I have each FET with its own 100 ohms on the gate pins.
schematic is like my original F5 version and I just quadrupled the output.
I use a PCB from Ebay.
turbo headache
The 2SK175/2SJ55 has about half the input capacitance as the IRF250, so four of them should work, even the F5 Turbo V1 uses two hefty IRF's or similar [=like four of my devices].
So the lack of steam should show up with low frequency (which it did, having a high roll-off of still 650 KHz instead of 1-2 MHz in my single pair version). The PCB by the way don't like an extra pair
I made a F5-turbo style feedback reducer (now 102 ohms/10 ohms); added an input filter 80 kHz.
I did some testing: connected just one pair again instead of 4 pairs in the right channel.
The 2SK175/2SJ55 has about half the input capacitance as the IRF250, so four of them should work, even the F5 Turbo V1 uses two hefty IRF's or similar [=like four of my devices].
So the lack of steam should show up with low frequency (which it did, having a high roll-off of still 650 KHz instead of 1-2 MHz in my single pair version). The PCB by the way don't like an extra pair
I made a F5-turbo style feedback reducer (now 102 ohms/10 ohms); added an input filter 80 kHz.
I did some testing: connected just one pair again instead of 4 pairs in the right channel.
- right channel driven, OK, driving both channels gave oscillation.
- I noted the left channel with 4 pairs could not stand zero load, it immediately oscillated.
- Can it come from the common power supply? It is easy for me to split the final capacitor cell as I have two per rail.
Last edited:
thanks james
This is a good idea as my drain connection is based on a pin with a semi-star halfway the heatsink (not four separate wires to the PCB). Same as with gates. The PS rail connection is also based on one long wire dropping down.
This could indeed give spurious interference.
Local decoupling is a good id, using some 20 pF drain-gate if I am correct. My TO-3 devices are flat on the heat sink, so impossible to add a cap across the pins now.
- - [sorry next week] I will try to work out some layout improvements.
Yeah, it's a "funny bugger" at times and it surprising how component changes alter the sound - I've not had any of your problems but just use the single pair of fets, altho the one I built with the triple units of the smaller 2013/313s didn't exhibit any particular problems apart from some jfet trimming - I began using jachinj's input jfet gate stopper/filter input arrangement on this one and it was a lot "smoother" but a bit touchy of resistor quality - used some Rhopoints, not cheap!
Maybe problems with your wiring - it sounds a bit casual, altho the amp is surprisingly pretty tolerant of this. I'm still a bit surprised at the way Nelson's F series production amps have the central 0volt point on the end of the pcb next to both the I/P & O/P sockets and no problems whatsoever.
Maybe problems with your wiring - it sounds a bit casual, altho the amp is surprisingly pretty tolerant of this. I'm still a bit surprised at the way Nelson's F series production amps have the central 0volt point on the end of the pcb next to both the I/P & O/P sockets and no problems whatsoever.
All OK now
Indeed it seems to have been a wiring issue.
To check my difficulties, I tried the single pair (as before) this was OK; next I connected the other three parallel pairs only. [And will add the fourth pair later]
So: Now I have my F5-turbo V1,
I did need the input jfet gate stopper/input filter to not excite the ringing in VHF.
The difference is now 0,5 dB between 8 Ω and 5 Ω - a very low DF like I had expected. [My very good sounding 300B has a low DF].
I have 21,5 volts and 1,4 A bias each side. [I have to restrict the voltage due to my speakers]
Maybe next year I will go towards a turbo version V2 with omitting the source resistors all together.
Indeed it seems to have been a wiring issue.
- I had one pair, the top ones, directly connected to the board placed on the bottom of my amplifier, not on the heatsink with the resistor on the board still in its proper place
- three parallel pairs distributed lower on the heatsink, all with the source resistors directly connected to the pins and one wire from the board to these fets.
To check my difficulties, I tried the single pair (as before) this was OK; next I connected the other three parallel pairs only. [And will add the fourth pair later]
So: Now I have my F5-turbo V1,
I did need the input jfet gate stopper/input filter to not excite the ringing in VHF.
The difference is now 0,5 dB between 8 Ω and 5 Ω - a very low DF like I had expected. [My very good sounding 300B has a low DF].
I have 21,5 volts and 1,4 A bias each side. [I have to restrict the voltage due to my speakers]
Maybe next year I will go towards a turbo version V2 with omitting the source resistors all together.
I'm not too sure what to make of your build, Al -
It seems that you have 4 pairs of the TO3 devices grouped in complimentary pairs and this will make all the wiring much longer than having all the P type together, and the same with the 'N' ones -
If you don't mind me asking, why do you need 4 pairs to operate a 5 - 8R load with a 1.4A current and a 21 volt rail? - seems a bit excessive and, unfortunately, not guaranteed to give better results - Perhaps I'm missing something obvious here, sorry....
I do like the big heatsink and having the gate stoppers resistors close to the transistor pins and a neat way of holding the power resistors down.
It seems that you have 4 pairs of the TO3 devices grouped in complimentary pairs and this will make all the wiring much longer than having all the P type together, and the same with the 'N' ones -
If you don't mind me asking, why do you need 4 pairs to operate a 5 - 8R load with a 1.4A current and a 21 volt rail? - seems a bit excessive and, unfortunately, not guaranteed to give better results - Perhaps I'm missing something obvious here, sorry....
