I measure the output of my tda1541a which is connected to the ad844 input. at this point, the voltage drift within 10mV max. I think this cause a larger drift at the ad844 output. I guess I have to live with the output cap :-(
This V drift is due to temperature for sure but I am not sure if it is cause by the tda1541a or the current source with 2sk170.
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I have just received this discret buffer but it seems to come with lousy quality chinese resistors. Not sure about quality of the transistors and whether they are really matched. I will try to replace all the resistors and see how. Based on my experience with other project low quality damage the sound a lot.
TDA1541A Offset
On the DDNF discrete circuit with the TDA1541's I have had no choice, must use a cap. To bad the BF245A has different pin outs. On one version I built with the BF245A, I was able to DC couple. At that time I had the triple stack AD844's. Here is what I did. Adjusted 2 mA current source to eliminate DC from dac. I then adjusted the AD844 null circuit to as close to zero as I could get at pin 6. The BUF03 off the TZ had a null as well so I was getting something less then 1 mV. Maybe I was lucky. 🙂
Question for George (or anyone else with the experience), Do you think the triple stack AD844 followed by OP627 buffer is as good or better than the Zapfilter?
I will be converting the PCM63k to the triple (or quadruple) stack but I'm wondering about the Sony DVPns9100es which has just 2134s as i/v and buffers.
The zapfilter would be easier (although a lot more expensive) but if the AD844 are as good (the DACs are DSD1796 with 4ma p-p output) then I would try building a cct to try out but I haven't got a zapfilter to compare with nor experience of them.
Do you have any opinions on the comparison?
Thanks as always.
I will be converting the PCM63k to the triple (or quadruple) stack but I'm wondering about the Sony DVPns9100es which has just 2134s as i/v and buffers.
The zapfilter would be easier (although a lot more expensive) but if the AD844 are as good (the DACs are DSD1796 with 4ma p-p output) then I would try building a cct to try out but I haven't got a zapfilter to compare with nor experience of them.
Do you have any opinions on the comparison?
Thanks as always.
I was a supplier/installer in Australia for the LC Zap years ago, and the Zap filter was a great buffer with the LC shunt regulated supply. (lots of heat).
If I had one still it would be nice to compare it to the opa627, as I liked the sound of it back then.
Cheers George
anjump123,
You can also try ADA4627 or ADA4898-1. They perform excellently when properly bypassed.
You can also try ADA4627 or ADA4898-1. They perform excellently when properly bypassed.
Pedja Rogic DDNF for PCM1704
Hi guys... Finally put that DDNF board on the PCM1704 dac. DC parameters changed while connected to the dac. Where I had measured it open input before I now have it terminated. For now I have the coupling caps installed. Running + and - 15 VDC rails, that is so I could share the power supply with the BUF03 buffer. At the dac output (0-1 mA) I am seeing -15 mV's offset. At the output of the DDNF I am getting less then -2 mV's in the left channel and just under +2 mV's in the right channel. So I guess I did better matching transistors then I had earlier thought. First listen is super smooth sound with a large sound stage. Think I should give it some more time before really making a comparison to the AD844 triple stack. Unknown is how stable the offset is. I should be able to null it at the BUF03 if it proves to be predictable.
Hi guys... Finally put that DDNF board on the PCM1704 dac. DC parameters changed while connected to the dac. Where I had measured it open input before I now have it terminated. For now I have the coupling caps installed. Running + and - 15 VDC rails, that is so I could share the power supply with the BUF03 buffer. At the dac output (0-1 mA) I am seeing -15 mV's offset. At the output of the DDNF I am getting less then -2 mV's in the left channel and just under +2 mV's in the right channel. So I guess I did better matching transistors then I had earlier thought. First listen is super smooth sound with a large sound stage. Think I should give it some more time before really making a comparison to the AD844 triple stack. Unknown is how stable the offset is. I should be able to null it at the BUF03 if it proves to be predictable.
Hi,
Why is there still DC offset after DDNF if you already installed a coupling cap? Did you measure it before the cap?
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There's probably no load (not enough) to ground after the coupling cap. Or the caps aren't doing their job.
I hate coupling caps, 10km of foil for that poor little signal to travel though before it gets anywhere, no wonder they all sound coloured to me.
