[JeffS]

So I finally got the nerve up this weekend to try my first DIY audio experiment. I pulled out my soldering iron, and decided to try the pinkfloyd crossfeed that I read about in this forum. What a mess!

The instructions were easy to follow, and it looked like a simple project so I figured, I should be able to handle this. Not being near any decent electronics stores, I went to RadioShack for parts.

The only thing I did different from the instructions, was I replaced the RCA jacks with a stereo minijack. Otherwise, the same.

I remember reading that this particular design was rather subtle. The one I built however was about as subtle as a brick through a window. It ended up sounding like I was listening to a very bad AM radio.

I'd rather try a rebuild before posting pics of my handywork to be critiqued. I'm sure I could have done a better job. My question to the group is this:
Does it sound crappy because of my technique in building?
Does it sound crappy because I bought cheap parts at RS?

If I rebuild, where should I go looking for parts?

I'm using this as a guage. If I can't build this, there is no way on earth I could handle a cmoy or mint.

thanks for any help

-Jeff

 

[tkerby]

Check your soldering. AM syle rdio noise could be dry jint somewhere where the solder does not properly flow. Reflow the joints by heating the component lead and the solder until it clearly flows onto both leads, perhaps adding a drop more solder for extra flux

 

[JeffS]

Ok, I will definitely recheck my connections when I get home.

I'm not sure "noise" describes it right. It sounds weak, faded, mono. Also and I don't know if this is the design, or my screwups, but I had to really crank the volume up to hear anything when running through the crossfeed.
Even then it wasn't lound, but I could hear it.

Also, I noticed on the website it says to use metal-film resistors. I didn't see any at Radio Shack, so I just grabbed the carbon-film. Does this make a difference? And more newbie questions... I used the 1/4 watt resistors.
does the wattage matter? I couldn't find 2k in 1/4 watt, so I used 2 1k in series.

thanks for any advice and help
I'm still learning.

-Jeff

 

[Excalibur]

Quote:

Originally Posted by JeffS ...Also, I noticed on the website it says to use metal-film resistors. I didn't see any at Radio Shack, so I just grabbed the carbon-film. Does this make a difference? And more newbie questions... I used the 1/4 watt resistors. does the wattage matter? I couldn't find 2k in 1/4 watt, so I used 2 1k in series. thanks for any advice and help I'm still learning. -Jeff

None of that stuff really matters but make sure you check all your ground connections.

 

[JeffS]

This may be a really stupid question, but as I've stated, I am new to this.
The only things I've seen in the diagrams that have a ground would be the two minijacks, and one of the capacitors. Do I just connect them together?
Is there some other way to ground them that I'm not aware of? should I ground it to the tin that it will be mounted in? Sorry if this is a very dumb question.

-Jeff

 

[llmobll]

Well i'm not familiar with the design, but all Grounds should be connected. EVERYTHING needs grounding, or else you get distortion, noise, and many other headaches.

 

[JeffS]

Ok, that I understand. I would assume that it this were a powered circuit, I would just connect ground to the negative lead of the battery.
Since this is passive, do I just connect the grounds to each other?

I'm assuming this is right, but I'm not really sure why.

thanks
-Jeff

 

[tangent]

Quote:

all Grounds should be connected.

That's probably true in the Pink Floyd crossfeed, but it is definitely not universally true. The PPA and PIMETA have two different grounds that mustn't be connected, for instance. Another example is connecting input ground on the PPA with earth ground on an AC-DC power supply -- you'll get a ground loop if you connnect them directly. You must add a ground loop breaker between them.

 

[jnewman]

In this crossfeed, the grounds of all the jacks should be wired to bottom pin of the 47nF cap. If you do that, your ground should all be fine.

 

[llmobll]

I'm assuming you're building this Crossfeed right??

http://www.rock-grotto.co.uk/crossproject2.htm

If you are, all the grounds are connected together, However your input and ourput RCA jacks should be touching the case. Since the circuit is grounded with the case you need to make sure they touch. Read the article:

"In the mint tin example you can see I have soldered both left and right ground tags together and run a hook up wire from the ground on the board to them... that's sufficient in a metal enclosure as the tin acts as a conductor. Be sure not to use the plastic washers that come with the RCA's as they insulate the ground tags from the chassis."

I wouldn't let your mistakes with this simple circuit stop you from building other more complicated circuits. Its a learning process which help you build better amps and crossfeeds later on. good luck.

peace.

 

[commanderkeen]

Quote:

Originally Posted by llmobll I wouldn't let your mistakes with this simple circuit stop you from building other more complicated circuits. Its a learning process which help you build better amps and crossfeeds later on.

That's right, I had similar problems with my cmoy that I built 3 weeks ago from RatShack components. After fixing the grounds I'm happy I didn't give up on the build and as a consequence I've ordered a couple of electronics books to aid me in my quest to become an audio guru in every sense of the word.

Keep it up, and you will reap the benefits of your labor.

 

[kloan]

:snipped:

 

[silmaauki]

JeffS,

I just finished yesterday with my first Cmoy. It took me slightly more than the weekend, and every now and then I felt like having crap in my hands. However it turned to be a very good sounding beutiful amp. Don't give up.

And now some guides, I found out to be helpfull.

When you test the amp section and you get some hiss, distortion or FM noise, make sure you have no wires or electronics nearby. I had the amp on table, where I had some test wires etc. lying around. When I lifted it up 10cm all noise was gone. So if it is'nt silent, try to move it. Later on when you have a good boxing and all groundings there it doesn't matter any more.

And there will be a lot of different gounding wirings. I just opened the lid and calculated 5 ones. You need to gound input and output jacks, volume pot, power switch and the case. And not only the bodies of these items but the appropriete pins as well.

Be patient. This isn't easy.

My amp did as well had some troubles somewhere in the middle, where the amplification did not work. Just like the way you described. However, without any reworking it did eventually turn out to be working. I just don't know what was the problem. (Or I do have an idea, which needs to be checked: I have to OP2134PA's and I suspect that the other one is not working any more.)

When you work with the casing the easiest way to do the holes in the mint tin was to first use a small drill (2-3mm) to center the holes. Only after that I used the right size of drill to finalize the holes. And use a piece of wood inside the casing when you drill. This way you avoid any accidental bending or other damage.

 

[JeffS]

Thank you to everybody here.
You've all talked me into reworking the crossfeed, and moving on
to doing an amp. Though I think the amp will be in a month or so.

I was ready to toss in the towel and jus breakdown and buy something,
but even with the setbacks, building it just seems like a lot more fun.

And I'm learning more about this stuff than I ever thought I would.

Thanks
-Jeff

ps. When I finish my build and it doesn't look horrible

I'll post pics.