Totally get it and hope I didn't offend. MIne's been in the family since the early 70s, along with the preamp and tuner, Thorens TD 125 and Tannoy Monitor Golds. I wish I had time to restore the Thorens. I have the "matching" speakers for that amp. Now they're something.
QUAD 303 repair
- Thread starter sozii
- Start date
That is a great explanation Mooly, thank you!
I will do the final setup tomorrow before giving it juice. Aiming at 9mV between 4-6.
From what I've read the Quad33 Outputs at 500mV so I assume that is the max that the 303 should be given. What would happen if I connected, let's say, a smartphone or a reel to reel(750mV)? The reason I'm asking is because preferably I don't won't to power the 33 before a revision/recap. It was in working order though, the last time it was powered up almost 20 years ago.
We have a pretty similar story, I also have the preamp and the tuner. Maybe I'll do the wooden box that Quad made plans for.
I will do the final setup tomorrow before giving it juice. Aiming at 9mV between 4-6.
From what I've read the Quad33 Outputs at 500mV so I assume that is the max that the 303 should be given. What would happen if I connected, let's say, a smartphone or a reel to reel(750mV)? The reason I'm asking is because preferably I don't won't to power the 33 before a revision/recap. It was in working order though, the last time it was powered up almost 20 years ago.
The electrostatic? Never heard one but for the price they should be good 😆
We have a pretty similar story, I also have the preamp and the tuner. Maybe I'll do the wooden box that Quad made plans for.
What will happen is a louder signal and premature clipping if you get that far.
I bias 303s at exactly 5mV across 4/6. More and it starts to run away. Viewing THD residuals at the same time, this is clearly enough.
I bias 303s at exactly 5mV across 4/6. More and it starts to run away. Viewing THD residuals at the same time, this is clearly enough.
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The 303 has a voltage gain of about -42 (which is high by modern standards) which means you get (rounding down) 4 volts of signal out for 0.1 volt in. RMS, peak, peak to peak, it doesn't matter as long as the units are the same.
Most listening takes place in the 1 watt and lower region. The -42 (minus) for gain denotes the amp is inverting of overall phase.
An input of 0.5 volts (500mv) would give 20 volts output and if we are working in rms values then 20 volts across 8 ohms is 50 watts so that is probably the figure you are thinking of.
It's a little hard to say what the price of an original QuadESL is. Most need to be refurbished... by someone. If you can arrange it, it's likely to be a bargain in terms of results (my experience).
Houston, we have a liftoff!
So happy to hear it after 20 years. Thank you so much to all of you for the much needed help. Special thanks to Mooly who went above and beyond 🙏
Some details:
First I let it warm up and started the setup. All went good. Since there was same debate on the bias I opted for the lower value, in this case 5mV.
As you know Quad doesn't like normal cables so I had to power up the 33 to get sound to the 303. It powered up nicely and I was presented with a very nice sound on one channel...the other one was silent. My immediate thought was that the channel that had the transistors change was still not good. After some digging I saw that one lead wire had broken from all the bending in the repair, I believe its a common thing. Lucky me it didn't touch anything and ruined my afternoon! After resoldering I now have a very nice sound on both channels 😀
The Quad33 had some pot noise that went away with a few rotations, apart from that everything is working nicely. Maybe delay the restoration?
I know that the caps will eventually give out but for now it is working. Didn't test the phono pre though.
I even got the FM3 out and it is working great!
The only thing that is missing is two of these connectors, only have two.
So happy to hear it after 20 years. Thank you so much to all of you for the much needed help. Special thanks to Mooly who went above and beyond 🙏
Some details:
First I let it warm up and started the setup. All went good. Since there was same debate on the bias I opted for the lower value, in this case 5mV.
As you know Quad doesn't like normal cables so I had to power up the 33 to get sound to the 303. It powered up nicely and I was presented with a very nice sound on one channel...the other one was silent. My immediate thought was that the channel that had the transistors change was still not good. After some digging I saw that one lead wire had broken from all the bending in the repair, I believe its a common thing. Lucky me it didn't touch anything and ruined my afternoon! After resoldering I now have a very nice sound on both channels 😀
The Quad33 had some pot noise that went away with a few rotations, apart from that everything is working nicely. Maybe delay the restoration?
I know that the caps will eventually give out but for now it is working. Didn't test the phono pre though.
I even got the FM3 out and it is working great!
The only thing that is missing is two of these connectors, only have two.
I know how annoying it when someone suggests something and you don't have or can't afford the test gear......that said....Try easing it back in into service at room temperature, dialling up the mains voltage gently with a variac.
Have a thermal camera 'live' on the PCB with everything connected and 'playing' whilst you dial up the voltage.
That would be the safest way to turn on old gear.
Capacitors in devices of that age really should be replaced, the sonic improvements are usually radical in a good way, as well as reliable.
Panasonic FM's /FR's are among the best, reliable audio capacitors and they are cheap.
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Mooly was exceptionally patient and thorough throughout your whole journey. Absolutely a tip of the hat and perhaps a pat on the back to him. People like him are what makes DiyAudio great.
Good quality, no nonsense 4mm Bananna plugs are Deltron 580-0500 580-0100
Panel Sockets and so on are best cleaned with earbuds in pure isopropanol alcohol.
