F5m kit

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#2,502
birdbox said:
incandescent bulbs are still available at big box stores
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I think that may vary country to country, but if that's true in the US that's certainly handy. Here in Aus there's no physical store that will sell them new to my knowledge. I've found a couple of bulk sellers of NOS bulbs on eBay, so that might have to be where I go. Hopefully a bulk amount means at least one survives the post. :spin:
 
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#2,505
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#2,506
Thanks for the guidance. I will be picking up what I need to put together a DBT from Lowes later today. In regard to bulbs, I recently inherited a very large box of bulbs that I think has the variety of watts I'll need. Just need to remember where the box went in my basement.
 
#2,507
What is the best way to monitor input levels? Can analog vue meters be connected to the input to ensure the pre-amp signal is at an optimal level? Should the vue meter be on the op-amp instead? ( not sure if iron pre has that ) My focusrite scarlett does not have any type of meter. With such a great sounding amp, I'm finding it important to ensure the input signal is peaking at 2V.

Maybe something from Sifam or ALPS meters? or LM3915/LM3916 LED display driver IC for digital.
 
#2,511
Extreme_Boky said:
Here... a pack of 4... you could build 4 amps! Not bad.

https://www.ebay.com.au/itm/1663889...dqKEVblMT7sk2U8mePEeR6K260TZOmNKYQh8QM8&gQT=1
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You can't get halogen light bulbs shipped to California. Nor smoke detectors with replaceable batteries. Nor large butane bottles to fill your cigar torch.

I had to have a bunch shipped to Washington St. Perhaps next time I go back and forth I'll ask the California folks if they want some and we can make a goup buy. I could take Hwy 1 and stop in Santa Rosa.

I always make a trade... I take bourbon from Costco up and come back with such things...
 
#2,512
I recently completed my f5m and can share the following observations on building and listening. First point regards using a variac. It totally saved my butt on this one. I decided to substitute 25-turn pots but didn’t realize the ones I ordered were mirror image. So I turned them full ccw and like an idiot didn’t bother checking resistance before soldering. At full ccw, these pots were full on. I started to turn up wall voltage but didn’t look at dmm showing bias. It was at about 95v or so that the fuse blew and I smelled something, but no smoke. The other twist is that instead of thermistor, I was using store version of soft start, which didn’t seem to click until much later than usual. I thought to myself that perhaps without full wall power, the relay didn’t click over properly and maybe I was smelling soft start resistors. Which raises a question - at less than full wall voltage, will soft start still work properly? I temporarily bypassed the soft start, replaced fuse, and turned pots full cw after realizing what happened. I was dreading that fets might be blown. Much to my surprise, everything worked fine. So first observation is that if you are ocd perfectionist, expect several hours of tweaking pots to get to whatever you consider acceptable. I got channel balance to 0.641 and 0.648V, with offset of 4.8 and 7.4mv. With cover on, bias and dc are (and should be) very stable. If I try to get dc lower, the bias matching gets worse. I’m happy. I’m using 5u store chassis and sinks are warm but I could keep my hands on them indefinitely. I was thinking of going to 0.7v on bias, but based on what I have read so far, it won’t make much difference and I’m done fiddling. I currently use F5t3 mono amps at 47v rails (soon to become balanced versions at 40v rails) which are simply amazing. What struck me first was how different the f5m sounds from the f5t3. My monos are incredibly transparent and detailed (I have p3 set midway on these - I don’t have distortion analyzer and am not inclined to go down that rabbit hole). The f5m has many of classic tube SET traits. Vocals are highlighted, front and center. Tone and textures are really brought out. Individual instruments sound beautiful. But also like SETs, when there is a lot going on, such as orchestra in full tilt, the sound and detail gets a little blurred (only a little). So ensembles, jazz quartets, that kind of thing, are incredible. Total tube-like fluidity and beauty. There is absolutely no stridency in the sound, so if something sounds harsh, you likely have a problem elsewhere in the system or the recording is truly awful. The amp makes less than stellar recordings sound really really good. Detail is excellent and what I would call “musically important detail.” Soundstage is very organic and defined. Whereas my monos seem to have details far deep into the stage, the f5ms have it all in a well defined bubble. But you hear everything in that bubble and where everything is placed is very precise. Don’t misinterpret this as “small” - the sound is big and bold. Everything in simply more upfront and within a defined space. Compared to my F6, the F6 seems a bit more vague and opaque. Compared to my Aleph 3 clone, the aleph shares the same organic SET quality and easy listening of the f5m, but falls a little short of f5m in terms of detail, and transparency and soundstage precision. The aleph however is dynamic as hell and sounds very powerful. The f5m has very tight and well defined bass, quite punchy, but not quite as powerful sounding as aleph 3. Also, I’m not sure of f5m drive capability. My speakers really need 25w minimum, and when I turn up and get loud, the f5m sounds like it strains, maybe even clips. Both the F6 and Aleph seem able to go louder before reaching their cap. The f5m is a remarkable amp and does so many things really well. I know folks on this forum like to try goofy stuff, like building amps in cigar boxes and so forth, but this amp deserves top quality components because it easily competes with $5000+ amps out there. But again, the thing that still gets me is how a design that is basically same as what I’m using can sound so different. . .
 
