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Old 26th November 2012, 01:48 AM   #1
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Default Help adding a fet buffer to WM8741 DAC V1.9

Hi All
I just got one of theas wolfson WM8741 & TE7022 & WM8805 DACs
Click the image to open in full size.

Itís only been running for an hour and seems to be a promising sounding dac with the standard op amps
I also have an AK4396 which I like but I think this wolfson WM8741 has the edge on the AK4396

I have also added a buffer to the AK dac which increases this dacs sound a good way up

I want to add this buffer to the WM8741 but unsure of the best take off point for the buffer perhaps at the Voutrp at LR1resistor 2.7k and Voutrl RR3 can anyone advice me on the best take of point

The buffer is this one
Attached Images
File Type: jpg Fet Buffer 1.JPG (533.1 KB, 390 views)
File Type: jpg fetbuffer Sch 1.jpg (19.5 KB, 375 views)
File Type: jpg TP Buffer points.jpg (24.7 KB, 369 views)
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Old 27th November 2012, 04:30 AM   #2
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hi Colin,
I would get it from the opamp out because the Vouts l&r are balanced at those points and you could at the opamp out point add a volume control,
If you need balanced you could run 4 seperate jfet amp off the Vouts,or run those single ended to rca connectors,lots of Ideas on google about DAC outs,
I hope I have helped!
NS
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Old 27th November 2012, 04:26 PM   #3
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Quote:
Originally Posted by noSmoking View Post
hi Colin,

If you need balanced you could run 4 seperate jfet amp off the Vouts,or run those single ended to rca connectors,lots of Ideas on google about DAC outs,
I hope I have helped!
NS
Hi NS
yes balanced to single ended but unsure of the best place for the take off point if Vout directly off the dac pins or from the 2.7k resistors as showing in the schematic
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Old 20th December 2012, 12:52 PM   #4
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Hi Colin - just curious.Did you use the same fet buffer on your AK4396?I was thinking about buying two for the balanced output from my AK4396 for a balanced valve amp that I'm about to build,and wondered at how good they were.I've read a lot of the threads on how best to implement this chip but am more confused now than I ever was.At the moment I'm taking the Vout directly to a valve buffer and it sounds terrific but something that does away with those coupling caps would be ace.Cheers Robin
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Old 28th December 2012, 06:04 PM   #5
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Quote:
Originally Posted by Cumbrian View Post
Hi Colin - just curious.Did you use the same fet buffer on your AK4396?I was thinking about buying two for the balanced output from my AK4396 Robin
Hi Robin
Sorry just seen your post
yes I use this buffer with the AK4396 DAC into a my 6SL7/KT88 SE works very well in my view even with my SS pre amp i am just using a 15volt LM317/337 regulator supply at the moment but plan on something better for the psu
Also want to have a go with a valve buffer using ether a 12AX7 or 6922 have you any good schematics recommendations for a valve buffer using these valves
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Old 2nd January 2013, 10:36 AM   #6
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Hi Colin - bought my valve buffer on fleabay from Raindrop Huey.It uses Russian mini tubes but only really started to sing when I swapped the in and out caps for Russian silver mica and PIO.Schematic is almost exactly the same as Lampizator.I would reckon that most valve preamp/buffer circuits run along those kinda lines.I also have a B1 FET buffer and that is also extremely transparent but has no gain so no good in my particular system,but again relies heavily on the quality of the coupling caps which is why I was interested in your opinion on the FET buffer that you have.You could agonize forever about the quality of coupling caps,but my own favourite Russian military M75 are so enormous you can't fit them on anything.Maybe I'll use a couple of trannies[another minefield and another thread]Cheers Robin.
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Old 4th January 2013, 07:52 AM   #7
Zoran is offline Zoran  Serbia
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You will have DC offset on the voltage outputs on the WM dac. cca +2.5V, half of the +V
The same one value like at Vmid pin.
Use that Vmid to acheive 0V at output of OP buffer.
And for JFET count on that DC at input to the jfet for biasing
if You want run without input capacitor...
cheers
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Old 5th January 2013, 12:50 AM   #8
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Hi Zoran
Not too sure what you mean here as the vmid is pins 11/17 with a 10uf cap on the end
the output pins are R12/13 L16/17 could you explain this in beginners terns
I was just going to take the outputs of the input L/R +/- side of first resistors or first RC filters +/- balanced outputs to fet single ended out
perhaps a quick sketch may help if pos
thank you
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Old 21st February 2013, 09:04 PM   #9
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Default output buffer

Quote:
Originally Posted by colin.hepburn2 View Post
Hi Zoran
Not too sure what you mean here as the vmid is pins 11/17 with a 10uf cap on the end
the output pins are R12/13 L16/17 could you explain this in beginners terns
I was just going to take the outputs of the input L/R +/- side of first resistors or first RC filters +/- balanced outputs to fet single ended out
perhaps a quick sketch may help if pos
thank you
Broskie Unbalancer

or

Broskie Unbalancer 6n16b-v {google and translate}

Unbalancer needs no input caps, it ignores the mid-rail DC on the DAC pins and takes differential in and spits out SE, with gain, you may have to pad it back doww?
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