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just "finished" cmoy/hansen pcb amp

post #1 of 8
Thread Starter 
It worked surprisingly well the very first time I tried it. However, I noticed that I had wired the noble pot incorrectly. I was just using one end of the pot, without wiring the other end to ground. Thus, my volume control was rather limited.

I opened it up once again and soldered the other end of the pot to the ground connection on my input jack, and now I have the ability to turn down the volume to 0; along with another problem, there's a ton of static at just about any volume. I figured this might not be a proper ground and decided to re-solder the pot's ground to the negative input of the battery. I still have the static at most volume levels. Another interesting thing about the pot is, as I'm turning it from full-left to full-right positions, it goes from 0 volume to middle really quick, and then goes to full volume.

Does anyone know what I'm doing wrong here? Am I using the wrong ground ? Do have to ground the pot separately somehow ? Could the pot be damaged by the repeated re-soldering ? It sounded ok when I was just using one end of the pot (4 of the 6 terminals, for L/R in/out), which basically means that I was running without a pot.

--k
post #2 of 8
Couple of things:

The pins on the Noble (6) all have their purpose. 2 to ground, 2 to L/R in, 2 to L/R out. They coincide exactly with C.E.'s layout on his board. You can also use Apheared's alternate pot wiring (which is easier in my opinion) and wire the input jacks directly to the input pins of the pot. Check Apheared's Project Scrapbook in Headwize. He explains the alternate wiring very clearly.

Second, if you still have an problem, you may have a bad pot. I found two bad pots in the supply of 5 that I have. I ended up just using the Panasonics.

Good luck!
post #3 of 8
Thread Starter 
Thanks for the pointer JMT. I re-wired the pot to follow that diagram, but now it works some times and other times I'll get a lot of static. This leads to a few questions:

1. What happens when the battery runs out of power ? Does this cause static ?

2. Is it normal to hear a popping sound when you turn the amp on/off ? I think I measured a spike of 1.1V on the output when I flipped the switch.

3. The pot's ground pins are now going to the ground connection of the input jack; should this also be connected to the (-) of the power supply ?
If not, in grounding the pot to prevent noise when I touch it, should it be connected to the input ground or the (-) of the power supply ?

confused,

--k
post #4 of 8
Hello,

1. Low battery will cause the amp to buzz ... You do not get static off of this.

2. You should get some thump when you toggle power switches. This is common for most DC coupled amplifiers/Dual Supplied amplifiers. You can only determine spikes using oscilloscopes. Reading off of multimeter to measure spike is completely unreliable. As long as the thump is not ear-splitting or some crashing noise, your "headphone" amp is OK. (Though you do not want to use this as your preamplifier.)

3. Please obtain a multimeter. Without this device, you could never ever be certain of anything. ... only cost like 20 bucks at RadioShack. The GND pin of the potentiometer should NOT touch - or + of battery. This will cause short circuit. Remove the connection immediately. This GND is the virtual ground and it is NOT + or - of battery.

--------------------------------
This static may be caused by many different things.

A. Miswiring or Poor contact ... This will probably wont sound like static. It will sound more like Buzz or morelikely HUM.

B. When you have two capacitors connected in series, you could have problems since the part between caps can run wild unless properly stabilized.

C. Your battery supply does not have +-4.5V or +- (whatever... important thing is they must have the same voltage difference from virtual ground.) Check the resistors with multimeters. Their color codes can be VERY deceiving.

D. RF problems ... Probably ain't ya problem.

E. CD player could have very bad grounding.

etc ... etc ...

Was this problem present when you were NOT using potentiometers?

Your potentiometer is "Linear." That is why "it goes from 0 volume to middle really quick, and then goes to full volume." Audio potentiometers are "logarithmic." This type of volume will go more naturally to your ears. We sense sound in logarithmic scale.

