After building my first tube amp (https://www.audiosciencereview.com/forum/index.php?threads/building-a-valve-amplifier.29903/ ; https://www.audiosciencereview.com/...ow-one-diy-kt88-amplifier.39332/#post-1468245 ) a friend of mine listened to it and said he wanted it. But being a prototype, I did not want to give it to him as it was and we decided that I will build a new one fro him. I took this occasion to try and improve on the existing design and I really wanted to test other tube manufacturers as many people from audiophile groups said that the JJ tubes I used are miserable. I was a bit skeptical as the measurements clearly showed that the amplifier performs more than OK. And almost all the time these audiophile characters start mentioning sound stage and instrument isolation and all sorts of words and expressions that have nothing to do with real measurements. Nevertheless, I really wanted to test other tube manufacturers. Most of the recommendations were for Gold lions but due to the political situation with Russia, it was, and still is, almost impossible to get Gold Lion KT88s. So I kept searching and I found a shop here locally that had a quartet of PSVANE KT88s for AIRAND amplifiers. PSVANE was one of the recommendations as well, albeit the more expensive ones. So for this built I used the following tube: 2x PSVANE 12AX7 for the input, 2x Electro Harmonix 12AU7 for the drivers and 4x PSVANE KT88s.
Inside the amplifier I modified the power supply PCB in order to fit all the auxiliary voltages so that I will no longer need extra toroidal transformers inside the amp. The power transformer was custom made by Toroidy and the output ones were the same as the original built. As a side note, the PSVANE KT88s are considerably less well built that the JJ ones. The JJs are heavier and the glass is thicker and seem a lot better built. We will see how the measurements look but from the bulit quality, the JJs are defenetly better made.
On the inside, I modified the power supply but the power amplifier boards remained the same. I used Mondorf MCap EVO Oil capacitors on the signal path but I do not expect to hear/see any differences in sound quality. Another difference is that I decided to use an opamp active gain stage before the power amps. I did this so that I can use a 10k pot instead of 50k or 100k and to be able to amplify the signal in order to reach full output power. The active gain stage can qo from -75dB to 10dB. Another difference is that I decided to not use DC filament (6.3V) voltages as I did not see the need for these.
The enclosure is from MODUSHOP but we decided to use a 10mm front plate instead of the 4mm one I used for the first proto.
I will start the measurements with the 1kHz, 1W into 8OHM:
5W into 8OHM:
Frequency response:
10kHz, 1W into 8OHM:
100Hz, 1W into 8OHM:
1kHz + 10kHz tones:
100Hz + 5kHz @ 1W:
As a conclusion, I have to say that a THD of -82dB for 1W into 8OHM is really good for a tube amp. The first prototype using JJ tubes achieved a very respectable -77dB but it seems that the PSVANE tubes perform a bit better. The improvement is seen across the measurements.
As the B+ voltage was increased to around 400Vdc, the max output power is around 30W per channel with a THD < 1%. It can output 28W with a THD of 0.1%. The bias current is ~45mA.
From the sound point f view, it sound really nice. Clear and with plenty of details. This is in accordance with the measurements. I do not hear any "warmth" that so many refer to when describing tube amps. In conclusion: great success
Inside the amplifier I modified the power supply PCB in order to fit all the auxiliary voltages so that I will no longer need extra toroidal transformers inside the amp. The power transformer was custom made by Toroidy and the output ones were the same as the original built. As a side note, the PSVANE KT88s are considerably less well built that the JJ ones. The JJs are heavier and the glass is thicker and seem a lot better built. We will see how the measurements look but from the bulit quality, the JJs are defenetly better made.
On the inside, I modified the power supply but the power amplifier boards remained the same. I used Mondorf MCap EVO Oil capacitors on the signal path but I do not expect to hear/see any differences in sound quality. Another difference is that I decided to use an opamp active gain stage before the power amps. I did this so that I can use a 10k pot instead of 50k or 100k and to be able to amplify the signal in order to reach full output power. The active gain stage can qo from -75dB to 10dB. Another difference is that I decided to not use DC filament (6.3V) voltages as I did not see the need for these.
The enclosure is from MODUSHOP but we decided to use a 10mm front plate instead of the 4mm one I used for the first proto.
I will start the measurements with the 1kHz, 1W into 8OHM:
5W into 8OHM:
Frequency response:
10kHz, 1W into 8OHM:
100Hz, 1W into 8OHM:
1kHz + 10kHz tones:
100Hz + 5kHz @ 1W:
As a conclusion, I have to say that a THD of -82dB for 1W into 8OHM is really good for a tube amp. The first prototype using JJ tubes achieved a very respectable -77dB but it seems that the PSVANE tubes perform a bit better. The improvement is seen across the measurements.
As the B+ voltage was increased to around 400Vdc, the max output power is around 30W per channel with a THD < 1%. It can output 28W with a THD of 0.1%. The bias current is ~45mA.
From the sound point f view, it sound really nice. Clear and with plenty of details. This is in accordance with the measurements. I do not hear any "warmth" that so many refer to when describing tube amps. In conclusion: great success
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