I gave him a twin brother 😀
Now I must give them an House $$$$$ €€€€€
And now, They are playing in stereo 😎
I have only one word to define the sound. Natural.
I have made some new measures.
The clipping, without load is simmetrical at +22.45 -22.75.
Under 8 hom load it is not +18.72 -21.2
The voltage drop at +/- 1.25V is 63mV so OI is 0.42 and DF is 18.8.
At +/-3.45V is 310 mV so OI is 0.8 and DF is 10
At clipping on the minus VD is 1.57 on the + is 3.74 and I don't know which one to use.
Offset rises as the volume goes up, reaching about 800 mV just before clipping. I don't know if this is normal or not.
Maybe swapping the 140N with a 240 could improve the performance. I have read somewhere that this pair is well matched. Have you any advice on this question?
Now I must give them an House $$$$$ €€€€€
An externally hosted image should be here but it was not working when we last tested it.
And now, They are playing in stereo 😎
An externally hosted image should be here but it was not working when we last tested it.
I have only one word to define the sound. Natural.
I have made some new measures.
The clipping, without load is simmetrical at +22.45 -22.75.
Under 8 hom load it is not +18.72 -21.2
The voltage drop at +/- 1.25V is 63mV so OI is 0.42 and DF is 18.8.
At +/-3.45V is 310 mV so OI is 0.8 and DF is 10
At clipping on the minus VD is 1.57 on the + is 3.74 and I don't know which one to use.
Offset rises as the volume goes up, reaching about 800 mV just before clipping. I don't know if this is normal or not.
Maybe swapping the 140N with a 240 could improve the performance. I have read somewhere that this pair is well matched. Have you any advice on this question?
Don't you fear, with a 350ma bias, to be a little bit far from the "sweet spot" Nelson is speaking about.
I am inquiring , as i plan to bias one of mines at about 500ma.( treble operation).
I fear to loose sound quality, doing this.
I am inquiring , as i plan to bias one of mines at about 500ma.( treble operation).
I fear to loose sound quality, doing this.
The lower the bias, the higher the distortion.
That is why you build Class A in the first place.
Patrick
That is why you build Class A in the first place.
Patrick
Hi Pro,
no wonder you have had to strangle the F5 by biasing it to 350mA.
That sink is not big enough for one channel and you have stuck two on it!
If you really want to run a pair of FETs in ClassAB mode then go to another thread, not the F5 one.
no wonder you have had to strangle the F5 by biasing it to 350mA.
That sink is not big enough for one channel and you have stuck two on it!
If you really want to run a pair of FETs in ClassAB mode then go to another thread, not the F5 one.
Bobo, I don't know how distorsions rises lowering the bias, but for shure, just listening, these distorsions don't seem to annoy the ear. The ampli has an his imprint, and I don't think it will change so much increasing the bias. At most it can increase the depth of the soundstage a little.
At the measures, probably the thing will be different.
Andrew, I know perfectly that heatsink is not enough for one channel, but at least I am listening at a F5 having spent 45€ for the PS, and having everything else on the shelf, so now I can decide if to spend other money for box and heatsink, or not, and since it seems that it is worthwhile, I am going to order this onee for 185€ out of the door.
Do you think i'ts enough?
At the measures, probably the thing will be different.
Andrew, I know perfectly that heatsink is not enough for one channel, but at least I am listening at a F5 having spent 45€ for the PS, and having everything else on the shelf, so now I can decide if to spend other money for box and heatsink, or not, and since it seems that it is worthwhile, I am going to order this onee for 185€ out of the door.
Do you think i'ts enough?
An externally hosted image should be here but it was not working when we last tested it.
If I recall at modushop they do tell you the rating of the heatsink. I think that its the 5U case that has enough heatsink but dont quote me on that. Check the ratings of those sinks.
