Funny you should ask that. My BA-3 is in a 5U Deluxe chassis, and unknown to me it was shipped without bottom cover. (I have it on the way now) So no, it never had the bottom cover, and I am sure this aids airflow. The F-6, which DID come with the bottom cover (and started the inquiry about the 5U missing its bottom cover) I will use for sure, as the amp just isnt that hot.
I also have every intention to use it on the hotter BA-3 amp as soon as it arrives. I think there will be plenty of air flow, and if it gets hot this summer, I am planning on a "Zen Mod Baby sitter" anyway, so I don't see it as an issue.
My F-5, which is in a chassis I made out of M&M heatsinks on the sides, bottom , top, and rear panel is of 1/8" inch thick 6061 aluminum. It is a dual mono rig and it has no venting at all, except the top cover sits about 3/4" proud of the rest of the chassis, and this gives plenty of ventilation, it is no hotter than others describe. I can "palm test" it indefinitely. The 3/4" space, if you do the math, has more area than most slotted chassis. Again, a babysitter would cure any problems...it has run for years now problem free.
Russellc
My BA-3 is push pull and it has 32 volt rails. Lots of gusto. Used to use a tube pre with F5, really for the gain. Never a big fan of tube pre with solid state power amps. I prefer solid state pre, phono amp etc. If I want tubiness I would do tube power amp.
My BA-3 throws a huge 3-D soundstage and has plenty of grunt, yet warm and pleasant.
Russellc
Dont get me wrong, I will try it with tube pre and every which way. It is an excellent amp for sure...all the Pass amps seem to be!
This amp also excels at huge 3-d soundstage, very wide.
Bass is strong too, I will need more listening then go back to the F-5 that was in this system. That F-5 has very nice bass, dual mono with dual 300VA transformers. At this point I think I like F-6 over F-5. Another thing, F-6 was by far the easiest to build and light up. Very straight forward, it was playing music in no time. Just turn until it got to .500 volt, other pot to zero offset. Hook up other channel and repeat. Burn a little while, touch up settings, burn a while and try with test speakers and into system!
Russellc
This amp also excels at huge 3-d soundstage, very wide.Bass is strong too, I will need more listening then go back to the F-5 that was in this system. That F-5 has very nice bass, dual mono with dual 300VA transformers. At this point I think I like F-6 over F-5. Another thing, F-6 was by far the easiest to build and light up. Very straight forward, it was playing music in no time. Just turn until it got to .500 volt, other pot to zero offset. Hook up other channel and repeat. Burn a little while, touch up settings, burn a while and try with test speakers and into system!
Russellc
Mini Disipante 3U is what I would use.Very Nicely built project.
Still hunting the elusive heatsink
Given the lowish heat of an F6 what would be a reasonable sized sink?
Would a Diy shop 3u case be adequate ...as example?
Couple of hours listening on large E-wave system last night seemed to show that while the F-6 sound field is very wide, it is deep and not a lot comes forward of the speakers...really extended far back from there. My Ba-3's sound stage is wide, deep, but also comes more forward from the front of the speakers. This is something I enjoy...The BA-3 has a lot of grunt, 1000VA 24 + 24 volt tranny I had from a Turbo F-5 project I sold.
Taking it upstairs to a system with high Quality 2-way stand mounted 6.5 inch mini monitors, it was different, imaging a little more forward. Hmmmm. More listening needed. Have not tried it with Large Altecs, and two other stand mount speakers, one with 91 dB efficiency.
Am currently working on an Open Baffle Speaker I want to try this on.
Russellc
Taking it upstairs to a system with high Quality 2-way stand mounted 6.5 inch mini monitors, it was different, imaging a little more forward. Hmmmm. More listening needed. Have not tried it with Large Altecs, and two other stand mount speakers, one with 91 dB efficiency.
Am currently working on an Open Baffle Speaker I want to try this on.
Russellc
Yes, and tonight something is happening, break in, whatever. This amp is coming into its own. Image now creeping forward... moved speakers slightly further out from the rear wall, removed one more "Zilch plug" giving basically identical tuning to the JBL 4430 monitor...5 cu ft, 34 hz tuning, JBL 2235H woofer. Now the sounds are moving all around, behind and in front, maybe not as powerful as my BA-3, but what this amp is beginning to do is true magic. Sounding really nice.
Russellc
Im going to keep listening a while. For continuity, I have a BA-3FE upstairs and downstairs. I will try other pre amps eventually, but for now I just want this amp to settle in so I can get a flavor of it in different rooms and speakers. Once it is settled and I feel familiar with it, I will try the moving the wire trick discussed back when everyone was considering the 3 different schematics, degeneration and so forth.
For now, just listening is getting interesting. After 2 or 3 hours, offset at 2.7 mV on both channels...bias steady as a rock at .527 and .538. One stable Amp! Making me itch for M-2!
Russellc
For now, just listening is getting interesting. After 2 or 3 hours, offset at 2.7 mV on both channels...bias steady as a rock at .527 and .538. One stable Amp! Making me itch for M-2!
Russellc
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It also took me weeks to get the rest of my system dialed in for the F6 and now all my amps I switch in and out sound better. A very revealing amplifier. It has a sound stage that rivals an SET amplifier with horns. I have noted you have multiple speakers to try it with so it should help with the review. Do try your tube pre with your Altec's but from what you have said you like the quicker SS BA3 better with the other speakers. I prefer a little more 2nd harmonic with my horns. I also have a BA3 pre and it is great, absolutely, I just prefer my tube pre with the F6. This is the reason for Chevrolet vs Ford.
Oh, fear not I will try it with a tube pre. I just want to be familiar before I through in more variables. Prior to Pass DIY, I was a straight tube guy. every preamp and power amp I owned was tubes. The F-5 build shook that up. So I fully understand the tube thing. Speaking of flea watt SE tube amps, I was never a big flea power SE guy. But something that is on my mind is to build a flea watt 45 tube amp with B-1 on the front end, (or just a volume pot) and drive the 45 amp into a F-4 amp. The notion of a 25 watt 45 amp gets my attention. My reading is that the F-4 adds very little, essentially letting the characteristics of the 45 amp "pass through."
Russellc
Apologies for OT, but this made me really giggle!!
Well what I mean is for instance, my Altec A7s are driven by a 65 watt P-P 6550/KT88 amp...rather than a 3 to 10 watt SE. I know people who just love the SE amps, they seem to really shine with (here's another one for you) little girl with guitar music, just don't handle rock or bombastic classical in the way I prefer. To each their own, its all good...and very nice to have choices. No disrespect to the SE crowd!
Russellc