Today I received the SMPS power modules and SMPS powered tube amp. Tubes are 6N3+6P1. It could be used as headphone amplifier as well as 3W small power amplifier. The first impression it's light weight. Don't have time to listen to it. Pics first. I will post more testing result later.
Attachments
Frequency Response
Sorry for so late. It's a time cost work to measure and adjust and measure and adjust. Now we are sure the R2 is in it's best condition. We are also sure it's the best status for a low cost 6P1 tube.
This design has no feedback from the output of the transformer. So the quality of transformer is important for the bandwidth. See the following result:
Instrument: HP3563A
Load: 8 Ohm
Signal Level: about 3V RMS
Sweep Freq: 10Hz to 100KHz
According to the curve, the amp has a very flat freq response between 40Hz to 20KHz, swing less than 1dB. 3dB bandwidth is 25Hz to 35KHz.
Sorry for so late. It's a time cost work to measure and adjust and measure and adjust. Now we are sure the R2 is in it's best condition. We are also sure it's the best status for a low cost 6P1 tube.
This design has no feedback from the output of the transformer. So the quality of transformer is important for the bandwidth. See the following result:
Instrument: HP3563A
Load: 8 Ohm
Signal Level: about 3V RMS
Sweep Freq: 10Hz to 100KHz
An externally hosted image should be here but it was not working when we last tested it.
According to the curve, the amp has a very flat freq response between 40Hz to 20KHz, swing less than 1dB. 3dB bandwidth is 25Hz to 35KHz.
Distortion
The distortion is tested at 1KHz, 8Ohm, 0.5W, 1W, 2W and 3W output power. THD is kept less than 1.8% when the output power is less than 3W. It goes high rapidly when the power is above 3W.
1.275% @ 0.5W
1.45% @ 1W
1.34% @ 2W
1.95% @ 3W
The distortion is tested at 1KHz, 8Ohm, 0.5W, 1W, 2W and 3W output power. THD is kept less than 1.8% when the output power is less than 3W. It goes high rapidly when the power is above 3W.
1.275% @ 0.5W
An externally hosted image should be here but it was not working when we last tested it.
1.45% @ 1W
An externally hosted image should be here but it was not working when we last tested it.
1.34% @ 2W
An externally hosted image should be here but it was not working when we last tested it.
1.95% @ 3W
An externally hosted image should be here but it was not working when we last tested it.
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Waveforms
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
SNR
I had thought the SNR would be high due to the switching mode power supply. To my surprise, the figure is even better than transformer powered amp, about 88dB!
I had thought the SNR would be high due to the switching mode power supply. To my surprise, the figure is even better than transformer powered amp, about 88dB!
An externally hosted image should be here but it was not working when we last tested it.
Listening
tested with a pair of full range with 91dB sensitivity. I don't know how to describ the listen due to my poor English. Just want to say it's the best small (<3W) tube amp I have ever heard. Human voice is very sweet, treble is clear, bass is soft. I believe it could be better if replace 6P1 with better tubes.
tested with a pair of full range with 91dB sensitivity. I don't know how to describ the listen due to my poor English. Just want to say it's the best small (<3W) tube amp I have ever heard. Human voice is very sweet, treble is clear, bass is soft. I believe it could be better if replace 6P1 with better tubes.
Comparing with transformer
We did a compare testing between SMPS and transformer.
Freq response: almost the same. slight higher (about 0.1dB) better than transformer.
Hum: Transformer has audiable hum at 20cm away from the speaker. SMPS may also has audiable hum, but I can't hear it even when my ear touched the speaker. Maybe a bat can hear it.
Distortion: SMPS has lower distortion, especially when the output power is close to 3W. SMPS is 1.85% while transformer is 3% when @3W 1KHz
SNR: 88dB vs 78dB, SMPS win
Sound quality: Similar in midrange and treble. But SMPS wins in Bass.
Weight: 4.2kg VS 2.5kg
We did a compare testing between SMPS and transformer.
Freq response: almost the same. slight higher (about 0.1dB) better than transformer.
Hum: Transformer has audiable hum at 20cm away from the speaker. SMPS may also has audiable hum, but I can't hear it even when my ear touched the speaker. Maybe a bat can hear it.
Distortion: SMPS has lower distortion, especially when the output power is close to 3W. SMPS is 1.85% while transformer is 3% when @3W 1KHz
SNR: 88dB vs 78dB, SMPS win
Sound quality: Similar in midrange and treble. But SMPS wins in Bass.
Weight: 4.2kg VS 2.5kg
- Status
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