Hi Nelson,
I would like to be able to drive a 4 ohm load with as much or almost as much class A power as the current circuit supplies. My questions in this regard are:
1) Can I simply increase the number of output devices to 10 per channel (5 N/P pairs) and re-bias, then use the J109/K389 combo with the pairs paralleled and giving each FET it's own source resistor, and still maintain the same general performance?
2) What is the Idss group of the FET's - BL or GR? Does it matter as long as the power dissipation is within reason?
Thank you much.
Graeme
I would like to be able to drive a 4 ohm load with as much or almost as much class A power as the current circuit supplies. My questions in this regard are:
1) Can I simply increase the number of output devices to 10 per channel (5 N/P pairs) and re-bias, then use the J109/K389 combo with the pairs paralleled and giving each FET it's own source resistor, and still maintain the same general performance?
2) What is the Idss group of the FET's - BL or GR? Does it matter as long as the power dissipation is within reason?
Thank you much.
Graeme
Congratulations Steen!
Very nice work. While it is always a pleasure to read a nice amp article from Nelson, after reading your review of F4, I must say I feel infected
.
But why, why?? We were happy with F1, F2, F3, and F4 is an overdose
.
I just want to enjoy my ZV9
....but...when I go to sleep, I hear F4, F4, F4........
Very nice work. While it is always a pleasure to read a nice amp article from Nelson, after reading your review of F4, I must say I feel infected
. But why, why?? We were happy with F1, F2, F3, and F4 is an overdose
. I just want to enjoy my ZV9
....but...when I go to sleep, I hear F4, F4, F4........
steenoe said:
Steen
I think you're crazy, Steen...
I can't blame you though. I think the magic lies in those tiny jfet frontends. They really transform the sound sooo sweetly...maybe if you replace your AX's frontend with jfets you won't want to tear it apart.If only EUVL will share how he did his AXs!
Nelson and Steen (our official amp test bed ) has got as by surprise once again… hope there is no F5 in the near future 
This call sounds like the Big Ben Bell (Westminster… that is)
) has got as by surprise once again… hope there is no F5 in the near future steenoe said:
Thats how amazing the F4 is! Drop all your other projects, and go straight to the F4! Beleive me, you wont regret it
Steen
This call sounds like the Big Ben Bell (Westminster… that is)
Mpmarino, they wont give you a hard punch in the stomach, like a pair of JBL studiomonitors with 15" woofers does, thats for sure. I like them pretty good, though. If you want big and impressive sound, you better look for something with a bigger woofer. I used Troels's pdf about the 2.5 clones here:
http://www.troelsgravesen.dk/download.htm Mine are the 2.95 version.
Euvl, the sound is more detailed and transparent. That the topend is better with the F4 was expected, but even the bottomend has more definition. Also the soundstage, width/depth, is better and more precise.
Yep Blues, I think the j-fets has a lot to do with the fine sound of the F4. I will let the A-X's live for now
I am installing the F4 in another room and hooking them up to the Abby-clones.Tony, dont hook up my name with Nelson's like that, I really dont think that I deserve it
I would like to see a F5, as long as its a preamp for the F4 I am a bit surprised to find, that the NS10 isnt able to drive it to its full output. Steen
Vix dont dispair, half the fun is in building the amps
> I think the j-fets has a lot to do with the fine sound of the F4.
I dare to disagree.
IMHO, I think it has more to do with the bandwidth, AND also that it has no global feedback. I have similar experience with preamps on both issues.
And I am most curious whether adding 20dB gain (like the circuit I published in post #185) would change anything. And only then is the comparison to AX an equivalent one. ( I would have consider performing the experiment myself had it not been for the fact that I do not have any P-type power FETS lying around. )
Patrick
I dare to disagree.
IMHO, I think it has more to do with the bandwidth, AND also that it has no global feedback. I have similar experience with preamps on both issues.
And I am most curious whether adding 20dB gain (like the circuit I published in post #185) would change anything. And only then is the comparison to AX an equivalent one. ( I would have consider performing the experiment myself had it not been for the fact that I do not have any P-type power FETS lying around. )
Patrick
EUVL said:
Very interesting point! I have been thinking along these lines too. With this current gain buffer don't you just end up with a 3 or more stage amplifier - only split in two chassis? The aleph design accomplishes both voltage and current gain in only two stages, but perhaps voltage gain is better off left in its own box...
IMHO, the idea of F4 as a product is that it gives a consumer (as opposed to a DIYer) the flexibility to choose between many different configutartions, as described in the manual.
