Hello, this is my first post on the forum.
Found a Quad 3-series system at a flea market about three years ago.
They didn't look much, but can be resprayed quite easily. Nothing was broken.
Of course, I recapped all of the units by the original value of components first.
Found some parts out of spec and replaced them, realigned the settings on the 303 and started listening.
I was stunned how such old equipment could sound so good!
On the internet there is much to learn about upgrading these units, and more than a few companies have specialized in supplying parts and even kits to renovate them.
I started taking things a little bit further than that, and have experimented with various parts from different suppliers.
First, my 303 is a serial number below 11501 and needed to be converted to the later bias adjustment system. I used plug-in boards I bought from Amplabs.co.uk.
Of course, you can change the output of a 303 to fully complemental, but being a purist I will not do that. So first I exchanged the output transistors from the original RCA ones to MJ15003 and listened for a while. Sound did improve somewhat but was still lacking "punch" in loud parts of the music. I found out that was because of the current limiting Quad built into the 303 to protect the power transistors.
Reading NET-Audio's website I decided to add two more diodes in series to the current limiters and replace the output coils, because the original coils saturate at around 4A. Now I was getting somewhere, the speakers came to life.
In addition, I replaced the original discrete rectifier with a Schottky-rectifier board from NET-Audio and added larger capacitors to the power supply (2x6800µF,100V in parallel)
I also exchanged the input transistor for BC560 and fitted WIMA MKS-4 1µF in place of the input capacitors.
Now things were really happening, the sound improved a lot. Firmer bass, more detail in the midrange but rather disappointing (dull) highs...
But when I placed bypass capacitors on the output capacitors as described on the NET-Audio website, the sound was amazing....
Things that IMHO do not make any difference at all:
Exchanging all resistors with 1% metal film,
replacing any other transistor on the driver board with newer "better" ones,
even replacing capacitors in the audio path with Silvered Mica ones did not improve anything.
I have tried all of these recommended upgrades, saves you the trouble.
But, as I found out, one thing really makes a big difference:
Larger diameter output capacitors (40mm) definitely sound better with this amp.
With the first recap, I put in a set of 30mm 2200µF 100V capacitors from BC Vishay. That made the amplifier sound dull.
I managed to source a set of -again BC Vishay- 2200µF 200V caps in Germany with the above mentioned 40mm diameter, and especially the bass improved a lot, it got deeper and better defined.
Anyone out there who can tell my why? Or am I imagining things?
Found a Quad 3-series system at a flea market about three years ago.
They didn't look much, but can be resprayed quite easily. Nothing was broken.
Of course, I recapped all of the units by the original value of components first.
Found some parts out of spec and replaced them, realigned the settings on the 303 and started listening.
I was stunned how such old equipment could sound so good!
On the internet there is much to learn about upgrading these units, and more than a few companies have specialized in supplying parts and even kits to renovate them.
I started taking things a little bit further than that, and have experimented with various parts from different suppliers.
First, my 303 is a serial number below 11501 and needed to be converted to the later bias adjustment system. I used plug-in boards I bought from Amplabs.co.uk.
Of course, you can change the output of a 303 to fully complemental, but being a purist I will not do that. So first I exchanged the output transistors from the original RCA ones to MJ15003 and listened for a while. Sound did improve somewhat but was still lacking "punch" in loud parts of the music. I found out that was because of the current limiting Quad built into the 303 to protect the power transistors.
Reading NET-Audio's website I decided to add two more diodes in series to the current limiters and replace the output coils, because the original coils saturate at around 4A. Now I was getting somewhere, the speakers came to life.
In addition, I replaced the original discrete rectifier with a Schottky-rectifier board from NET-Audio and added larger capacitors to the power supply (2x6800µF,100V in parallel)
I also exchanged the input transistor for BC560 and fitted WIMA MKS-4 1µF in place of the input capacitors.
Now things were really happening, the sound improved a lot. Firmer bass, more detail in the midrange but rather disappointing (dull) highs...
But when I placed bypass capacitors on the output capacitors as described on the NET-Audio website, the sound was amazing....
Things that IMHO do not make any difference at all:
Exchanging all resistors with 1% metal film,
replacing any other transistor on the driver board with newer "better" ones,
even replacing capacitors in the audio path with Silvered Mica ones did not improve anything.
I have tried all of these recommended upgrades, saves you the trouble.
But, as I found out, one thing really makes a big difference:
Larger diameter output capacitors (40mm) definitely sound better with this amp.
With the first recap, I put in a set of 30mm 2200µF 100V capacitors from BC Vishay. That made the amplifier sound dull.
