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 Posted: 20 Jun 2010, 03:07

Joined: 19 Jun 2010, 17:08
Posts: 71
Hi,

I want to try your headphone amp with pc sound card output. What is the optimal value volume pot and R1 in this case?

What's the purpose of C2? increasing the value changes the sound?

When adjusting P1, where are you measuring and what voltage are you looking for?

Do you know of any voltage double circuit that keep the 12V for psu and increase the +B to 24VDC? should sound better?

thanks

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 Posted: 20 Jun 2010, 08:12

Joined: 31 Dec 2008, 15:34
Posts: 441
Hi

An important thing about the LM317 regulator, is the recommended operating conditions

VI – VO Input-to-output voltage differential ( MIN 3 V ) ( MAX 37 V ) UNIT.

Gio, you're right about 15 VDC or greater ( 15 - 3 = 12 V ). 15 VDC, is minimum, don't use anything lower, if so the regulator won't be able to regulate for a clean output voltage . I would go for a wallwart powersupply typical between 18 - 25 VDC, min. 800 mA or higher, or even better a laptop supply. I had tried a few of these and it seems, they are great for this project. SMPS ( Switched Mode Power Supply ).

Datasheet from TI, with good details: http://www.datasheetcatalog.org/datashe ... /lm317.pdf

Gio wrote:
If you have a 15VDC (or greater) supply, you can run it through a LM317 voltage regulator to make a 12V regulated supply which will be very clean. All the info you need is on that page, but if you have questions or need help, feel free to ask.

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 Posted: 20 Jun 2010, 12:04

Joined: 19 Jun 2010, 17:08
Posts: 71
Hi,

for C2, is the schematic correct or the layout/details? C2 + connects to tube or ground?

thx

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 Posted: 20 Jun 2010, 21:44
 Editor

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
Lynxo323 wrote:
for C2, is the schematic correct or the layout/details? C2 + connects to tube or ground?

The schematic is correct.

Lynxo323 wrote:
When adjusting P1, where are you measuring and what voltage are you looking for?

Here are instructions on how to set the bias

Lynxo323 wrote:
Do you know of any voltage double circuit that keep the 12V for psu and increase the +B to 24VDC? should sound better?

And some info on voltage doublers:
http://en.wikipedia.org/wiki/Voltage_doubler
http://www.kronjaeger.com/hv/hv/src/mul/

Cheers

_________________

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 Posted: 21 Jun 2010, 00:01
 Project Author

Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
Lynxo323 wrote:
What's the purpose of C2? increasing the value changes the sound?

C2 - The short explanation is it increases gain.

Here is a link with some more info http://www.aikenamps.com/CommonCathode.htm

Rogers

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 Posted: 21 Jun 2010, 09:20

Joined: 18 Jun 2010, 14:55
Posts: 4
Location: Spain
Quote:
Since you are only loading the pc power supply about 300mA, try disconnecting the fan. Check if the heat stays within a reasonable temp. If anything you can run the pc supply without the top for passive airflow.

hi, I disconnected the fan, and I connected to another source, a small transformer with a bridge rectifier installed in the same box. works perfectly! no fan noise is heard but a little AC noise.

while I'm still looking, I use a battery, but when fully charged, provides 13.5 v
if the maximum is 12.6 v Is it bad for the tube?

Quote:
If you have a 15VDC (or greater) supply, you can run it through a LM317 voltage regulator to make a 12V regulated supply which will be very clean. All the info you need is on that page, but if you have questions or need help, feel free to ask.

thanks
My idea was to use a 7812, I have several sources 18v AC, 15VAC, 24VAC, but are 600 mA maximum
I measured the power consumption of the amplifier, 750mA ...
i looking for better source

Greetings!

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 Posted: 21 Jun 2010, 09:53

Joined: 13 Apr 2010, 10:39
Posts: 37
Location: Dallas, Texas, USA
jaume wrote:
while I'm still looking, I use a battery, but when fully charged, provides 13.5 v
if the maximum is 12.6 v Is it bad for the tube?

A 12V tube is good usually for 12.6V, plus or minus about .4 volts, no problem-o.

