Marantz CD63 & CD67 mods list - Page 1427 - diyAudio
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Old 5th March 2010, 03:15 PM   #14261
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Ray, i need help!!!

First hello to everyone.

Quincie is my name (not realy:its Ruud)

I`m a newbee with electronics, but i love great music.

I have a Marantz cd67 MKII OSE and i want to upgrade this beatiful player.

I looked around youre site and i love it, but here is my problem.
I don`t understand a lot of your schema`s etcetc, but i want still upgrade my player.

Is there anyone, or do you know someone who can do that for me.

Please help meeeee!!!!

Quincie.
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Old 12th March 2010, 06:54 AM   #14262
6h5c is offline 6h5c  Netherlands
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Wow, it's awfully quiet here, with so little posts in one week!

Let's stir things up a little: there's a new tweak for the DOS available!!

This tweak was kindly brought to my attention by Steve (stvnharr) from this forum, thanks a lot Steve!

Now what is it? There's no how-to yet, only this PDF, so it's highly DIY . The tweak consists of two extra transistors (BC560C) and two resistors that are added to the DOS' input stage. Together with the existing transistor or FET, they form a Complementary Feedback Pair. This configuration is more linear and produces less distortion compared to a single input device, and that is a good thing of course! It is often used to linearize the input stage of power amps, so why not use it in the DOS!

I haven't tried it myself yet (gathering parts at the moment...) but Steve reports a major upgrade in sound. In time, there will be a page dedicated to this tweak on my website, and I will probably adapt the DOS boards to fit this tweak. Untill then, it's happy soldering

Regards,

Ray
Attached Files
File Type: pdf DOS_CFP_CD67.pdf (64.7 KB, 276 views)
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Last edited by 6h5c; 12th March 2010 at 06:56 AM.
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Old 12th March 2010, 07:26 AM   #14263
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Yeah I noticed this thread is drying up! Ray, guess who wouldn't mind being a guinee pig for the new tweak? Surely there is some more goodness to be squeezed out of our medieval machines. Computer audio is taking over the world! fight back!
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Old 12th March 2010, 07:41 AM   #14264
6h5c is offline 6h5c  Netherlands
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Computer audio? That's for the deaf!
I will keep spinning discs untill the last lasunit is gone!

It will certainly do some squeezing. Considering the low part count and < $1 cost, it's a must-try tweak!

Ray
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Old 12th March 2010, 08:08 AM   #14265
Thomo is offline Thomo  United Kingdom
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Ray, this is timely as I'm building a dos today so I'll adapt and test this new circuit.

I'm using the dos without the preceding filter section as a discrete I/V stage in my dac and so far the test rig is working well. Is it possible to implement the filter after the summing input pair(s)?

Cheers, Lee.
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Old 12th March 2010, 08:52 AM   #14266
6h5c is offline 6h5c  Netherlands
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Cool, i'm curious what your findings will be. Good timing

The filter is passive, and in theory it can be implemented anywhere in the signal chain. It will give about 6dB signal attenuation. But i'm not sure the output-side is the best place for it. The idea is that the filter clears the incoming signal of the DAC from a large amount of HF noise, so the input transistors are not affected by this. Distortion numbers will probably be worse without the filter, because this HF trash often causes TIM.

Regards,

Ray
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Old 12th March 2010, 09:06 AM   #14267
Thomo is offline Thomo  United Kingdom
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Thanks Ray, I thought it would be possible to do that. I realise that it will increase distortion in the input transistors, but there's no getting around that for me.

The trouble is that the current out dac (AD1853) isn't happy at all driving the filter section, so I need the current to voltage conversion before it, then the filter. I'll then add a gain stage and buffer at the output.

The filter will really only be approximate because it's not specifically designed for this chip.

Thanks again, Lee.
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Old 12th March 2010, 10:25 AM   #14268
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Very interesting indeed. I have been talking with Lee about changing the output side of the dos to eliminate dc offset.
Combining the two could produce some very interesting results

Brent
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Old 12th March 2010, 02:53 PM   #14269
6h5c is offline 6h5c  Netherlands
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Lee,

Do you use two low-ohmic resistors for I/V?

Eliminating the DC will be a challenge, you will need some form of feedback to accomplish that, to have a stable 0V output.

Ray
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Last edited by 6h5c; 12th March 2010 at 03:02 PM.
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Old 12th March 2010, 05:23 PM   #14270
Thomo is offline Thomo  United Kingdom
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Hi Ray, no I/V resistors here. I like active I/V as it always seems to sound better for me, something to do with the dac liking a constant zero-ohm load on it's outputs I think.

Unfortunately, although it worked and sounded great, using just the DOS for I/V wasn't giving enough gain, I lowered the emitter resistors as far as I could before distortion kicked in but it still isn't loud enough. After I posted earlier, I adopted an opamp I/V stage and am using the dos to sum its outputs and while it does sound really, really good, fully discrete is the only way to go.

Lee.
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