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Old 21st June 2009, 06:59 PM   #1
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Default help with b1 + gainclone build

i have a pair of fostex 127e drivers in a monitor currently being powered by a t amp. needless to say after hearing them with a good pre amp and a power amp the t amp is pushing them to maybe 50% of their capabilities.

my skill set - i can solder and put things together as long as i have a paint by numbers kind of instruction set. i have access to the school electrical engineering lab so can get any instruments required.

i have been eyeing a gainclone for a while for the sake of simplicity to build and low cost (biggest factor in everything me being a rather poor college student and all). the b1 was to be used for a preamp. now the questions.

1. if i were to get the b1 boards and just solder on the components, do i have a working preamp or is there a power supply circuitry that is separate that i am not aware of. i think my biggest problem is being able to integrate the power supply sections of any design with the amp sections. i dont know how to connect it all once i have the two pieces done separately. perhaps learning how to read a schematic would help here.

2. IF i were to put both the gainclone and the b1 in the same chassis, could i just connect (solder a wire from the b1 board to the gainclone board) the output of the b1 to the input of the gainclone thereby removing any need for rca cables? if there is any reason (practical or theoretical) why this is not a good idea, kindly let me know.

3. i am in south florida. what would be the cheapest way to box both items up? separate chassis for b1 and gainclone? same chassis that resembles a 2 storey house with the gainclone on the bottom and the b1 on the top? wood? metal? again, the cheapest means would be best. (the person i am building this for has a ton of pets so just mounting everything on a naked plank of wood is not very practical)

4. keeping cost and ease to build in mind, is there anything else you would suggest (any other projects)?

thanks,

cj.

edit : i just saw a bunch of other variations of the b1 preamp. i have only seen the one the first watt website and that was the one i referred to in this post. if there is a "better" or "easier to put together(keep my psu phobia in mind)" pcb available kindly direct me to that as well. thanks much.
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Old 23rd June 2009, 07:24 PM   #2
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anyone?
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Old 23rd June 2009, 07:39 PM   #3
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Default A Possibilty

You have asked a few different questions.

First: The power supply on a B1 buffer is a piece of cake. You need a wall wart and inside the chassis is simply some filtering provided by caps and a resistor. Since the wall wart is located away from the chassis (transformer and rectification) there is very little noise to contend with.

Second: keep in mind the B1 provides no voltage gain. So the source must be at least line level (about 3/4 of a volt). CD players can easily do this, but phono can not.

Third: You may not require a buffer at all since the you intend to put this in the same chassis as the amp. There is a possibility that if the source (CD player output) has a low enough output impedance AND the amp has a high enough input impedance, then you might get away with simply using a pot for a volume control and a switch if you have multiple inputs.

This last possibility relies on the those two conditions being true (the two impedances). This solution goes by the misnomer "passive pre-amp" and there are plenty of threads on the topic. Sometimes folks will use a transformer based solution rather then a potentiometer. Be warned however that transformers are expensive and not all transformers sound good.

Again, search the threads and investigate whether this could be a solution in your situation.
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Old 24th June 2009, 07:11 AM   #4
rabbitz is offline rabbitz  Australia
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If you use a LM3875 such as the kit from AudioSector then you can get away with a pot only.

http://www.audiosector.com/
Peter Daniel has a good guide to the build in the Chipamp section.

Other chipamps such as the LM4780 etc can benefit from a buffer or active pre stage.

Best way is to build the Chipamp and try if it's fine with a pot only.
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Old 25th June 2009, 09:56 PM   #5
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thanks for the reply. i shall get my feet wet with the audio sector kit.
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