Something like Servisol Super 10, now Kontakt Super 10 Switch Cleaning Lubricant
is a must for all internal connectors and external connectors. Don't spray it into Pot's though, if you can dismantle them, clean with alcohol and then like a tiny amount of Vaseline on the wipers, superb.
The amount of intermittent connection problems that combo will fix is impressive..
Panel Sockets and so on are best cleaned with earbuds in pure isopropanol alcohol.
Something like Servisol Super 10, now Kontakt Super 10 Switch Cleaning Lubricant
is a must for all internal connectors and external connectors. Don't spray it into Pot's though, if you can dismantle them, clean with alcohol and then like a tiny amount of Vaseline on the wipers, superb.
The amount of intermittent connection problems that combo will fix is impressive..
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Thank you for the kind words 🙂 and I'm really pleased its all turned out well. The 303 is a real classic... hang on to it. A great result, enjoy.
Those just look like ordinary banana plugs so should be easily available.
Yeah I guess I should just bite the bullet and upgrade the 33. It would almost guarantee a smooth operations for years to come.
I had made a BOM for the Dada upgrade that I believe is no longer available. The guide is easly found online. It ups the voltage to 16V and changes the gain for more modern inputs.
All resistors are
metal film low-noise 1% 0,5W; all capacitors are audio-grade (except for the power-supply ones) and
10 Volt or more.
power supply
2x 27ohm
1x 1,3W 16 V Zener
2x 1N400x (1N4001 … 1N4008) Diode
1x 1000, 1500 or 2200μF 25V radial
1x 1000 or a 1500μF 25V axial, or a radial
Balance-caps on the motherboard
2x 100μF 10V
Upgrading the amplifier boards
2x 2,2 or 4,7μF (radial)
2x 47μF (radial)
2x 22μF (radial)
2x 1K **gain change
2x 1K3 **gain change
Phono preamplifier board
1x 2K7
2x 82K
6x 47μF (radial)
2x 100μF (radial)
1x 220 or 470μF a 16V (radial)
Adapting the Disc Adaptor Board
2x 560R **gain change
2x 120R **gain change
Tape Adaptor board
4x 220K **gain change?
2x 2,2 or 4,7 μF (axial)
True but irrelevant. Quad have specified a range for the total bias current between pins 4-6, which by definition already includes that from the drivers and pre-drivers. No need to sweat this issue.
I was going off this which as a method is correct and this does not include driver currents.
I have a couple of other Quad documents that describe the circuit and they simply say 'see setting up' for how to adjust the bias but these documents appear not to have anything with that title in them. I looked a few times because the breaking the circuit method is open to accidently shorts etc and not one I would automatically recommend. That is why I came up with the method I posted.
I have a couple of other Quad documents that describe the circuit and they simply say 'see setting up' for how to adjust the bias but these documents appear not to have anything with that title in them. I looked a few times because the breaking the circuit method is open to accidently shorts etc and not one I would automatically recommend. That is why I came up with the method I posted.
Electrolytic caps are the ones to replace, semiconductors generally never need replacement on the grounds of being old unless they have obvious signs of running very hot where it might be a sensible precaution.
Carbon film resistors are usually fine, its the old carbon composition ones that are not so great.
Always replace like for like value wise and always replace as fitted, don't always take service manuals as accurate.
I was suggesting the low noise resistors for the Pre, it's not as important in the Power amp, though it will make a difference in the input stages.
There is a 'top five' of low noise resistors, but you'll get better results with low noise semiconductors in sensitive areas.
These are not my diagrams, but are a rough overview, availability is always a factor!
I dont have a reference to the quote...
"RS components often get the "RS-branded" metalfilm resistors, which I found out are cheaper and better spec'ed than the KOA types like MRS25."
I will be posting my 'back burner' 303 refit.
The fact that Walkers design is still in discussion six decades later is compelling, but the downside is that much of the component selection is from the 1960's. Replacing all Lytic caps and semi conductors upgrading these to modern devices left me awe struck at the transparency and delivery a total refit produced.
There is a 'top five' of low noise resistors, but you'll get better results with low noise semiconductors in sensitive areas.
These are not my diagrams, but are a rough overview, availability is always a factor!
I dont have a reference to the quote...
"RS components often get the "RS-branded" metalfilm resistors, which I found out are cheaper and better spec'ed than the KOA types like MRS25."
I will be posting my 'back burner' 303 refit.
The fact that Walkers design is still in discussion six decades later is compelling, but the downside is that much of the component selection is from the 1960's. Replacing all Lytic caps and semi conductors upgrading these to modern devices left me awe struck at the transparency and delivery a total refit produced.
Earths, wow! That is a hell of an upgrade.
Did you go for two monoblocks? How does that work inside? I see that some people just use one channel, I believe so there is no crosstalk?
Here is the cosmetic condition of my 33 and fm3:
Any suggestion on how to deal with that nasty volume knob? It is the only thing that needs a touch up. The paint overall is in very good condition 🙂
Did you go for two monoblocks? How does that work inside? I see that some people just use one channel, I believe so there is no crosstalk?
Here is the cosmetic condition of my 33 and fm3:
Any suggestion on how to deal with that nasty volume knob? It is the only thing that needs a touch up. The paint overall is in very good condition 🙂