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PostPosted: Sun Mar 10, 2013 10:12 am 
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Location: Malvern
I'm not a valve specialist (like you, last time I did any was back approx 1980), but I know a man who is. I'll show this to him tomorrow and see what he thinks, but I'm guessing that it will be pretty hard to troubleshoot from pics alone. Personally, I'd replace the damaged parts and switch it on...


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PostPosted: Sun Mar 10, 2013 10:21 am 
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Location: Nth Somerset, UK
My inclination was to replace the resistor and capacitor and then fire it up without vales and look for similar meter readings on both sides of the circuit.

If I replace the valve, I should really replace the pair. I have not looked up what the valves are yet, it may be possible to find a cheapie just to sick in there in the hope the whole thing does not do a repeat performance.

I'll be interested to hear what your friend thinks; scrap or fix?


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PostPosted: Sun Mar 10, 2013 2:06 pm 
retrobike rider
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Location: Looking at my bike from the comfort of my sofa!!
I was round a friends house last night, he is currently running Teddy Pardo everything!!! He only ever plays Vinyl or FLAC through Itunes.
he has been running Shahinian Arcs for a while now, but took a punt on some Kef LS50's.....we tried them last night!!!

All I can say is.... :shock: :shock: :shock: :shock: :shock: :shock: :shock:

.......but he thinks hes sticking with the Shahinian Arcs 8)


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PostPosted: Fri Mar 15, 2013 12:05 am 
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So I lied - I'm gonna leave the headphone amp for another day as the idea of a new phono amp just inspired me more.

This is where I am so far - no power supplies shown as I'm not sure whether to go for battery power (rechargeable, which charges batteries when pre-amp is off) or shunt regulated mains powered yet.

I've built a large part of the gain into the first stage, to improve signal to noise in the RIAA filtering (which you may note is passive!) and then a little bit more gain in the second active stage. It's DC coupled but there should be negligible offset as, whatever way I supply power, I'll probably build a tracking regulator so the power rails stay balanced. The signal path is very short and simple, which IMO should be a primary aim.

Two identical channels as shown

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PostPosted: Mon Mar 18, 2013 5:54 pm 
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Thought about going for this for a while - interesting bit of kit and went cheaply. Didn't in the end. I really don't need another project just yet!

http://www.ebay.co.uk/itm/CARVER-C-1-PR ... 3a7f483e4f


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PostPosted: Sun Mar 24, 2013 12:59 pm 
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Changed the input stage of my phono preamp design to reduce noise floor of first stage, and increased gain of said stage to improve sn through eq stage. Last stage is now just a unity gain buffer to negate any loading effects on RIAA curve accuracy. Off to the workshop now to breadboard it and try it out. One channel shown only.

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PostPosted: Wed Apr 03, 2013 5:37 pm 
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Just bought another Marantz CD player for a snip from eBay as a modification hack so I dont keep having to cart mine t the shed.


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PostPosted: Wed Apr 03, 2013 5:37 pm 
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Just bought another Marantz CD player for a snip from eBay as a modification hack so I dont keep having to cart mine t the shed.


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PostPosted: Thu Apr 11, 2013 9:24 pm 
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So the Marantz is in bits now, and I've started on mods. The list is :-

1) secure DAC clock crystal to the board, ground and damp the can. Doing this to my CD67 had a quite significant effect.
2) Separate PSU for the analogue stage. This may have a bigger effect on this player as the stage is currently fed from unregulated 15v rails so noise performance is not optimum. I have built a separate regulated +/- 15v psu with its own transformer as there is space for it in the case.
3) Replace the caps in the signal path with new ones, and match the channels by replacing the carbon resistors with lower noise 1% metal film.
4) Screen the uP with RF absorbing material to prevent radiated digital hash getting into the rest of the circuitry.
5) Replace the audio Op-Amp with an LME xxxx (forget the part number - they're in the shed!)

This is the main board from the CD48

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PostPosted: Sat Apr 13, 2013 10:04 pm 
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Well, we're done!

Image

Mainboard again. Analogue O/P stage replaced with LME49720 op amp, a studio grade audio specific device. Decoupling caps replaced, output DC blocking caps replaced with Silmic (again, and audio grade type) of higher value (100uF instead of 47uF to extend LF further). Wurth Elektronik RF absorber added to CPU, DAC and decoder (DAC and decoder under the board). Clock crystal can grounded, bonded and damped with rubber grommet (crystals are very microphonic - this is a seriously good idea on ANY cd player!). External low noise regulated supply built for LME49720.

Image

Everything back together again, new supply on veroboard on right, with it's own independent transformer as the one in there doesn't supply sufficient headroom for regulated +/-17v rails. I went for +/-17v as the LME allows it, and a higher voltage swing = better signal headroom / lower distortion.

Image

Soak testing, spinning The Pixies 'Surfer Rosa' :D

Sounds pretty damned excellent, noticed a smooth almost 'analogue' style of presentation and some seriously good 'attack' and transient ability. Drums on 'Where is my mind' are in the room!

Image

Just for laughs, this the distortion plot for the LME on a 17v supply. As you can see, at standard CD output voltage level of 2V, the distortion figure is 0.00004%, which is to all intents and purposes, un-measurable, so the analogue stage in this player isn't contributing to the overall distortion performance, which is now down to the DAC. Nice...


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