Google "How to measure low resistances". See if that helps. See also the specs for your DMM and/or the DMM you're considering.
See the schematic re: whether you think you could leave them in the circuit while measuring their resistance accurately. If in doubt, measure each of the source resistors in circuit. How close are your measurements to 1 ohm?
More importantly, congrats on the build! Is there a particular issue or concern you're trying to address.
See the schematic re: whether you think you could leave them in the circuit while measuring their resistance accurately. If in doubt, measure each of the source resistors in circuit. How close are your measurements to 1 ohm?
More importantly, congrats on the build! Is there a particular issue or concern you're trying to address.
380mV over each source resistor give you a standing current of 3.04A. That is giving you 280W power dissipation pr monoblock. For 100W class A at 8ohm you need 2.5A
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Thank you all for input. As I read the many posts from folks diagnosing Hum problems or complete meltdowns, I feel very lucky because my f5tv3 monoblocks worked perfectly from day one and are dead quiet. they Also sound amazing. I have built and own many of papa’s designs, and was regularly using f6 prior to this project. The f6 is a great amp but I was asking too much of it driving my revel speakers. the f5tv3 gave me the extra power I needed. Best analogy I ever heard was comparing car with 400 hp v8 engine, and one with small turbo engine that can reach 400 hp but has to be run at screaming rpm level to achieve. There is something to be said about the headroom and “ease” of sound using a larger amp with power in reserve. I encourage everyone on the fence about building the amps to just do it. They really are amazing. Some of this is a function of monoblock format - zero crosstalk combines with the already killer imaging and soundstaging inherent in pass amps to create a truly holographic soundstage that is tangible - like you can walk around each performer on the set. Incredible. The large class a envelope is also huge benefit. These are natural sounding amps, not clinical or cold like the early versions of f5. detail Is off the chart. Thank you all for helping me get this level of sound into my home, and thank you Nelson for sharing your gift.
Very nice and congrats to your successful build!
Did you build your monoblocks fully balanced/symmetrical and which power supply and filtering did you end up using?
am trying to understand whether the bias difference between n and p channel can be nudged to be closer. Yes, I can feel your eyes rolling but indulge me please. I read in a prior post that how closely matched the Output devices are is big factor. I also understand that closely matched source resistors are important. Post 138 was helpful. my Mosfets are diyaudio store matched so I believe them to be close. I also used milliohm meter to measure source resistors (thank you itsallinmyhead) and they all seem to be .501 to .504 across the pairs. Is this small difference in source resistor values enough to skew bias? In other words, if I were to hand-select lower resistance resistor [say by .01] on p channel, would that increase (decrease??) bias reading on that p channel? I would think that increasing source resistors slightly would increase voltage drop and therefore display a lower MV bias reading. Am I understanding any of this correctly? Still learning…
Thanks starcat. Just standard monobloc without diodes using store’s 5u chassis. 46vdc rails. i can bias to about 350mv to get to target heatsink temp. Power supply is standard store version. I used 63v 18kuf caps from Cornell dublier. Would have preferred more capacitance but can’t find higher uf at 63v+ without paying $25-30 per cap.
So you must be running one FE board per monoblock and the signal is coming in unbalanced via chinch input?
Thanks on the other info.
You can always use more caps in parallel to get higher uF at lower price.
That's the difference between the Vgs of the N transistors and the P transistors. (which basically never match)
Nothing to worry about at all and doesn't effect anything. If your offset is stable you are done. Hook up some speakers and plan your next project.
Thank you 6L6. Definitely enjoying the amps and no intention to mess with a good thing. Just trying to understand whether minor changes in source resistance can offset Vgs imbalance. And would increasing source resistor values lower the bias or raise it? I’m talking about 0.01 ohm variation up or down in source resistance. Thanks.
This is pretty confusing right in the beginning and needs some clarification I guess.
2 FE board will be left over if the amp is single ended. If symmetrical/balanced then all 4 FE boards get used; 2 FE boards are needed per channel handling both + and - halves of the signal (as minus would not touch GND).
