Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Using the AD844 as an I/V
Using the AD844 as an I/V
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th February 2019, 08:24 AM   #2241
diyiggy is online now diyiggy
diyAudio Member
 
Join Date: Jan 2019
wow ! And seems also abble to drive headphones.



C4 & C6 with a foilded styren cap (or a silver mica) or a less good 5 mm pitch MKP (avoiding XR7) should be usefull to preserve the clarity of the previous stage.


And for the same purpose : C4+R10 / C7+R18 could be removed if one has an input cap on the pre or amp... (but headphone?)



Btw, just has been looking at your Lingdac shematic. Is this AD8017arz a sort of AD844/OPA860(/1) transconductance IC ? Or why do you prefer it over these last ones to stay in the thread topic (whether an embeded feedbackloop in it?)


Anyway, many thanks for that.
  Reply With Quote
Old 11th February 2019, 08:52 AM   #2242
abraxalito is offline abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Send a message via Yahoo to abraxalito
Headphones can be driven yes - just need to check that the bias current is set (via R8 & R16) in accord with the impedance of the 'phones. Also since its classA there's a fair amount of power being dissipated in Q1/Q2/Q4/Q5 - the PCB layout (found on the lingDAC thread) has areas of copper on both sides to act as heat spreaders. One point I just noticed - the PSU is shown as +9V but in fact this buffer only needs 7V to swing 2VRMS at the output, so to keep the FETs as cool as possible its best to run only as high on the rail as needed to swing the full signal.

C4 and C6 are NP0 types, not X7R so no need to swap them out. NP0 are quite blameless as caps. Yes you could remove output coupling caps if you know the next stage has them - definitely do not remove when feeding headphones.

AD8017 is a current feedback amp with high output drive capability. I chose it mainly because its very cheap on Taobao, excellent bang-for-the-buck. AD811 performs slightly better SQ-wise but is more difficult to employ as its output doesn't swing as close to the rails, demanding more volts on the supply. It also runs very, very hot. Incidentally lingDAC only uses discretes in the OPS, its PhiDAC which uses the ADs.
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant - Alan Greenspan

Last edited by abraxalito; 11th February 2019 at 09:00 AM.
  Reply With Quote
Old 11th February 2019, 09:02 AM   #2243
pistollero is offline pistollero  Portugal
diyAudio Member
 
Join Date: Apr 2016
Location: portugal
Quote:
Originally Posted by georgehifi View Post
Forget the AD844's own buffer it's not very good sounding. Come off the 844's pin5 to your own buffer, I found a "genuine" OPA627 to be exemplary, make sure it's genuine by getting it from an authorized TI distributor, as there are many fakes of these.

Forget the BUF03 in the pic that's the first one I tried, too dirty sounding great bass though.

Cheers George
Hello George, could i use this schematic for the pcm1702 instead of 1704?
are all the component values ok? use 3x ad844 or only 1?
i īm using lt1028 as i/v but i would like to try this alternative.
thks.
  Reply With Quote
Old 11th February 2019, 09:52 AM   #2244
diyiggy is online now diyiggy
diyAudio Member
 
Join Date: Jan 2019
With good layouts I noticed NP0 in the final direct signal path gives subjectivly something not so neutral at ears (so in the listen frenquency range) : often too thin and a little brighty. Although it depends on the width of the traces on the pcb as well ! When I have choice I swap them for Panasonic PPS if SMD designs where the capicitance is notof an importance (serie signal)- Wima FKP2 (non metalized) are good too. or foilded styrens if vias (silver mica being a little too much brighty and thin as NP0 and not tin foilded styrens less good either). YMMV. I like AWG30 (or more little)width and short length output traces for some reasons before RCAs or any gears output stage (trying to have low mass serie contacts). As for the serie resistors I try to use cheap metalized Yageo which are very low noise or RD if not better RS Sussumu in the digital stage AND after.


Again YMMV, all being subjective at ears in the last details (but the Devil often in its for sure)
  Reply With Quote
Old 19th March 2019, 02:04 PM   #2245
IDM is offline IDM  United Kingdom
diyAudio Member
 
Join Date: Apr 2005
Location: Newcastle upon Tyne
Just looking at the Pedja Rogic DDNFS IV schematic and I see it is marked as using +/-19V power rails. How critical is this? It would be far easier to implement +/-15V as per the AD844. So does anybody have any experience of running the stage with 15V?

