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Sugden P128. Replacing Caps.
Sugden P128. Replacing Caps.
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Old 26th July 2021, 10:47 AM   #1
Byron Bae is offline Byron Bae  Australia
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Default Sugden P128. Replacing Caps.

Hi all,



I'm replacing the capacitors and a few bad looking resistors in my Sugden P128 monoblocks.

Something I would like some clarification on is, should I replace the ceramic and tantalum caps or only if they show signs of failing? I'd obviously rather not have to but if it's recommended, I will.
Also should I reset the bias after recapping?



Regards,
Byron
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Old 26th July 2021, 11:03 AM   #2
Mooly is offline Mooly  United Kingdom
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Sugden P128. Replacing Caps.
1/ Be careful. We see so many threads on here of damaged and blown equipment following a recap. It is so easy to get something wrong if you are replacing a bunch of parts. If you do it right and replace like for like there is no problem. All the issues are always man made.

2/ Old tants are/often/can be prime failure items. Personally I would definitely replace those.

3/ Ceramics should not normally need replacement although 'compressed disc types' can be failure prone on very rare occasions. Again, more to get wrong if you start changing a bunch of parts.

4/ Replacing caps will have no effect on the DC conditions. Whether the bias needs setting or whether an old and crusty trimmer has caused an incorrect setting is another issue. Either replace the trimmer and readjust (always from minimum bias) or measure the bias now and confirm its status.
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Old 27th July 2021, 03:06 AM   #3
Byron Bae is offline Byron Bae  Australia
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I'll be extra careful and replace the tantalums but leave the ceramics then.
What are good brands for tantalums? Rubycon don't seem to make them.
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Old 27th July 2021, 06:01 AM   #4
Mooly is offline Mooly  United Kingdom
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Sugden P128. Replacing Caps.
Leaded tants are not so common these days but look at KEMET and Vishay. Always buy from a reputable supplier like Farnell, Mouser etc.
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Old 27th July 2021, 09:31 AM   #5
johnmath is offline johnmath  Australia
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I've given up trying to get good leaded tantalum capacitors. Where possible fit WIMA MKP2 or MKP4 film capacitors which in values up to a few F can often fit in the same place as electrolytics. For larger values I use Elna Tonerex, Nichicon Fine Gold, or Elna Silmic II. Where a large value coupling capacitor is needed and there is little or no bias voltage across it (for example some input, output and interstage coupling capacitors), it is better to use bipolar electrolytics such as Nichicon Muse.

It's often not apreaciated that the capacitors used for feedback decoupling and onboard supply bypassing are handling audio signals, and the quality of these capacitors is just as significant as those used for coupling. The purpose of onboard supply bypass capacitors is to ensure that () rails are effectively audio ground, and audio grade capacitors should be used in those positions.
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Old 27th July 2021, 09:47 AM   #6
Byron Bae is offline Byron Bae  Australia
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So these aren't good qualit? https://au.mouser.com/ProductDetail/...BERAu5cw%3D%3D


Also another question, when choosing an aluminium capacitor, apart from a good brand, what else should I go off? Is more life hours the better? And low impedance? It seems I can buy 10,000hr for not much more money. And also max temp rating I assume? Doesn't seem like there's much above 105 in-stock anyway, sadly.
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Old 27th July 2021, 09:50 AM   #7
Mark Tillotson is offline Mark Tillotson
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Supply bypass caps typically carry non-linear (half-cycle) currents, so the quality is pretty irrelevant. What matters is the capacitance and ESR which determines the net attenuation they give to unwanted rail noise - in other words their job is to be low impedance, not linear.
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Old 27th July 2021, 09:58 AM   #8
Mooly is offline Mooly  United Kingdom
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Sugden P128. Replacing Caps.
I haven't bought a tant in decades tbh. Historically they were useful for low leakage current but modern electrolytics have improved a lot. Personally I would make a judgement call by studying the design to see whether other options were suitable. Only use a tant where nothing else will do.

Do you ever see tants in modern audio designs... not really. And tants are expensive.

When comparing electrolytics it is important to compare like with like when it comes to specs.

The lifetime is usually quoted at maximum ripple current and max temperature and so a 1000 hour rated part might well last decades when used more normally. Is the test done at 50/60Hz ripple or at some much higher frequency. Differences like that can really skew results and make one seem much better than another.

105C is the preferred choice these days (85C was the norm years ago). Low impedance on the face of it is good but isn't a primary consideration for this type of application. It is of more importance in high speed switching type power supplies where things like board layout is also optimized for high frequency high current use.

Any well known and well respected brands will be much better than anything fitted back in the day when the amps were first made.
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Old 27th July 2021, 10:14 AM   #9
tiefbassuebertr is offline tiefbassuebertr  Germany
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check out this thread:
Sugden p128
there is also posted a schematic.

P.S.: in the headline must actually add "Sugden P128"
Otherwise this thread sinks into nowhere
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Old 27th July 2021, 10:18 AM   #10
johnmath is offline johnmath  Australia
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Quote:
Originally Posted by Mark Tillotson View Post
Supply bypass caps typically carry non-linear (half-cycle) currents, so the quality is pretty irrelevant. What matters is the capacitance and ESR which determines the net attenuation they give to unwanted rail noise - in other words their job is to be low impedance, not linear.
Apart from power supply ripple as a result of circuit quiescent bias currents, they also carry ripple from the currents of the audio signal, after all that is what the power supply in an audio circuit exists for.
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