Hello starcat,
your above statements are correct. It is all described in the F5T-article of Mr. Pass.
The picture below shows the SingleEnded-version of a F5T - V3-Monoblock (=one channel) with
one FE-board and 2 N-ch-boards and 2 P-ch-boards. (the amount of N- and P-channel-boards is
upscalable).
Cheers
Dirk
Attachments
The F5T in the balanced version as a Monoblock (=one channel) has
2 FE-boards connected (check schematic)
and minimum
2 P-ch-outputboards
and
2 N-ch-outputboards.
The number of outputboards is also upscalable ( as more FE-boards will be as leftovers / reserve/
headphoneamp/...)
Cheers
Dirk
2 FE-boards connected (check schematic)
and minimum
2 P-ch-outputboards
and
2 N-ch-outputboards.
The number of outputboards is also upscalable ( as more FE-boards will be as leftovers / reserve/
headphoneamp/...)
Cheers
Dirk
Attachments
Thanks, Dirk.for the balanced version:
I wish a happy and relaxed biasing - procedure
Basically each balanced monoblock is a dual channel single ended stereo amp. Only difference is that both channels amplify two halves instead of left/right channels with reference to ground.
What happens with the frontend actually in case the F5T v3 balanced monoblocks are connected behind a balanced UGS preamp with an UGS v3 in place?
Hello starcat,
if I understand your question right, you run your music-signal balanced into the UGS-preamp and from there balanced into the (balanced version of the) F5T-V3.
Balanced signal in the sense of 'fully differential mode'. So you have a signal with normal polarity and a second signal (but with inverted polarity) + Ground.
I have to search for the UGS v3-board-schematic. But I think it also works as a balanced pre-stage (balanced circuit)?
But what should happen to the frontendboards of the F5T-V3-balanced amp? It would have to work in balanced operation mode - if I understand your question right?
so the entire signal path (cables) and the all amplifiying stages would work in balanced operation.
Or is the UGS v3-board working single - ended? - I don't think so.
Cheers
Dirk
if I understand your question right, you run your music-signal balanced into the UGS-preamp and from there balanced into the (balanced version of the) F5T-V3.
Balanced signal in the sense of 'fully differential mode'. So you have a signal with normal polarity and a second signal (but with inverted polarity) + Ground.
I have to search for the UGS v3-board-schematic. But I think it also works as a balanced pre-stage (balanced circuit)?
But what should happen to the frontendboards of the F5T-V3-balanced amp? It would have to work in balanced operation mode - if I understand your question right?
so the entire signal path (cables) and the all amplifiying stages would work in balanced operation.
Or is the UGS v3-board working single - ended? - I don't think so.
Cheers
Dirk
Yes, right. Everything balanced, in fully differential mode. Not only cabling and signal transmission between components but source/preamp/amps being all 4-channel devices where the signal do not touch ground at any point.
I was kind of thinking loud if the FE boards are really necessary in case there is already an output buffer and strong pre-amplification, i.e. not a low voltage source fed directly into the F5Tv3/bal/mono's...
2x SE amp wired as a bridge amp is not the same as a fully differential circuit designed as such.
See discussions on supersymmetry, and Pass Labs products.
See also :
http://pmacura.cz/diyaudio/jfetdist.htm
Patrick
No one talks here wiring two SE channels as a bridge. I only said that in a balanced amp there are two channels amplifying the plus and minus halves of a balanced input signal. For setting the bias both channels are detached, bias set and then linked together again.
And yes, generally two channels can be wired as single ended stereo, balanced mono or bridged mono while bridging wasn't the point here.
Also nothing speaks against wiring two F5Tv3 FE boards with 2N+2P boards (from the diyaudio store) in a balanced manner and also Nelson Pass is showing exactly this in his F5T paper.
Or do you say that the F5Tv3 is not designed/can't be used as a balanced amp?
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