Yes, you have to lower the bias, but I would go for 0.22 Ohm, then you can bias twice as high as with 0.47 Ohm before the diodes start conducting.
Lower bias is more distortion, higher bias less.
But I don't know how big your heatsinks are.
BTW: why don't you parallel two of the 0.5 Ohm resistors? When using 2sj201 and 2sk1530 you have to adjust some other resistors also.
Walter
There were hum problems original so I redesigned the power supply 3 times and the 3rd using tea bags boards and worked well with no hum, this amp I spent hours and hours on over a course of 3 months or more without payment for my time, mainly because it was being built for a friend! I could have done other things with my life in that time.... in this world you try to do something nice and you sometimes just end up with unhappy people all roundid rather not take the money if it was offered anyway to keep the owner not so unhappy with me.
with my previous experience of building a couple of F5's I decided to build this F5t but knew at the time it was a bit out of my league.
I presume this amp has some instability but to me the problem is unlikely to lie with the temp of the heatsink or fets.
I might be wrong but I don't see the ground link on the front end board.
On my build I stayed with 2 1R source resistors in parallel even though I am using the Toshiba outputs. I am using the Teabag boards with all outputs populated, so I won't be able to bias it high enough in any case for a lower Rs to be of benefit. On the Teabag boards the outputs are just too close to each other to really open the taps. But then I knew the limitations and I am happy to live with it. I don't currently have speakers that can tax the F5T in any case, so I don't mind.
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Hi Jim,
My heatsink has a profile of H=260 W=75 X D=150 each.
Total of 6 per mono. Safe to say it can handle more than 150watts Class A
per mono
. At any rate, I have same thinking as yours going higher bias (tends to significantly improve the sounds)
with lower rail as compare to higher voltage (which a question of economy due to large dissipation of power),
in which I cannot bring up the bias compare to lower rails.
Im still analyzing my NEEDS over my WANTS
It is about more than just high bias per fet. In another thread, Jim states that above a certain bias level, the improvements were not dramatic. If this is the case, you have to honestly look other places for the possiblity of larger performance gains. While having 1 fet biased at 4A may sound great, how will it compare to 4 fets at 1A. What if you have 8 fets at .5A, but a higher rail. In reality, i would imagine that the answer is not simple. Consider each scenario and what you gain and what you give up. A considerable amount of time could be spent answering just these questions. Now add your room, speakers, and music taste, and the answer may change. It is a terrible circle or a wonderful one. Depends on how you approach it.
Advice needed from MosFET expert
I would like to build a F5T1 version.
I has several well matched Toshiba 2SJ200/2SK1529 mosfet to these project.
I made my own PC boards I can use 3 or 4 pair of these mosfet per channel, have enough of them.
I have a 820VA 24-0-24V transformer to these project, which would give 28-29V rail voltage under load.
also have a 1000VA 30-0-30V but with these the JF et need to be cascoded and my PC board was not designed with the cascode option so probably better to stick with the lower V transformer.
These transformer was ordered for the KSA50 clone (not finished yet)
My question can I use successfully these Toshiba Fets without some major mode.
I do have some IRFP mosfet at my hand to but I would really like to use these Toshibas 2SJ200/2SK1529 for these project. Those cost me 3x as much than the IRFP and I soldered into the PC boards so I must use them...
Someone who mosfet xpert guy can you take a look if I can go on with these project based on the Turbo V1 schematic
Thank you for your help, advise in advance
Monday I need to order some resistors from Parts Connexion for some another project it would be great to order the same time the resistors to these project to if I can build with the Toshiba Fets..
I coud save some buck on the shipping in that case
Greetings G
I would like to build a F5T1 version.
I has several well matched Toshiba 2SJ200/2SK1529 mosfet to these project.
I made my own PC boards I can use 3 or 4 pair of these mosfet per channel, have enough of them.
I have a 820VA 24-0-24V transformer to these project, which would give 28-29V rail voltage under load.
also have a 1000VA 30-0-30V but with these the JF et need to be cascoded and my PC board was not designed with the cascode option so probably better to stick with the lower V transformer.
These transformer was ordered for the KSA50 clone (not finished yet)
My question can I use successfully these Toshiba Fets without some major mode.
I do have some IRFP mosfet at my hand to but I would really like to use these Toshibas 2SJ200/2SK1529 for these project. Those cost me 3x as much than the IRFP and I soldered into the PC boards so I must use them...
Someone who mosfet xpert guy can you take a look if I can go on with these project based on the Turbo V1 schematic
Thank you for your help, advise in advance
Monday I need to order some resistors from Parts Connexion for some another project it would be great to order the same time the resistors to these project to if I can build with the Toshiba Fets..
I coud save some buck on the shipping in that case
Greetings G
Walter,
I do have 1 Ohm resistors actually, but enough units to // them .. giving me the quoted O.5 Ohm.