Whatever the combinaion, it does not change the fact that in the end, you would still need a source (e.g. CD), an attenuator, a voltage amplifier, an impedance converter, some form of crossover and filter (assuming that you are not using Fostex, etc.), and speakers. The combination of how to split and in what sequence is (almost) infinite.
The idea of an impedance converter like the F4 is that it allows you to design your voltage gain block only to drive (high) resistive load. Whereas an amplifier like Aleph has to perform voltage gain WHILE having to cope with a reactive load at the output, with whatever limitations and compromises that comes with it.
If you do happen to need the additional gain before the F4 (i.e. you are not putting all 30~40dB gain you might required in your preamp), then I woud argue a circuit like that in post #185 would save you at least one (unity gain) stage, namely the JFET input buffer of the F4.
And I would also argue that if you want to have an audio chain with no global feedback (a la Ayre), then you would most likely end up with an impedance converter at the end of the chain (before the speakers).
Patrick
Whatever the combinaion, it does not change the fact that in the end, you would still need a source (e.g. CD), an attenuator, a voltage amplifier, an impedance converter, some form of crossover and filter (assuming that you are not using Fostex, etc.), and speakers. The combination of how to split and in what sequence is (almost) infinite.
The idea of an impedance converter like the F4 is that it allows you to design your voltage gain block only to drive (high) resistive load. Whereas an amplifier like Aleph has to perform voltage gain WHILE having to cope with a reactive load at the output, with whatever limitations and compromises that comes with it.
If you do happen to need the additional gain before the F4 (i.e. you are not putting all 30~40dB gain you might required in your preamp), then I woud argue a circuit like that in post #185 would save you at least one (unity gain) stage, namely the JFET input buffer of the F4.
And I would also argue that if you want to have an audio chain with no global feedback (a la Ayre), then you would most likely end up with an impedance converter at the end of the chain (before the speakers).
Patrick
Is anyone planning to create some pcbs ? I would certainly be interested (as the board design is already in the service manual, I guess it's OK for Nelson if it is a non-commercial effort).
Some questions:
- If I change my route on DIY-amplifier from finishing my AX-100 towards the F4-route: Couldn't I get much more power out of the F4 ? I think my heatsinks have been calculated for 8 devices 044 per channel (source and gain together) with 2 ampere going through each device. heat sink temp is approx. 55 degree celsius, so hot, but still ok. I read now in the service manual, that only 0.53 amps goe through the devices: So why not more if heatsinks allow it ? I thought Nelson is a big fan of more current per device.
- My experiences with jfet: These little devices behave quiet a bit different, even if it is the same type, depending on the circuit and the Iss max. So what is the selection-criteria on the 2sk370 and the 2sj108 ? Both are out there in versions GR: 2.6~6.5 mA, BL: 6.0~12 mA, V: 10~20 mA, but I guess it is even better to know what the ideal value is and to select accordingly. Nelson, you said they run 5ma: Is that Idss max ?
- On the capacitor-coupling: What is the smallest value really needed ? 220u is an electrolytic. I really had to have that in the signal chain. so, could this one be smaller and be at least a MKP-Highend-version like Mundorf Supreme ?
- Last point: I would bet quiet a bit on the fact that a LcLc-power-supply would make a significant difference in sound to this standard crc-supply. Steen, any chance in testing this ?
Best Regards
Frank
Some questions:
- If I change my route on DIY-amplifier from finishing my AX-100 towards the F4-route: Couldn't I get much more power out of the F4 ? I think my heatsinks have been calculated for 8 devices 044 per channel (source and gain together) with 2 ampere going through each device. heat sink temp is approx. 55 degree celsius, so hot, but still ok. I read now in the service manual, that only 0.53 amps goe through the devices: So why not more if heatsinks allow it ? I thought Nelson is a big fan of more current per device.
- My experiences with jfet: These little devices behave quiet a bit different, even if it is the same type, depending on the circuit and the Iss max. So what is the selection-criteria on the 2sk370 and the 2sj108 ? Both are out there in versions GR: 2.6~6.5 mA, BL: 6.0~12 mA, V: 10~20 mA, but I guess it is even better to know what the ideal value is and to select accordingly. Nelson, you said they run 5ma: Is that Idss max ?
- On the capacitor-coupling: What is the smallest value really needed ? 220u is an electrolytic. I really had to have that in the signal chain. so, could this one be smaller and be at least a MKP-Highend-version like Mundorf Supreme ?
- Last point: I would bet quiet a bit on the fact that a LcLc-power-supply would make a significant difference in sound to this standard crc-supply. Steen, any chance in testing this ?
