I finally got round to re-building my QUAD 303 PSU and was pleasantly surprised at the big difference it made to the sound. We are talking night and day here 🙂. I can now hear the lower bass and the upper treble!!
The 303 had been re-capped by QUAD in late 2001 and the output and PSU capacitors replaced by 6800uF 63V cans. The caps are date-marked 1992 so QUAD must have had a lot of old stock capacitors to use up. Secondly, the change to the PSU was quite unusual because it meant that the PSU capacitors were connected in series to double the voltage rating to around 120/130V but at the expense of reducing the capacitance to half i.e. 3400uF, less than the original 4000uF fitted. It was this and the original bridge rectifier looking like something out of the Ark that prompted me to re-build the PSU.
I bought all the parts from eBay for less than a tenner and used other stuff that I had lying around. The idea was to get the 25A bridge rectifier and the caps on the same plane so they are easier to wire together, using the solid copper earth wire from a scrap piece of power cable. Then its really easy to re-connect the existing wiring loom and 0.1uF 250V decoupling caps across component legs. I used 2off 3300uF 100V Vishay BC filter caps
(£3 each) because they already have low ESR = 0.064 ohm, halved when in parallel. Considering the existing wiring loom looks like its constructed from 1 amp bell-wire 😉, I thought that made better sense than just upping the capacitance to a high level.
The driver board capacitors had also been replaced but since they were 13 years old, I replaced them anyway with 105 deg low ESR types. Initially, I overlooked the input dc blocking capacitor (0.64uF 64V electrolytic) but when I removed to check value they had both dried out to approx. 1/3 of their original value. That might explain the dull bass. I replaced with 1uF 100V ERO MKT, the big green one in the pics.
My verdict: a very easy, cheap re-vamp that appears to have re-juvenated a previously dull, lacklustre QUAD 303 into something which sounds very good indeed.
The only other mod that I may consider is to increase the 4.3A current limit of the output transistors using the extra diodes and new 6A rated output inductor. Has anyone done this mod and does it lower distortion/improve sound quality further?
The 303 had been re-capped by QUAD in late 2001 and the output and PSU capacitors replaced by 6800uF 63V cans. The caps are date-marked 1992 so QUAD must have had a lot of old stock capacitors to use up. Secondly, the change to the PSU was quite unusual because it meant that the PSU capacitors were connected in series to double the voltage rating to around 120/130V but at the expense of reducing the capacitance to half i.e. 3400uF, less than the original 4000uF fitted. It was this and the original bridge rectifier looking like something out of the Ark that prompted me to re-build the PSU.
I bought all the parts from eBay for less than a tenner and used other stuff that I had lying around. The idea was to get the 25A bridge rectifier and the caps on the same plane so they are easier to wire together, using the solid copper earth wire from a scrap piece of power cable. Then its really easy to re-connect the existing wiring loom and 0.1uF 250V decoupling caps across component legs. I used 2off 3300uF 100V Vishay BC filter caps
(£3 each) because they already have low ESR = 0.064 ohm, halved when in parallel. Considering the existing wiring loom looks like its constructed from 1 amp bell-wire 😉, I thought that made better sense than just upping the capacitance to a high level.
The driver board capacitors had also been replaced but since they were 13 years old, I replaced them anyway with 105 deg low ESR types. Initially, I overlooked the input dc blocking capacitor (0.64uF 64V electrolytic) but when I removed to check value they had both dried out to approx. 1/3 of their original value. That might explain the dull bass. I replaced with 1uF 100V ERO MKT, the big green one in the pics.
My verdict: a very easy, cheap re-vamp that appears to have re-juvenated a previously dull, lacklustre QUAD 303 into something which sounds very good indeed.
The only other mod that I may consider is to increase the 4.3A current limit of the output transistors using the extra diodes and new 6A rated output inductor. Has anyone done this mod and does it lower distortion/improve sound quality further?
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sorry to destroy your party .....
--Fine with the big capacitors you probably gained a few things
--25A rectifier overkill but will not harm anyone
--Bypassing here and there ??? yeah ok ..fine with me but for once the values are selected by luck and why "need for speed " in an amplifier/rectifier that has dead slow transistors ??? will help nowhere
--There is a few things said about capacitors in series which i didn't understand but that's ok i guess
--You did bothered about the 1A bell wire that supply your amplifier from the rectifier with DC to the capacitors .... but the bell wire remains to feed your amps from the capacitors
---Then again haven't you noticed that just right in front of your eyes there is a structure with cables that includes everything like input /output/ signal /mains/low supply ground and so on from both Ch ...Now days a design like that will take the designer directly to jail ..
