Semmyroundel,
Both Alan and Jim T are right.
But we don’t know enough about your system overall, particularly your source (is it 2V RMS or more?), your speaker’s overall efficiency, your listening position/distance from the speakers and your listening habits (ie how LOUD do you listen, in SPL; you can use a mobile phone app to measure this).
Even without knowing all of those details, my recommendation would be to have a preamp with a minimum gain of 6dB around. It will work great as not all recordings (from your source, assuming digital) is at 0dB fs (max volume). You will have some “quieter” recordings too that you need to compensate for.
Best,
Anand.
Both Alan and Jim T are right.
But we don’t know enough about your system overall, particularly your source (is it 2V RMS or more?), your speaker’s overall efficiency, your listening position/distance from the speakers and your listening habits (ie how LOUD do you listen, in SPL; you can use a mobile phone app to measure this).
Even without knowing all of those details, my recommendation would be to have a preamp with a minimum gain of 6dB around. It will work great as not all recordings (from your source, assuming digital) is at 0dB fs (max volume). You will have some “quieter” recordings too that you need to compensate for.
Best,
Anand.
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The output from the phone fluctuates a bit but on average 0.37v.
Out ACA without speakers 1.4v.
Out ACA with speaker 1.17v.
This gives an amplification of 3.2 and not that far from your 3.6 and probably well within measurement uncertainty.
So I guess the conclusion is that my ACA is OK which is good news.
I connect the ACA to my desk speakers and used my phone as input. Really low output. Then I used the output on my pc (not laptop) and that changed everything. Suddenly I got a sound level that was usable.
So... how do I know if a preamp is usable?
How much gain is required?
None of my present gear works and I before buying (or building) a preamp I would like to be sure I am doing the right thing.
A nice sunday to all you ACA'ers
Glad to know you are a bit better.
Yes your figure of 3.2 is spot on. It is working fine.
The pre-amp question is difficult to answer with a ''get this one'' recommendation. It will depend on your source in the first place and what voltage it gives out.
Both my CD player and Squeezebox have 2 volt outputs. Neither is enough to drive the ACA to near full volume.
But you only need a small amount of extra gain. 2 times(6dB) or 3.2 times(10dB) are fine. (Just make sure it is not a buffer or unity gain stage, it has to have gain.)
I have tried several types, Naim, NAD, valves etc, they all give enough to get to clipping and sound fine. At this moment I have a 'Death Of Zen' in there http://sound.whsites.net/project37.htm , I really like it with the ACA. (It was a junk box find too! Just needed a case and power TX.)
Next though I am collecting parts for a MooseFet to try that e0ltaipa spoke about. DIY Audio Projects Forum • MooseFET Preamplifier It is a very simple design just like the ACA. And it might be able to share the 24 volt power from the ACA brick...
Alan
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Thank you Mooly.
Another question...
I used to have class B and D amplifier and they used to be warm. I estimate their temperature used to be about 45-50 Celsius.
I have the CA powered up for about 30-40 minutes and it is really hot (it was getting hotter and hotter with every minute). It is hard for me to say, how much, but i think it is more like 70-80 Celsius now. Is that normal?
Cheers,
Max
Another question...
I used to have class B and D amplifier and they used to be warm. I estimate their temperature used to be about 45-50 Celsius.
I have the CA powered up for about 30-40 minutes and it is really hot (it was getting hotter and hotter with every minute). It is hard for me to say, how much, but i think it is more like 70-80 Celsius now. Is that normal?
Cheers,
Max
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Absolutely normal for it to run really hot. That is one of the downsides of Class A
To be sure all is well you can measure the voltage across R1 and R2 (both 0.47 ohms). You should have approx. 0.375v across each which if you calculate the current using ohms law will be around 0.8 amps per resistor and 1.6 A total current draw.
Be careful not to short anything out if you check this.
To be sure all is well you can measure the voltage across R1 and R2 (both 0.47 ohms). You should have approx. 0.375v across each which if you calculate the current using ohms law will be around 0.8 amps per resistor and 1.6 A total current draw.
Be careful not to short anything out if you check this.
and confirms the amp is not drawing to much current. Thanks Alan, but they are still mono apart from the basic 8watts stereo version.
I haven't measured them exactly, but I assume that all inputs are line level (around 2v), my speakers are 8 ohms.
The target speakers are either Qacoustics concept 20's or Mordaunt short pageant series 2 (which I'm redesigning the cabinets for).
The Pageants are around 93db/95db, and the concept 20's around 85db, BUT I didn't want to be tied to any particular speaker, though for the purposes of these questions, I understand I need to be at least for now
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semmyroundel and Toaster
Yes you are both sort of correct... but
The normal method of quoting sensitivity is by 1 Watt per 1 Metre. (8 ohms, 1 kHz etc., etc.)
Mordaunt Short used their own method (for the Pageants and Festivals anyway) quoting 96dB at 1 metre but at 5.6 Watts. No idea why or perhaps it was marketing.
What it does mean though is they are not going to be Tannoy or Klipsh 'loud' for the same 1 Watt input.
Alan
Yes you are both sort of correct... but
The normal method of quoting sensitivity is by 1 Watt per 1 Metre. (8 ohms, 1 kHz etc., etc.)
Mordaunt Short used their own method (for the Pageants and Festivals anyway) quoting 96dB at 1 metre but at 5.6 Watts. No idea why or perhaps it was marketing.
What it does mean though is they are not going to be Tannoy or Klipsh 'loud' for the same 1 Watt input.
Alan
Thanks Jim, just wondering though why they changed it, would the extra gain cause clipping?
I mentioned the O2 in a previous post as I use this with the ACA. The O2 has a selectable gain switch on the front panel, and you can configure this by choosing which resistors to fit when you build it (all the various gain settings are catered for if you buy as a kit from HeadnHiFi).
Many thanks, I'll look into that. I don't need blasting out sound, but I do like my rock, and that largely requires power. Samsara Blues Experiment just doesn't sound right weakly delivered....
I'm very happy with it. I listen to everything from classical to reggae, heavy metal and electronica to folk and it works perfectly with the ACA. Having the selectable gain on the front is a help as I find some recordings need the lower gain (primarily modern loudness mastered music). I think I have it set to x2 and x6 gain.
Sorry, I'm a novice so can't comment on the suitability of something I haven't tried.
If you have the Cmoy's already, why not swap the headphone jack for RCA jacks and swap the R3 resistor to 2K ohms to get x6 gain. Have a look at Tangents website for more info.
If you have the Cmoy's already, why not swap the headphone jack for RCA jacks and swap the R3 resistor to 2K ohms to get x6 gain. Have a look at Tangents website for more info.