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Old 30th November 2006, 12:14 AM   #4881
jksmurf is offline jksmurf  Hong Kong
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Cheers Simon,

I think I must be a bit thick when it come sot this sort of thing (wrong kind of Engineer). I also missed the "not" in

"Big caps before regs have never not been recommended by anyone to my knowledge."

So what you and Brent say tallies and I'm happy with that.

k.
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Old 30th November 2006, 02:25 AM   #4882
jksmurf is offline jksmurf  Hong Kong
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Wife has soldered in most of the parts in rays 67SE list, we just have to solder together some "Raygulators" and I'm waiting on the PCB for a PFM Flea for a clock. Might use another one for +5V reg too, (Martin Clark said no good for +/-12V though).

Can't wait to get it back together and test it out, might do that before the clock and the raygulators, then stick those in and see how it goes. Case damping and wooden feet too. Just takes a while with 2 wee kids 2+3 yrs!

Replacing the 12V regs at Q801/Q802 seems fairly straight forward so next its onto 5V regs, which are less well documented as they are not "drop-in" replacements, correct? Is the attached arrangement for Digital/Clock/Analog parts of the DAC OK? I got it from Post #593, #995, #1963, #3825 and others, except I will use LM317/337 regs rather than LM340 regs.

I know from reading that I should eventually be "feeding" the seperate regs with a new psu (presume one PSU for all 3 is OK?) and I will also need to build a separate 18V (min.) PSU for the PFM Flea-based clock), but until then presume U268 is OK as a +ve take-off point for all 3 regs? Is the GND to U267 (the minus of C813) OK for the 5V regs (Ray noted this as a ground for a clock earlier) or should these regs go through to the ground plane?

If I feed the clock with a flea+ext. PSU, am I correct in saying I then no longer need (i.e. I then MUST remove) the 5V reg feeding the clock?

ta

k.
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Old 30th November 2006, 01:29 PM   #4883
ian21 is offline ian21  England
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Many thanks Ray , Simon. Ebay bashing it is then.. probalby a few more q's in the future. and in case i'm not the last person to add a radial circuit at the front of the busbar just for cdp most defi recommend it.
Ian
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Old 30th November 2006, 01:32 PM   #4884
SimontY is offline SimontY  United Kingdom
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Quote:
Originally posted by ian21
and in case i'm not the last person to add a radial circuit at the front of the busbar just for cdp most defi recommend it.
Ian
Excellent! I wish I could do it!!
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Old 30th November 2006, 03:19 PM   #4885
ian21 is offline ian21  England
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Also ' slug barrier tape ' 5 from b&q 4 metres x 20mm self adhesive copper tape .. and it solders well .
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Old 30th November 2006, 03:30 PM   #4886
SimontY is offline SimontY  United Kingdom
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Quote:
Originally posted by ian21
Also ' slug barrier tape ' 5 from b&q 4 metres x 20mm self adhesive copper tape .. and it solders well .
Wow, that's the shielding tape we've been waiting for! Or was that suggestion to help keep animals out of my infested kitchen cupboard?

On my large chip I used a piece of unetched pcb. That's the chunky solution!

Simon
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Old 30th November 2006, 03:47 PM   #4887
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Now then girls, have any of you messed around with attenuating your cd output.

Well I have. The audio is more spacious with finer details.
The amp is at 12 oclock instead of 9 oclock for the same given volume.
You have more adjustability of the volume too.

Most modern cd players are 2v rms on the output and most amps are now 150mV on their input. Basically whats happening is distortion as the input of the amp overloads.

The ideal attenuation for 2V output on cdp and 150mV on amp is -14db ish.
I have mine at -13.5db. This is due to me using 0.1% tol res and they are bizzare values.

Fit it right before your RCA sockets

Here is the simple circuit ive spent hours testing (-14db)(tested @ 900mV on it input and 188mV on its output)


Click the image to open in full size.

Brent
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Old 30th November 2006, 06:31 PM   #4888
AndrewT is online now AndrewT  Scotland
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Hi Rowe,
why did you choose a T attenuator?

It gives a higher source impedance seen by the amp.

A plain L attenuator using 1k & 270r will give Zout=213r

Will the cdp like feeding a near 1k load?

Or fit it inside the RCA plug that goes into the amp.
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Old 30th November 2006, 06:54 PM   #4889
6h5c is offline 6h5c  Netherlands
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IMHO attenuating the output is not the way to tackle a too sensitive preamp input. Like Andrew says, the higher output impedance is something to steer away from. Also there's extra components in the signal path that can be avoided. Furthermore S/N ratio will be worse; the signal through the interlink will be weaker, etc. etc...

It's better to cure the problem at the source, like lowering the amplification of the first opamp in the input stage for example. Or losing it completely. Nowadays a preamp with an input sensitivity of 150mV is a bit ridiculus in my opinion. Why do you need a preamp anyway (unless you are into vinyl of course)? A rotary switch and a volume pot is all it takes. All sources like the TV, CD-player and DVD player are about the same volume level.

Regards,

Ray
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Old 30th November 2006, 07:31 PM   #4890
6h5c is offline 6h5c  Netherlands
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Here's a preview of the discrete output stage PCB i'm working on at the moment. Don't mind the electrolytics in the passive filter, i'm too lazy to draw a shape for the inductors . The idea is to put the regulators on the PCB too, and I hope I've left enough room around them for dedicated super-regs to fit in. The post-reg caps can be bypassed with a big 100n PPS if desired. There's room for a 100u Black Gate N output cap, any other bigger film cap is better to be fitted outside the PCB I think. The current-sink-with-two-diodes is replaced by a version with two transistors. Any comments?

Ray
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