Its amazing how a persons (mine anyway) thinking can do a complete 180. When I decided to re-pursue my audio interests after almost 2 decades, I brought with me the baggage of the 80’s. Specifically “The more power the better” line of thinking that went along with the efficiency of the better speakers of the era (my favorite speakers were the Celestion SL6’s and anything from the Apogee ribbon line, in the low 80’s in efficiency all ). Knowing that I eventually wanted to play around with some diy ribbons, I figured that if I was to do SE, I would have to go BIG with an 813 or two.

That all changed when I came across this thread…

http://www.diyaudio.com/forums/showthread.php?s=&threadid=50162

Bottom line, with the availability of extremely powerful “Rare Earth” magnets, ribbons in the 96-106 dB range can and have been made. Using the info and software mentioned in the thread, I have come up with a dual 36”x .75” design with a projected efficiency of 106dB@ 1W. I soon realized that 4 Watts behind this kind of efficiency is comparable too more than 400 Watts driving Apogee’s… I’ll take it .

Being a firm believer in the “simple as it can be” school of thought, I was really intrigued with the “spud” amps, particularly Brian Clark’s “el Spuddo” and Stefano Perugini’s “ST” amps. These guys really inspired me.

Without further ado, I give you the ” ‘Tater Patch”…

To be clear I have not made this amp yet, and I hope the collective wisdom here can point out any errors.

I intend to run my ribbons down to 100hz, so I need a sharp rolloff. The amp does double duty as a quasi 4th order highpass filter. By jiggering the coupling and de-coupling cap values I was able to get a progressively sharper rolloff with a 3db down point of 100 hz . As a bonus, this reduced the value of the cathode by-pass caps to the point that I don’t have to use electrolytic…beauty.

Simulating in LtSpice at 1 Watt gives this distortion breakdown…

Harmonic Frequency Fourier Normalized Phase Normalized

Number [Hz] Component Component [degree] Phase [deg]

1 1.000e+03 4.987e-01 1.000e+00 8.27° 0.00°

2 2.000e+03 2.681e-03 5.376e-03 -77.40° -85.67°

3 3.000e+03 1.095e-04 2.195e-04 17.35° 9.08°

4 4.000e+03 1.330e-05 2.667e-05 -156.88° -165.15°

5 5.000e+03 1.200e-05 2.407e-05 -140.97° -149.24°

6 6.000e+03 1.068e-05 2.142e-05 -135.54° -143.81°

7 7.000e+03 9.912e-06 1.988e-05 -131.01° -139.29°

8 8.000e+03 9.382e-06 1.881e-05 -127.15° -135.42°

9 9.000e+03 8.997e-06 1.804e-05 -123.80° -132.07°

Total Harmonic Distortion: 0.538053%

And at 4 Watts…

Harmonic Frequency Fourier Normalized Phase Normalized

Number [Hz] Component Component [degree] Phase [deg]

1 1.000e+03 9.951e-01 1.000e+00 8.32° 0.00°

2 2.000e+03 1.085e-02 1.090e-02 -76.94° -85.27°

3 3.000e+03 1.011e-03 1.016e-03 17.97° 9.64°

4 4.000e+03 2.964e-05 2.978e-05 139.86° 131.54°

5 5.000e+03 2.455e-05 2.467e-05 -123.78° -132.10°

6 6.000e+03 1.927e-05 1.936e-05 -111.98° -120.30°

7 7.000e+03 1.869e-05 1.878e-05 -108.80° -117.12°

8 8.000e+03 1.853e-05 1.862e-05 -106.48° -114.80°

9 9.000e+03 1.835e-05 1.844e-05 -104.44° -112.76°

Total Harmonic Distortion: 1.094966%

The 1Watt FFT , and the 4 Watt FFT show a nice harmonic progression that’s mostly second order.

As shown, the the tubes are running with 240V at the plates, -3.1V at the grids, and at 37.25mA .

