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PostPosted: 04 Jun 2010, 01:10 
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Joined: 11 Apr 2010, 01:54
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Location: Tel Aviv, Israel
Gio thanks.

The problem happen only with one 600 milliampere adapter and others driving the amp fine.
So i think the odd problem come from the specific cheap adapter.
And i wanted to report this if someone else have same problem (hum starting from specific voltage) one of the options is replacing the adapter.

Dan.


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PostPosted: 04 Jun 2010, 07:41 
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Joined: 13 Apr 2010, 10:39
Posts: 37
Location: Dallas, Texas, USA
I think you're seeing clean power with 'no load', but once you put around 200ma to 400ma load on it there begins to be significant ripple or hum.

Use a couple of 1000uf capacitors before the LM317, and perhaps a 1uf tantalum after the LM317.
Additionally, you can include a .1uf before or after for RF suppression (just in case of nearby transmitters).
For what it's worth, I used just the LM317 circuit from the Millet Max:

http://diyforums.org/MAX/schematic/MAXsch75.jpg

I used 3 1000uf / 50V capacitors before the LM317 (instead of 4), from basically from CR1A to CR5.
(parts values are on the BOM on the same site, http://diyforums.org/MAX/bom/MillettHybridMax.html)

Agreed viz. 'cheap adapters' - the little wall-wart cubes are little more than a step-down transformer and a diode, with maybe one capacitor on the DC side. Also, try a higher wattage converter - if the wall-wart is near 500ma output, that's too close to the maximum that will be required. Look for a 1000ma / 1A output, or at least 800ma.

I'm having swell luck with an old laptop supply - 18V, 1.5 amp.These are switching supplies - they will bring high-frequency switching artifacts to the output, but these are usually filtered easily enough through a good regulator circuit - 60hz (or 120hz as through a bridge rectifier) is somehow harder to filter.

High-frequency switching is usually done at 100khz - so it probably won't even show up in the audio output! I have a harder time with 100khz and other switching noise in RF applications (amateur radio).

Mike Yancey
Dallas, Texas
(edited: Hey! your English is great! ...better than lots of folks I know!)

AndrAKondrA wrote:
Connected the amp to the battery - here is the place the solution comes. 7-9-10 volt I hear the music without hum. OK it's supply voltage problem. Changing cheap AC/DC adapter to better quality adapter helps. But, still why until 7 volt zone i didn't hear the hum noise? Connected again the cheap adapter and oscilloscope to the output of the LM317 regulator. If the amp is disconnected no ripple seen in output voltage, when I connect the amp to the regulator I see ripple (after 7 volt zone) in the input voltage!

Bottom line:
1. I think its some sort of resonance between the amp and cheap power source.
2. Stay away from very cheap adapters they are unpredictable!


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PostPosted: 04 Jun 2010, 08:54 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
I'm having swell luck with an old laptop supply - 18V, 1.5 amp.These are switching supplies - they will bring high-frequency switching artifacts to the output, but these are usually filtered easily enough through a good regulator circuit - 60hz (or 120hz as through a bridge rectifier) is somehow harder to filter.


Yes, I agree, sometimes it takes a bit of trial and error to find the perfect wall wart. I use a Canon AD360U, it is from a compact portable printer and is 13v 1.8A and is dead silent. There are many on eBay, but is would be best to find an OEM. I have not tried the third party version.


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PostPosted: 04 Jun 2010, 14:57 
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Joined: 06 Apr 2010, 05:48
Posts: 17
Hiya all, just a couple of questions: cap polarity. Output with + toward 317 pin 3/input 2.2 (have'nt a poly cap - sorry) so will have to go with electrolytic for now but, here's the deal - it's all done point to point and as tight as i can get things, so really want to do it once to save possibly frying components :mad: . In a nice veneered box i had lying around, in the 'spirit of' i've pulled most from bits lying around and have only bought output caps and 2xLM317. I'll put up pics when done but i only hope it's right cos i can't get 'back in there' without destroying nicely bent bits and bobs. Any help appreciated as i'm itching to try it out. Thanks to you everyone


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PostPosted: 05 Jun 2010, 21:29 
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Joined: 14 Oct 2008, 17:35
Posts: 901
Location: Dartmouth, Nova Scotia
There is not much to wiring an LM317, if you need more info you can just do a google search and you will come across many links but here are some to make things easy....

