I can't find anyone that supplies matched MOSFETs for amps like the Son of Zen.
I really want to build this amp because it's simple and has just enough power for me.
I refuse to buy 100 $4 MOSFETs to match 2. I want to buy 2. Even if I have to pay 5 times the price.
Digi-key does not sell them.
Any other suggestions?
Thanks,
Pixie
I really want to build this amp because it's simple and has just enough power for me.
I refuse to buy 100 $4 MOSFETs to match 2. I want to buy 2. Even if I have to pay 5 times the price.
Digi-key does not sell them.
Any other suggestions?
Thanks,
Pixie
For the Son of Zen, you need to get the mosfets as close as possible, but they don't need to be exact. Also, if my memory servers me correctly, you can adjust the value of the resistors.
I heard that if you find mosfets from the same batch of production, they will be very close. I think that a company like Digi-Key could help with finding simular batched mosfets. It's worth a try.
I copied part of the article for you below. Good luck!
The choice of power Mosfets for the gain devices is somewhat broader than those for the Zen amplifier. In general, any reasonably matched pair of power Mosfets will work, assuming that they meet the dissipation requirements of the circuit. I prefer to use the newer generation of Mosfets with higher transconductance figures and lower distortion than some of the early Mosfet parts. The actual Mosfets used in this project were IRFP240, simply because I have a good stock of them. It is also possible to use P channel Mosfets for the project, simply by reversing the polarity of the power supplies. I have tried it, and it works fine.
The matching of the Mosfets helps achieve low DC offset voltage as seen by the loudspeaker and also helps to lower the distortion. If you want to match your own devices, you can simply place them in the working circuit, noting their Gate-to-Source DC potentials with a multimeter, and matching devices for the same DC voltage. Alternatively, you can swap devices in and out until you get low DC offset at the output across the drains of the Mosfets. A procedure for matching Mosfets is also presented in the A75 amplifier project published in The Audio Amateur.
If you cannot manage to match your Mosfets, you can get some adjustment of the DC offset by placing resistors in parallel with R5 or R6. Start with trial values like 100 ohms
I heard that if you find mosfets from the same batch of production, they will be very close. I think that a company like Digi-Key could help with finding simular batched mosfets. It's worth a try.
I copied part of the article for you below. Good luck!
The choice of power Mosfets for the gain devices is somewhat broader than those for the Zen amplifier. In general, any reasonably matched pair of power Mosfets will work, assuming that they meet the dissipation requirements of the circuit. I prefer to use the newer generation of Mosfets with higher transconductance figures and lower distortion than some of the early Mosfet parts. The actual Mosfets used in this project were IRFP240, simply because I have a good stock of them. It is also possible to use P channel Mosfets for the project, simply by reversing the polarity of the power supplies. I have tried it, and it works fine.
The matching of the Mosfets helps achieve low DC offset voltage as seen by the loudspeaker and also helps to lower the distortion. If you want to match your own devices, you can simply place them in the working circuit, noting their Gate-to-Source DC potentials with a multimeter, and matching devices for the same DC voltage. Alternatively, you can swap devices in and out until you get low DC offset at the output across the drains of the Mosfets. A procedure for matching Mosfets is also presented in the A75 amplifier project published in The Audio Amateur.
If you cannot manage to match your Mosfets, you can get some adjustment of the DC offset by placing resistors in parallel with R5 or R6. Start with trial values like 100 ohms
Forget it.
You're right Digi-Key won't match them for me. I can't(don't want to)
afford to buy 10 $4 MOSFETS.
I'm going to build the original Zen with most of the modifications. The parts are on the way.
It's purely single-ended. So, I don't have to worry about this stuff.
Thanks anyway,
pixie
You're right Digi-Key won't match them for me. I can't(don't want to)
afford to buy 10 $4 MOSFETS.
I'm going to build the original Zen with most of the modifications. The parts are on the way.
It's purely single-ended. So, I don't have to worry about this stuff.
Thanks anyway,
pixie
I don't want to keep putting in my 2 cents, but be careful of how you put in the active components on the circuit board!! I can't stress this enough, if you are using a pre-made PCB from Old Colony! I had so many problems building the Zen amp because of how its silk screening is drawn. The caps, diodes and resistors are easy enough, but mind how you insert the mosfets and small signal transistors!
The mosfets go in upside-down and markings face inward toward the board. (Also makes it easier to bolt them to the heat sink.) If you place the small trans on the "capacitor's side", it's opposite of the silk-screening. Best thing you can do is know the pin markings on the trans. and follow the traces to the next component & follow the schematic.
Again, I'm not trying to be a now it all. Mine caught fire twice at start-up. It's a mess!! I didn't understand what happened until I got interested in it again and found a site on the net where another guy was having the same problem. He wasn't getting help from anyone, and finally got a hint from an unrelated article.
You will surely like the sound! Have fun!
The mosfets go in upside-down and markings face inward toward the board. (Also makes it easier to bolt them to the heat sink.) If you place the small trans on the "capacitor's side", it's opposite of the silk-screening. Best thing you can do is know the pin markings on the trans. and follow the traces to the next component & follow the schematic.
Again, I'm not trying to be a now it all. Mine caught fire twice at start-up. It's a mess!! I didn't understand what happened until I got interested in it again and found a site on the net where another guy was having the same problem. He wasn't getting help from anyone, and finally got a hint from an unrelated article.
You will surely like the sound! Have fun!
Custom
Thanks, but I'm going to make my own circuit boards.
The amplifier will break down into three separate boards easily. The first one has all the big caps. The second one is the section with the small transistors. The third is the
output stage.
I'm doing this so I can keep the power supply away from
the rest of the circuit, keep the leads short between the transistors but still mount them off board, and if I screw up etching a board it's only a third of the circuit to re-do.
Anyone see any flaws in my approach?
Thanks,
pixie
Thanks, but I'm going to make my own circuit boards.
The amplifier will break down into three separate boards easily. The first one has all the big caps. The second one is the section with the small transistors. The third is the
output stage.
I'm doing this so I can keep the power supply away from
the rest of the circuit, keep the leads short between the transistors but still mount them off board, and if I screw up etching a board it's only a third of the circuit to re-do.
Anyone see any flaws in my approach?
Thanks,
pixie
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