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Old 31st August 2003, 02:15 AM   #1
Ilianh is offline Ilianh  Canada
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Default GC and batteries psu

I'm my endless quest to find a suitable xformer for my GC mono blocks locally, I suddenly realised that using batteries would be actualy cheaper and better.

Why not? sealed lead/acid 24v, 2 per GC (or 2 for the 2, w'ell see)
(like 15$ each....)

and a simple circuit to charge them (and you know how simple they can be).

with current peak up to 500 amps, I guess they will beat any standart power supply. Shine! Bright yellow, little 1 inch thick rod.
(taken from a personal experience with some batteries when I was young)

So, anyone has any comments or things to say that I could take into consideration?
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Old 31st August 2003, 02:22 AM   #2
ronc is offline ronc  United States
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All i use is battery P/S. The sound is very clean, clear and powerful.I just run +/- 12v and 6.8uf caps on the P/S pins to ground and a 1uf between the pins.Try it you will like it.
ron
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Old 31st August 2003, 12:45 PM   #3
mikelm is offline mikelm  England
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for LM3875 +/- 24V sounds considerably better that +/- 12V

to get nice earthing you need separate battery supplies for each amp.

some kind of quality electrolytic bypass cap improves the sound. I have not experimented to find optimum but I would guess 47uF - 470uF would be a good starting point.

don't forget to use fuses on the battery terminals !

mike
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Old 31st August 2003, 01:10 PM   #4
ronc is offline ronc  United States
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I tried +/- 24 v on the rails and to be honest i really couldnt hear any difference.I also tried larger caps on the rails to ground, found that the lowest value (that could do the job) was better,also the 6.8 uf caps sounded like it gave a better HF response.The caps on the rails are there to keep out any AC hum (and provide current on instant demand) and with battery P/S this is not a problem.The cap between the power pins is there to keep out HF hum and as stated i found out (trial and error, and lots of error LOL) that the lowest that you can get away with ,the better.
I am using fostex fe-103e horns and as i am in a small apt i really dont need the greater power of the +/- 24v P/S.I am also using 250K feedback resistors as the gain is more than adequate and i hardly ever go beyond 10 o clock using 10k/50k pot shunted to ground.I am also using a 500k multi turn pot from pin 7 to ground and after letting the amp warm up for 2 hrs i just dial in 0 offset.
ron
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Old 31st August 2003, 01:25 PM   #5
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I use 2 Interstate Gel cel Batteries in my test Jig with a 1 farad cap but never incorperated them in a final design because of size

they did come in handy when we had a power outtage I just hooked up my inverter to them


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Old 31st August 2003, 02:00 PM   #6
mikelm is offline mikelm  England
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I have to confess that I went straight from the 1uF that thorsten suggested to DNM 10,000uf T network slit foil caps.

the T networks were clearly better than the 1uf so I left it there.
I guess the ideal supply voltage depends on the speaker sensitivity at the time I was using 89db/w/m and +/- 24V helped.

cheers

mike
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Old 1st September 2003, 11:17 AM   #7
protos is offline protos  Greece
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To me batteries sound much better too even compared to a maximised gc power supply.I can tell easily because in my set up I can switch between the two almost on the fly.It reminds one more of the advantages of good SET or tube amps without the disadvantages.There is more depth and liquidity while the hard to describe word "musicality" pops in your mind.All this and excellent speed and dynamics in the bass as well.
The AC ps while not bad at all sounds a bit dry and constricted in direct comparison.
I would also vote for 24V , at least on my OPA 549 chip it sounds more dynamic.With 12v everything sounded a tad slow and it will only work with very efficient speakers needing only a few watts but it is easy to experiment with this and find the best solution for you. Don't forget batteries in numbers can get expensive.A dual mono 24v set with 8 batteries will cost much more than a simple AC gainclone.
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Old 1st September 2003, 11:49 AM   #8
mikelm is offline mikelm  England
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I did get an AC supply to sound pretty much the same as batteries but it consisted of

0.1cap/transformer/4.7cap/bridge/2200cap/choke/4700cap/choke/10000cap
( this was for a balanced working amp so I did not have +/- rails and thus halved the number of caps used )

so the cost is about the same or more that 8 batteries & 2 chargers ( the chargers where just transformer & bridge )

so perhaps batteries pro rata are cheaper !

mike
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Old 1st September 2003, 12:02 PM   #9
protos is offline protos  Greece
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Mikelm,
What chokes did you use (make and uH) ? Do you have a schematic for reference?
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Old 1st September 2003, 06:52 PM   #10
mikelm is offline mikelm  England
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Your asking the question has highlighted in my mind that I used very nice caps, DNM slit foil, throughout and the most make shift chokes as is possible - the secondaries of multicomp El 20VA 4.5V + 4.5V transformer from Farnell.

The increasing cap values towards the amp tends to reduce ringing or overshoot on turn-on.

this pic shows the stuff from the diodes onwards but the 4.7uf after the transformer really smooths out the sound.

K1 + K2 are inductive coupling
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