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Unity-gain "amp" for high-efficiency speakers
Unity-gain "amp" for high-efficiency speakers
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Old 21st January 2021, 07:25 PM   #21
MarsBravo is offline MarsBravo
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Quote:
Originally Posted by mudihan View Post
I believe the calculator assumes that Vmin would be negative 5.7v, i.e., Vmax is half of Vpp.
Wrong assumption by the calculator. There is no negative 5.7V. Calculators are not to believe in.

Quote:
Originally Posted by mudihan View Post
See attached.
The output is approx 6Vtt -> 3Vt -> 2Vrms.
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Old 22nd January 2021, 06:57 AM   #22
mudihan is online now mudihan  United States
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Thanks all. I built an amp with OPA548 at unity (i.e., connecting output to inverting input), and although the sound was good, it was not loud enough for classical solo music (i.e., no loudness war there). My room is about 18' by 26' and 10', and the speakers a bout 15' away from me. I think I may need 2x to 5x voltage gain.
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Old 22nd January 2021, 11:20 AM   #23
MarsBravo is offline MarsBravo
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Try a bridge (#8) first, twice the voltage swing, four times the power (if current reservoir is sufficient).
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Old 22nd January 2021, 11:30 AM   #24
indra1 is online now indra1  Indonesia
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Or configure the OPA548 to give desired gain using appropriate feedback.
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Old 22nd January 2021, 11:34 AM   #25
Rodeodave is offline Rodeodave  Austria
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Unity-gain &quot;amp&quot; for high-efficiency speakers
The First Watt F4 is just that, a power buffer. Check out the manual for a full schematic:
FIRST WATT

PCBs and Mosfets are available from the diyaudiostore.
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Old 22nd January 2021, 12:40 PM   #26
marconi118 is offline marconi118  Germany
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Quote:
Originally Posted by MarsBravo View Post
Try a bridge (#8) first, twice the voltage swing, four times the power (if current reservoir is sufficient).
To do a bridge you need an inverted phase with an additional inverter buffer

If your DAC has symmetric balanced outputs 2x 2vrms you are good to go.
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Old 23rd January 2021, 01:14 AM   #27
mudihan is online now mudihan  United States
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Originally Posted by marconi118 View Post
To do a bridge you need an inverted phase with an additional inverter buffer

If your DAC has symmetric balanced outputs 2x 2vrms you are good to go.
Unfortunately it's just plain singled-ended 2vrms.
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Old 23rd January 2021, 02:26 AM   #28
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Unity-gain &quot;amp&quot; for high-efficiency speakers
Quote:
Originally Posted by mudihan View Post
Thanks all. I built an amp with OPA548 at unity (i.e., connecting output to inverting input), and although the sound was good, it was not loud enough for classical solo music (i.e., no loudness war there). My room is about 18' by 26' and 10', and the speakers a bout 15' away from me. I think I may need 2x to 5x voltage gain.
Since you are looking for some gain, and given all the Class A suggestions by other folks, you should look at Diegomj’a DLH amp. Really a superb sounding amp. I actually built it based on his schematic before he even tested it. It has about 12w and a superb harmonic distortion profile that’s adjustable for relative H2/H3.

Really simple and few parts too.

There are Gerbers and iron on transfer PDFs available.

Here was my home etched version using a Sharpie for acid resist:
Click the image to open in full size.

The Sharpie etch worked so well I had to do a proper iron on transfer etch:
Click the image to open in full size.

But look at the measurement at 2.83v:
Click the image to open in full size.
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