All this cloak and dagger stuff is kind of killing the fun of this for me.
Fraudsters armed with official schematics aside, I don't recall ever hearing the Boss complain about our naive efforts.
I suspect he must get as much enjoyment from seeing our naive efforts develop as we do 😀
Fraudsters armed with official schematics aside, I don't recall ever hearing the Boss complain about our naive efforts.
I suspect he must get as much enjoyment from seeing our naive efforts develop as we do 😀
For commercial reasons, I avoid labeling any schematic "official" while still
in production as commercial cloners seem to rely on one.
At the same time I think DIY efforts to deduce circuits from first principles are
instructive and entertaining, and more in the spirit of DIY.
in production as commercial cloners seem to rely on one.
At the same time I think DIY efforts to deduce circuits from first principles are
instructive and entertaining, and more in the spirit of DIY.
Let's just say Antoinel circuit is extremely close.
It's missing one simple but important component.
I won't post it publicly.
It's missing one simple but important component.
I won't post it publicly.
I am a little reluctant to post here but I would like to share some comments about a couple of versions of F7 type amps I have built. Basically as someone said earlier an F5 with appropriate removals and trial and error playing with the PCF resisters. I use one on the lower midrange of an LX521 and the other on the upper midrange. Lower is an 8 ohm load and the upper is 4 ohms. The sound is as described above and on the Six Moons site. I am lucky enough to have several of the original 2SK147's and J72's and used them in the original F5's so not quite a fair comparison to other efforts as above. I did not try to match the Allfets and may account for my findings. The offsets tend to start rather far to the negative side and then as things warm up come closer to 0mv. Depending on the ambient temps in the room may run +/- 25mvs. The situation is exagerated in the 4 ohm amp as I don't feel you can use axactly the same Rsense despite the formulas presented earlier and may be on the edge of instability although sound fine. These are just some observations I thought others might be interested in. Moderator please remove if you feel inappropriate.
Very interesting and valuable observations thank you..
As for the drift +/- 25 millivolts is pretty enviable already 😉
As for the drift +/- 25 millivolts is pretty enviable already 😉
Hey Everybody, (a la Dr. Nick 😉 )
Couple of observational things.
First, you don't have to do this, but you might want to match the P3 pots that adjust H2 and H3. (You might not even use a P3.) This might be especially true if you are not using a FFT right away and plan on centering the pots on both channels. I did not match them and then ran FFT analysis and found enough variation to affect the sound. Pots are off by almost a couple of ohms. I mean it could all be in my head, but I think I hear a shift in frequencies between channels. I think it sounds OK, but there's a strange shift in frequency balance or depth and width. Like one channel if projected more forward than the other.
The thing I haven't done yet is setup the bias and offset of the amp while watching the FFT.
Also think the choice of preamp will have an affect on sound with this amp. The power amp itself is like a lie detector for the front end, much like the F5.
So maybe anything you use on the frontend will show it's goods. So far tried BA3-Pre and B1 v1. Will later try BOZ-J.
That's my two cents.
Vince
Couple of observational things.
First, you don't have to do this, but you might want to match the P3 pots that adjust H2 and H3. (You might not even use a P3.) This might be especially true if you are not using a FFT right away and plan on centering the pots on both channels. I did not match them and then ran FFT analysis and found enough variation to affect the sound. Pots are off by almost a couple of ohms. I mean it could all be in my head, but I think I hear a shift in frequencies between channels. I think it sounds OK, but there's a strange shift in frequency balance or depth and width. Like one channel if projected more forward than the other.
The thing I haven't done yet is setup the bias and offset of the amp while watching the FFT.
Also think the choice of preamp will have an affect on sound with this amp. The power amp itself is like a lie detector for the front end, much like the F5.
So maybe anything you use on the frontend will show it's goods. So far tried BA3-Pre and B1 v1. Will later try BOZ-J.
That's my two cents.
Vince
Attachments
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F7 Schematic
Guys is not rocket science. F7 is an F5 with negative feedback like F6 and added positive feedback. Some people did an F6 with PFC and worked nicely.
See attached. My schematic has 7 resistors but I know Nelson used 8. I can't figure it out where he put the 8th one.
Guys is not rocket science. F7 is an F5 with negative feedback like F6 and added positive feedback. Some people did an F6 with PFC and worked nicely.
See attached. My schematic has 7 resistors but I know Nelson used 8. I can't figure it out where he put the 8th one.
Attachments
That's a way to do it.
My dream F7 has sense before the loudspeaker and a pot to fine tune the PCF . Shame I cannot find a way to make it... yet[emoji2]
Will continue to hit my head on the wall but if somebody knows for sure that it can't be done please tell me. It will save me a few hours of sleep [emoji4]
Sensing resistor before the speaker is wrong. It has to be connected to ground like in my schematic, is the only way.