The ZD25-Mini (aka. the Holy Grail Follower).
The ZD25 is an amplifier I built that is similar to the Pass Labs XA25, that was discussed in the "F4 Beast Builders" thread: https://www.diyaudio.com/community/threads/f4-beast-builders.300233/post-4907053.
The ZD25-Mini is a simplified, lower power implementation of the ZD25 output stage.
Implementation:
The amplifier combines three experiments (for me):
This is a FirstWatt scale amplifier with a PCB that conforms to the diyAudio UMS and can operate with either linear or switching power supplies with +/-23V to +/-27V rails. The output stage FETs are not degenerated which has the benefits described in the Nelson Pass article "Art of the Square Law": https://firstwatt.com/pdf/art_the_square_law.pdf.
Specifications: (as configured Jan 16, 2024)
The ZD25 is an amplifier I built that is similar to the Pass Labs XA25, that was discussed in the "F4 Beast Builders" thread: https://www.diyaudio.com/community/threads/f4-beast-builders.300233/post-4907053.
The ZD25-Mini is a simplified, lower power implementation of the ZD25 output stage.
Implementation:
The amplifier combines three experiments (for me):
- The optocoupler bias circuit described in post #1.
- Using a opa551 high voltage opamp for the front end, thanks to EUVLs “The M2 Output Stage in Class A/B, and maybe a Power WHAMMY?” thread
- Use of inexpensive SMPS for the power supplies. A regular linear supply would be fine, but cost more and be heavier. More about this later.
This is a FirstWatt scale amplifier with a PCB that conforms to the diyAudio UMS and can operate with either linear or switching power supplies with +/-23V to +/-27V rails. The output stage FETs are not degenerated which has the benefits described in the Nelson Pass article "Art of the Square Law": https://firstwatt.com/pdf/art_the_square_law.pdf.
Specifications: (as configured Jan 16, 2024)
- Voltage Gain: 22dB
- Global Feedback: 12dB
- Distortion: THD <0.01% at 1W, THD < .05% at 25W
- Input Impedance: 46K
- Damping Factor: 120
- Frequency Response: 1Hz to -3dB @270 kHz.
- Power Dissipation: 60W-70W per channel
- Noise: below 100uV
I tried IRFP140/9140 and IRFP240/9240. Both exhibited the IRF P-channel problems that Nelson has described in the past.
I happened to have the Fairchild FQA28N15 and FQA36P15 FETs in stock so I tried them and they look very good for this output stage.
I have on order some IXYS IXTQ36N30P and IXTQ36P15P FETs that I will also try.
I really want to use FETs that are in current production.
Do you have other suggestions?
I happened to have the Fairchild FQA28N15 and FQA36P15 FETs in stock so I tried them and they look very good for this output stage.
I have on order some IXYS IXTQ36N30P and IXTQ36P15P FETs that I will also try.
I really want to use FETs that are in current production.
Do you have other suggestions?
https://www.diyaudio.com/community/threads/complementary-power-mosfets.378024/post-6889027
Only for your reference.
Patrick
Only for your reference.
Patrick
What I have posted so far is work in progress. There are many component options parameter values that can be tuned.
What I found amazing is how the amplifier sounds and measures. I keep rechecking my instrumentation because the measurements seem unbelievable.
In future posts, there are three major subtopics to discuss:
What I found amazing is how the amplifier sounds and measures. I keep rechecking my instrumentation because the measurements seem unbelievable.
In future posts, there are three major subtopics to discuss:
- Performance of the magic-modified optocoupler bias circuit. Hint: It works as predicted in simulations.
- Performance of the opamp front-end.
- Performance of the SMPS supplies. Hint: No filters (except to RC filter at opamp) and I cannot detect SMPS noise.
Yes, I the SMPS noise is very low without serious filtering.
- Output stage has good PSRR
- RC filters at the opamp
- Careful star grounding
- opamp common-mode rejection by RCA shield ground-loop breaker resistor.
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