Hello Nag. Type 3 schematic in post 442 [by DIYer lhquam] is interesting.
BUT your simulation begs the following comments/questions regarding its PSU.
1. It shows the schematic of a mono block. The center tap of the power transformer is no longer ground or common. It is now the source of a phase inverted signal [relative to power output] which fulfills the requirement of positive feedback [PF].
2. Point [1] suggests the need for two independent PSUs so as to cater to a stereo power amp. One independent sense resistor per channel! The two center taps of the two power transformers become the independent sources of [PF] for each channel.
3. The 6 moons pictures of F7 show a clear and close-up picture of one power toroid with two secondary windings. It is believed to be a classic Pass PSU.
4. Is it possible to have one PSU with one sense resistor [like your simulation shows]; but which services; meaning it injects a common positive feedback signal to both channels? That will be utter simplicity and least expense!
5. Point 4 suggests that stereo separation will be affected; for better [more] or worse [less].
6. Therefore, a picture of the solder side of F7's PSU is suggested to see so as to dispel the hypothetical scenario of points 4-6.
Best
Anton
Dear Anton,
Honestly, don't have that much knowledge. Mr. Pass added more capacitance in PSU to reduce noise. As per my understanding, the only 3rd one in #442 is positive current feedback remaining all are positive voltage feedback. my sixth sense saying 3 rd one is nearly 99% matching to F7. 🙂
Thanks,
Nag.
Honestly, don't have that much knowledge. Mr. Pass added more capacitance in PSU to reduce noise. As per my understanding, the only 3rd one in #442 is positive current feedback remaining all are positive voltage feedback. my sixth sense saying 3 rd one is nearly 99% matching to F7. 🙂
Thanks,
Nag.
Dear Nag. Please find attached a simplified schematic for the two identical channels of your suggested diyF7. Each channel in my drawing is identical to the recent one you showed. I hope that it sheds more light on the contents of my earlier post which were vague. Notable are:
1. One dual voltage power supply unit [PSU] for both channels.
2. One 0.3 Ohm load current sense resistor per channel. But note that the sense resistors sum the Right and Left load currents at the center tap [CT] node of the [PSU]. This generates a common [or a mono] signal which is the source of simultaneous positive feedback [Vpf] to both channels .
3. Note the phase of the shaded portion of the signals. The resultant mono [Vpf] signal is out of phase with the rest.
4. In operation, [Vpf] is offered to the inverting input of either amp. It emerges in phase with [Vout]; due to [Vin], and thus augments its amplitude; meaning a positive feedback outcome.
5. All indications from the simulations of DIYer lhquam [post #442], and yours say it works. I agree.
6. It is apparent that the "stereo" information which inherent in each of the sensed load currents for actual music signals has been summed [lost!] at the [CT] node of the shared [PSU]. Other schematics of possible diyF7 do not have this unique condition. Their Left and Right [Vpf] are not summed; except acoustically.
7. Is the resultant channel separation or the stereo image affected by the +2 dB voltage gain due to the mono [Vpf]? You'll have the answer once you listen to your assembled stereo amp.
Best
Anton
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Antoine, you forgot about this :
"Dear Anton, Honestly, don't have that much knowledge "
the man said it all , he's one of us , he likes diy as we all do , but he's not a masters , like many of us ...
remenber , there is one master here , of F7 and others nice stuff obviously 😀
.
"Dear Anton, Honestly, don't have that much knowledge "
the man said it all , he's one of us , he likes diy as we all do , but he's not a masters , like many of us ...
remenber , there is one master here , of F7 and others nice stuff obviously 😀
.
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Dear Anton,
Thanks for taking the time and draw the circuit. I am surprised(happy 🙂) to see pen and paper. I need some time to understand the concept.
Thanks for taking the time and draw the circuit. I am surprised(happy 🙂) to see pen and paper. I need some time to understand the concept.
It's come to my attention that the F7 might make a great match with my current speakers, so I've bumped this thread. I've attached (perhaps) an impedance plot. I know that some of you clearly know how to build the amp, but I'll have to look forward to the release by Nelson.
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Got first good sound tonight out of my amplifier. Oreo862 was so kind to send me a pair of the boards he worked up a while back in this thread. I won’t go into a high level of detail since the official schematic is still not out, of course. But a little about my build. I was having major issues with my Diyaudio PSU board. Whether it was the board’s issue, or something I messed up, the ground loop was so loud when first hooked up I shut down the amp before getting any real sound out of it. I tried to chase the ground loop but was in unsuccessful and unfortunately gave up on this amp for a while. About 6 months later I decided to build up the PSU boards you see in the photo, a cap multiplier board by Prasi, gtose and Mark Johnson. First channel tested out great. No hum or noise. I got the next board soldered up today and finished all my wiring (the usual rats nest before cleanup) finished tonight. No hum or noise on either channel. Amazing! If anyone is looking for a great PSU these boards really did the trick for me.
