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Old 26th April 2013, 02:27 PM   #21
srinath is offline srinath  United States
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I am trying to build an L20 in a fisher BA6000 chassis.
I have a 58V dc in that amp - I removed the power amp boards due to some problems.
Its only a 6.3 ampere supply.
Will this power supply for this amp work ?
Will it sound good ?
Will it blow more easily ?
and what will blow ? the fuse or the amp ?

Thanks.
Srinath.

Last edited by srinath; 26th April 2013 at 02:28 PM. Reason: forgot something
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Old 26th April 2013, 03:56 PM   #22
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You will need 2 pairs of output transistors per channel as already pointed out a few times.
A 2x40VAC transformer rated 6.3A RMS, for 2x58VDC rails, is likely 500VA.
That is a substantial transformer, plenty big enough for 2x135W 8R or 2x 230W 4R
provided the output stage and heatsink(s) are adequate to supply that safely.

However, If the BA6000 used 100W/8R rated hybrid modules, I think there is something odd in the transformer rating there.
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Old 26th April 2013, 04:40 PM   #23
xslavic is offline xslavic  Moldova
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it will work whatever transformer you use,important is the power for driver stage thats at least 40vdc ,then your choice.mine is running on center tapped 54Vdc > 2 x 6A
so i cant get more than 45% volume in my room ,it will blow my 120w 6ohm speakers
and its very loud,integrated dac.
Help biasing more into class A,50w if possible
-i have big heatsink from both sides,doesnt even get warm
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Old 27th April 2013, 12:46 AM   #24
srinath is offline srinath  United States
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I got +/- 58 vdc.

The BA6000 has a 7 amp main fuse, and 6.3 X 2 in the 58v B+ outputs from the trafo.
One of the things about this amp was that it has a huge hefty toroidal transformer. It simply is a monster.
It also has a 12 v 1 amp for lights, and 65v X 2 1/2 amp to run the tone/meter/AC/DC control board.

They put the stk0100ii in the amp it had. 100 watt output lets say it uses 200, that is 2 ohm in +ve circuit and 2 ohm in the -ve. 6.3 amp fuse means some major available extra power.

Cool.
Srinath.
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Old 27th April 2013, 03:43 AM   #25
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Hello,

Last week I put two L20 boards into an old Samson Servo 240 amp case and used the original heat sink for the boards. I'm running a transformer that I pulled out of a Sony stereo receiver which puts out 68 volts DC after the bridge rectifier, so a combined voltage of 135VDC is running to each board. I have two 10,000uf 71volt caps on the supply that also came out of the sony receiver which seems to be enough as the voltage doesn't sag much when at full volume.

I powered up the boards and they sound great! No hum or hiss when the input is muted and the heat sinks are staying cool at this time. The only trouble is a lack of power. It seams that the L20 boards could use a pre amp as the line level doesn't seem to be high enough and I can't get the amp boards to clip at full volume. When I connect a 60watt speaker up to the amp and I can barely get it to distort at full volume and a 100 watt speaker will not distort at all. I tried a larger transformer (same voltage, but higher wattage) and had the same result so a small pre amp is going to be placed inside next week to see it it will boost the volume level.

So far I'm really happy with the sound and hope that the new pre amp will give it some more volume.

Dale P.
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Old 27th April 2013, 08:52 AM   #26
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Quote:
Originally Posted by srinath View Post
......One of the things about this amp was that it has a huge hefty toroidal transformer. It simply is a monster.....
Well, that's fine and perfect for your project - you certainly dont need a 24A or 2kVA
rated transformer for 2 x 130W 8R etc, if that's what you were asking.

The other questions about blowing fuse(s) depend on the amplifier's rated requirements. Each amplifier should be fused separately so that its current draw is curtailed when the amp's power limit is exceeded for a particular period of time. It can all be calculated precisely but I suspect that within typical broad F/Blow fuse tolerances, a ROT figure is appropriate. 5A fuses should be OK as a conservative start for 8R loads, 8A for 4R.

The 6.3A transformer secondary rating is a max, continuous current rating whilst audio is anything but continuous power output. Transformers can deliver vast currents many times their rating for brief periods until they heat up. This comfortably allows smaller transformers than continuous ratings might suggest.

Will it sound good? About as good as other posters here say. This is a general purpose, low cost design as I see it. I don't think throwing money at it in the form of boutique parts is going to turn it into a Goldmund or any kind of audiophile amplifier, if that's what you hope for, but you can make it clean and sweet by (for starters) ensuring your power wiring is properly twisted and routed away from signals as per any worthy guide to amplifier construction.
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Old 1st May 2013, 02:30 AM   #27
srinath is offline srinath  United States
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OK digesting these 2 posts ...

So the 60v 1/2 supply in my amp going to the front board - its doing nothing other than power the meters ? cos the switching of input from DC to AC/subsonic works fine without even powering up the amp (I mean chassis ... I mean trafo ... I mean carcass) Whatever its called.
So what does the 60v supply do ?

Cool.
Srinath.
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Old 1st May 2013, 07:28 AM   #28
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So, you need to work out how the BA6000 is arranged first, before you transplant the L20 modules which is fair enough, but a long O/T subject for this thread. FWIW, the indicator board is a small discrete peak indicator circuit run from ~25V and an IC for the meters, run from 22/-18V rails. It appears to derive from the main 57V power rails supply as the only low voltage secondary supply is solely for light bulbs.

I assume you are also talking about the input switching that bypasses the input cap and HF filter. This is a really bad idea for a DIY amp, period. Don't try to incorporate in the L20s.

The schematic I found is fragmented and very hard to follow so the reply is sketchy, sorry.
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Last edited by Ian Finch; 1st May 2013 at 07:36 AM.
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Old 1st May 2013, 08:58 AM   #29
xslavic is offline xslavic  Moldova
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hey people, how to bias it in class A at least 50w
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Old 1st May 2013, 02:32 PM   #30
srinath is offline srinath  United States
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Default DC/AC subsonic

Quote:
Originally Posted by Ian Finch View Post
So, you need to work out how the BA6000 is arranged first, before you transplant the L20 modules which is fair enough, but a long O/T subject for this thread. FWIW, the indicator board is a small discrete peak indicator circuit run from ~25V and an IC for the meters, run from 22/-18V rails. It appears to derive from the main 57V power rails supply as the only low voltage secondary supply is solely for light bulbs.

I assume you are also talking about the input switching that bypasses the input cap and HF filter. This is a really bad idea for a DIY amp, period. Don't try to incorporate in the L20s.

The schematic I found is fragmented and very hard to follow so the reply is sketchy, sorry.
Sorry about the schematic. I will try to find a better one.
But I was not going to use the input cap+HF filter switch in that DC/AC subsonic switch, I was going to send say the DC to the power amp boards, but send the AC one into a pre out jack ... so you can use this with input controls etc as a pre, yea crappy idea, but it saves me having a knob that does nothing cos its disconnected.

Thanks.
Srinath.
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