IvarNy,
Take a look at the last paragraph on page 2 of the F5 service manual https://www.firstwatt.com/pdf/prod_f5_man.pdf, there is info regarding oscillation that may help.
Andy
Take a look at the last paragraph on page 2 of the F5 service manual https://www.firstwatt.com/pdf/prod_f5_man.pdf, there is info regarding oscillation that may help.
Andy
Yeah, might be something there, I am using (thightly) twisted pair as input wire, and it could be a bit too close to output cabling, even with output down the center and inputs close to sidewalls, but actually it seems it was not occillation as such but more broadband high frequency noise coming from my DAC. If you get oscillation it tends to be a single frequency, but may be wise to go coax or mic cable in the F5 chassis.
Nothing good comes from high Idss JFETs. But you can change their source resistors to 15 ohms if you like. This may cause some changes in the gain structure and should ideally be measured to verify.
If you use them in the default circuit without changes, typically the available OLG will also be lower as a result of higher gm of the input devices - drain resistance to get similar drive voltage for the MOSFETs will be quite a bit smaller than expected. In either case, do be prepared for a slightly different (note, not necessarily worse) experience than a build with 6mA JFETs.
If you use them in the default circuit without changes, typically the available OLG will also be lower as a result of higher gm of the input devices - drain resistance to get similar drive voltage for the MOSFETs will be quite a bit smaller than expected. In either case, do be prepared for a slightly different (note, not necessarily worse) experience than a build with 6mA JFETs.
Got rid of my hum issue with my F5. Solution: change my aging trusty Linn Kern preamp with the fabulous Iron Pre from the shop and Zenmod. Thanks to all who has contributed to the pre! When I tested with shorted inputs, on the F5 and got hum, I must have missed disconnecting both channels from the Kern, or the Kern was doing something on the mains side to create trouble. Anyhow all is good now and the F5 is sounding fabulous with the IP. Now the only trouble is deciding what I like most: my F5 or my F4! My F4 is also online now. Currently the F5 is in the lead as I find with my speakers that it has a more solid sound-stage. The F4 seems to have a bit of a "hollow" in the center, and placement of vocals and instruments is not quite solid. Especially disturbing on vocals where the singer seems to be floating around and is placed wherever you look for it kind of.. Otherwise the F4 is sounding great as well, so I suspect it must be some kind of phase issue that occur in the F4..
Hello everyone and happy new year. I have 6 pairs of original J162 and K1058 and I would like to know if I can use them in this F5 with or without modifications. Maybe this topic was talked about in the thread, but since it is so long it is very difficult for me to find it. Thanks in advance and greetings to all.
There's a modification required in the feedback circuit discussed earlier thread, and is conceptually similar to the F7, at least the first drawings presented by Nelson in that thread. I've successfully used 3 pair output with the original feedback network and values (50/10R ~15dB gain) with no issues, three pairs LATFET at ~1.7A cumulative bias are required to yield similar CLG to a single pair of vertical MOSFETs @1.3A
It still has less feedback, which is something you might like, or not.
It still has less feedback, which is something you might like, or not.
The pinout of these MOSFETs differs from the IRF/Vishay. They are somewhat less robust (see the safe operating area) and have a lower Vgst (threshold voltage)
Hello Mr. Pass. Since I don't speak English, I'm using an online translator. It seems that he does not translate very well and I am not clear about his answer. Do you mean to tell me that I can use the j162/k1058 without problems because they were better than the IRFP? If so, can you tell me more about that?
@cucu70, J162/K1058 are lateral mos fets, which are different than the vertical mos fet IRF/Vishay/Harris/etc. that are used in many Pass designs. Typically, mos fet output amplifiers are designed with a specific type (lateral, vertical, hex) and interchanging fet type requires significant schematic changes.
I would suggest searching for a design that uses your fets, specifically (like the Profet amplifier Nelson mentioned). Or, sell those and use those funds for parts for an F5.
I would suggest searching for a design that uses your fets, specifically (like the Profet amplifier Nelson mentioned). Or, sell those and use those funds for parts for an F5.
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In the F5, Vds is ~23V. The output MOSFETS are biased for Class A operation at @1.3A (0.6V/4.7R) so you are within the safe area of operation.
See this thread: https://www.diyaudio.com/community/threads/f5-with-2sj162-2sk1058.249757/
See this thread: https://www.diyaudio.com/community/threads/f5-with-2sj162-2sk1058.249757/