Best Regards
Frank
Hi Frank. You can easily adjust it to get more amperes/heat, you might need to adjust the value of R9 though. R9 in mine (and cvillers) are about 6K. The schematic says 10K.
I agree. When I build the monoblocks, I will use a CLC filter, with big Rifa's
Unfortunately, I wont be able to test the F4 with a different supply for a while. I am pretty hung up in the nearest future. Keep in mind that the F4 needs a decent preamp, especially if your speakers arent very effecient. One could get dissapointed about the soundlevel. I would also like to mention that all the other amplifiers are still as good as before
ZenV9, Aleph-X, Babbelfish's and so on, are still superb sounding amps. The F4 is just a further step forward sonically, at least to my ears Here are the words that made me want to try it: http://www.diyaudio.com/forums/showthread.php?postid=1151518#post1151518 Together with Mr. Pass remark in the F4 pdf that this could be the best sounding amp Who can resist building one? Not me
Nice big heatsinks
Looks cool Steen
One needs to consider the environment in which the amp is being used.
If you compare all amps with a preamp, then certainly F4 may have biggest advantage for performance.
However, I like F3 because I can use it without a preamp (source connected directly, no attenuator) or with a passive preamp (12db of gain is still enough for me).
Untill I was forced to use it with an active preamp, F3 was not appealing to me that much and I kept it on a side for almost half a year. But then, I switched to a source with higher output level and F3 can be now used with passive attenuator, and in a configuration when the output caps can be minimized or bypassed completely (3 way active system). Now, that brings the best out of it and I don't think F4 would be much of a contender here as removing the active preamp from a system can be actually the biggest advantage.
If you compare all amps with a preamp, then certainly F4 may have biggest advantage for performance.
However, I like F3 because I can use it without a preamp (source connected directly, no attenuator) or with a passive preamp (12db of gain is still enough for me).
Untill I was forced to use it with an active preamp, F3 was not appealing to me that much and I kept it on a side for almost half a year. But then, I switched to a source with higher output level and F3 can be now used with passive attenuator, and in a configuration when the output caps can be minimized or bypassed completely (3 way active system). Now, that brings the best out of it and I don't think F4 would be much of a contender here as removing the active preamp from a system can be actually the biggest advantage.
Lets take a look at what happened in car audio some 15 years ago. The competition circuit (Iasca) helped to make a lot of changes for the better. Competitors realized that driving the signal as hard as possible and gaining the amplifiers down greatly improved things. Better S/N ratio, less need for megabuck cables, overall better sound. Fortunately the head unit manufacturers responded by making sources with upwards of 12v unclipped at the RCA jack. The whole dang thing got way way better. I think it is the most important thing that happened in car audio.
I don't do cars anymore - did for 15 years professionally though. Heck, I was putting 8" pro midbases in kickpanels years before anything like that made it to a magazine. It was fun.
Granted, a car is not a living room unless you happen to drive a Bentley. BUT I wonder if the current state of affairs shouldn't be improved. I know - there are standards CD - 2v out/ pre - 5v out/ amp- whatever gain it happens to have. These things came about a long time ago and really never nudged.
I think with DIY we may realize a better way in this regard. Nelson, thanks for bringing this forward
I don't do cars anymore - did for 15 years professionally though. Heck, I was putting 8" pro midbases in kickpanels years before anything like that made it to a magazine. It was fun.
Granted, a car is not a living room unless you happen to drive a Bentley. BUT I wonder if the current state of affairs shouldn't be improved. I know - there are standards CD - 2v out/ pre - 5v out/ amp- whatever gain it happens to have. These things came about a long time ago and really never nudged.
I think with DIY we may realize a better way in this regard. Nelson, thanks for bringing this forward
Peter Daniel said:
I fully agree. When I built Zen V9, I was using it with the Bride of Zen pre. It was ok, but I had a feeling that something was missing. Until a few days ago, when I built a tube buffer. Wow! Only then I heard how good Zv9 can sound, albeit I can't play it very loud. Maybe I will reduce the amount of feedback on Zv9 or remove it completely and run it as a current amp.
Regards,
Vix
When playing with this circuit i noted that the capacitors driving the mosfets are rather large. I reduced size to 22uF to see what impact it had on the lower end frequency response. Taking the low drive current available through the Jfets into account, these two capacitors must be of ultimate quality, hence the desire for reducing the size. Anyway at 22 uF the frequency response extends to app 5 Hz and no phaseshift above 10 Hz.
Has anyone else been working with this issue??
Has anyone else been working with this issue??