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#2,515
algg - your characterization of the f5m totally matches my listening experiences - very well articulated w/o the audiophile-adjective-babble. Right now I'm lining up parts for some kind of SIT build, yet I'm feeling no rush. About the only trait I'm looking for is the ability to handle orchestral music and some rock stuff, and my curiosity around the ability of some kind of THF51s implementation to handle the more demanding stuff (orchestra/rock) will be front of mind.

Anyway, nice share - thanks
 
#2,516
algg said:
I decided to substitute 25-turn pots but didn’t realize the ones I ordered were mirror image. So I turned them full ccw and like an idiot didn’t bother checking resistance before soldering. At full ccw, these pots were full on.
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Thank you very much for sharing this. I am gathering parts at the moment, and also decided to be very clever and order multiturn pots. I didn't consider the possibility of a different pinout. I just checked the datasheet and, sure enough, pins 1 and 3 are reversed for the 4 turns I bought. You have just saved me considerable expense and heartache.
 
#2,518
Zman01, The build is nothing special and is embarrassingly messy (my F5Tv3 are much nicer). This was my F6 - I reused the same power supply. At some point I plan to go back in and dress up the wires a bit better, but it’s completely silent in present condition. For those who plan to use F6 style power supply, or the dual bridge version F5m power supply, I would recommend getting transformer with 20v secondaries. With typical bridge Vf drop and under load, I’m getting 24.2 +/- rails using 400va antek 20v. Also, soft start is absolutely unnecessary for the F5m. I’m using it because I have it, but this same power supply with thermistor worked perfectly and effectively for F6. The F5m has no turn off or turn on thumps or other noises. Speakers are Harbeth C7es3 xd. For 75% of listening, 25w can be sufficient, but they are in a large room and sometimes I like to turn it up (we all do!) at which point they need more power to avoid sounding compressed.

1736985658694.jpeg
 
#2,519
Okay brains trust, I have 2 questions that I have tried and failed to answer with the search function:

1) With respect to the trimmer pinout question earlier, is the 'full CCW' setting Mr Pass mentions for the R8/R9 trimpot 0 ohms? Looking at the circuit it seems like as trimmer resistance increases, R6 and R7 become the path of least resistance, causing more current to flow through them to Q3/Q4, so you'd want to start with trimmers at 0? I figure if I have the resistance I need to start with, I can use a multimeter and remove all doubt re: CCW vs CW on the trimmers I've ordered.

2) Is there any reason to not use non-inductive resistors for the 3w resistors (R3-7), other than expense? I was thinking of using some Dale NS series resistors in those positions, just because I'm feeling fancy, but I can just as easily not if a teeny bit of inductance is somehow a desireable quality.
 
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