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Old 4th March 2014, 09:16 PM   #661
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Really nice. I already have Subbu dac..This is made to order. I would like one, as well.
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Old 4th March 2014, 11:15 PM   #662
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I'm watching this latest version develop with keen interest.
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Old 5th March 2014, 11:00 PM   #663
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Quote:
Originally Posted by Rudi_Ratlos View Post
TUO: my passive Pre-Amplifier is able to connect to (to choose between) five - music-sources (by means of the 5 relays on top of the PCB).
Was switching sources using LDR's ever considered? In this fashion the inputs each see their own LDR, and only one is activated at a time to let signal through(and attenuate at the same time).

I'm starting to put together a plan for a dac/pre combo and i'm leaning towards this solution, but i do need a way to switch digital sources into my JP/Subbu DAC, so i'm actively looking for solutions.
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Old 6th March 2014, 09:05 AM   #664
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yacuza: I have never considered LDRs to replace a relay.
It is already a hard job to find matched LDRs to do the attenuation of the selected signal, and I do not like to make it even more complicated.

I have some problems currently "marrying" the new version of the VCPre with the line buffer.
On the oscilloscope, with no amp connected, the output of the line buffer looks fine, but when I connect it to an amplifier, the music sounds "distorted".

I suspect my very cheap 7818/7918 line-buffer-PSU to be the reason for the distortion and have to wait for the delivery of a more "sophisticated" PSU.

Best regards - Rudi_Ratlos
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Old 6th March 2014, 12:04 PM   #665
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Gentlemen: please do not misunderstand my last post!
The VCPre itself does a very, very good job - provides the best attenuation that I have ever heard!

The implemented line-buffer is a gem as well, as I have been reported by many of my German DIY-friends!
So it must be due to the poor design of my line-buffer's PSU (+/-18VDC) that the marriage of the two of them does not sound as it shall!

Best regards - Rudi_Ratlos
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Old 7th March 2014, 12:58 AM   #666
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Rudi,
My VCpre is sounding pretty good, I went with the modified JBIS for the gain. I used Owen's wire power supply board. It is a little overkill but is a nice design that is available, Granted some smt soldering but nothing as small as your regulator.

"The Wire" Official Boards for All Projects Available Here! BAL-BAL, SE-SE, LPUHP

Many thanks for a great preamp.

Bill
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Old 7th March 2014, 11:27 AM   #667
atupi is offline atupi  Romania
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Rudi what buffer you will use, if is not confidential of course ?
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Old 8th March 2014, 11:35 PM   #668
wineds is offline wineds  Australia
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Quote:
Originally Posted by Rudi_Ratlos View Post
Gentlemen: please do not misunderstand my last post!
The VCPre itself does a very, very good job - provides the best attenuation that I have ever heard!

The implemented line-buffer is a gem as well, as I have been reported by many of my German DIY-friends!
So it must be due to the poor design of my line-buffer's PSU (+/-18VDC) that the marriage of the two of them does not sound as it shall!

Best regards - Rudi_Ratlos
Rudi, I recommend you try this power supply :

Scalable PSU/regulator GB

Many years ago when I built an active pre I tried numerous power supplies. This one was by far the standout. Compared to 3 terminal regulators the difference was night and day. Maybe Jens or Bob will give you permission to use it.

Last edited by wineds; 9th March 2014 at 12:04 AM.
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Old 13th March 2014, 04:20 PM   #669
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Gentlemen, I have connected a Version -1 VCPre to the Calvin-Buffer prototype and measured and listened to it!

Click the image to open in full size.
http://abload.de/img/ldr005k6qri.jpg

It worked as designed and sounded delicious (even using a 7818 / 7918 PSU)!

Then I ordered one piece of the "All-in-One" (VCPre and Buffer on the same PCB as shown in post #637)) prototype PCB.
I soldered the PCB, it did not work, I managed to find the error (in the interface between VCPre and buffer - I have mixed input and output tracks), but was unable to fix the issue.

I will therefore not offer the "All-in-One" PCB.

On the one hand: it is very (too) complex to troubleshoot, in case you made an error, on the other hand: if you are going to build an integrated amplifier that has a suffienctly high input impedance (>20K, f.e. the SYMASYM),
you do not need a buffer at all.

I will instead offer two distinct PCBs (see the attached images):

- Buffer (the PCB-size is 50x60mm)
This is a Stereo-Buffer based on Calvin's buffer and has a 3 - connector - interface: Power, 2-channel Input and 2-channel Output

- Passive Pre-Amplifier (the PCB size is 100 x 80mm)
It is equipped with LDR-attenuation, LCD-interface, 5 source input selection, mute, SoftPowerOn interface, ..., everything can be remotely controlled

I will order 10 pcs of each of the PCBs this weekend - and restart again.
I am quite sure that everything will work this time.

As PowerSupply I will use LM317 / LM337 circuits (already ordered), but I do have an eye on building a PowerSupply based on TI's TPS7A - regulators as well (even on WINEDS's recommendation).

I will keep you informed.
This is DIY.

Best regards - Rudi_Ratlos
Attached Images
File Type: png Buffer.PNG (146.4 KB, 246 views)
File Type: png R-Pre.PNG (167.4 KB, 239 views)
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Old 15th March 2014, 01:09 PM   #670
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Gentlemen, I will give my R-Pre- and Buffer - PowerSupply the best available transformer and received it today.

Best regards - Rudi
Attached Images
File Type: jpg R-SYM_Transformer 001.jpg (217.3 KB, 167 views)
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