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Upgraded Single Board PCM1794 NOS DDDAC
Upgraded Single Board PCM1794 NOS DDDAC
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Old 10th January 2017, 10:20 AM   #721
stefan646 is offline stefan646
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Join Date: Nov 2016
Sorry for the duble post, but in the mean time I documented myself more about transformers an line matching impedance, so I am looking to buy the Cinemags
My only questions ramain:
1)what is the output impedance of the buffer used in this topic
2) in the Cinemags datasheet it says " It is designed to operate well when driven by 600 ohm lines" - that it means that the optimal buffer output impedance should be 600 ohm?
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Old 10th January 2017, 01:28 PM   #722
valvemaniacuk is offline valvemaniacuk  United Kingdom
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Default Broskie cathode follower

Hi All,

I hope you don't mind me chipping in on this thread, but I have been following it with interest as I purchased a single board DDDAC a few months ago.

Although I have the latest version 4.4 boards (Blue main board and Tent DAC board) I have been looking at options regarding using both sides of the balanced output. (I currently use the basic setup with the +ve output only in single ended mode)

The cost of the Cinemags, plus 3 more boards to drive them properly seems a little excessive, and having a huge aversion to any silicon in the analogue side of the signal path I started looking at alternatives using a tube buffer stage. A number of people have mentioned the Broskie cathode follower in other posts / threads, and so to cut a long story short, I built one, using the design that John has on his website, and a simple regulated PSU off the web.

The results are absolutely superb. Much more detail in general and a significant increase in bottom end weight and control. This seems to me to be a really cost effective solution to some of the issues debated here, and I would encourage anyone who has the confidence to work with high voltage tube circuits to give it a go. Although I haven't heard a fully tricked out DDDAC with multiple boards and cinemags I am delighted with the improvements the BCF has generated and would be more than happy to provide further details if anyone would like them

Cheers,

Steve.
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Old 11th January 2017, 09:20 PM   #723
SimonJ is offline SimonJ  United Kingdom
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Please note you don't need 4 modules for the cinemags only the Sowters need 4, cinemags are fine with one.

Can you post a link to the johns website?
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Old 12th January 2017, 07:19 PM   #724
valvemaniacuk is offline valvemaniacuk  United Kingdom
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Hi Simon,

Thanks for the note. I was sure I had seen comment to the fact that more than one board is needed for the cinemags, but happy to be corrected if 1 is sufficient.

The BCF user guide can be found here -

http://glass-ware.com/User_Guides/BCF%209-Pin.pdf

Photo of my DAC below.

I am already thinking about stage 2 on this, as I ideally need a little more gain, so am looking at the Broskie Unbalancer which is basically the BCF with a differential gain block on the front. Will let you know how it goes.

Cheers,

Steve
Attached Images
File Type: jpg BCF photo.jpg (115.9 KB, 656 views)
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Old 27th February 2017, 07:02 AM   #725
stefan12 is offline stefan12  South Africa
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Hi Steve and others
I am very interested in you experience with the BCF/unbalancer. I have an older DDDac(without Tent reg) and need to make a decision on the path ahead.
I run it into a single-ended hybrid integrated amp and it has served me well over the past 2 years but in comparison to a commercial NOS pcm1704 dac(aqua La Scala) it just doesn't have the verve and drive of the higher output unit from Italy. A bit higher output might come in handy as well as the ability to convert the balance to the SE output.

I use the DDDac without output caps and one of my concerns is the signal caps of the Valve buffer?

I also wonder what valves you use, ecc82 and ecc99 would be my 1st stab if I had to make a call on it?

Thanks
Stefan
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Old 18th April 2017, 06:21 PM   #726
jonatan is offline jonatan  Netherlands
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Hi there, quick question. Bit late to the party, but I wonder if anyone could help with this. I have a few jfets 2sk246bl. What would be the negative side effects of using the bl version over the y version for the ccs circuit? I can dial both in, I would just need some more resistence right?

http://pdf.datasheetcatalog.com/data...shiba/1031.pdf
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Old 10th January 2018, 07:41 AM   #727
stefan646 is offline stefan646
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Quote:
Originally Posted by carlsor View Post
IMO it is important to upgrade the RLoad resistors above the stock Dale RN's. The TX2575 z-foils and Rhopoints are reported to be the best, but are expensive and 133ohms are special order. The Tantalums are a more reasonable priced upgrade but the closest I was able to get was 2X270ohms. The Susumu RG SMD transistors have greater clarity than the Dale RN's and sound at least as good as the Tantalums to me.

What I can do is provide ten 0.1% 270ohm SMD Susumu 1206 RG resistors plus a 2cm X 4cm piece of adhesive backed tinned copper sheeting for SMD installation for $8 plus shipping in an envelope. No extra shipping if mailed with other parts order. Paralleling 270 ohm resistors provides 135 ohms for a single board DAC. The large Susumu RG is not available in 133 ohms, but this difference should not be audible. The purist can add a 3rd 10K resistor in parallel to get 133.2 ohms. Four 10K SMD resistors add $3 to the price. For 2 Board DACs needing 66-67 ohms - three 200 ohm SMDs in parallel equal 66.7 ohms. Cost for 14 0.1% 200 ohm Susumu's and copper sheeting piece is $11 plus shipping. The wattage load for a 4+ board DAC is too much for SMD resistors. PM or email me if interested.

Attached is a picture of the Susumu RG resistors installed in the Rload position using the adhesive backed tinned copper sheeting. Both sides measure 134.9 ohms which should minimize DC offset. There is room for 3 SMD resistors in parallel if needed. Looks more secure than using wires to bridge the gaps.
Hello,

I don't understand this statement.
I have 4 boards and intend to use 6 200 ohm Susumu 1206 RG. If 3 270 ohm resistors in parallel could drive 2 boards, why would't 6 parallel resistors be enough for 4 boards? What I am missing?
Thank you !
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Old 7th November 2018, 09:30 AM   #728
Cney is offline Cney
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Ok, also late at the party. I built the ccs with the 2sk246y.
I made it on a protoboard and checked it 4 times. I'm getting 2.4V when connected to lab power supply and in my DAC but no current anywhere I connect my multimeter.

I'm not building this on a DDDac but in a different 1x PCM1794 DAC and it worked but I can't say that it was better than the 6k resistor.

Anyone have a clue? Am I doing something wrong?
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Old 7th November 2018, 10:04 AM   #729
Cney is offline Cney
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Well after careful 5th measurements with the lab power supply it seems I am at 0.2 uA (micro A) which ofcourse is no bueno
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