Another issue I thought I had was that when I used my iPhone as a source I was getting very faint sound. As I should have known this amp takes a good Preamp to drive it. I’m currently using my WHAMMY. The sound so far is fantastic! Can’t wait to get more hours on it.
Parts wise, a few things. For mosfets I’m using Exicon’s from Profusion and genuine Toshiba jfets from Spencer.
Big thanks to vdi_nenna, huge thanks to Oreo862 for trusting me with the boards and helping me throughout the build, and of course, a huge thanks to NP for giving enough hints along the way.
Another issue I thought I had was that when I used my iPhone as a source I was getting very faint sound. As I should have known this amp takes a good Preamp to drive it. I’m currently using my WHAMMY. The sound so far is fantastic! Can’t wait to get more hours on it.
Parts wise, a few things. For mosfets I’m using Exicon’s from Profusion and genuine Toshiba jfets from Spencer.
Big thanks to vdi_nenna, huge thanks to Oreo862 for trusting me with the boards and helping me throughout the build, and of course, a huge thanks to NP for giving enough hints along the way.
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Are the transformers off the chassis base?
Avoid the "L" formation around the transformer's sides.
Separate them a little if possible. Hard to tell if they are touching on sides and each other.
Avoid the "L" formation around the transformer's sides.
Separate them a little if possible. Hard to tell if they are touching on sides and each other.
Thanks vdi. I will definitely be tidying up the chassis including finding a better placement for the transformers. This was the first stereo test of the amp. Still a ways to go before I close up the case.
Also, made a typo in my last post. Credit goes to Oreo382, not 862. Sorry about that!
Also, made a typo in my last post. Credit goes to Oreo382, not 862. Sorry about that!
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The general location and vertical orientation of your transformers are actually fine. They do need to be fixed in place so that they don't roll around though. 🙄
There are steel brackets available for mounting transformers in a vertical orientation. It is also possible to make your own out of acrylic or even wood. The important thing is to avoid creating what is called a "shorted turn" around the transformer. A shorted turn may occur whenever there is a 360° conductive path through the center of the toroid and around the outside, in parallel with the actual copper windings. This is avoided by preventing conductive supports (whether bracket or chassis) simultaneously on both sides of a steel mounting bolt. Using a non-conductive center mounting bolt such as nylon will also break the possibility of a shorted turn.
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Thanks TungstenAudio. I believe I have enough space to lay the transformers down horizontally and bolt through the base plate of the chassis. And yes, I certainly didn't intend to leave the transformers rolling around. Again, this is a progress photo of the amp, not the finished product. Appreciate the feedback though.
I'll be reporting back on the sound soon hopefully.
I'll be reporting back on the sound soon hopefully.
Hi,
In progress of trying out F7, I don't understand anything about anything, but my friend helped me out with this one.
It seem that I have only V-grade J-fets available. Is BL-grade required on this one? I think that about 8mA idss would probs be best choise, these are just so hard to find nowdays.
I know there will be couple of others obstacles before I have working amp 😀
In progress of trying out F7, I don't understand anything about anything, but my friend helped me out with this one.
It seem that I have only V-grade J-fets available. Is BL-grade required on this one? I think that about 8mA idss would probs be best choise, these are just so hard to find nowdays.
I know there will be couple of others obstacles before I have working amp 😀
Problem solved, managed to source matched original BL's, you can never have enough of these! They will be about 8mA's.
I'll try to keep that in mind, thanks Papa 🙂. Trying to replicate this amp will probably teach a lesson or two once more..
BL grade fets came finally. One pair ids 8.06 and second pair 8.35.
I'm very close to fire it up, hopefully not literally. I just don't get one thing that I really should understand; measuring resistance from bias (and offset) trimmer pot center pin - JFet drain, should my initial setting be max (500R in this case) or 0R? My guess is 0R, but I wan't to be sure.
I'm very close to fire it up, hopefully not literally. I just don't get one thing that I really should understand; measuring resistance from bias (and offset) trimmer pot center pin - JFet drain, should my initial setting be max (500R in this case) or 0R? My guess is 0R, but I wan't to be sure.
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if we are speaking about something having resemblance of F5 , for starters you need zero resistance in JFet drains