Digital Pre-Amp Build Help Request

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Hello Folks,

I have been bimbling around on here asking inane questions for about a week now but I think I am now ready for my first proper thought out request. This will look very familiar to those who helped me in my very similar previous thread. I have started this new thread as I think I now have a better idea of what I would like to end up with.

I no longer have any analogue components to plug into my pre-amp as all my music has been transferred to a networked external hard drive accessed via a Media Centre PC that I recently assembled. This feeds its digital signal to a Yamaha DSP E800 AV Processor that does the converting and sends the analogue signal to the power-amps.


The Plan

I want to build a high quality DAC pre-amp using my old Cambridge Audio C500 as a basis. What I would like to have is:

1) Highest quality DAC I can afford to build (don't we all).
2) Selectable multiple inputs including USB, Toslink, Coaxial, 3.5mm Jack (just in case).
3) An optical and/or Coaxial pass through for forwarding the digital signal to other devices (just in case).
4) Preferably powered by existing on-board toroidal power supply.
5) I would like to utilise the existing input selector to switch between the inputs.

Here again are a couple of pics to show what I have to play with:

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.



Initial Progress

First of all, after spending the last week re-assessing my Hi-Fi and doing some re-plumbing, I have finally decided what I want to do as outlined above. Until, that is, you lot tell me I'm dreaming!

As the C500 is currently redundant, I'm happy to have a serious go at DIY and make something myself.

I have already received these two recommendations:

http://www.diyaudio.com/forums/digital-source/186245-dac-2496-ak4393-dac-kit-cs8416-ak4393-5532-a-194.html (thanks boblamont)

MUSE Mini 24Bit 192Khz Coaxial Optical USB Input DAC Headphone Out,66*60mm | eBay (thanks Pano)

and also the ODAC (thanks orpheus) but as stated above, I have decided I want to try DIY. (I'd also like to thank qusp for his input in the previous thread, it all helps un-muddy the water).


Next Step

More information gathering and recommended products.

So does my wish list look achievable?

Are there any other DAC kits out there to consider? If there are any that perform outstanding results after a few choice mods, I'd like to build those mods in from the start as I doubt I'll have the chance to do too much experimenting.

As for budget, over a period of time I would like to keep the cost below £100 but if this causes too much of a restriction I would rather go over budget a bit and get a better quality result. The kits I've seen so far all seem to be around the £30 mark which considering how much a commercially built digital amp sells for, seems rather cheap!

Finally, many CD players now come with multiple DACs. Is this a direction worth pursuing? I haven't seen much mention of it on here.

I'm no electrical engineer and am woefully unfamiliar with many of the terms used on here. But I am handy with a soldering iron, can follow instructions, have access through work to some decent kit and have access to a number of electricians who are willing to help.

Many thanks for any help and guidance, I have already had my eyes opened in the past week on here.

Cheers,

Simon.
 
I have found the below DAC that has multiple inputs and includes a switching device to select them. Does anyone have any experience of these? I'm not too fussed about the remote or the display, especially if I can substitute the existing input selector on the pre-amp in place of this boards selector.

Dual CS4398 CS8416 24Bit/192KHZ DAC+ VFD Display+Remote | eBay

Or would I be able to incorporate the input selector into the wiring of the other two DAC boards easily enough?
 
CS4398 Dual Dac kit

I have found the below DAC that has multiple inputs and includes a switching device to select them. Does anyone have any experience of these? I'm not too fussed about the remote or the display, especially if I can substitute the existing input selector on the pre-amp in place of this boards selector.

Dual CS4398 CS8416 24Bit/192KHZ DAC+ VFD Display+Remote | eBay

Or would I be able to incorporate the input selector into the wiring of the other two DAC boards easily enough?

Simon -

Just seen your thread about conversion of your preamp..

With the above dac, it takes full control of the media center (via USB), so becomes it's own multiple input switching / track selection (skip Forward or Reverse), AND controls it's volume output - All via the supplied remote control ! It's totally cool :D

Also, you can configure your laptop to use 'Advanced Touchpad' and control mouse functions via your smart phone - OR - use 'Unified Remote' to turn said smart phone into a wifi remote control which will again give you track selection/volume command from any room in your property (or as far as your wifi allows).

Hope this helps - let us know how you get on with your project !

-Andy-
 
Wow, it sounds like quite a piece of kit! I'll have to be carefull however as my media centre PC also operates via a media remote.

An externally hosted image should be here but it was not working when we last tested it.


Could you please confirm that it does have both optical and coaxial digital inputs?

I might end up bypassing even more of the existing pre-amps circuitry with this board. If the volume control has the range, I won't need to risk muddying the signal by sending it through the Pre-amps rotary analogue volume control and the tone controls are set to bypass anyway (though this again means sending the signal through the potentialy dirty contacts of a mechanical sliding selector). In fact all that may remain of the original at this rate is the case and possibly the power supply!

It would be nice to retain one analogue input just in case as I do still own a ver nice Yamaha KX580SE tape deck but it has been boxed up for a while now.

Thanks for the reply.

Simon.
 
Right, I have finaly managed to measure the output voltage of the toroidal transformer in the pre-amp.