Higher voltage:
It's just like the (incandescent) light bulbs in your house - run 'em at a higher voltage and it will have some shorter life. But around + 0.4 volts is completely within their tolerance. I'd say +10%, or 13.8V would be an absolute maximum and that's gonna start affecting life, over the longer run. There are some old tube books available on-line (in PDF format) where tube life and design parameters are discussed at length... It's wonderful reading some of that material - it's a world of lost art.
(With grateful thanks to Pete Millett...) See: http://www.tubebooks.org/technical_books_online.htm

Lower voltage:
Tubes will work quite well at a lower filament voltage. In fact, on a tube-tester there's usually a 'life' test switch - that just runs a lower filament voltage which will simulate an older, weaker filament. Usually you don't see (or shouldn't see) much of a drop in performance switching it to 'life' test. If you do, that tube is old.

12AU7/IRF510 Power - personally, I built a little regulator / filter box to go along-side. There are good 'pre-regulated' wall-warts (the Canon printer supply is a good one!) but I was attempting to build mine out of ALL materials that I had on-hand. eBay has the Canon 13V supply for not very much. I used the LM317, with a multi-turn trim pot for the base resistor - that way you can dial in the voltage you need.

And, surprisingly, I had all that crap in my stash of stuff! I think I bought one enclosure box and a couple of larger heat-sinks.

Mike Yancey
Dallas, Texas

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 Posted: 21 Jun 2010, 12:18
 Editor

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
mikeyancey wrote:
12AU7/IRF510 Power - personally, I built a little regulator / filter box to go along-side. There are good 'pre-regulated' wall-warts (the Canon printer supply is a good one!) but I was attempting to build mine out of ALL materials that I had on-hand. eBay has the Canon 13V supply for not very much. I used the LM317, with a multi-turn trim pot for the base resistor - that way you can dial in the voltage you need.

Hi Mike, this question has come up a couple times now. Any chance you could post a schematic and some photos for the other builders. If you need help with the schematic. I can draw it up. you can email me at the address shown in the site banner at the top of the page.
Cheers

_________________

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 Posted: 21 Jun 2010, 13:17

Joined: 13 Apr 2010, 10:39
Posts: 37
Location: Dallas, Texas, USA
Gio wrote:
Hi Mike, this question has come up a couple times now. Any chance you could post a schematic and some photos for the other builders.

Aye, sir!
Well, as they say, amateurs plagiarize, and professionals steal *cough* here I've stolen the Millet Max regulator circuit (see: http://www.diyforums.org/MAX/schematic/MAXsch75.jpg).

I've filled in the component values, which are kept on a separate MillettMAX BOM.

For the (listed) 4 x 1000uf/50V filtering capacitors at CR1A-D - this is way overkill - I used 3; you can probably get away with 2... depends on how clean the input. Use what ya have...

The Millet Max uses a raw, 24 VAC input, rectified, and also uses more current, so there's reason for 4 there. If you're wall-wart is even somewhat filtered, you can do with much less here.

DR3 may be eliminated - it's present per LM317 datasheet - if a voltage exists upstream and power is removed from the left it could damage the LM317 - not a problem here, as the CR1A,B... would remain charged, and the voltage at the amp will collapse first. DR2 protects against discharge from CR4 (which is present to provide a nice, stable voltage reference).

Use a multi-turn for RR3 - you can dial in, under load, your exact desired voltage.

You'll need a heat sink on LM317T - normal load (the tube amp) is 400ma x 12.6V = 5 watts, plus any voltage you 'buck' from the input (datasheet gives a formula for computing the exact amount, but generally you can get away with a small-ish PC graphics-card sized sink). The higher the input voltage, the more heat. The closer to 14.5 or 15 volts, the cooler...

Tantalums? - probably can use whatever you have on-hand: film, mono, a small electrolytic for CR5... values for pretty much all of the capacitors aren't terribly critical.

Mike Y
Dallas, Texas

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 Posted: 21 Jun 2010, 22:14
 Editor

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
Thanks Mike, that is great. I made a link to your supply from the first post in this thread.
mikeyancey wrote:
Tantalums? - probably can use whatever you have on-hand: film, mono, a small electrolytic for CR5... values for pretty much all of the capacitors aren't terribly critical.

CR4 - a 10uF/35V tantalum is recommended on the application/datasheet. An alternate would be a 100uF/35V electrolytic.
CR5 - a 1uF tantalum is recommended on the application/datasheet. A 0.1uF to 1uF film capacitor can be used as an alternate.

Cheers

_________________

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