---Do your self a favor and exclude mains cable ( at least ) from the structure Rewire them in some better way and obviously with proper wire for 230 ....Other option : Get a better insurance ...
--Fine with the big capacitors you probably gained a few things
--25A rectifier overkill but will not harm anyone
--Bypassing here and there ??? yeah ok ..fine with me but for once the values are selected by luck and why "need for speed " in an amplifier/rectifier that has dead slow transistors ??? will help nowhere
--There is a few things said about capacitors in series which i didn't understand but that's ok i guess
--You did bothered about the 1A bell wire that supply your amplifier from the rectifier with DC to the capacitors .... but the bell wire remains to feed your amps from the capacitors
---Then again haven't you noticed that just right in front of your eyes there is a structure with cables that includes everything like input /output/ signal /mains/low supply ground and so on from both Ch ...Now days a design like that will take the designer directly to jail ..
---Do your self a favor and exclude mains cable ( at least ) from the structure Rewire them in some better way and obviously with proper wire for 230 ....Other option : Get a better insurance ...
Don't worry, you are not destroying my party and I welcome your comments.
I am pretty much well aware of the technical shortcomings of the Quad 303, its a 1970's audio amplifier and as you say its imperfections are right in front of your eyes. Still, that doesn't stop hundreds of thousands of Quad owners listening to it and enjoying its sound, without any intention of up-grading to a myriad of other amplifiers with much more impressive paper specifications usually costing thousands of pounds more.
I don't want to significantly change its design or sound, I want to improve its sound quality without losing its sound characteristics by making simple, easy changes. The PSU re-vamp was quick and easy to do and seems to have improved the sound, based on before and after listening tests. The only other change I would consider is to increase the current limit which only involves replacing one diode with 2 or 3 in series and replacing the output inductor. These are simple mods. Re-wiring the cable loom not so. Your comment about the signal/mains/output/grounds all being combined in a single loom is valid. However, at full volume with no music playing I cannot hear any significant hum with ear to the speakers, therefore its also irrelevant. Even listening to music at low-moderate listening levels, any crosstalk between cables will be swamped and go unnoticed. You could do yourself a favour, forget about the data-sheets and technical specifications, just listen to the music instead 🙂
I am pretty much well aware of the technical shortcomings of the Quad 303, its a 1970's audio amplifier and as you say its imperfections are right in front of your eyes. Still, that doesn't stop hundreds of thousands of Quad owners listening to it and enjoying its sound, without any intention of up-grading to a myriad of other amplifiers with much more impressive paper specifications usually costing thousands of pounds more.
I don't want to significantly change its design or sound, I want to improve its sound quality without losing its sound characteristics by making simple, easy changes. The PSU re-vamp was quick and easy to do and seems to have improved the sound, based on before and after listening tests. The only other change I would consider is to increase the current limit which only involves replacing one diode with 2 or 3 in series and replacing the output inductor. These are simple mods. Re-wiring the cable loom not so. Your comment about the signal/mains/output/grounds all being combined in a single loom is valid. However, at full volume with no music playing I cannot hear any significant hum with ear to the speakers, therefore its also irrelevant. Even listening to music at low-moderate listening levels, any crosstalk between cables will be swamped and go unnoticed. You could do yourself a favour, forget about the data-sheets and technical specifications, just listen to the music instead 🙂
hundreds of thousands of Quad owners......
here is a joke alike yours freely translated from Greek
In the village pub the crowd is waiting the heroes of the village ( the fisherman and the hunter ) to tell their stories :
The Fisherman :
You remember dont you ? It was "that" night i was trying to pull up my fishing net but it was impossible to pull ........way to heavy !!!
Crowd goes : wooooow !!!!! What did you do ?
I called captain John which has a very powerful winch to pull them up ...so we pull and pull and after serious effort what comes up ????
Crowd goes : wooooow !!!!! What? What ?
It was a tuna fish probably 10 meters long !!!
Crowd goes : wooooow !!!!! 10 meters long ??????
Now the crowd turns to the hunter
Crowd goes : tell us !!! tell us !!!
