F-5 builders: Plans on building B-1?

I just found a couple of these Honeywell transformers, NIB. Rated at 24v , 40va secondaries. You will be at the high end of supply voltages for the B1, even with regulation. I also found a 16v, NIB, on the shelves. In the attached picture is the aforementioned 24v Wallwart, 500ma.

BTW, I believe the wallwart has a cutoff circuit (at least an indicator) for use as a battery charger. You could have battery capability, too.
 

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If you're going to run at 24V a series pair of smallish (say 7AH), 12V SLA batteries should last a while.

BTW, if anyone needs a low current 12V battery charger these are a real bargain. Not pretty, mine has significant marks in the case where the cables actually look like they melted into the housing. Melted as in chemical melting, not heat, but it works perfectly fine and voltages are dead on for the proper float and cyclic charge voltages for SLAs.

http://www.allelectronics.com/make-a-store/item/BC-100/12V-1A-CHARGER-FOR-LEAD-ACID-BATTERIES/1.html

This is the charger I'm now using with my battery powered DAC. I used a 4pdt switch that puts the batteries in series for use with the DAC and changes the connection to parallel for charging.
 
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Purchased a Dell PA-10 laptop power supply for the B-1. 19.5 volts, should be perfect. At least until I can cobble together something fancier. I think this will serve the purpose well!:yes:

Russellc
 
While the Dell PS I ordered will work for a while, I've just found a link to using just the shunt regulated power supply on the board I'm to get through a group buy for the DCB-1, a hot rodded B-1. Later, I can build out the entire DCB-1.:scratch2:

russellc
 
Maybe you guys can help me out on this B1 topic.
I have an adapter rated at 24vdc that I put on the dvm and got 30.2 vdc.
Think that will be a problem for the B1 since the B1 is rated at 24vdc?
 
b1buffer003.jpg
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1MOR, are those knobs the clear matte or clear gloss version?
 
Thanks. I've been thinking about changing my black matte ones for the silver/clear matte. Gives the front panel a bit of definition over the all black "stealth" appearance mine currently has.
 
Anyone played with different values of potentiometers?

I'm currently using 50k and thinking of reworking my single-ended B1 into a fully balanced unit (I have a 2nd B1 board w/matched FETS). So, in doing this, I'll need to replace the two mono pots with two stereo pots. I know Pass's parts list calls out 20 or 25k but seems to imply just about anything works fine.

Have you tried higher or lower and noticed any difference?

Also, I think the Pass list calls out linear taper pots. Any reason to stick with linear vs audio/log taper?
 
I thought that Nelson suggested log pots but it is all a blur, now.

FWIW, I'm using 100k mono pots and they work great. There is thought that the best mate is a 50k or less pot but I think you can use anything between 10k and 100k without worry.
 
Nelson recommended the 25K PEC linear pot, but like several here have said, he also indicated playing around with the value was fine.

My Dell power supply came, now to figure out which chassis plug for it to mate to. Sure wish this thing had a little gain! With a Rotel CD player combined with the B-1 and the F-5, driving my large JBL E'waves, full throttle yields an average of 90 db at the listening position. Peaks a little higher here and there. With The Van Alstein pre amp there is plenty of gain to get to surprising levels, all things considered.

Russellc
 
Probably will just go with a pair of Alps Blue 50k stereo pots. Thought about a pair of stereo stepped attenuators but since these also act as balance control, the fine resolution of the pots may be slightly better in this regard.

Working the numbers, the F5 looks like it would require roughly 2.5V input to reach full output. That's about 1 volt more than what I would say is typical/average for most amps, but the typical SS amp has gain in the 26-29dB range, vs 15dB for the F5.

Looks like Mundorf has some new(?) 10uF polypropylene film caps that will drop right in too (33mm long) for about $7 each. I may go with those and 0.1uF MultiCap polystyrene for bypass. OTOH, I've been told the readily available 9.1uF Axons for $2.95 each will perform just fine in lieu of 10uF.
 
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While the Dell PS I ordered will work for a while, I've just found a link to using just the shunt regulated power supply on the board I'm to get through a group buy for the DCB-1, a hot rodded B-1. Later, I can build out the entire DCB-1.:scratch2:

russellc


I suppose I could read all about it, but is there supposed to be something special about the shunt regulated supply vs a decent external supply, or is it more a matter of convenience and or cost?
 
I suppose I could read all about it, but is there supposed to be something special about the shunt regulated supply vs a decent external supply, or is it more a matter of convenience and or cost?

There's supposed to be something about the "shunt" regulated supply, I'm not sure what.

russellc
 
OK, now I've got the power supply jack, (from RS) and the plug on the end of the Dell power supply. Top can be buttoned down now. A great buffer stage, but what it does with the Tube Mcintosh MC-225 is down right unbelieveable! I figured I'd get flamed no matter where I posted that tid-bit, but it is a stupendous match!

Russellc
 
This project is an extremely nice sounding piece. Anyone who is contemplating
a pre amp build, this is a winner. Can sound down right glorious with expansive sound stage.

The price is a real winner as well. The boards can be purchased along with the 4 required matched fets directly from the Firstwatt site. I believe it was around 40 bucks. The recommended volume pots, (and the exact same ones that come with the commercial version) are only 9 bucks or so from most suppliers.
Then one needs 3 pairs of RCA jacks, and a toggle DPDT switch, a few caps and resistors. A lap top power supply ( dell ) was less than 10 with shipping from the auction site we all know and love/hate. A box and you are done. While I would like a little more gain when coupled with the F-5, for any other amp I've tried it on, it could drive them very loud. An absolute natural for the Mc-225 tube amp!

Very cheap, very high end sound.

Russellc
 
Got this back on track! This is where I left off.

http://www.audiokarma.org/forums/showpost.php?p=3844177&postcount=212

Wired it up and, it sounded great through the left channel. After doing voltage checks, continuity checks and another visual check of wiring and solder joints, I was unable to bring up the right channel. It was most likely a bad cap or JFET, as those were the only parts that I could not check. I had ordered two boards and two sets of matched JFETS. I stuffed a second board and she works!

I have 18 and 24 volt wall warts and need to see which sounds best. She gets moved to the big rig tomorrow, driving the ST-70.
 

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