I am currently working on changing the electrolytic capacitors in my
Quad 33/303 amplifier. After nearly thirty years of daily use, they
are probably at or beyond the end of their useful life.

So far, I have replaced the four large electrolytics in the power
amplifier. (Two are for power supply smoothing, connected in parallel,
and two are for decoupling the speaker output.) These were last
replaced in 1985 after the original components leaked and damaged the
amplifier board underneath. Renewing these parts has produced a marked
improvement in the sound quality. (The replacements have larger
capacities than the originals - from 2,000uF to 4,700uF for smoothing
and 10,000uF for decoupling.)

The next job is to replace the remaining 'small' capacitors in the
preamplifier and the earlier stages of the power amplifier. Having
spent a evening looking through the RS and Farnell catalogues I am
looking to use solid aluminium capacitors wherever possible. (Farnell
sell Sanyo SG series 'audio grade' devices.) Where suitable solid
aluminium devices are not available I am considering 'ultra low' ESR
electrolytics with low leakage, primarily intended for switch mode
power supplies. (Typical part numbers are 664-492 and 769-794
respectively.)

Comments on these choices would be appreciated.

Thanks,


--
Chris Isbell
Southampton
UK

In article , Chris Isbell
wrote:
I am currently working on changing the electrolytic capacitors in my
Quad 33/303 amplifier. After nearly thirty years of daily use, they are
probably at or beyond the end of their useful life.

So far, I have replaced the four large electrolytics in the power
amplifier. (Two are for power supply smoothing, connected in parallel,
and two are for decoupling the speaker output.) These were last replaced
in 1985 after the original components leaked and damaged the amplifier
board underneath. Renewing these parts has produced a marked improvement
in the sound quality. (The replacements have larger capacities than the
originals - from 2,000uF to 4,700uF for smoothing and 10,000uF for
decoupling.)

You may already be aware of what I'm about to say, however two points occur
to me which you might like to bear in mind. I can't recall the details of
the 303 off-hand, though.

The larger smoothing caps may mean a higher peak current through the power
diodes. Might be useful to check their rating, and perhaps uprate them to
avoid the risk of a failure at some point due to high current inrush at
switch-on.

Changing the output cap value may alter the details of the electronic
resonance between this capacitance and the speaker inductance. In general,
this may be 'good news' but this will depend upon the circumstances.

The next job is to replace the remaining 'small' capacitors in the
preamplifier and the earlier stages of the power amplifier. Having spent
a evening looking through the RS and Farnell catalogues I am looking to
use solid aluminium capacitors wherever possible. (Farnell sell Sanyo SG
series 'audio grade' devices.) Where suitable solid aluminium devices
are not available I am considering 'ultra low' ESR electrolytics with
low leakage, primarily intended for switch mode power supplies. (Typical
part numbers are 664-492 and 769-794 respectively.)

Comments on these choices would be appreciated.

Better grade of caps is probably fine. One point may be to check if the
caps have a can that is connected to one lead, or if it is 'floating'. This
may affect field coupling to components around the cap. I've encountered
examples (not in a 303) where this affected stability, etc.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Chris Isbell" wrote in message
...
I am currently working on changing the electrolytic capacitors in my
Quad 33/303 amplifier. After nearly thirty years of daily use, they
are probably at or beyond the end of their useful life.

So far, I have replaced the four large electrolytics in the power
amplifier. (Two are for power supply smoothing, connected in parallel,
and two are for decoupling the speaker output.) These were last
replaced in 1985 after the original components leaked and damaged the
amplifier board underneath. Renewing these parts has produced a marked
improvement in the sound quality. (The replacements have larger
capacities than the originals - from 2,000uF to 4,700uF for smoothing
and 10,000uF for decoupling.)

The next job is to replace the remaining 'small' capacitors in the
preamplifier and the earlier stages of the power amplifier. Having
spent a evening looking through the RS and Farnell catalogues I am
looking to use solid aluminium capacitors wherever possible. (Farnell
sell Sanyo SG series 'audio grade' devices.) Where suitable solid
aluminium devices are not available I am considering 'ultra low' ESR
electrolytics with low leakage, primarily intended for switch mode
power supplies. (Typical part numbers are 664-492 and 769-794
respectively.)

Comments on these choices would be appreciated.

Thanks,


--
Chris Isbell
Southampton
UK

I did mine years ago - and the 33 as well. Almost anything you get now will
be better quality than the originals - I think mine originals were Mullard!
Solid aluminium electrolytics will do fine - just make sure the voltage
rating is the same or higher. If you can't get them then try tantalums -
more expensive but equally effective.

After doing some frequency and phase sweeps on the 33 I built replacement
amp boards usinf TL074 bi-fet op-amps. The effect was noticable. They went
from a response of 50Hz-18KHz at -1dB to 22Hz-243KHz! Mind you, that may be
because I took the tone controls out of circuit in the process! The only
disadvantage was slightly increased hiss.


--
Woody

On Sun, 6 Jul 2003 16:46:41 +0100, "harrogate"
wrote:

I did mine years ago - and the 33 as well. Almost anything you get now will
be better quality than the originals - I think mine originals were Mullard!
Solid aluminium electrolytics will do fine - just make sure the voltage
rating is the same or higher. If you can't get them then try tantalums -
more expensive but equally effective.