The Hunter :
It was "that" afternoon you do remember don't you ? i was walking in the park the hunting season wanted about a couple of months to start but in any case i had my rifle behind my back .Just before sunset a look at the woods and what did i see??
Crowd goes : Tell us !! tell us !!!
I see a female rain deer above 250Kg probably pregnant....
Crowd goes : wooooow !!!!!
Before you even think about it i just grab my gun and bang she goes !!!!
Crowd goes : wooooow !!!!!
I was pulling the animal to my 4X4 and out of the woods the sheriff is showing up !!!
Crowd goes : wooooow !!!!! What did you do ????What did you do ????
Before you even think about it i just grab my gun and bang goes the bastard !!!!
Crowd goes : wooooow !!!!!
I said to my self i need to dig a hole to place the sheriff so i grab my sovel and get to work but !! out of the woods a couple of old timers was looking at me with a dead deer and a dead sheriff....
Crowd goes : wooooow !!!!!
Before you even think about it i just grab my gun and bang goes the granpa and his wife !!!! said to my self i need a bigger hole !!!! while i was digging a bigger hole the school bus is showing up with a bunch of kids taking an afternoon ride to the woods....
At this point the crowd goes bananas like :"you bastard what have you done with our kids !!! "
While the hunter is looking seriously at the fisherman telling him :
I think you should cut down a few meters of your fish otherwise i am going to start shooting to those kids !!!!
hundreds of thousands of Quad owners......
here is a joke alike yours freely translated from Greek
In the village pub the crowd is waiting the heroes of the village ( the fisherman and the hunter ) to tell their stories :
The Fisherman :
You remember dont you ? It was "that" night i was trying to pull up my fishing net but it was impossible to pull ........way to heavy !!!
Crowd goes : wooooow !!!!! What did you do ?
I called captain John which has a very powerful winch to pull them up ...so we pull and pull and after serious effort what comes up ????
Crowd goes : wooooow !!!!! What? What ?
It was a tuna fish probably 10 meters long !!!
Crowd goes : wooooow !!!!! 10 meters long ??????
Now the crowd turns to the hunter
Crowd goes : tell us !!! tell us !!!
The Hunter :
It was "that" afternoon you do remember don't you ? i was walking in the park the hunting season wanted about a couple of months to start but in any case i had my rifle behind my back .Just before sunset a look at the woods and what did i see??
Crowd goes : Tell us !! tell us !!!
I see a female rain deer above 250Kg probably pregnant....
Crowd goes : wooooow !!!!!
Before you even think about it i just grab my gun and bang she goes !!!!
Crowd goes : wooooow !!!!!
I was pulling the animal to my 4X4 and out of the woods the sheriff is showing up !!!
Crowd goes : wooooow !!!!! What did you do ????What did you do ????
Before you even think about it i just grab my gun and bang goes the bastard !!!!
Crowd goes : wooooow !!!!!
I said to my self i need to dig a hole to place the sheriff so i grab my sovel and get to work but !! out of the woods a couple of old timers was looking at me with a dead deer and a dead sheriff....
Crowd goes : wooooow !!!!!
Before you even think about it i just grab my gun and bang goes the granpa and his wife !!!! said to my self i need a bigger hole !!!! while i was digging a bigger hole the school bus is showing up with a bunch of kids taking an afternoon ride to the woods....
At this point the crowd goes bananas like :"you bastard what have you done with our kids !!! "
While the hunter is looking seriously at the fisherman telling him :
I think you should cut down a few meters of your fish otherwise i am going to start shooting to those kids !!!!
hundreds of thousands of Quad owners......
Not a bad thing as they should be quite common and therefore cheap if I need another couple 😉
Good joke 😀
Regads
Good joke 😀
Regads
Quad 303 is what it is. It worked well enough that the BBC used it in a few well respected monitoring systems. I once came across their biamp version that had an active crossover inside and used the 2 channels as woofer and tweeter.
probably ...but let us not forget that this was 35 years ago .... I go for the Japanese as you probably know since those was far more stable and better sounding from most of the aspects ...
At the time many mistakes made by many manufacturers while the British hold the Crown for details like that ( wiring , class B Circuits , often circuits that left without thermal compensation while ambient Temperature was something unknown for the British at the time )
In any case the 303 and the expression ""hundreds of thousands"" was a good "start " for a nice joke !!
Happy regards
Sakis
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