Marantz CD63 & CD67 mods list - Page 1840 - diyAudio
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Old 6th September 2012, 06:01 AM   #18391
Puffin is offline Puffin  United Kingdom
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We have been talking a lot about super duper regs. What about using bog standard
7805s?

I have a Cambridge Dacmagic1 which has a load of 7805s in it's supply. Is there any good reason not to use these without fancy add-ons?

Rob.
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Old 6th September 2012, 05:37 PM   #18392
6h5c is offline 6h5c  Netherlands
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Hi Rob,

A standard 7805 does it's job, it keeps the voltage constant and rejects incoming 100/120Hz ripple quite well. But in audio, high frequency noise is also an issue, and the standard regs don't perform very well here.

Read the Acoustica article. Part two is about noise rejection.

Ray
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Old 6th September 2012, 05:42 PM   #18393
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Just adding a dab of RC filtering ahead of such things is always worthwhile though. Quite small values are effective, 4.7R and 10-100uF, say - if there's enough voltage headroom to stand dropping an extra volt or two.

All the resistor, cap and transistor do is allow you to use much larger resistors and smaller (film) caps, with the transistor providing buffering for useful amount of current output as Ray said. You have to pick a suitable transistor to suit the load current. For currents over say 50mA it will work better to use smaller resistors, say 1-2Kohm - and larger capacitors - say 10uF - for a couple of reasons. Mainly becasue you'll find the voltage drop becomes quite large as the transistor needs more and more base drive current - and higher current transistors generally have less current gain, needing more base drive... (and no, mosfets are not a panacea)

(Just catching up on this thread - I've no idea who added that 10K resistor to the 7812 schematic on the previous page !)

Last edited by martin clark; 6th September 2012 at 05:47 PM.
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Old 6th September 2012, 06:06 PM   #18394
mcd99uk is offline mcd99uk  United Kingdom
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Just a thought. Would adding a ferrite bead to the output of the voltage regulator help with the high frequency noise??
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Old 6th September 2012, 06:25 PM   #18395
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Actually at best they don't do anything that is useful where we are interested -in the audio band and maybe a decade or so above. In any case the noise from the reg is probably rather smaller than the noise created by the load...

The key things remain the circuit being fed must have a tight decoupling layout for the circuit served*, and then preferably a very low impedance feed - regulation.


* fancy decoupling caps on the output of voltage regs, esp aftermarket boards = exactly no use to the load; simply too far away. HF decoupling always, always they belongs right at the load, as tight as can be arranged.
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Old 6th September 2012, 06:56 PM   #18396
Puffin is offline Puffin  United Kingdom
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I fitted the reg mentioned in post 18381 (the one with the LED's) and it has been playing for some hours with no probs. In fact I measured 5.6v at the resistor I removed.
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Old 7th September 2012, 02:55 AM   #18397
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Quote:
Originally Posted by 6h5c View Post
Hi Badri,

All the mods for the 63 can be applied to the 53. Look on my website for more recent modslist. The one for the 63-KI is the most fancy one.

You should start by upgrading the capacitors and rectifier diodes in the power supply. Then upgrade the capacitors around the IC's. Remove the muting transistors and the output capacitors. Add a decent clock. For the 53, add some low-drop 8V regulators for the +/- 10V driver voltage and increase the capacitors for those voltages, or add an extra transformer for the driver section. Upgrade the filter components around the opamps and the opamps too. Or go fancy right away and add a DOS output stage that replaces all the opamp circuitry.

It will already be a completely different player after this, in a positive sense

Regards,

Ray
Thanks Ray. Can we use 3300uF/63Vdc in place of C803/804 and c814, 4700uF/40V in place of C813 and c815, and in C611..C614 can I replace 220u/25v caps or Can i go higher values like 470uF? And regarding bitumen sheet. I dont have access here in my place. But I have access to Stinger RoadKil sound deadening sheets but cost around 40$. Is it worth to buy? How much bitumen will cost per sheet?

Thanks
Badri

Last edited by badrisuper; 7th September 2012 at 03:12 AM.
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Old 7th September 2012, 12:59 PM   #18398
6h5c is offline 6h5c  Netherlands
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Yes sure, a higher voltage does no harm, but it also doesn't add anything though. And the capacitors will probably be too large to fit on the board properly.

Bitumen costs around 4 euro's here for a 50x20cm mat. So $40 is way too expensive I think.
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Old 7th September 2012, 09:17 PM   #18399
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Having a problem with my clock,Checked the frequency output 16.934 dac and 8.46 servo.Should any voltage be present last two players servo went ape, so i removed it any ideas ?.
alan
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Old 12th September 2012, 07:26 AM   #18400
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Hi Ray,
Can I use 220uf 6.3v caps in DAC section and opAmp section? You have mention in your modlist that it must be 220uf 16v BG STD? But I have 220uf 6.3v in BG NX? Can I try this?

Thanks
Badri
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