I looked into tants but have generally avoided them, especially in the
303 power amplifier because the can fail as a very low impedance short
circuit. Also, the ESR is often higher than for an equivalent solid
aluminium device.

After doing some frequency and phase sweeps on the 33 I built replacement
amp boards using TL074 bi-fet op-amps. The effect was noticable. They went
from a response of 50Hz-18KHz at -1dB to 22Hz-243KHz! Mind you, that may be
because I took the tone controls out of circuit in the process! The only
disadvantage was slightly increased hiss.

One reason for replacing the capacitors is to reduce hiss and,
especially, hum. This is much more audible now that the amplifier is
driving more efficient speakers. It is possible to buy replacement
boards for the 33 which also use IC amplifiers - see the URL in my
earlier post. (I remember the early publicity for an amplifier that
boasted using ICs, providing more than 100 transistors. To which one
might add, every one of them a potential source of noise.)


--
Chris Isbell
Southampton
UK

In article ,
harrogate wrote:
After doing some frequency and phase sweeps on the 33 I built
replacement amp boards usinf TL074 bi-fet op-amps. The effect was
noticable. They went from a response of 50Hz-18KHz at -1dB to
22Hz-243KHz!

Quad *deliberately* restricted the frequency response to within the audio
band. BC 109s are quite capable of going above 100kHz. But this makes any
circuit more open to interference.

Did you increase the supply rail? IMHO, the 12 volt rail was the biggest
shortcoming of the 33, when used on the high gain pickup setting.

--
*Why isn't 11 pronounced onety one? *

Dave Plowman London SW 12
RIP Acorn

After doing some frequency and phase sweeps on the 33 I built replacement
amp boards usinf TL074 bi-fet op-amps. The effect was noticable. They went
from a response of 50Hz-18KHz at -1dB to 22Hz-243KHz! Mind you, that may be
because I took the tone controls out of circuit in the process! The only
disadvantage was slightly increased hiss.



But is this really a Quad 33 anymore, other than it looks like one?..
--
Tony Sayer

In article , Dave Plowman
writes
In article ,
harrogate wrote:
After doing some frequency and phase sweeps on the 33 I built
replacement amp boards usinf TL074 bi-fet op-amps. The effect was
noticable. They went from a response of 50Hz-18KHz at -1dB to
22Hz-243KHz!

Quad *deliberately* restricted the frequency response to within the audio
band. BC 109s are quite capable of going above 100kHz. But this makes any
circuit more open to interference.

Did you increase the supply rail? IMHO, the 12 volt rail was the biggest
shortcoming of the 33, when used on the high gain pickup setting.


What do you reckon it should be Dave and have you done it?..
--
Tony Sayer

hi Chris
there are a few other electrolytic capacitors in the 303 on the circuit
boards that could also do with changing wile you have your knife out. with
regard to the preamp caps i recommend Elna OsCons for the audio coupling
caps (RS) if value available otherwise Sanyo sg fine. all other el caps with
low esr types is fine.
regards bob
"Chris Isbell" wrote in message
...
I am currently working on changing the electrolytic capacitors in my
Quad 33/303 amplifier. After nearly thirty years of daily use, they
are probably at or beyond the end of their useful life.

So far, I have replaced the four large electrolytics in the power
amplifier. (Two are for power supply smoothing, connected in parallel,
and two are for decoupling the speaker output.) These were last
replaced in 1985 after the original components leaked and damaged the
amplifier board underneath. Renewing these parts has produced a marked
improvement in the sound quality. (The replacements have larger
capacities than the originals - from 2,000uF to 4,700uF for smoothing
and 10,000uF for decoupling.)

The next job is to replace the remaining 'small' capacitors in the
preamplifier and the earlier stages of the power amplifier. Having
spent a evening looking through the RS and Farnell catalogues I am
looking to use solid aluminium capacitors wherever possible. (Farnell
sell Sanyo SG series 'audio grade' devices.) Where suitable solid
aluminium devices are not available I am considering 'ultra low' ESR
electrolytics with low leakage, primarily intended for switch mode
power supplies. (Typical part numbers are 664-492 and 769-794
respectively.)

Comments on these choices would be appreciated.

Thanks,


--
Chris Isbell
Southampton
UK

On Sat, 05 Jul 2003 23:36:04 +0100, Chris Isbell
wrote:

I am currently working on changing the electrolytic capacitors in my
Quad 33/303 amplifier. After nearly thirty years of daily use, they
are probably at or beyond the end of their useful life.

[snip]

The new capacitors are in place and the 33/303 appears to be working
well and not producing any smells or strange noises (apart from some
of the weirder music I like :^). There was a concerning moment when I
thought there was a bass oscillation, but this turned out to be a
nearby petrol lawn mower! Many thanks for all the advice received.

Working on the amplifier has been instructive. Studying the circuit
and the construction reveals the care and attention to detail that
went into the original design. For example, all of the electrolytics
on the plug-in modules of the 33 are orientated with the +ve terminal
at the top, which makes servicing easier on boards with no silkscreen
component overlay.

The next job is to replace the connectors between the pre-amp and
power amp. These use 4-pin DIN plugs and sockets and, having failed to
find any reasonable alternative, I have obtained some lockable 4-pin
DIN connectors. Any suggestions for something better that will fit the
16mm(ish) DIN socket mounting holes would be welcome. (I've drawn a
blank so far.)


--
Chris Isbell
Southampton
UK