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In Reply to: RE: How will efficient speakers/amp on batteries compare? posted by ggking7 on March 17, 2012 at 15:39:09
I found that the original T-amp was not very good, even when used with batteries. I later stepped up to a Charlize (DIYParadise), which was a fairly optimized design IMO, and used it with a 12V SLA. Not very good. I would try again with the newest units from Hypex, when they are available. My Gainclone experiments were consistently better than the Class-D stuff.
My very simple 2A3 SET beats them all IMO, if you can live with the power output -- an amp like this is best at 103db+, and even better at 107db+. Even better is my fully battery powered (B+ and heaters) 10Y-45 SET, when used on compression drivers.
I've used battery power supplies for triodes for about ten years now. It is not that big a deal. Just find surplus 1.5-2.5Ah batteries on eBay for $5 or less each. Put them in strings of four batteries to produce 50V. Charge in parallel on a fixed 55.2V supply. My present 400V supply (eight stacks of four batteries each) fits in a box about 24"x14"x8" and weighs about 100lbs. I would bypass the batteries with a cap of some sort. Batteries are not designed to pass AC.
Follow Ups:
I have found the same things, Gainclone is the nicest but still very far away from even a simple SET.
Still have not yet found the guts to go battery loaded SET, Have you been using batteries for 10 years already? are they the same batteries?
You have to charge every 50 volt pack separately I suppose.
How long can your batteries go for with full charge?
Very interesting!
I buy surplus batteries cheaply, and they tend to last about 3-5 years. The 50V stacks are charged in parallel on a single 55.2V fixed supply (a Mastech adjustable powersupply from eBay, set at 55.2V).The general rule for trickle charging is a charger with current delivery of 0.2x the capacity of the battery you are charging, thus a 1.2Ah stack would draw about 1.2A*0.2 or 240mA in charging current. I have eight stacks in parallel so that is 240mA*8 or 1.92A. The charger is a 3A charger so it works fine here, with a little headroom.
My present batteries are 1.2Ah I believe, which is rather small. In general, you should aim to discharge a battery by no more than 50% on a regular basis, so the effective Ah is 0.6Ah. My amps run about 100mA for both channels, plus another 50mA or so for the preamp, for a total of 150mA or so. Thus, you can expect about 4 hours of use from it to a 50% discharge. If you use something like a 300B at 80mA per channel, then of course you would discharge them faster.
If you can live with the large size, the 7Ah batteries seem to be a very good value. You can sometimes find them as cheap at $5 or so each. I would make boxes of 100V (two stacks) each and wire them in series. This would give you a lot more capacity, at the cost of larger size and weight of course.
I would again recommend using a bypass capacitor of at least 10uF, in the amplifier. You could even have a choke-capacitor combo. Batteries are not designed to pass AC.
I wouldn't necessarily say that you can't achieve similar effects with a standard wall power supply. However, to make a comparable wall-power supply would also take a lot of gear and money, and you would end up with something nearly as large and heavy IMO, and probably more expensive.
Very interesting NL, thanks!
I am about to start multiamping... so more batteries will be needed!
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