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Old 20th January 2012, 03:30 AM   #1
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Default Pass B1 DIY - Need Help

OK, so after some pushing by a friend who wanted a Pass B1 for less than the $1k retail price, I agreed to build him one. I've read through all the build threads, the reviews, etc. to get acquainted with the project. Intrigued, I decided to build myself one as well to go with a little 2050 Sure amp I have from Parts-Express and turn that into a small integrated amp for the garage or nursery.

While I'm no EE, I've been involved with basic electronics, mainly audio (Pro, Car, and Home), for my whole life and can get around a bit more than your average joe.

That said, I put together the BOM, starting with the board from Pass DIY with matching JFETs, and the rest from Digikey and Parts-Express. As at least a test power supply, I had a few Dell Laptop bricks laying around that are 18.5V DC @ 3.3Amps. Plenty for the B1 and enough to test the 2050 setup for functioning.

I assembled mine last night as a single input version and ran the outputs into the 2050 input, hooked up my iphone as a test signal (vs. pulling out the SACD player from the rack), wired some spare B&W bookshelf speakers, and gave power to the setup. The power supply when hooked just to the amp works fine, but as soon as hook up the B1 (alone, or in parallel with the amp), the LED on the B1 comes on faintly for short moment then the LED on the Power Supply goes out and nothing works.

It's like something is shorted on the B1, but I can't figure it out.

You'll see for the inputs I simply mated a ground with input that feeds to the Pot, though I could have wired them to the Pot leads corresponding with input & ground.

Is something obviously wrong here?

Is there any issue with the B1 sharing power with the amp?

Anything I should triple check?

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Old 20th January 2012, 09:54 AM   #2
AndrewT is offline AndrewT  Scotland
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Remove the amp and test the B1 alone.
What is the supply voltage at the B1 PCB?
What is the DC output voltage from each channel? (before the output capacitor)

Connect the amp.
Have those voltages changed?
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Old 20th January 2012, 11:19 AM   #3
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The B1 is about as simple as simple gets.

FIRST and FOREMOST, are you absolutely certain that all the component values are correct and that everything has been orientated correctly ?

SECOND, are you absolutely certain that there are no shorts on the PCB ?

The ONLY route for significant current to pass is around R1, C1.

If R1 is touching the PCB, there is a potential current path through R1 to the Ground PLANE. Try lifting R1 ever so slightly clear of the PCB.

This might now sound stupid, but, is C1 a reputable cap ? Is it the right way round ? Is it faulty ? Do you have a poor joint at R1 ?

Is the PSU still outputting 18V even though the B1 is not working ?

Last edited by KatieandDad; 20th January 2012 at 11:23 AM.
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Old 20th January 2012, 11:49 AM   #4
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Using a meter measure the resistance between Vcc (+ve) and the Cathode of D1.

It should be 1 Ohm.

Then try measuring between Vcc (+ve) and 0V. This should start at a very low resistance and gradually increase as C1 charges using the meter battery.

If these are OK try another PSU with the B1. 2 x PP3 batteries in series for example.

MN1604 6LR61 for those in foreign parts.

Last edited by KatieandDad; 20th January 2012 at 11:53 AM.
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Old 20th January 2012, 12:01 PM   #5
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What Andrew T and I are both trying to ascertain is wether this is a B1 or a PSU issue.

It's possible that the enormous C1 on the B1 is affecting the computer PSU. Post #4 will iron this out.

If it's late at night and you are short of 9V batteries. Just remove C1. You might get a bit of hum but it will prove where the problem lies.

I had no problems with mine.
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Last edited by KatieandDad; 20th January 2012 at 12:04 PM.
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Old 20th January 2012, 12:37 PM   #6
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Don't worry about the position of D1 on my homebrew PCB. Yours is correct - so is mine. The two PCBS are slightly different.

My C101 and C201 are obviously very different. I used Obbligato PIOs which take up some serious space.

I also used Siemens 1.0uF MKP 400V for C100 and C200.

The caps wouldn't cause the issues that you have though.

It is possible that you've got a FET conducting when it shouldn't be.

I'm suspecting that the PSU doesn't like the huge capacitive load.

Removing C1, will iron that out. Or you could try putting a 100R resistor in series with Vcc.

Last edited by KatieandDad; 20th January 2012 at 12:42 PM.
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Old 20th January 2012, 02:09 PM   #7
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i WOULD TRY IT WITH A PAIR OF 9 VOLT BATTERIES. sOUNDS LIKE SOMETHING WITH THE POWER SU[PPLY. DID YOU MEASURE ITS OUTPUT VOLTAGE? i'M USING SOMEKIND OF A LAPTOP POWER SUPPLY, RARELY DO THEY HAVE A STANDARD SIZED PLUG, AND THERE IS USUALLY A THIRD WIRE WHICH HAS SOMETHING TO DO WITH CHARGING THE LAPTOPS BATTERY. dID YOU CUT OFF THE EXISTING PLUG AND REPLACE IT? i HAD A PLUG AT FIRST THAT SHORTED, REPLACED IT WITH A BETTER ONE.

sTUPID CAPS LOCK!

rUSSELLC
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Old 20th January 2012, 02:46 PM   #8
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There you go. Another member suggesting that the PSU is causing the problem.
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Old 20th January 2012, 06:04 PM   #9
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Quote:
Originally Posted by KatieandDad View Post
There you go. Another member suggesting that the PSU is causing the problem.
Well, the B-1 is so simple that the power supply is all that's left. I guess you could mis orient an electrolytic cap, or put in a fet backwards, but when he said the LED came on then went off, I figured power supply. On the other hand, my laptop PS worked fine.

Russellc
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Old 21st January 2012, 08:41 AM   #10
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Im not saying that the PSU is faulty - However, it is possible that the regulator / protection in the PSU may be being tripped by the huge C1.

If the B1 can be made to work with two batteries as suggested then the OP will know in what direction to head.
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