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Solo ULDE: Maximum Input Voltage?

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    Posted: 30 Apr 2019 at 3:24pm
Just a small curiosity here...

As a digital source I use the excellent Oppo BDP-105D player. I usually have it set at 100% volume (0 dB) because I prefer to regolate listening volume downstream in the chain, at the amplification stage (i.e. on the TV/Home theater if watching movies, or on the Solo if I am listening to music with the headphones).

The Oppo, when set at 100% volume, outputs a very solid 2.2 V RMS from the RCA outs.

I see in the Solo ULDE specifications that it has an input sensitivity of 511 mV RMS input, but of course this doesn't say anything about what the MAXIMUM allowed input is.

Personally I don't hear any clipping, and as I was saying once, when listening to CDs I rarely go beyond 1-2 o' clock on the Solo. But I'd really like a confirmation of that 2.2 V RMS being in a safe range for the input of the Solo not to clip.

Thanks!










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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2019 at 7:21pm
Rather deviously I put the volume pot on the input before the amp, and it will often suffice by adjusting it to personal taste, which is usually considerably lower than 511 mV.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lucabeer Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2019 at 7:48pm
Really? Wicked indeed! It's the first time I hear of such a design choice (usually I read about the volume control being at the END of the chain, to attenuate the amplification from its maximum value).

But now that you make me think of it, it definitely makes A LOT of sense: you actually adjust the input to a "standard" level via the volume control (thus avoiding clipping due to a "too hot" input) and then you apply the same gain regardless of the level of what comes in!

It's brilliant because in a conventional design you would get clipping, and then attenuate an already clipped signal until comfortable in level for listening... but it STILL would be clipped. This way, you avoid clipping from the beginning of the circuit!




Edited by Lucabeer - 30 Apr 2019 at 7:51pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 2019 at 8:10pm
Attenuating the input rather than the output would be more energy efficient too? Electronic components won't have to dissipate as much heat. (which may also help to prolong their working lifespan)

Edited by Ash - 30 Apr 2019 at 8:12pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lucabeer Quote  Post ReplyReply Direct Link To This Post Posted: 01 May 2019 at 12:52pm
Well, theoretically the most energy efficient solution would be not to attenuate neither the input nor the output, but to have a true variable amplification gain. But this would probably be a mess in terms of guaranteeing the same level of performance in terms of bandwidth, phase integrity and distortion: they would be variable according to playback volume, and this is not exactly a thing that a good designer would want.

But yes, attenuating the input is more efficient (in terms of energy wasted in thermal losses) than attenuating the output.

Viceversa, theoretically, this could also mean a worse S/N ratio, because if you attenuate a good healthy input to a lower level, you would then have to amplify it more than if you had left it at its original level. But I don't see it as a problem, when the noise floor in the Solo is already so low as to be not noticeable even at the insane volumes I listen to.


Edited by Lucabeer - 01 May 2019 at 12:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 01 May 2019 at 1:29pm
Yes, I was going to comment that the volume control does not have any effect on output noise. It will always be there irrespective of volume control setting.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lucabeer Quote  Post ReplyReply Direct Link To This Post Posted: 01 May 2019 at 1:54pm
Originally posted by Graham Slee Graham Slee wrote:

Yes, I was going to comment that the volume control does not have any effect on output noise. It will always be there irrespective of volume control setting.


It confirms what I hear (or rather, what I don't hear: the Solo is completely silent to me), and it definitely makes sense, since with the choice of attenuating the input the amplification gain remains the same.

BTW, if I did my maths correctly from the published specs (140mW max RMS output for 511 mV RMS input), the gain of the Solo ULDE at 32 Ohms is just a tad more than 4X (12 dB), right?

With even lower impedance phones (20-25 Ohm), how does it change? Is it still the same max mW output?






Edited by Lucabeer - 01 May 2019 at 1:54pm
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