I do like the big heatsink and having the gate stoppers resistors close to the transistor pins and a neat way of holding the power resistors down.
Actually it is one set top to bottom N-fet and the other side the complementary ones. Each set of devices is now 'fed' from a pin in the middle, obviously making it very balanced in capacity and inductance (even if both are low).
Yes, with these devices the lines get long.
I originally wanted to mount the PCB's in the center of the heat sink, that would have given neat layout and proximity almost like IRF devices - but I noticed then my capacitors would not fit (width of 4).
And yes, a bit overdone, one pair is OK too, has a lower DF even what brings out the bass a little bit more, and it works without any artifices like input filters . But on the other hand, the high is better handled now.
And for the rest, shifting into turbo-mode is just curiosity.
albert
Yes, with these devices the lines get long.
I originally wanted to mount the PCB's in the center of the heat sink, that would have given neat layout and proximity almost like IRF devices - but I noticed then my capacitors would not fit (width of 4).
And yes, a bit overdone, one pair is OK too, has a lower DF even what brings out the bass a little bit more, and it works without any artifices like input filters
. But on the other hand, the high is better handled now. And for the rest, shifting into turbo-mode is just curiosity
.albert
Last edited:
Audio san,
Some differences with standard F5:
I must say i like the improvement in resolution and authority.
albert
Some differences with standard F5:
- parallel outputs
- feedback lowered to get 21 dB
- I must say I still have to add the P3
- I am tempted to try the C3/C4 of V3
I must say i like the improvement in resolution and authority.
albert
maybe a silly question, but:
what is the "better" load for the F5 amp?
- 4 Ohm
- 8 Ohm
I know it can drive both loads without problems, but I'm going to build the next pairs of speakers, and so I have to take a decision...
I thought it is more powerful in 4 Ohms, but I'm not 100% sure...
Thanks&Regards,
Matthias
what is the "better" load for the F5 amp?
- 4 Ohm
- 8 Ohm
I know it can drive both loads without problems, but I'm going to build the next pairs of speakers, and so I have to take a decision...
I thought it is more powerful in 4 Ohms, but I'm not 100% sure...
Thanks&Regards,
Matthias
Thanks guys!
hmmmm, my problem is no more place inside my enclosures, so using the shop's F5c boards is no option...
So I'm going to build a three way speaker with 8 Ohms, I think. Maybe this one:
BlueNote | Lautsprecherbau
Regards,
Matthias
hmmmm, my problem is no more place inside my enclosures, so using the shop's F5c boards is no option...
So I'm going to build a three way speaker with 8 Ohms, I think. Maybe this one:
BlueNote | Lautsprecherbau
Regards,
Matthias
Thanks guys!
hmmmm, my problem is no more place inside my enclosures, so using the shop's F5c boards is no option...
So I'm going to build a three way speaker with 8 Ohms, I think. Maybe this one:
BlueNote | Lautsprecherbau
Regards,
Matthias
The tweeter is 4 ohms, the other speakers seem to be 8 ohm-ish. Also the system is only 87/88 dbSPL. I would look for a more efficient speaker system in the 90 + range. I use Snell E2, bi-amped (2 way). They work well and Audio Note has E2 kits with various drivers according to your price point. Lots of other ones out there.
Rush
Finally I concluded my F5.
It was an extremely interesting project from the standpoint constructive. It was fundamental support and technical advice from Carlomar.
Now I can enjoy delight, the sound of this amp, Project Engineer Mr. Nelson Pass, a big name in high fidelity and has done much for DIY.
As for the sound, I can tell you that I am generally delighted with the sound of this amp. Especially appreciate your detail. I love jazz, instrumental and vocal, and this amplifier reproduces very well either voices like the metals. Gives the feeling of the artist being there, in our presence, in our living room.
I'm on the lookout to start building the preamp, also Project Engineer Nelson Pass, and that will "marry" the F5.
I enclose some photos of F5.
My special thanks to Mr. Nelson Pass.
My thanks to members of the forum to give their input, in particular:
Carlomar, formula 22, Alazira, Lanchile, Jameshillj, CeeVee, Blues, Peter Daniel
It was an extremely interesting project from the standpoint constructive. It was fundamental support and technical advice from Carlomar.
Now I can enjoy delight, the sound of this amp, Project Engineer Mr. Nelson Pass, a big name in high fidelity and has done much for DIY.
As for the sound, I can tell you that I am generally delighted with the sound of this amp. Especially appreciate your detail. I love jazz, instrumental and vocal, and this amplifier reproduces very well either voices like the metals. Gives the feeling of the artist being there, in our presence, in our living room.
I'm on the lookout to start building the preamp, also Project Engineer Nelson Pass, and that will "marry" the F5.
I enclose some photos of F5.
My special thanks to Mr. Nelson Pass.
My thanks to members of the forum to give their input, in particular:
Carlomar, formula 22, Alazira, Lanchile, Jameshillj, CeeVee, Blues, Peter Daniel
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