Iv’e attached the Ltspice .asy file along with the files for the output transformer for Yvesm’s OPT Assistant in case anybody wants to play with them.

Ok, be brutal…let me know if/were I’m screwing up here, as well as any suggestions to improve on it.

Thanx,

Casey

That all changed when I came across this thread…

http://www.diyaudio.com/forums/showthread.php?s=&threadid=50162

Bottom line, with the availability of extremely powerful “Rare Earth” magnets, ribbons in the 96-106 dB range can and have been made. Using the info and software mentioned in the thread, I have come up with a dual 36”x .75” design with a projected efficiency of 106dB@ 1W. I soon realized that 4 Watts behind this kind of efficiency is comparable too more than 400 Watts driving Apogee’s… I’ll take it .

Being a firm believer in the “simple as it can be” school of thought, I was really intrigued with the “spud” amps, particularly Brian Clark’s “el Spuddo” and Stefano Perugini’s “ST” amps. These guys really inspired me.

Without further ado, I give you the ” ‘Tater Patch”…

To be clear I have not made this amp yet, and I hope the collective wisdom here can point out any errors.

I intend to run my ribbons down to 100hz, so I need a sharp rolloff. The amp does double duty as a quasi 4th order highpass filter. By jiggering the coupling and de-coupling cap values I was able to get a progressively sharper rolloff with a 3db down point of 100 hz . As a bonus, this reduced the value of the cathode by-pass caps to the point that I don’t have to use electrolytic…beauty.

Simulating in LtSpice at 1 Watt gives this distortion breakdown…

Harmonic Frequency Fourier Normalized Phase Normalized

Number [Hz] Component Component [degree] Phase [deg]

1 1.000e+03 4.987e-01 1.000e+00 8.27° 0.00°

2 2.000e+03 2.681e-03 5.376e-03 -77.40° -85.67°

3 3.000e+03 1.095e-04 2.195e-04 17.35° 9.08°

4 4.000e+03 1.330e-05 2.667e-05 -156.88° -165.15°

5 5.000e+03 1.200e-05 2.407e-05 -140.97° -149.24°

6 6.000e+03 1.068e-05 2.142e-05 -135.54° -143.81°

7 7.000e+03 9.912e-06 1.988e-05 -131.01° -139.29°

8 8.000e+03 9.382e-06 1.881e-05 -127.15° -135.42°

9 9.000e+03 8.997e-06 1.804e-05 -123.80° -132.07°

Total Harmonic Distortion: 0.538053%

And at 4 Watts…

Harmonic Frequency Fourier Normalized Phase Normalized

Number [Hz] Component Component [degree] Phase [deg]

1 1.000e+03 9.951e-01 1.000e+00 8.32° 0.00°

2 2.000e+03 1.085e-02 1.090e-02 -76.94° -85.27°

3 3.000e+03 1.011e-03 1.016e-03 17.97° 9.64°

4 4.000e+03 2.964e-05 2.978e-05 139.86° 131.54°

5 5.000e+03 2.455e-05 2.467e-05 -123.78° -132.10°

6 6.000e+03 1.927e-05 1.936e-05 -111.98° -120.30°

7 7.000e+03 1.869e-05 1.878e-05 -108.80° -117.12°

8 8.000e+03 1.853e-05 1.862e-05 -106.48° -114.80°

9 9.000e+03 1.835e-05 1.844e-05 -104.44° -112.76°

Total Harmonic Distortion: 1.094966%

The 1Watt FFT , and the 4 Watt FFT show a nice harmonic progression that’s mostly second order.

As shown, the the tubes are running with 240V at the plates, -3.1V at the grids, and at 37.25mA .

Iv’e attached the Ltspice .asy file along with the files for the output transformer for Yvesm’s OPT Assistant in case anybody wants to play with them.

Ok, be brutal…let me know if/were I’m screwing up here, as well as any suggestions to improve on it.

Thanx,

Casey