Roots of the F5 Turbo
I just ran across this. Perhaps it has been mentioned before in this thread, but I have not seen it.
http://www.diyaudio.com/forums/soli...-interview-bjt-vs-mosfet-248.html#post1294203
Nelson says:
I just ran across this. Perhaps it has been mentioned before in this thread, but I have not seen it.
http://www.diyaudio.com/forums/soli...-interview-bjt-vs-mosfet-248.html#post1294203
Nelson says:
BTW, there is a pair of diodes - I also used a trick that I got from
Barney Oliver of using power diodes to shunt across emitter
resistance so as to limit the maximum voltage at high current.
It made the job easier for my (admittedly crude) bias circuit.
Barney Oliver of using power diodes to shunt across emitter
resistance so as to limit the maximum voltage at high current.
It made the job easier for my (admittedly crude) bias circuit.
Similar trick. Actually I didn't get it from Barney Oliver, but later discovered
that he had done it before me.
😎
that he had done it before me.
😎
In the F5 Turbo, would you say that the goal of the diodes was to increase transconductance by decreasing the effective source resistance, or to increase the output voltage swing at high currents, or something else?
In user point of view, may I consider this diode trick as a kind of power saving solution for class A schematic 😉
We don't need to set highly idling current (Id) but we still can get large, intact output power out signal (without clipping at negative half cycle)
Not too hoot, not bad at all. Sorry, if may I wrong!
For 100W V3, you are gonna be dissipating about 250W per channel. I would think 800 per channel or monoblock is more ideal.
Gain on the Turbo versions?
On the original F5, the voltage gain was about 6 (or 15 dB). What is the voltage gain on the Turbo F5 versions 1, 2 & 3?
On the original F5, the voltage gain was about 6 (or 15 dB). What is the voltage gain on the Turbo F5 versions 1, 2 & 3?
Let me ask my question a different way.
The required votage input on the original F5 was about 2.4 volts to get the nominal 25 watts. Is the required input voltage the same for the Turbo version(s) (with nominal outputs of 50 to 100 watts)?
Let me ask a question as Ive only asked 2 million already!
Is there a way for me to attach a volume control to the front of F5turbo instead of having to use B1 or a pre-amp.
and how would this be done ? i have a 25k attenuator somewhere here!
Is there a way for me to attach a volume control to the front of F5turbo instead of having to use B1 or a pre-amp.
and how would this be done ? i have a 25k attenuator somewhere here!
The buffer serves the purpose of trying to diminish any negative affects associated with using just a pot. It can be done, but seems a shame to build a nice amp and them handicap its performance out of the gates.
Understood thanks, well if the change In performance will be that big a drop then Ill go down another route 🙂
If you have the potentiometer, just put it in place of R2, and take the output from the wiper.
Try it, as it will take only a few min to try and you can hear for yourself of there is an adverse effect. (Which I bet, if there is, will be very minimal.)
Try it, as it will take only a few min to try and you can hear for yourself of there is an adverse effect. (Which I bet, if there is, will be very minimal.)
I've just sourced 4ea 2SJ74 and 2SK170 (hopefully reliably sourced..) - now looking for someone who's got experience with a working example replacing FQA12P20 and FQA19N20?
Of course, these are discontinued / obsolete but possibly still available (just like the JFETS). It might be possible to get the exact P/N but I think I'd rather substitute in this case. I've read here in this thread about some possible replacements but would still like to know if someone's got a life F5T running with them. I was planning on using the diy-store heatsink chassis and pcb - not sure what impact the substitution would have?
Of course, these are discontinued / obsolete but possibly still available (just like the JFETS). It might be possible to get the exact P/N but I think I'd rather substitute in this case. I've read here in this thread about some possible replacements but would still like to know if someone's got a life F5T running with them. I was planning on using the diy-store heatsink chassis and pcb - not sure what impact the substitution would have?
before you do anything else, test your jFETs
Measure the Idss.
Measure The Vpinchoff (Vp).
Compare Vp to Idss to determine that they are k170 & j74.
I used the source 6L6 mentioned some time back - hoping they are still as reliable as he found them to be. Their service so far has been impeccable (fast process, cheap shipping, arrived well packed etc).
OK thanks - I'm going to build a tester. Mr NP seems to favor these JFET devices and I wouldn't mind having a 'screening' tool since I doubt this is my last amp. Do you know offhand what values I should be looking for? I'll post all my measurements and take any advice you have on:
Whether to use these parts.
Which ones to match up. It might be obvious but I'm not sure.
OK thanks - I'm going to build a tester. Mr NP seems to favor these JFET devices and I wouldn't mind having a 'screening' tool since I doubt this is my last amp. Do you know offhand what values I should be looking for? I'll post all my measurements and take any advice you have on:
Whether to use these parts.
Which ones to match up. It might be obvious but I'm not sure.
Look at the 170/74 datasheets.
The graphs in there give a good guide to the Vp for different Idss.
Expect a low Idss of 6mA to give a Vp~500mV and a high Idss of 12mA to give a Vp~800mV.
Borbely and others give a formula for Vp & gm that should confirm you have the correct devices.
The graphs in there give a good guide to the Vp for different Idss.
Expect a low Idss of 6mA to give a Vp~500mV and a high Idss of 12mA to give a Vp~800mV.
Borbely and others give a formula for Vp & gm that should confirm you have the correct devices.
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