Can I use a 24V transformer?
I bought one of these kits this past February and am just getting around to building it. The DAC is going to go into a DIY integrated amp based on a popular LM3886 gainclone.
The transformer I am using for the amp is an Antek AS-3224 (300VA, 24-0-24 Vdc). I know that the DAC wants transformer with a much lower voltage but is there some way I could bypass part of the DAC's power supply and feed the DAC's regulators from the amp's power supply (rectified & smoothed power)? If so, would it be a good/bad idea to use a resistor to drop the voltage some? And what should the wattage rating be be used for the resistor?
Thanks for your help,
goody75
I bought one of these kits this past February and am just getting around to building it. The DAC is going to go into a DIY integrated amp based on a popular LM3886 gainclone.
The transformer I am using for the amp is an Antek AS-3224 (300VA, 24-0-24 Vdc). I know that the DAC wants transformer with a much lower voltage but is there some way I could bypass part of the DAC's power supply and feed the DAC's regulators from the amp's power supply (rectified & smoothed power)? If so, would it be a good/bad idea to use a resistor to drop the voltage some? And what should the wattage rating be be used for the resistor?
Thanks for your help,
goody75
Hi Goody,
Please do NOT do this.
Buy two separate transformers (see order numbers below), or buy them at local radio store or where ever.
The DAC kit should be galvanically isolated from the main amp.
The numbers
RS: 278-6908
Farnell: 9531548
You can have any type transformer (block or toroidal). The "big one" should be able to supply 5VA at least and have 2 x 18V as secondary windings.
The other one CAN have one secondary winding at 9V and at least 3VA. You can also have two secondary, then put them in parallel.
The transformers are so small, you can fit them probably anywhere. Put a 150 mA fuse at the primary side for both transformers.
Please do NOT do this.
Buy two separate transformers (see order numbers below), or buy them at local radio store or where ever.
The DAC kit should be galvanically isolated from the main amp.
The numbers
RS: 278-6908
Farnell: 9531548
You can have any type transformer (block or toroidal). The "big one" should be able to supply 5VA at least and have 2 x 18V as secondary windings.
The other one CAN have one secondary winding at 9V and at least 3VA. You can also have two secondary, then put them in parallel.
The transformers are so small, you can fit them probably anywhere. Put a 150 mA fuse at the primary side for both transformers.
Interesting discussion on transformers and fusing. Has anyone actually compared the results for this DAC with a single transformer vs two? Many have reported good results with the C-style 30VAC transformer (e.g, marked AC4.265.5387) sold by the ebay suppliers of this DAC kit.
Regarding fusing, you may want to refer back to post from member Col_s 29 July, post 406]... Post explains rationale for "Each transformer should have its own appropriately sized fuse on the mains side of the transformer ... based on the rating of the transformer .... Further fuses can be used on the secondary side to protect the devices that you will be powering ... sized for the load." Also rec'ds star grounding, and has links to discussions on other forums.
If others agree, feel free to chime in. I'm a newbie here, so I'm not able to offer a recommendation from my own experience.
Regarding fusing, you may want to refer back to post from member Col_s 29 July, post 406]... Post explains rationale for "Each transformer should have its own appropriately sized fuse on the mains side of the transformer ... based on the rating of the transformer .... Further fuses can be used on the secondary side to protect the devices that you will be powering ... sized for the load." Also rec'ds star grounding, and has links to discussions on other forums.
If others agree, feel free to chime in. I'm a newbie here, so I'm not able to offer a recommendation from my own experience.
Thanks for the warnings and the suggestions. I have another question about the bridge rectifier. I bought a blank board and am trying to finish up my part order. The KBP206 that the BOM calls for is not stocked at mouser. Can anyone tell me if any of the following will work.
Vishay 2KBP06M-E4/45
GenieSIC Semiconductor KBP208
Fairchild 2KBP08M
Thanks again,
goody75
Vishay 2KBP06M-E4/45
GenieSIC Semiconductor KBP208
Fairchild 2KBP08M
Thanks again,
goody75
You're wrong.
