Hi all. I have two old Quad 303 power amps here that are pretty well toast. I was thinking, wouldn't be a great idea to modify them in Monophonic amplifiers to give more power from each to drive some difficult speakers I have. So I've been searching for some physically small amps that ideally have dual power transformers that I can dismantle and retro-fit into the two Quads. I haven't had much luck so far. Another friend gave me a really badly beaten Bryston 2B LP amp that still works. It could be subdivided into two chassis but there isn't much point to doing this because there wouldn't be a significant gain in the power output. I want something that produces 100 to 120 watts minimum into an 8 ohm load and is stable into 4 ohm speakers.
My soldering and sheet metal working skills are fairly good and I feel quite confident about tackling this.
Does anyone out there have any ideas? Which amps should I be looking for for this project?
Conversely, are there any amp designs out there that can be had for free?
After all, this IS the internet, right?
My soldering and sheet metal working skills are fairly good and I feel quite confident about tackling this.
Does anyone out there have any ideas? Which amps should I be looking for for this project?
Conversely, are there any amp designs out there that can be had for free?
After all, this IS the internet, right?
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Apart from a travesty, trying to squeeze a 250W/4Ω power into a 303 case with its inefficient heatsink, will be troublesome exercise. Such a design will probably be an EF3 for the current to drive low impedance easily and these don't run cool, like the stereo 303 does.
As you have the metalworking talent, start with something conventional, more suited to your heatsinking and power supply needs (and capable of larger too, for you next project!)
As you have the metalworking talent, start with something conventional, more suited to your heatsinking and power supply needs (and capable of larger too, for you next project!)
The 303 casework, as you have probably noticed has the output transistors
on a heat sink behind the transformer, the wiring for the transistors has
received not a lot of praise, as they are distant with that wiring from the accompanying
other two transistors that make up the triple configuration.
You could always rebuild the 303 there are many good boards for doing this
that stick closely to what Quad designed. At 45w per channel they are still
a nice amp that partner well with the ESL57.
If I was approaching what you require with 100w per channel as a end result.
I would take some measurements to see if a 35v 0 35v AC 160VA toroidal
would fit neatly. Needing then a 35A bridge rectifier and 2x 5600uf caps to also fit,
into each mono block chassis. The space where the original 4x 2200uf
caps were would be then where the transformer is likely to fit - once the
cap clamps were removed. So pretty extensive rebuild.
I would then use a Net Audio Mk 3 Quad 405 board in each amp
arranging the heat sink to match where the original transistors
were placed. Given these boards are standard 405 dimensions
- one for each amp you could soon see how well they might fit extending back
into the 303 chassis where the transformer previously was ,
hopefully without too much modification.
If the dimensions are all good, you would end up with a very nice
sounding pair of mono blocks.
Cheers / Chris
on a heat sink behind the transformer, the wiring for the transistors has
received not a lot of praise, as they are distant with that wiring from the accompanying
other two transistors that make up the triple configuration.
You could always rebuild the 303 there are many good boards for doing this
that stick closely to what Quad designed. At 45w per channel they are still
a nice amp that partner well with the ESL57.
If I was approaching what you require with 100w per channel as a end result.
I would take some measurements to see if a 35v 0 35v AC 160VA toroidal
would fit neatly. Needing then a 35A bridge rectifier and 2x 5600uf caps to also fit,
into each mono block chassis. The space where the original 4x 2200uf
caps were would be then where the transformer is likely to fit - once the
cap clamps were removed. So pretty extensive rebuild.
I would then use a Net Audio Mk 3 Quad 405 board in each amp
arranging the heat sink to match where the original transistors
were placed. Given these boards are standard 405 dimensions
- one for each amp you could soon see how well they might fit extending back
into the 303 chassis where the transformer previously was ,
hopefully without too much modification.
If the dimensions are all good, you would end up with a very nice
sounding pair of mono blocks.
Cheers / Chris
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