DIY Sony VFET pt 2 (N-Channel Build)

[rayma]

In both channels?

 

[Enochrome]

Yeah, in both.

 

[rayma]

Measure the power supply voltage at each board, from the V+ (hot) to ground.
Watch the probes, and don't slip or short anything.

 

[Enochrome]

Sounds good. I'll give it a try.

Thanks for the help!

 

[wwwtttwww]

Add a cap on N V-Fet amp

After listening for while, I added 300p mica capacitor on C4(220p). It calms down the little bit too sharp treble.

 

[TungstenAudio]

^ Yes, this is a component specifically meant for tuning the sound of the FE to match one's needs/preferences.

 

[nicoch58]

wrong way to me the c4 is for trafo ringing just try new input caps ....

 

[Enochrome]

Measure the power supply voltage at each board, from the V+ (hot) to ground.
Watch the probes, and don't slip or short anything.

I measured both boards and I am getting 33.6v on both. I checked the wiring and everything looks like the diagram, but the diagram has the order of the ground inputs on the vfet board in a different order than what's on the board. The only thing I didn't do was something for "Switch 2" because I am not sure what's it for?

 

[davidjt]

There is a lot of discussion in this thread about the SPST switch provided, and substituting a DPST. Or not.

Yes, you can just short where the 2nd pole goes and use it - it will just have a larger turn-off thump, but not a turn-on thump. This was simply the simplest approach.

So, have you put a link across SW2?

 

[Enochrome]

There is a lot of discussion in this thread about the SPST switch provided, and substituting a DPST. Or not.



So, have you put a link across SW2?

No, I haven't put a link. I read last night the part of the thread that has to do with the switch. I just used the switch that came with the kit, while leaving "Switch 2" blank.

 

[Enochrome]

I measured both boards and I am getting 33.6v on both. I checked the wiring and everything looks like the diagram, but the diagram has the order of the ground inputs on the vfet board in a different order than what's on the board. The only thing I didn't do was something for "Switch 2" because I am not sure what's it for?

Could this be my problem with the voltage adjustment issue that I initially posted about or is it mainly a turn-on thump suppression?

I am going to triple-check the wiring this morning and see if there are any discrepancies with it.

 

[Signal lost]

Looking at the schematic, no connection on SW2 will leave the relay coil un-powered (I think) keeping the speaker output shorted. You could jumper SW2 or disconnect O+ going to the power supply board. Careful to insulate them as they are the main output of the amp.

Some one please correct me if I am mistaken about this.

 

[astouffer]

Jumpering SW2 will work (mine is wired that way) but you get a bigger turn off click.

 

[Baobei]

Finally finished 128 today and listening to sweet sweet music now.

Thanks a lot again everyone involved!

I built it with DPST and the turn on thumb is quite small. At turn-off it's quite a bit more prominent, but not enough that I'd feel uncomfortable (96db speakers).

 

[Enochrome]

I'm getting the same reading of 1.3 at the anode where it was instructed to measure in the build guide. Adjusting the pot does not do anything. I will ask the obviously stupid question: where should I be measuring in order to achieve proper bias?

 

[rgolan]

For the N-Channel Sony VFET amps, the bias voltage should be measured between the IRF250 and ground. I clipped leads to the screw head on the IRF250 and the ground wire on the output stage board.

From the Nelson Pass PDF:

"Also, P1 wants to be adjusted to give +14 volts at the Drain (case) of the IRF250, and trimmed after it warms up."

 

[Enochrome]

I measured both boards and I am getting 33.6v on both. I checked the wiring and everything looks like the diagram, but the diagram has the order of the ground inputs on the vfet board in a different order than what's on the board. The only thing I didn't do was something for "Switch 2" because I am not sure what's it for?

For the N-Channel Sony VFET amps, the bias voltage should be measured between the IRF250 and ground. I clipped leads to the screw head on the IRF250 and the ground wire on the output stage board.

From the Nelson Pass PDF:

"Also, P1 wants to be adjusted to give +14 volts at the Drain (case) of the IRF250, and trimmed after it warms up."

I checked from the IRF250 and ground, but I'm still getting 1.3? I've attached photos:

 

[Enochrome]

Also, thanks to everyone for the help, it's much appreciated.

 

[rgolan]

I checked from the IRF250 and ground, but I'm still getting 1.3? I've attached photos:

Measure from ground to the screw circled in this image.

 

[Zen Mod]

case of IRFP - red probe