The BOM for bare boards on my Google folder indicates this mouser code: 621-KBP206G
that code is available (479 on stok in this moment)...
Here is a reply I stumbled across from the guys at JRiver that might shed some light on the 192K search.
Playing 192k files
Playing 192k files
By the way, for anyone looking for part numbers from Mouser for Dario's Simple Shunt build, I looked up the following. Some of these are slight substitutions, so make your own choices accordingly. But this could save you some legwork....
MOUSER BOM for Simple Shunt Regulator
IC101 / IC301: ON Semi LM317 IC .... 863-LM317TG
IC201: ON Semi LM337 IC .... 863-LM337TG
R301: Caddock MP915 .... 684-MP915-20
R101 / R201: Caddock MP915 (2 X 20; 39 Ohm not stocked) .... 684-MP915-20
R102 / R202 / R302: Caddock MK132 (100 x2; 200 Ohm not stocked) .... 684-MK132V-100
D101 / D201: Fairchild Semi. Zener, 12V .... 512-1N5242BTR
D301: Fairchild Semi. Zener, 4.3V .... 512-1N5229BTR
T101 / T101: Fairchild BD139 transistor .... 512-BD13916STU
T201: Fairchild BD140 transistor .... 512-BD14016STU
C103 / C203 / C303: Nichicon FG 100uF 50V ... 647-UFG1H101MPM
MOUSER BOM for Simple Shunt Regulator
IC101 / IC301: ON Semi LM317 IC .... 863-LM317TG
IC201: ON Semi LM337 IC .... 863-LM337TG
R301: Caddock MP915 .... 684-MP915-20
R101 / R201: Caddock MP915 (2 X 20; 39 Ohm not stocked) .... 684-MP915-20
R102 / R202 / R302: Caddock MK132 (100 x2; 200 Ohm not stocked) .... 684-MK132V-100
D101 / D201: Fairchild Semi. Zener, 12V .... 512-1N5242BTR
D301: Fairchild Semi. Zener, 4.3V .... 512-1N5229BTR
T101 / T101: Fairchild BD139 transistor .... 512-BD13916STU
T201: Fairchild BD140 transistor .... 512-BD14016STU
C103 / C203 / C303: Nichicon FG 100uF 50V ... 647-UFG1H101MPM
Regarding the Simple Shunt regulator, at some point earlier this thread, there was discussion of extending it to power the +3.3V leg of the DAC. (Thus, the corresponding parts were named IC401, T401, R401, R402, D405, etc).
Dario, did you try this out? If so, did 43 ohms prove to be the appropriate value for R401?
Dario, did you try this out? If so, did 43 ohms prove to be the appropriate value for R401?
No, sorry, too busy with the My_Ref Fremen Edition project.
BTW I don't think it would improve things much.
That simple regulator is well suited for analog PS, I don't know if it fares well with digital.
PS
Caddock MK132 are costly, swapping a single 200R with two 100R...maybe it's better order them from PCX that has stock, isn't it?
Hi Dario,
Good thought on price ... yet I'm finding shipping costs keep adding up, as I go to different vendors to get just the right part -- (ebay, Mouser, Parts Connexion, Elfa Distrelec...). So far, almost 1/3 of my cost has been shipping (though this includes some upgrades to my workbench tools
But my luck ... Mouser USA now stocks the 200 ohm Caddock !
Part 684-MK132V-200
Problem solved !! ;-) !!
Good thought on price ... yet I'm finding shipping costs keep adding up, as I go to different vendors to get just the right part -- (ebay, Mouser, Parts Connexion, Elfa Distrelec...). So far, almost 1/3 of my cost has been shipping (though this includes some upgrades to my workbench tools
But my luck ... Mouser USA now stocks the 200 ohm Caddock !
