F5 pcb group buy...

[AndrewT]

Originally Posted by regiregi22

Is it OK one slow-blow 1.25A fuse to protect one F5? I am going dual psu for it, but Nelson Pass psu schematic doesn't specify if it is for one channel or two. I live in 230v. I will use the thermistors in the transformer.

the normal fuse value for a motor or transformer is 3 * watts / voltage.

If you implement soft start properly then that factor of 3 can be reduced to near 1times.
Due to the way we specify our audio PSUs. I have found that the factor can even be less than 1. I commonly use 0.8 * VA / voltage without incurring nuisance blowing when the soft start is scaled to suit the transformer VA.

[regiregi22]

I don't know the total wattage, so without more concrete advices, I will go with twice the recommended. I am not sure if 1.25A fuse will suffice for two F5 channels.

Regards,
regi

[regiregi22]

I've been looking for inside the official F5 thread but I couldn't found info about matching the jfets idss (2sk170 and 2sj74). Is there anything expected to gain, performance wise?
I have seen some BOMs that recommends to match them. I think that I have to find one 2sk170 and one 2sj74 with the same idss.

AFAIK, offset is adjusted by trimming pots, so I suspect that there should be small advantages in that sense.

Can anyone apport something to this?

I have almost all my components collected to start building, only need the jfets

Thank you very much to all,

Regards

[chchyong89]

Originally Posted by regiregi22

AFAIK, offset is adjusted by trimming pots, so I suspect that there should be small advantages in that sense.

Regards

It used to adjust the bias too.

[wdavis009]

Peter,

What is the largest gauge wire that will fit the output holes on the amp board?

[kpaiss]

Im really having hard time locating the panasonic 3w 0.47 resistors.
If anyone knows where can i find them.

Many Thanks !!!!

[cjkpkg]

I get mine from Digikey. 3W panasonics

[kpaiss]

Originally Posted by cjkpkg

I get mine from Digikey. 3W panasonics

oh...
I was sure that from digikey there was a limit order of 1500 pieces for this specific resistor.
My mistake.

Thank you !!!

[shmulik]

I experience some hum, or at least I think it is hum (some small multiple of 50Hz). one has to put his ear to speaker in order to hear the hum, but the target speaker is a 106DB sensitive one and the noise will be much more noticeable there. I measured the ripple of the rails while one channel is attached and properly biased (~0.59 Volts) on a scope and it is ~150mV peak to peak and similar on both rails. when the input is shorted to ground there is no noise at all. when the ground crocodile of the scope prob is attached, the nature of the noise changes.
Has anyone else experienced such noise?
one more odd thing - the rectifier bridge of the positive rail is getting hotter (by hand) than the negative one. I don't know what that hints.

Shmulik

[HaflerFreak]

At Wdavis009:
The absolute largest wire you can use for power/output with the original PD F5 boards is 16-gauge stranded if you twist it up nice and tight.