Tomo
post #5 of 8
Quote:
3. The pot's ground pins are now going to the ground connection of the input jack
The pot's ground pins still need to be connected to the ground loop on the PCB, as does the ground of the input jack. Apheared's wiring simply changes the L/R in wiring to go directly to the pot rather than the input on the board.
Quote:
3. Please obtain a multimeter. Without this device, you could never ever be certain of anything. ... only cost like 20 bucks at RadioShack.
Tomo is right. Your multimeter can be your best friend. I highly recommend investing in one too.
post #6 of 8
Thread Starter 
Quote:
Originally posted by Tomo
Hello,

1. Low battery will cause the amp to buzz ... You do not get static off of this.
I guess it was buzzing, but it sounded very much like static to me. Of course, I was listening to it with a pair of Grado SR60's with the "large" pads.

Quote:

2. You should get some thump when you toggle power switches. This is common for most DC coupled amplifiers/Dual Supplied amplifiers. You can only determine spikes using oscilloscopes. Reading off of multimeter to measure spike is completely unreliable. As long as the thump is not ear-splitting or some crashing noise, your "headphone" amp is OK. (Though you do not want to use this as your preamplifier.)
It's a pretty large thump on my Grado SR60's. Much less so on my Sennheiser HD570s.

Quote:

3. Please obtain a multimeter. Without this device, you could never ever be certain of anything. ... only cost like 20 bucks at RadioShack. The GND pin of the potentiometer should NOT touch - or + of battery. This will cause short circuit. Remove the connection immediately. This GND is the virtual ground and it is NOT + or - of battery.
I was using a multimeter, some BK Electronics model. So it was correct when I had the pot grounded to the ground of the input jack, as this is connected to the virtual ground of the PCB.

Quote:

--------------------------------
This static may be caused by many different things.

A. Miswiring or Poor contact ... This will probably wont sound like static. It will sound more like Buzz or morelikely HUM.

B. When you have two capacitors connected in series, you could have problems since the part between caps can run wild unless properly stabilized.

C. Your battery supply does not have +-4.5V or +- (whatever... important thing is they must have the same voltage difference from virtual ground.) Check the resistors with multimeters. Their color codes can be VERY deceiving.

D. RF problems ... Probably ain't ya problem.

E. CD player could have very bad grounding.

etc ... etc ...
I think it was the battery. I replaced the battery and the static is now gone.

Quote:

Was this problem present when you were NOT using potentiometers?

Your potentiometer is "Linear." That is why "it goes from 0 volume to middle really quick, and then goes to full volume." Audio potentiometers are "logarithmic." This type of volume will go more naturally to your ears. We sense sound in logarithmic scale.

Tomo
Nope, this problem wasn't there before I connected the pot properly. Before, it was connected just as a variable resistor. The battery may have been used up just enough in between the re-wiring that the buzzing/static was about to appear. The linear/logarithmic stuff makes a lot of sense. Whew, I guess I'm really finished now.

PS. If anybody's wondering about using the large opened pads with the Grado SR60s, I highly recommend against it. They make the treble way too harsh and kill a lot of the bass.

--k
post #7 of 8
Thread Starter 
Quote:
Originally posted by JMT

The pot's ground pins still need to be connected to the ground loop on the PCB, as does the ground of the input jack. Apheared's wiring simply changes the L/R in wiring to go directly to the pot rather than the input on the board.
Yeah, I realized this while I was looking through the schematic for the virtual ground. I think I'll be using Apheared's pot wiring in my next project. The problem turned out to be the battery dying--I was reluctant to change the battery because it's a pain in the arse for me to open the battery cover on the Pactec case when everything's screwed in. It's a good thing I built in a DC adapter plug.

I'm already thinking about my next project, an Apheared version of this amp without the crossfeed, built into a DLT tape cover.
At the very least, I should have a lot more room to place the inputs/output/controls and opening/closing the box should be pretty easy.

Do you guys know what's the thinnest wire I can use to wire the controls ? With this amp, I used 24 gauge solid core. These wires are fairly inflexible, and result in a wad of wires close together in the case.

BTW, thanks a lot to both of you for helping me out with this.

--k
post #8 of 8
Quote:
I'm already thinking about my next project, an Apheared version of this amp without the crossfeed, built into a DLT tape cover.
I do not know how big a DLT tape cover is, but I just finished building Apheared's amp into a Penguin mint case as illustrated in Apheared's project page on HeadWize. I used 22 gauge solid core wired, and it works just find.
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