Part 684-MK132V-200
Problem solved !! ;-) !!
Alrighty, I 've playing with the AK4396 Version. I put it in my Arcam Alpha 7. There is plenty of room. I am using the 15-0-15 0-9v transformer that you can get with these boards. I have configured the DAC output resistors for the AK4396. (2.4K and 150 ohm). Thanks Clave!
Using a value of 680pF for the DAC output filter seems kinda harsh and bright. I can quickly switch back and forth from the Arcam output to the AK4396 output.
The DAC output is filtered by this circuit:
Multiple Feedback Low-pass Filter Design Tool
So you can calculate the cutoff frequency at 177K. I saw some room to lower that!
I switched out the 680pF caps and now have 2.2nF polypropylene Panasonics in their place.
http://industrial.panasonic.com/www-data/pdf/ABD0000/ABD0000CE17.pdf
The cutoff frequency is down to 98K now but it sounds every bit as good as my Arcam.....even better bass!
Also I am using LM4562 opamp.
Other "improvements":
I am not using the rectifier bridges that came with it. I have made up bridges using 40v Schottky diodes to reduce switching noise.
6800uF 25V caps on the 15-0-15 line and a 10,000uf 16v on the 0-9v line. (They fit!)
Resistors on the DAC output are Carbon film.
2200uf 16v caps after the 12v regulators.
My 12v regulator really does not get that hot...maybe 45 degrees Celsius. (Could be the Schottky's?)
Using a value of 680pF for the DAC output filter seems kinda harsh and bright. I can quickly switch back and forth from the Arcam output to the AK4396 output.
The DAC output is filtered by this circuit:
Multiple Feedback Low-pass Filter Design Tool
So you can calculate the cutoff frequency at 177K. I saw some room to lower that!
I switched out the 680pF caps and now have 2.2nF polypropylene Panasonics in their place.
http://industrial.panasonic.com/www-data/pdf/ABD0000/ABD0000CE17.pdf
The cutoff frequency is down to 98K now but it sounds every bit as good as my Arcam.....even better bass!
Also I am using LM4562 opamp.
Other "improvements":
I am not using the rectifier bridges that came with it. I have made up bridges using 40v Schottky diodes to reduce switching noise.
6800uF 25V caps on the 15-0-15 line and a 10,000uf 16v on the 0-9v line. (They fit!)
Resistors on the DAC output are Carbon film.
2200uf 16v caps after the 12v regulators.
My 12v regulator really does not get that hot...maybe 45 degrees Celsius. (Could be the Schottky's?)
See this post on the FE thread.
You're welcome
The problem is not the filter but the LM4562, IMHO.
LM4562 has problems with capacitive loads and not that big output current.
So it can easily sound harsh and bright.
Isolating his output with a small value resistor could help a lot (see in the first pages of the thread).
The best solution would be to have a buffer after it or, easier, change opamp...
Good choice.
I have some of these coming:
2* Dual SOIC to DIP-8 Convert PCB Adapter SMD OPA627 | eBay
and then I can try out my OPA827's. I ordered them not realizing they were NOT dual channel.
2* Dual SOIC to DIP-8 Convert PCB Adapter SMD OPA627 | eBay
and then I can try out my OPA827's. I ordered them not realizing they were NOT dual channel.
I have some of these coming:
2* Dual SOIC to DIP-8 Convert PCB Adapter SMD OPA627 | eBay
and then I can try out my OPA827's. I ordered them not realizing they were NOT dual channel.
Maybe on BOM is not so clear but I've specified they must be mounted on a BrownDog adapter...
I lke best the ones from Cimarron but the ones you ordered should do as well.
OPA827 to give full potential should run for 50-100 hours (at first bass is not so controlled).
Burn-in can be greatly reduced using Isotek System Enhancer CD (2-3 runs of track 2 will do).
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Simply to be coherent with original BOM.
In fact I'm using 15V ones in my DAC, obiously they should be On Semi ones.