Cheers
Ian
  Reply With Quote
Old 19th March 2019, 03:30 PM   #2246
triode_al is offline triode_al  Netherlands
diyAudio Member
 
triode_al's Avatar
 
Join Date: May 2004
Location: Westland
Lower is OK - I have used 12V even without problems.
Higher voltage = much hotter!
__________________
SPU --> tube MC/RIAA;
Pass buffer -->300B SE + DN2540 CCS/Buffer; --> 165GMF in TQWT; working on a HYPEXed sub.
  Reply With Quote
Old 19th March 2019, 03:35 PM   #2247
Torchwood421 is offline Torchwood421  United States
diyAudio Member
 
Join Date: Jul 2011
Location: Prior Lake, MN
Thumbs up + and - 15 is OK

Quote:
Originally Posted by IDM View Post
Just looking at the Pedja Rogic DDNFS IV schematic and I see it is marked as using +/-19V power rails. How critical is this? It would be far easier to implement +/-15V as per the AD844. So does anybody have any experience of running the stage with 15V?

Cheers
Ian
Hi Ian, I run at + and - 15 on my builds. Having said that it will have less current in the mirrors. As long as your OK with that it is quite OK. I would not go lower then 15 VDC. I adapted the DDNF to work with a PCM1704 based dac with great results.
  Reply With Quote
Old 19th March 2019, 03:44 PM   #2248
IDM is offline IDM  United Kingdom
diyAudio Member
 
Join Date: Apr 2005
Location: Newcastle upon Tyne
Thanks for the swift responses!

There is so much info in this thread it has taken me ages to get my head round everything. I am using a TDA1541a and plan to use the Pedja Rogic DDNFS IV and probably feed that into OPA1641 op-amps. From what I could gather over the pages that unless you have OPA627 then the OPA1641 are the best for sensible amounts of money. Do I have that right and if so anybody have a rough schematic and or conditions for the 1641 buffer?

I will have to start matching transistors now!

Thanks
Ian
  Reply With Quote
Old 19th March 2019, 04:20 PM   #2249
diyiggy is online now diyiggy
diyAudio Member
 
Join Date: Jan 2019
So this DDNFS I/V needs sorting out the transistors ? What margin please ?
I have been asking about op amps for I/V task at johnc124 from TI in the opa1656 thread in the Vendors Bazar folder.

His answer : "For a DAC chip with a low output current, I would suggest op amps with FET type inputs, either JFETs or CMOS. Low output current would mean the transimpedance gain of the I/V circuit will be high, and the input current noise of the op amp will be a significant contributor. There's no shortage of candidates here, and the new OPA1656 is a great option, but you could also check out: OPA1642, OPA1678, OPA827, and the newer OPA828, or also OPA2810. If you just wanted to use a single 5V supply, the OPA1671 is good. " OPA1656: High-Performance CMOS Audio Op Amp

could be better than AD844 or OPA861 ?
  Reply With Quote
Old 19th March 2019, 07:20 PM   #2250
Torchwood421 is offline Torchwood421  United States
diyAudio Member
 
Join Date: Jul 2011
Location: Prior Lake, MN
Wink DDNF + Buffer

Quote:
Originally Posted by IDM View Post
Thanks for the swift responses!

There is so much info in this thread it has taken me ages to get my head round everything. I am using a TDA1541a and plan to use the Pedja Rogic DDNFS IV and probably feed that into OPA1641 op-amps. From what I could gather over the pages that unless you have OPA627 then the OPA1641 are the best for sensible amounts of money. Do I have that right and if so anybody have a rough schematic and or conditions for the 1641 buffer?

I will have to start matching transistors now!

Thanks
Ian
Hi Ian, I no longer use the OPA627 as a buffer for the DDNF. I switched to the Sparkos SS3601. I used a capacitor between the DDNF output and sized it for the lower impedance of the discrete op amp. I did have some good results with the OPA1641 and as I recall it was drop in. I remember you lose offset adjustment with the 1641. So for me it was the same schematic as the OPA627. Do check the datasheet pin outs. It was a long time since I looked at this. Transistors... There is a benefit to matching. I also bonded all of mine to a heatsink so as to eliminate excess drift. I used a heat sink adhesive for that.
  Reply With Quote

Reply


Using the AD844 as an I/VHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
AD844 as a common base stage in the I/V converter Pedja Digital Source 44 14th September 2015 10:10 AM
WTB AD844 Opamps apassgear Swap Meet 6 31st January 2007 02:57 PM


New To Site? Need Help?

All times are GMT. The time now is 10:22 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki