you, Andrew. Now we may be getting somewhere. The Chorbely is advertised as having "Output residue noise <50uV(20Hz-20KHz)" compared to "Noise : <0.1mV" for the Kubota, both falling considerably short of the standard you suggest. And it may be that neither is up to what is needed.

Fortunately the choice of regulator is highly modular in the power chain and thus particularly amenable to testing but if the Kubota can be rejected now, great. We will soon have participants with regulators ranging from genuine Borbely through Chorbely to Kubota. The SuperTeddyReg has repeatedly been suggested but I have no comparative noise measurement for it. Perhaps we should consider a pair of beefy 24vDC batteries as well. Anybody know the noise levels for 1)genuine Borbely, 2)SuperTeddyReg, and 3)truck or solar batteries?
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Old 14th February 2012, 12:24 PM   #375
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If you're going to use batteries you'll want LiFePO4 cells for minimum noise on output.
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Old 14th February 2012, 01:06 PM   #376
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Wolfsin View Post
The Chorbely is advertised as having "Output residue noise <50uV(20Hz-20KHz)"
Apply the gain of a +28dB power amp and you have <1250uVac of noise at the speaker.
For a 50w Amplifier that is just -84dB ref. max power.
That would be atrocious in my book.
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Old 14th February 2012, 01:16 PM   #377
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Quote:
Originally Posted by AndrewT View Post
Apply the gain of a +28dB power amp and you have <1250uVac of noise at the speaker.
For a 50w Amplifier that is just -84dB ref. max power.
That would be atrocious in my book.
But we're not talking about power amps in this thread so you said is not relevant.
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Old 14th February 2012, 01:18 PM   #378
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Quote:
Originally Posted by Wolfsin View Post
Thank you, Andrew. Now we may be getting somewhere. The Chorbely is advertised as having "Output residue noise <50uV(20Hz-20KHz)" compared to "Noise : <0.1mV" for the Kubota, both falling considerably short of the standard you suggest. And it may be that neither is up to what is needed.

Fortunately the choice of regulator is highly modular in the power chain and thus particularly amenable to testing but if the Kubota can be rejected now, great. We will soon have participants with regulators ranging from genuine Borbely through Chorbely to Kubota. The SuperTeddyReg has repeatedly been suggested but I have no comparative noise measurement for it. Perhaps we should consider a pair of beefy 24vDC batteries as well. Anybody know the noise levels for 1)genuine Borbely, 2)SuperTeddyReg, and 3)truck or solar batteries?
You're forgetting that the line stage circuit has some kind of power supply rejection ratio which would reduce the effects of power supply noise. A good op amp has a PSRR of 100 dB! So, that "noise" from the power supply is comprised of ripple and a small amount of random hiss. This will be attenuated by 100dB by the line stage, if it's a good one.

Last edited by dirkwright; 14th February 2012 at 01:24 PM.
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Old 14th February 2012, 01:54 PM   #379
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Quote:
Originally Posted by hochopeper View Post
If you're going to use batteries you'll want LiFePO4 cells for minimum noise on output.
I believe that even these high performance batteries have higher source impedance than a good power supply regulator. Even large capacitors with low ESR have more source impedance than a good regulator.
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Old 14th February 2012, 01:56 PM   #380
AndrewT is offline AndrewT  Scotland
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Dirk,
are you deaf?

A source that has an output noise of 0.1mVac 20Hz to 20kHz is atrocious.

Apply that to a headphone or to a power amp or to any subsequent music replaying system and the signal to noise ratio is unacceptable.
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