I managed to source a set of -again BC Vishay- 2200µF 200V caps in Germany with the above mentioned 40mm diameter, and especially the bass improved a lot, it got deeper and better defined.
Anyone out there who can tell my why? Or am I imagining things?
Nope, bigger value caps measureably reduce low frequency distortion. 2,200uF would be considered small for low impedance output now. Try even doubling the cap, value to reduce bass distortion, regardless of particular brand/grade. No need for 200V ratings, however.
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Thank you for your reply.
I already found out larger capacity output caps on a 303 improve bass response.
My question was about the diameter of the caps used, if someone can explain why larger diameter output capacitors sound better than smaller diameter ones.
Perhaps this is only the case with specific amplifiers, I do not know.
So my question was related to the physical size of them.
Originally my 303 was equipped with 30mm diameter caps, they had already been partially recapped with the previous owner about five years ago, looking at production codes on the capacitors.
I was wondering if anyone out there had the same results as I had after replacing with larger diameter capacitors, retaining original specification values.
The difference in diameter is very much audible IMHO.
Perhaps someone could explain this to me or prove me to be terribly wrong about this?
I already found out larger capacity output caps on a 303 improve bass response.
My question was about the diameter of the caps used, if someone can explain why larger diameter output capacitors sound better than smaller diameter ones.
Perhaps this is only the case with specific amplifiers, I do not know.
So my question was related to the physical size of them.
Originally my 303 was equipped with 30mm diameter caps, they had already been partially recapped with the previous owner about five years ago, looking at production codes on the capacitors.
I was wondering if anyone out there had the same results as I had after replacing with larger diameter capacitors, retaining original specification values.
The difference in diameter is very much audible IMHO.
Perhaps someone could explain this to me or prove me to be terribly wrong about this?
Consider volume of any flat electrochemical cell rolled up in a tube. It has little to do with just diameter.
If the cell must be thicker or of geater area to accommodate higher voltage or reduce current density,
it will be larger in volume, and likely have different AC properties too.
If the cell must be thicker or of geater area to accommodate higher voltage or reduce current density,
it will be larger in volume, and likely have different AC properties too.
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Check other parameters such as ESR, max current.....you might find answer.
I've used epcos caps in my 303. Those LL screw type...
Cheers
I've used epcos caps in my 303. Those LL screw type...
Cheers
Member
Joined 2009
Paid Member
The reason is the higher voltage rating, not the cap diameter. The higher voltage rating means that the electrode/electrolyte interface is thicker = better.
Thank you, Bigun, I did not think of that... you are right.
The reason I chose 200V versions, Ian, is: they were available from a German seller.
And they have the look of the original ones the Quad 303 came with.
I still enjoy listening to my old Quads every day.
I know they are certainly old, but you have to invest a lot of money to outclass them, IF they are in good shape.
The reason I chose 200V versions, Ian, is: they were available from a German seller.
And they have the look of the original ones the Quad 303 came with.
I still enjoy listening to my old Quads every day.
I know they are certainly old, but you have to invest a lot of money to outclass them, IF they are in good shape.
Old thread. I know .........
Resurrecting an old thread....
What ripple current should the output caps be ?
I have the choice of BC/Vishay 3300uF 100v with a ripple current of 3.84A
or a BHC 10,000uF 63v ( Slit Foil ) 5.15A .
Andy
Resurrecting an old thread....
What ripple current should the output caps be ?
I have the choice of BC/Vishay 3300uF 100v with a ripple current of 3.84A
or a BHC 10,000uF 63v ( Slit Foil ) 5.15A .
Andy
Member
Joined 2009
Paid Member
Ripple current is all about self-heating. Unless you are constantly driving them hard or mount them where they will be heated I don't think you need to choose between these types based on their ripple current rating.
Please beware, Poyton!
A Quad 303 will not break down that easy, but in the event the power output transistor on the high side of the power supply (67,3V) shorts out, your output capacitor with a rating of 63V might fail causing serious damage to your speaker.
Better be on the safe side and choose any capacitor for this purpose to have a rating of at least 80V.
More than 6800µF is spending money only, as I found out. It will bring you no increase in bass response/linearity any more.
You can buy them from ELNA, Nippon Chem-Con and Kendeil and they won't cost you an arm and a leg.
A Quad 303 will not break down that easy, but in the event the power output transistor on the high side of the power supply (67,3V) shorts out, your output capacitor with a rating of 63V might fail causing serious damage to your speaker.
Better be on the safe side and choose any capacitor for this purpose to have a rating of at least 80V.
More than 6800µF is spending money only, as I found out. It will bring you no increase in bass response/linearity any more.
You can buy them from ELNA, Nippon Chem-Con and Kendeil and they won't cost you an arm and a leg.
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