Amount of volts needed to use Purifi amp without buffer

[thanossapiens]

Hi guys,
this is probably really simply but just to be sure I want some confirmation.
This amp has 12.8db of gain which is roughly 20x.
So, if my speakers can take a maximum of 50 watts at 6 ohms, then a 4 volt output from a dac(which is normal for XLR), will be enough, I assume?
Since 4 volts at 6 ohms is 2.6watts, which will become ~52 after passing through the amp?
Or is my logic completely flawed?
Thanks

 

[restorer-john]

If the amplifier has 12.8dB of gain, it has a voltage gain of 4.37 times.
So, if you input 4 Volts, you will get out 17.46 Volts.
17.46 Volts over 6 ohms is only 50.81 Watts.

To obtain the full rated power (425W@4R/1% THD) of the module without a buffer, you'd need a preamplifier capable of swinging 13.34V RMS or 37.74V peak to peak. I know of a small number of traditional preamplifiers capable of that. Most preamplifiers have internal rails of +/-12V to +/-15V and top out around 8-10V RMS.

The module should not be used without a buffer as its input impedance is also too low as it stands. 2.2k SE or 4.4k Bal.

 

[thanossapiens]

Thanks for your reply.
I guess a 6 volt dac with a 100 ohm output, like the Gustard A18, ought to be enough then? I have seen people here say that a 10x difference in impedance is enough, and its double of that, in this case.

 

[VintageFlanker]

May I ask what is the point to use 1ET400A modules without buffer, anyway?

Your "50W/6Ohms" don't work by the way, since there is no "6Ohms" speakers whatsoever.

 

[thanossapiens]

It just sounds more appealing to remove an extra part if it's not needed

 

[restorer-john]

Your "50W/6Ohms" don't work by the way, since there is no "6Ohms" speakers whatsoever.

His speaker is a 6R nominal impedance. There are, and have been plenty of 6R nominal rated loudspeakers. I have several myself.

 

[VintageFlanker]

There are, and have been plenty of 6R nominal rated loudspeakers. I have several myself.

Rated, sure. But how many "real" 6 Ohms nominal impedance (IEC)?

 

[thanossapiens]

Anyways, amount of watts aside, is this actually a bad idea? If its like 100 ohms, wouldn't it be "better"(even if unhearable), since an extra component will be eliminated?

 

[VintageFlanker]

Anyways, amount of watts aside, is this actually a bad idea? If its like 100 ohms, wouldn't it be "better"(even if unhearable), since an extra component will be eliminated?

Measurably, yes. But you can't hear any difference between this:

And this:

... Not to mention your DAC doesn't output enough voltage as @restorer-john said. Whatever max power handling or impedance, you will just need this extra gain with the Gustard.

 

[thanossapiens]

... Not to mention your DAC doesn't output enough voltage as @restorer-john said. Whatever max power handle ot impedance, you will just need this extra gain with the Gustard.

You mean even a 6 volt one wouldn't be enough?

 

[NTK]

Just go ahead and try it. At least the LME49860 opamps can drive down to 600 ohm.