Uriah
Uriah
Dissipante Pesante 4U x 300 mm should be ok for F5
4U x 400 mm is ok for Aleph J or similar. Each side can dissipate 100 W
4U x 400 mm is ok for Aleph J or similar. Each side can dissipate 100 W
Hi Massimo, I think i'll go for 4U 400, so I'll have a bit more room for the PS that is a bit overkill (ingombrante è dir poco) 😀
4U may work, depending on air temperature
Heat sink is 300x165x40
My guess is that its Fischer heatsink
Sk501 sem to fit the specced size used in modushop box
Increasing from 150mm to 200mm height doesnt seem to make significant improvement
Its about 0.3K/W in both sizes
Curve is almost horisontal at 150mm height, so no further improvement with increased size, it seems
But 40mm fins is on the small side and not the most effective
SK157 from Fischer has 83mm fins, that seem to be very effective
Its close to 0.2K/W at 200mm, and still more to gain, it seems
Heat sink is 300x165x40
My guess is that its Fischer heatsink
Sk501 sem to fit the specced size used in modushop box
Increasing from 150mm to 200mm height doesnt seem to make significant improvement
Its about 0.3K/W in both sizes
Curve is almost horisontal at 150mm height, so no further improvement with increased size, it seems
But 40mm fins is on the small side and not the most effective
SK157 from Fischer has 83mm fins, that seem to be very effective
Its close to 0.2K/W at 200mm, and still more to gain, it seems
pro said:
The only problem with the 400 mm unit is that each side/heatsink is devided into two 200 mm pieces mounted side by side.
good post 
With one side split into two heatsinks you actually get a tiny bit more efficiency out of the heatsinks.
Uriah
Uriah
To get the max efficiency, one should fix the two mosfet exactly at the center of each heatsink. That means about 200 mm apart and at 82 mm high
A question regarding j-fet.
Is it normal that while k170 at 6ma bias, on 30 units, I have found a Vgs which varies between 20 and 80 mV while the J74 varies between -500 and -1500 mV?
Is it normal that while k170 at 6ma bias, on 30 units, I have found a Vgs which varies between 20 and 80 mV while the J74 varies between -500 and -1500 mV?
> while the J74 varies between -500 and -1500 mV?
Did you mean between -500 and -1500 mV or between 50 and 150 mV ?
If you meant -500 and -1500, then it is not normal. Firstly I expect your Idss to be larger than 6mA, in which case Vgs should be POSITIVE and not negative for 2SJ74, and vice versa for 2SK170.
But suppose that Vgs is positive, and even with the V-grade at 16mA Idss, the Vgs should not be more than +400mV at 6mA bias. Please refer to Page 2 of datasheet.
If you indeed measured -1500mV (i.e. the gate voltage is lower than source), you are for certain forward biasing the JFET, and I would have expected a much larger current than 6mA.
Or I misunderstood you completely.
Patrick
Did you mean between -500 and -1500 mV or between 50 and 150 mV ?
If you meant -500 and -1500, then it is not normal. Firstly I expect your Idss to be larger than 6mA, in which case Vgs should be POSITIVE and not negative for 2SJ74, and vice versa for 2SK170.
But suppose that Vgs is positive, and even with the V-grade at 16mA Idss, the Vgs should not be more than +400mV at 6mA bias. Please refer to Page 2 of datasheet.
If you indeed measured -1500mV (i.e. the gate voltage is lower than source), you are for certain forward biasing the JFET, and I would have expected a much larger current than 6mA.
Or I misunderstood you completely.
Patrick
Hi Patrick. Thank you for the answer.
I arranged this small schematic, and the values I have read between ground and source are from -500 to -1500 with the most, on 30 units, between -800 and -1300 mV. Only one is -60 mV.
I arranged this small schematic, and the values I have read between ground and source are from -500 to -1500 with the most, on 30 units, between -800 and -1300 mV. Only one is -60 mV.
An externally hosted image should be here but it was not working when we last tested it.
I can't understand (may be the warm weather) your schematic: gate-drain is 50v? No load? Source resistor = 3870R? Source at 0V ?