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rajapruk
212
Mar 18, 2018
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What input-levels can be taken before clipping XLR-input? 22dBu "pro" input level OK?
AndrewMason
558
THX Ltd. Analog & Power Engineering Expert
Mar 19, 2018
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rajaprukHi Rajapruk. In "gain 1" (0 dB) setting, you can input up to +19 dBu or 7 Vrms without clipping. That's pretty close to "pro" level.
L-Train
3
Mar 20, 2018
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AndrewMasonHi Andrew, is it possible that this specification will improve before the amps ship? I had joined this drop because the amp looked to be the perfect complement to my Lynx Studio E44 (which has selectable +8.23 dBu or +20 dBu full scale output), and was hoping to use +20 dBu to maximize signal to noise. Given this amp's technical accuracy it would fit right into a studio environment, and I'm sure there are others who have joined this drop with the intention of using it in a professional setting.
rajapruk
212
Mar 20, 2018
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L-Train+1
It would be very nice if it could handle +22dBu. My dac can only output +22dBu.
(BSS Blu-160 with dac-cards)
AndrewMason
558
THX Ltd. Analog & Power Engineering Expert
Mar 20, 2018
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rajapruk@L-Train @rajapruk satisfying all use cases is tough. Even with a sample space of 2 users, we see a difference in requested input sensitivity. No guarantees we can/will change it, but what does the community propose the 3 gain & sensitivities should be?
Given that: 1) The front switch has only 3 gain positions. Each has corresponding sensitivity. So you can't choose gain & sensitivity independently. 2) The amp output voltage in single-ended is ~7 Vrms. 3) The architecture doesn't permit gain much lower than 0dB... we might be able to squeeze down to -3 dB minimum. And we presume many users want a 0 dB (1 V/V) gain position to make good use of the volume pot. 4) This amp will be driving all types of headphones incl sensitive IEMs, planars, and high impedance e.g. HD6xx. 5) This amp will be used with a variety of DACs. 6) Most DACs with studio level output have a lower output voltage setting too. And this often has lower THD, at expense of slightly worse SNR.
Given that: 1) The front switch has only 3 gain positions. Each has corresponding sensitivity. So you can't choose gain & sensitivity independently. 2) The amp output voltage in single-ended is ~7 Vrms. 3) The architecture doesn't permit gain much lower than 0dB... we might be able to squeeze down to -3 dB minimum. And we presume many users want a 0 dB (1 V/V) gain position to make good use of the volume pot. 4) This amp will be driving all types of headphones incl sensitive IEMs, planars, and high impedance e.g. HD6xx. 5) This amp will be used with a variety of DACs. 6) Most DACs with studio level output have a lower output voltage setting too. And this often has lower THD, at expense of slightly worse SNR.
rajapruk
212
Mar 20, 2018
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AndrewMasonI double-checked my BSS dac cards, and they are actually +19dBu maximum output. I was wrong about +22dBu.
So I am perfectly happy with the current design! Sorry for any inconvenience.
rajapruk
212
Mar 20, 2018
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rajaprukAnother thing I would like is full potentiometer bypass, if possible. I will not use the volume control.
But my use-case is not the normal one. I want to try it as amp for a 16ohm compression-driver in a horn.
L-Train
3
Mar 21, 2018
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AndrewMasonThanks for the reply Andrew. I'm quite okay with the current gain settings, and totally agree that the minimum setting should be unity/0 dB.
I suppose then that the +19 dBu maximum input signal is due to the input being buffered prior to attenuation (in a manner similar to Bruno Putzeys' balanced volume controller or otherwise), and is therefore limited by the supply voltage? If so, I would have instead liked to see a 28V or 30V supply being used for greater head room, but given the ubiquity of 24V power supplies and the cost increases associated with using a higher supply voltage I understand the design choice.
I suppose then that the +19 dBu maximum input signal is due to the input being buffered prior to attenuation (in a manner similar to Bruno Putzeys' balanced volume controller or otherwise), and is therefore limited by the supply voltage? If so, I would have instead liked to see a 28V or 30V supply being used for greater head room, but given the ubiquity of 24V power supplies and the cost increases associated with using a higher supply voltage I understand the design choice.
pospos
70
Mar 21, 2018
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AndrewMason0dB is fine as a minimum gain setting, but it is +6dB gain on the balanced output which is a bit hot.
It results in a +13dBu sensitivity, and even only +10dBu for a 16 ohms load.
Would it be feasible to have the same gain settings on the SE and balanced outputs?
Would it be feasible to have the same gain settings on the SE and balanced outputs?
hifiZen
10
Mar 24, 2018
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AndrewMasonEven with my least-sensitive phones (Sennheiser HD-600) and 0dBu line level in, I generally run my amps at 0dB gain... I don't listen at insane SPLs, and I prefer to minimize attenuation in the signal chain. So yes to point #3 exactly. An even lower gain setting would be welcome with me, for use with sensitive IEMs.
Speaking of attenuation, I wonder what kind of volume potentiometer will be used, and whether there will be room inside for those of us who are DIY-inclined to swap it out for something higher-end like the TKD CP2500 series? If PCB-mounted, that probably precludes the possibility of swapping for mechanical reasons. However, it seems to me that such high-performance active circuitry deserves to be paired with first-rate passives, in particular the volume pot, where tracking, rotation noise, etc. can play a significant role in the overall performance.
Speaking of attenuation, I wonder what kind of volume potentiometer will be used, and whether there will be room inside for those of us who are DIY-inclined to swap it out for something higher-end like the TKD CP2500 series? If PCB-mounted, that probably precludes the possibility of swapping for mechanical reasons. However, it seems to me that such high-performance active circuitry deserves to be paired with first-rate passives, in particular the volume pot, where tracking, rotation noise, etc. can play a significant role in the overall performance.
hifiZen
10
Mar 24, 2018
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hifiZenHmm, I missed your earlier response to a similar question: "I don't think we're going to reveal much regarding the volume pot. It's special." ... Fair enough, it seems obvious that this needs to be true in order to meet the stated performance. So I'll take your word for now, and look forward to seeing what you deliver. :)
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