LM317 Pinout, Data sheet and calculator: http://diyaudioprojects.com/Technical/V ... Regulator/

Below is a higher current regulated power supply using the LM317, and TIP32C. You should be able to get a continuous 1.5-2 Amps Likely more, I am not really sure. The amplifier I used it for did not draw as much current as I expected.
Attachment:
Hybrid tube LA4270 amplifier PS.JPG


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


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PostPosted: 06 Jun 2010, 02:59 
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Joined: 06 Apr 2010, 05:48
Posts: 17
Thankyou very much for that. It seems despite being in the 12au7/irf510 headamp thread that my posts have 'wondered'? It was a question based on the DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier circuit specifically and i have no idea where the other's gone?


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PostPosted: 07 Jun 2010, 03:26 
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Joined: 06 Apr 2010, 05:48
Posts: 17
Guys (rogers) I had a good look at schematic and figured the polarity of output cap. Now, the real problem is i can't get my 'bias' level to 1/2 B+ ?? Running a flat batt to test i have 11.42 v B+ / 10 ish at anode but 7.3 at junction of LM/output cap. I didn't have irf510 and couldn't get quickly so used 630 . Seems the ciss is 3 times 510 but nowhere near 540/740 levels. Used the 4k7 option as it felt right but really and truly, with my point-point it's a pain in the £$%" to keep messing, any ideas? I tried the forum and read 9v ish at anode on other builds but even with 20k it still never got that low? I admit, getting stuck now good and proper. Any and all ideas gratefully received. Thankyou


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PostPosted: 07 Jun 2010, 14:53 
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Joined: 20 Apr 2010, 13:29
Posts: 8
I'm a little confused about the 10k trimmer vs 4.7k static resistor. What are the advantages of either one?

Also, I know this is a total n00b question, but it seems that if I connect the ground of the output 1/8" jack, I only get mono. Leaving it disconnected I get stereo. Why does that happen?


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PostPosted: 08 Jun 2010, 12:16 
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Joined: 28 May 2008, 21:53
Posts: 4580
Location: Winnipeg, CANADA
nat wrote:
I didn't have irf510 and couldn't get quickly so used 630 . Seems the ciss is 3 times 510 but nowhere near 540/740 levels. Used the 4k7 option as it felt right but really and truly, with my point-point it's a pain in the £$%" to keep messing, any ideas?

From the project text:
The MOSFET (Q1) can be replaced by an IRF610, IRF611 or IRF612, all of which will work as well. Stay away from IRF530 or IRF540 types (commonly found in power supplies) as there will be terrible roll-off of the highs.

Try using one of the devices noted above they are very common and inexpensive. I've used the IRF510, IRF610 and IRF612 in pretty much the same output stage and they all work just fine.
dgadling wrote:
I'm a little confused about the 10k trimmer vs 4.7k static resistor. What are the advantages of either one?

4k7 is easy to find and dirt cheap
10k trimmer is adjustable
dgadling wrote:
Also, I know this is a total n00b question, but it seems that if I connect the ground of the output 1/8" jack, I only get mono. Leaving it disconnected I get stereo. Why does that happen?

Sounds like you have a wiring error, check your input, pot and output wiring.
Cheers

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PostPosted: 09 Jun 2010, 08:17 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
nat wrote:
Used the 4k7 option as it felt right but really and truly, with my point-point it's a pain in the £$%" to keep messing, any ideas? I tried the forum and read 9v ish at anode on other builds but even with 20k it still never got that low?

Nat

I started with point to point and sometimes it can get crazy. As Gio stated recheck your wiring, many of the connections terminate to ground so it is easy to mix them up. If all else fails you can always add a 100 or 200 ohm dropping resistor between the anode and the gate of the mosfet.

7 volts is not a show stopper, it will allow the amp to work you just will be limited in the amount of voltage swing.

Rogers


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