29.78V D.C. (2. off) Regulated

35v D.C. (1. off) Unregulated

So it doesn't look like it is going to be suitable for any of the DAC's I've seen so far.

That kind of knocks that idea on the head then. Oh well, I'll just have to start from scratch.
 
stay focused glasshopper...

That kind of knocks that idea on the head then. Oh well, I'll just have to start from scratch.


No it doesn't - you have the power, all you need is to reduce it !

Take a look at these :-

DC Buck Converter Power Supply 4.5-35V to 1.25-30V 3A Stepdown Voltage Regulator | eBay

As you mentioned, you haven't much electronic experience, but like all of us you have to start somewhere ;)

The dac has regulation onboard (that's why it requires the A.C input power feeds), but this doesn't matter as you
already have D.C power already available.. Happy days ! :D
 
Ooh this is looking good again! Thanks for that! :)

Will this give a clean power source still or is it liable to induce noise?

Thanks also for confirming the presence of the electrical digital inputs.

ApogeeLover, I am hoping to use the above converted Pre-amp to feed my pair of long serving Cambridge Audio P500 power-amps that are Bi-Amping a pair of Mission 734i Speakers.

Thanks very much for the help, Time to start doing some serious saving. I feel an eBay purge coming on! :D Anyone want any old VW Campervan bits?
 
Hi Autotat,

Are you aware that your media center is probably and rather nastily upsampling everything it sends over "Digital" to 48000 Hz?

Configuring MPD for Bit Perfect Playback with an external DAC Init

I use MPD on a Linux media center bypassing the software mixer and my DAC says 44100 Hz when I play some of my ripped flacs. I don't know if your Yamaha tells you the sampling rate or not.
 
Hi Autotat, Interesting project. I'm doing something along those lines. I'm still in a debugging phase. I'm using a Sheldon Stokes upsampling CS4398 dac with Lundahl LL1690 output transformers. I designed a line stage more or less from datasheets. AD8065 with Buf03. Have built up switching relays for source selection. My version of a DacPre. :) So far it sounds really nice. Have to get that thing in an enclosure. Dave
 
Hi Autotat, I think it will be an interesting project. I'll put the 4398 dac in it's own shielded enclosure inside the preamp chassis to minimize rf noise. I used a Tent labs clock on the upsampler (better then Sheldon's spec'd clock) and that runs in the 24-25 Mhz range. So I have some concerns about noise. I'm also adding a Hagerman phono board and still thinking about shielding that as well. I found the AD8066's (dual opamp) worked well here also. The AD8065/Buf03 was inspired by a Buf03 headphone amp at the Headwise website. I thought why not make that into a Preamp/headphone amp. So the gain is set by the AD8065. The Buf03 is the output buffer. Works well with Grado SR80 headphones that are about 30 Ohms or so. I plan to assign input one to the CS4398. Our audio club hosted Audio Research last season and we listened to their new Dacpre. I thought wow. I think I could equal or better that. Maybe? :) Time will tell. They didn't have shielding around there digital stage or phono as I recall. I'm keeping mine simpler as well. Will you need shielding in yours? Dave
 
Hi Dave,

Wow, I'm afraid you've gone well beyond my limited knowledge with that lot. As time allows I am trying to get to grips with the basics of all this, but google is throwing up some quite advanced detailed information which is a bit over my head at present. Did you shield the entire PCB?

I've also hit another slight stumbling block, my delightful 5year old son has thrown a stone up into the air out the back gate which has landed on a neighbours car windscreen (sorry, windshield). So I now have to fork out £60 to cover there insurance excess to get the screen replaced! That's slightly more than I had managed to save up for the DAC kit. The little darling! My kids should be sponsored by Durex!

Simon.
 
Hi Simon, DIY Audio Forums is a great place to learn. Just stick with it. You will learn a lot in a little time. My project has been in the works for over a year now. The dac I plan to have in a LMB or Bud box inside the Preamp. My preamp runs quite warm so I plan to leave that where airflow is available. The dac runs cool so in a box it goes. :) The phono board runs cool as well so I think that should benefit from a box too. I believe your adding bits to a digital device so maybe shielding the new stuff from the old would be easier? So sorry to hear about the mishap with the stone and the windshield. 5 years old... Doesn't probably fully understand what he did. Hard to get to angry I suppose. My budget for DIY is poorer these days. I have gathered most of what I need to get my DacPrePhono 90% complete. My winter project. The wife isn't amused with circuits and wires all over the livingroom. :) ha ha....
 
ApogeeLover, nothing bought yet. I wanted to build a plan of what I needed first and then as long as I didn't get told I was dreaming on here I'd start buying bits. I think those step down voltage regulators will be a safe bet as anything I build is going to need power.

Then hopefully the DAC if it's still available by the time I have saved up. Unfortunately, due to the combined efforts of a young family and the car project nearing fruition, spare cash isn't all that easy to gather. So sons efforts really haven't helped. At this rate it'll be christmas by the time I have the money for the DAC! I will build one though! My Hi-Fi is lost without one.

fastbike1, I am very much in the frame of mind of wanting to build something myself. However, it will need to be within my limitations so there'll be no home designs, hence the kits.
 
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