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Replacement Parts for Quad 909
Replacement Parts for Quad 909
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Old 7th November 2017, 11:40 AM   #271
Sonic77 is offline Sonic77
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Thankyou : )

If the cap i'm going to use is identical in length to the original, but is 7mm taller, in terms of input coupling caps is that considered "larger", or is this difference considered "negligible"?
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Old 7th November 2017, 11:51 AM   #272
jazbo8 is offline jazbo8
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Replacement Parts for Quad 909
@Sonic77 - starting multiple threads on the same/similiar topic is against the Forum Rules, as a result, your threads have been merged.
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Old 7th November 2017, 03:05 PM   #273
anatech is offline anatech  Canada
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Replacement Parts for Quad 909
Hi Sonic77,
7 mm may be fine, but as it has been pointed out by other members, it may also be too large for your application. If it doesn't come close to other components, you should be fine. It is a judgement call that an experienced person who had the unit in front of them could make more easily. Just make sure that the component will sit on the PCB like the original did. If you have to "fly" the component above the other parts, it is too big.

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Old 9th November 2017, 07:34 AM   #274
Sonic77 is offline Sonic77
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Thankyou everyone really appreciate the feedback.

Can this issue also arise when "flying", or raising an "electrolytic capacitor" slightly above the PCB? Or is this only a problem with input coupling caps ect?

I would also love to replace C7 with Nichicon KZ, but they are only available in 100V (original voltage is 63V) and the Nichicon may be too large to sit flush on the board. If i install the Nichicon and have a few mm's of space between the cap and the board can that also cause issues?
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Old 9th November 2017, 09:51 AM   #275
Ian Finch is offline Ian Finch  Australia
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The issue arises when you attempt to fit almost any oversize component. Because of their mass and potential to tear out if the amplifier is mishandled, larger electrolytics are fitted with multiple or stronger "snap-lock" pins to secure them so they remain firmly on the PCB at all times. Many manufacturers also glue them in with large beads and gobs of silicone mastic to ensure they will remain in position both in use and transit.

If by "install" you mean to raise the capacitor to the extent of its snap-in pins, then that is not secure and a bad idea because any vibration or accidental drop of the amplifier will peel the copper foil from the underside of the PCB or loosen the pins. That could be disastrous with today's minimal trace and pad size PCBs. If you make a thin ring of as large a diameter as the original cap. from insulating material such as PVC tube and place this in the gap between cap. and PCB for support, it may help, as long as the cap still sits squarely and securely and the pins are both mechanically secured before being very well tinned and soldered.

Don't just "float" parts precariously. They were not intended to just hang anywhere on big, stiff wires as in the the old days of steam radio; prone to movement, susceptible to noise and physical damage etc. Large, unshielded foil caps at the input are also a bad idea in many amplifiers as they make ideal aerials for RF and EMI reception. You cannot shield a foil input cap by connecting the outer foil layer to ground, so you either have to wrap it all in conductive foil and ground that or just get used to the compromised audio.
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Last edited by Ian Finch; 9th November 2017 at 10:07 AM.
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Old 9th November 2017, 01:27 PM   #276
anatech is offline anatech  Canada
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Hi Sonic77,
I couldn't agree with Ian any more than I do. Aside from the mechanical issues which Ian pointed out, there are also electrical issues. Consider that a capacitor is a big cylinder of metal like an antenna. It's either going to transmit or receive signal from other places in the circuit. You wouldn't stick antennas throughout your unit, so why would you fly an oversized component?

Basically, the only upside to mounting a larger component in the air is that you can connect it to the circuit. Every other consideration is a strong negative. Never mind the safety aspect if you decide to fly filter capacitors.

Nope, if a component doesn't physically fit where the old part was, you shouldn't use it. Basic, simple, common sense.

-Chris
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Old 10th November 2017, 08:55 AM   #277
Sonic77 is offline Sonic77
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Thankyou for the feedback guys, very informative and much appreciated.

For the input coupling cap (C2) I actually managed to find a nice polypropylene with the exact same dimensions as the original (and using same values), literally a drop in replacement so very happy with that.

As for the electrolytics, i would really like to replace C9 & C11 with Nichicon KZ, as i have heard a lot of positive feedback for these caps and genuinely believe they will improve the sound quality by a noticeable degree. These positions (C9 & C11) are on the side boards and the caps are originally positioned horizontally by Quad.

Unfortunately the Nichicon KZ are rather large, but perhaps if i were to place something in the gap between the cap and the pcb as Ian suggested this might be workable?

Trying to flesh this out because i would really love to install the KZ if possible.
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Old 10th November 2017, 02:40 PM   #278
anatech is offline anatech  Canada
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Hi Sonic77,
Quote:
Nope, if a component doesn't physically fit where the old part was, you shouldn't use it. Basic, simple, common sense.
You will find that reports of one capacitor's high performance over another is exaggerated. While it may sound slightly better, and I will give this one the benefit of a doubt, it is still too large and that closes the matter.

I have to repair a lot of equipment where large parts were installed. Once it is returned to the customer with a proper, improved part that fits, they are normally very pleased with the result. Remember, the product has to operate properly once the work is done and you have to live with it. Large parts can also kill air circulation which may cause some other parts to run at a higher temperature. So if a part doesn't fit, don't use it!

-Chris
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Old 11th November 2017, 08:04 AM   #279
Sonic77 is offline Sonic77
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Thankyou for that, i'll heed your advice and appreciate your feedback.

Just on a separate note regarding the input coupling cap, some people recommended changing from the original value of 330nF up to 470nF, and i just wanted to ask the question, by raising the value to 470nF does this chop off some of the high frequency information?
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Old 11th November 2017, 10:43 AM   #280
DF96 is offline DF96  England
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No. It includes very slightly more low frequency information.
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