Pedja Rogic DDNF circuit boards
Hi George, Just assembled my first Pedja DDNF discrete circuit board today. I had a small batch of circuit boards made. After adjustment and 30 Minutes burn in I must say I am surprised it beats my other board. The one Oliver dvb projekt built. Have no idea why that is. My opinion is it also easily beats my triple stack AD844. Plan now is to build one for my PCM1704 DAC. I am using a BUF03 behind the DDNF board so I could use the best quality 0.1 uF cap I could find. So it is kind of in the same configuration as the AD844 more or less. I know how you feel about caps in the signal path. 😱 Sadly there is some small variation in DC offset based on local heating at the transistors. Maybe some sort of DC servo could solve that? Anyway I have a few spare boards if anyone is looking for one. 😀
Attachments
I would like to purchase a board Torchwood. Please pm me with details to pay you etc.Cheers,
Gordon
How much is it as pictured, I'd like to give it a go if reasonably priced.
Also I'd like to know what dc offset is there without that coupling cap with the PCM1704?
Cheers George
PCM1704 with a DDNF stage
Hi George, Just offering a few blank boards at this time. I don't know how much I have in that one pictured. It was built for the Mark II TDA1541 DAC. PCM1704... I still need to build that version. I can omit the 2SK170 offset nulling scheme on a 1704. I am still pondering if I need to do some matching to keep the offset minimal. Matching for hfe is straight forward. I have 125 BC557C's on order and 100 BC547C's as well. On the M2 1541 DAC I am seeing + and - 30 mV's or so. What troubles me is that it is constantly changing so it might be a case where a DC servo could take care of that. I have about 3 hours run time and I have to say this has dynamic slam and jump factor. Something I find missing on the AD844 triple stack. Although the stack is nice and analog sounding. 🙂 I will need more time to really answer the PCM1704 question.
Maybe that +-30mV fluctuations can be fixed with thermally coupling together pairs of transistors together, either by super gluing the faces together or a common heatsink.
I had this same problem on discrete phono headamps back in the 70's and thermal coupling fixed it.
Cheers George
I had this same problem on discrete phono headamps back in the 70's and thermal coupling fixed it.
Cheers George
Heatsink...
Hi George, Actually that is a good idea. I will probably have to get creative. Some face each other and others go the other way. I have the top of the cases level so... I could see about bonding a heat sink on top of the transistors. I'd need to make a it slim and could likely bond all left channel together and all right channel together separately. Thanks for the tip. 😀
May I ask how the BC547C or BC557C are matched? PNP/NPN matched pair or PNP/PNP (NPN/NPN) matched?
Hi, is this PCB still available for sale somewhere? Sorry, I have not read the whole thread.
Matching
I am investigating that. So far hfe is good for current gain. I think vbe (hope I got that right) likely would be more DC operating points that effect DC offset. I have a lot of reading to do and need to get a transistor test jig built or bought. In general terms the BC557C and BC547C are designed as a working push pull pair. 😉
Pedja Rogic DDNF circuit boards
I have a few unspoken for so far. If there is enough interest I could have the board house make some more. The price gets better if you buy more then 10 boards in a run. Ideally something like 15 boards would get the price where I'd like to see it. 😀 So a group buy makes sense. I had a use for a fair number of boards so I bought a lot of 10.
thanks. I am interested in one or two boards if there is a group-buy and assuming that shipping cost is not too much.
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Please have a look at this. I am planning to use AD844 in NFB mode first, followed by OPA861 I/V or this DDNF I/V. A lot of things to do.
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Might be worth looking at thin strips of copper foil wrapped round the transistors (sa a sort of cap) as heatsinks, with a bit of creativity you could link both banks of transistors across the top as well. It's something I've done in the past.
Would a j-fet buffer or discrete or op-amp buffer be needed after your board,or even on your board. I'm thinking a DIY version of a complete post dac stage (as the Zap-filter) might be possible.
Would a j-fet buffer or discrete or op-amp buffer be needed after your board,or even on your board. I'm thinking a DIY version of a complete post dac stage (as the Zap-filter) might be possible.
I am also interested in two boards, if there is a group-buy and assuming that shipping cost to Europe is not too much...
Thank you!
Thank you!
Torchwood,
I would like a couple of the boards. No hurry, I can wait for the eventual group buy.
Greg in Mississippi
P.S. Glad to hear you've been healing up ok.
I would like a couple of the boards. No hurry, I can wait for the eventual group buy.
Greg in Mississippi
P.S. Glad to hear you've been healing up ok.
I would also be very interested in a couple especially if they are at least as good as the stacked 844s using pin 5 as o/p. I can also wait for a group buy as there seems to be, deservedly, a lot of interest. Many thanks to all concerned in this thread.
Could these be used on any DAC in particular the PCM63k or the DSD 1796.
Could these be used on any DAC in particular the PCM63k or the DSD 1796.
Transistor matching...
Hi, Yes that is an interesting paper. Thanks for sharing. I have done the AD844 thing both in standard feedback and without. Used the TZ pin to feed a BUF03. Even a triple stack. Have not tried the OPA861. 😀
Pedja Rogic DDNF circuit boards
I plan to build a version for the PCM1704. I think the only criteria is that the DAC has a current output. One would forgo populating the 2SK170 2 mA current source for nulling the TDA1541's output offset. Most modern DAC's I believe have little or no offset. At the moment I will be look at the transistor matching thing and see what I need to do there. Otherwise the I/V resistor for the PCM1704 would likely be 2.5K Ohm or so. I will report my findings with the 1704. 🙂 This might take me some time.
Pedja Rogic DDNF circuit boards
Hi Greg, Thanks on the well wishes. The shoulder works these days although it kind of aches sometimes. I had a large tear in there. Now I am soon looking at a knee replacement. The date has been set. Guess when it rains it pours. Will advise on the boards. I am taking inquiries in the order received. 😀
Pedja Rogic DDNF circuit boards
Sorry for the late reply here. The circuit uses a 10 uF coupling cap with a parallel 100K Ohm resistor. So if your preamp input is high enough input impedance you could give it a go. My feeling here is to load it as lightly as possible. I also feel the BUF03 or an OPA627 would likely sound better then a 10 uF capacitor. So I went with 0.1 uF film and foil changed the parallel resistor to 3 M-Ohms. I have some of the old BUF03 Aunt Corey style boards so that made it super easy. I am attaching the schematic PDF for those who can't find it. 🙂