Heatsinks are Seifert KL-288 (2 output boards per heatsink), 400mm x 200mm x 85mm, 16mm baseplate, 0.13 K/W.
What resistors did you change for unsig the Toshiba outputs ?
Thanks,
Max
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I changed R5 and R6 of the original F5 Turbo pdf to 475 Ohm instead of 1K because the Toshibas have a lower Vgs than the IRFPs. Around 2,5 Volt instead of 4.5 V.
Also the R11 and R12 were lowered to 1K2, to have better thermal tracking.
I also fiddled around with R25 to R28 so I get around 12 Volts on the JFets. Don't know which values I used anymore...
Those heatsinks are very, very nice! Where did you bought them? I looked for them in the past , but did not find any retailer who sells them.
Walter
Also the R11 and R12 were lowered to 1K2, to have better thermal tracking.
I also fiddled around with R25 to R28 so I get around 12 Volts on the JFets. Don't know which values I used anymore...
Those heatsinks are very, very nice! Where did you bought them? I looked for them in the past , but did not find any retailer who sells them.
Walter
Thanks for the detailed info on the value changes, will go that way using 0.5R on the outputs and see how it goes like that... I am settled with R25/R28 to give me around 15V on the jfets (+/- 1/3 of rail voltage as per NP is the article).
Heatsinks: They only sell to compagnies directly off the factory, one reason it took me 3 months to place my order.. let's call it work-around-time
Bedankt & Merci Vielmal
I am thinking to build a F5 turbo v.3 100WPC. I am planning to use it to drive two AE dipole12 woofers per channel. The drivers will be mounted according to the M-frame (push-pull) design as in this link:
Subwoofer Origami
I am confident that the LF will have all the texture, sweet tone, and details desired. However, will this provide enough speed and attack when neccessary?
Thanks a lot.
Subwoofer Origami
I am confident that the LF will have all the texture, sweet tone, and details desired. However, will this provide enough speed and attack when neccessary?
Thanks a lot.
I would like to build a F5T1 version.
I has several well matched Toshiba 2SJ200/2SK1529 mosfet to these project.
I made my own PC boards I can use 3 or 4 pair of these mosfet per channel, have enough of them.
I have a 820VA 24-0-24V transformer to these project, which would give 28-29V rail voltage under load.
I do have some IRFP mosfet at my hand to but I would really like to use these Toshibas 2SJ200/2SK1529 for these project. Those cost me 3x as much than the IRFP and I soldered into the PC boards so I must use them...
Someone who mosfet xpert guy can you take a look if I can go on with these project based on the Turbo V1 schematic
Thank you for your help, advise in advance
Monday I need to order some resistors from Parts Connexion for some another project it would be great to order the same time the resistors to these project to if I can build with the Toshiba Fets..
I coud save some buck on the shipping in that case
Greetings G
Hello
No advise or help from no one?
Remember my interest on Turbo v1...
Probably would need some minor adjustment to compensate the difference between the IRFP and and Toshiba fets
Please someone help with these
If is enough if I change the 47.5R resister to 100R?
Thank you guys
Greetings Gabor
Hi all,
This is my first post on this forum. I've taken on Gabsta's F5T as a project with a view of building my own sometime in the Future.
As posted previously, one half of the amplifier, the right channel is completely fried. That half is now disconnected awaiting parts for a rebuild. I've just been checking the left channel as if its a new build.
I am biasing the N & P channels but I cannot get the voltage between the source resistors to match exactly. By that I mean I cannot get them closer to within 40mV of each other regardless of the DC offset. If I adjust P1 or P2 the voltages rise and fall together.
Is 40mV difference at ~300mV acceptable or is there an issue?
The power supply rails is reading ±32.35V so it doesn't seem to be an issue with the PSU. With the power off and the resistances of the source resistors measured, both reads 0.7ohms.
Any help would be greatly appreciated.
This is my first post on this forum. I've taken on Gabsta's F5T as a project with a view of building my own sometime in the Future.
As posted previously, one half of the amplifier, the right channel is completely fried. That half is now disconnected awaiting parts for a rebuild. I've just been checking the left channel as if its a new build.
I am biasing the N & P channels but I cannot get the voltage between the source resistors to match exactly. By that I mean I cannot get them closer to within 40mV of each other regardless of the DC offset. If I adjust P1 or P2 the voltages rise and fall together.
Is 40mV difference at ~300mV acceptable or is there an issue?
The power supply rails is reading ±32.35V so it doesn't seem to be an issue with the PSU. With the power off and the resistances of the source resistors measured, both reads 0.7ohms.
Any help would be greatly appreciated.
offset and voltage at one Rs is what you need to measure
later just check voltage on other Rs , to confirm that you're in ballpark , nothing else
I can bet that your ears aren't exactly identical ....... so you can't expect more from two F5 halves
Just out of curiosity, would matching the N & P channels make any difference to these values? Sorry I am a bit of a perfectionist