Cheers George
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Offset measurement
I measure just before the cap. After the cap you don't really see anything as the cap blocks DC. 😉
Offset measurement
I measure before the cap. Only way to see what is going on in the current mirrors. I have had it on for 6 hours now. Really love the PCM1704. I hope I may be able to remove the caps. Long term stability is still an unknown.
Offset measurement on DDNF with PCM1704
Update... Have reason to believe the thermal bonding isn't quite up to my standards. Ordering thermal conductive epoxy to bond the heatsinks to the transistors. At least before giving up on the DC coupling idea. Sound quality is really quite good even with the coupling caps. Feel I should give this thing every chance for success.
Update... Have reason to believe the thermal bonding isn't quite up to my standards. Ordering thermal conductive epoxy to bond the heatsinks to the transistors. At least before giving up on the DC coupling idea. Sound quality is really quite good even with the coupling caps. Feel I should give this thing every chance for success.
I found the smallest amount of super glue on one of the faces then pressed together, to work the best, as it's so thin (water) you get great thermo coupling.
Cheers George
Cheers George
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Heatsink... DDNF for the PCM1704
Hi George, Thanks for the tip. Sadly the heatsinks are not exactly flat. So a thermal conductive epoxy is likely the only way to go. I am not exactly idle at the moment even though I am waiting for the special epoxy. Built up another I/V stage to test with some positive results. Not a DDNF. Working better then expected and simple. May share it at the right time. 😉
I found 8 pin dip IC heatsinks ideal to super glue across the top of 2 x TO92 type trany's with their faces super glued together as well.
https://www.sparkfun.com/products/11510
Cheers George
https://www.sparkfun.com/products/11510
Cheers George
Epoxy... DDNF for PCM1704
Update... Epoxy arrived yesterday. Just finished installing the heatsinks. Cure time is something like 7 hours. It was thick like I had hoped so it made the interfacing easy. Probably won't try it until tomorrow. I have done some experiments with a clean I/V build using the ADEL2020. It is the best sounding feedback type op amp I have tried. So my results which are just my opinion is the ADEL2020 beats the AD844 triple stack using 3X internal output buffers. To be fair I will add pin 5 outputs to my triple stack board to allow using a BUF03. Listening tests suggested more low level bit clarity and much better dynamics and bass snap with the ADEL2020. The low level detail was a surprise as the AD844 has always done well with that. Round 2 will be ADEL2020 versus AD844 triple stack + buffer. I think that is a more fair match up.
Update... Epoxy arrived yesterday. Just finished installing the heatsinks. Cure time is something like 7 hours. It was thick like I had hoped so it made the interfacing easy. Probably won't try it until tomorrow. I have done some experiments with a clean I/V build using the ADEL2020. It is the best sounding feedback type op amp I have tried. So my results which are just my opinion is the ADEL2020 beats the AD844 triple stack using 3X internal output buffers. To be fair I will add pin 5 outputs to my triple stack board to allow using a BUF03. Listening tests suggested more low level bit clarity and much better dynamics and bass snap with the ADEL2020. The low level detail was a surprise as the AD844 has always done well with that. Round 2 will be ADEL2020 versus AD844 triple stack + buffer. I think that is a more fair match up.
I agree, the AD844's buffers while very nice sounding, do miss out on dynamic balls to the wall impact.
The BUF03 is very powerful sounding Torchwood, but it is not as clean and transparent as the OPA627 in the upper mids and highs and which is almost as powerful sounding as well.
Cheers George
The BUF03 is very powerful sounding Torchwood, but it is not as clean and transparent as the OPA627 in the upper mids and highs and which is almost as powerful sounding as well.
Cheers George
PCM1704 + ADEL2020
Hi George, Actually I am considering putting OPA627 buffers together. As an option to the BUF03. I think under the circumstances I need to be as fair in the comparison as I can. I took the 1704 dac to my cousins and we had a nice listening experience with the 1704 + ADEL2020. I will likely repeat that with the AD844 + 627. He has a Nelsen Pass Bride of Zen pre a modified B&O Cold amp (input stage was adapted for the Zen). His speakers are Alon 4's that have rebuilt crossovers. A very clear focused sound with great depth and detail. Very musical. It was nice to get another opinion in a different system.
If you do the OPA627, give it 2 x gain and 50ohm output series resistor even though it's suppose to be unity gain stable. I run it off - +15vdc rails.
Cheers George
Cheers George