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Old 14th August 2012, 01:09 AM   #481
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Quote:
Originally Posted by gvelim View Post
@ClefChef, here is an interesting project using WM8740 with Lundahl output transformers, however it gets expensive as this will need 4 x Lundahls so the question is how can I connect only one transformer per DAC to sum up the dual-differrential output ?

Interesting also to see the use of oscon caps on the analog bypass section.

USB DAC 1 - Hi-Resolution System
Click the image to open in full size.
I like Andrea's designs a lot, I built AD1865 DAC (similar to DAC END). In my experience transformers (used with tube stages or without) tend to sound better than coupling caps - better dynamics and super delicious bass. However, good sound comes with a price...
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Old 16th August 2012, 09:04 PM   #482
Portll is offline Portll  Australia
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Originally Posted by Snook View Post
Hi Guys,

Does anyone else notice the Dac Magic plus has a very audible high pitched ring from the unit around the area where the power supply plugs in?
Mine was initially so bad I thought there was something wrong with the unit

However, it turned out to be totally unrelated to the issue I'm having, which is (as a beginner) proving very difficult to isolate for me. I'm not sure if this is the right place to post, but it seemed tidier than starting a new thread.

I've lost the right channel of the RCA. I haven't tested the XLR, but I'm after some advice where to start out! The input capacitors all hold charge, I think one of the output relays (RL3) is kicking in due to an issue in the audio circuit somewhere. Although I have a DMM I've only used it for temp measurement in coffee roasting so need to read a few guides again on how to measure caps - no access to a signal generator & scope here! While I have the service manual (thanks for sharing sonic!) I don't have a printer and the last thing I want to do is burn more of it out by shorting pins accidentally on the back side of it.

thanks,

Portll

PS. I'm new here, hi
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Old 24th August 2012, 09:37 AM   #483
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A quick question, can I use both the RCA and XLR(will use adapter) output on the same time?

Will connect it to a Headphone amp and a receiver.

Using these adapters:
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Old 24th August 2012, 09:45 AM   #484
Portll is offline Portll  Australia
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yes you can.

Having said that, if your headphone amp, like the musical fidelity m1hpa, has a pre out, and compare the two ways, and as the balanced output is better in nearly every way.
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Old 9th September 2012, 11:05 PM   #485
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Quote:
Originally Posted by gvelim View Post
Hi aptsys, here is the setup with the AD797

Opening the new DacMagic????

All 4 of them feel equally hot on the browndogs.

Assuming in this setup, 15mA go to the SRegs + 2 x OPA2120 and with
1) R400 at 100ohm I measured 5.86 voltage drop which gives 11mA per opamp
2) R400 at 56 ohm I measure 3.84 volatge drop which gives 13mA per opamp

hope that clarifies the situation

What are the factory values for R400 and R401?
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Old 10th September 2012, 02:59 PM   #486
gvelim is offline gvelim  United Kingdom
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Quote:
Originally Posted by Atom Shop View Post
What are the factory values for R400 and R401?
The factory ones are 56 ohm 2W carbon resistors. I measure 72C on the AD797 using an infrared thermometer which I think appears to be within its operating range.
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Old 17th September 2012, 06:50 AM   #487
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Does anyone out there have a schematic for the DacMagic?
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Old 17th September 2012, 08:01 AM   #488
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Quote:
Originally Posted by nickbojko View Post
most of the dac chips today use voltage output instead of current output,so the iv convertion is done internally.the wolfson has a negative signal as well as a positive signal coming out of the dac,your balanced out is already there,just use it.for unbalanced use only the positive or + signal for your output,one for each channel.use a really good cap here,you could use a 47uf silmic II or nichicon zk,bypassed with 1-2uf polystyrene or polypropylene.no additonal low pass filtering is needed!!!!!!!go from dac output to rca jack.once you have done this you will never go back to op amps.you already have 2 volts output from the dac to drive anything.enjoy.p.s. make sure you cut the trace going to the rca jack.
Has anyone ever tried this?
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Old 16th November 2012, 01:39 PM   #489
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Have not tried this, but it should not be any technical problem to do this. There are many DAC schematic's using the output of the DAC directly.
The question is: Why would Camebridge spent money on all the extra components: power supply; 4 additional opamps; etc..... ?

I don't say Nickojko is not right, but I am just asking........
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Old 16th November 2012, 02:52 PM   #490
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Here is the upgrade I performed on the DACMagic after gathering all info on this forum

1) Replaced all capacitors for Panasonic FC Capacitors
2) Replaced the 7805 for NewClassD UWB power regulator
3) Replaced all NP capacitors for Panasonic NP capacitors (higher voltage)
4) Replaced the unbalanced opamps (4x) for LME 49720
5) Bypassed the output caps (shortened), after measuring the ouput = <3mV
6) Disconnect the RCA outpput and reconnect to balanced +output to bypass the last OPA opamp
7) Higher the capacity of the "Villard" capacitors from 470/220 to 680/470 to allow higher current flow
8) Add additional 220uF capacitors to 15 volt outputs
9) Replaced the power adapter for a 9VAC 36VA to overcome the heat problem (7X15 regulators)

Incredible improvement of sound! Compared to original unit, my sister owns one.

20121110-1143_02.jpg
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