[Fishline]

I have a couple of friends with more PCs than people in their household, so I figured they must have some old CPU heatsinks that I can salvage. I got a few, but this is the only one that will fit on the case I used.

 

[nkk]

Mine works, but has a hum. The hum disappears whenever I touch the case, so I am guessing it is ground related. I am not sure how to fix this, as it is not a short or anything. It just seems to want much more grounding resource. Where would I even start?

thanks,
Nkk

 

[Juaquin]

Check all your ground solder connections. One is probably a cold joint or bad in some way, especially since it has a large ground plane that takes a lot of heat to get warm and make a good connection.

 

[Fishline]

I second that. I had hum in my first build as well that turned out to be bad solder joints to ground.

 

[Llama16]

Fishline, that's a beautiful build. It looks so tiny

I love the heatsinks.

Can't wait to begin on my kit when it arrives, i'm planning on using the case that comes with it, do some inside measurements and then try to go for selfmade woodwork with some badass heatsinks. I've got a carpenter in my street whose daughter is friends of my sis. If I'm lucky i'll try and ask if he wants to get me started/use his tools.

 

[tomb]

Quote:

Originally Posted by nkk /img/forum/go_quote.gif Mine works, but has a hum. The hum disappears whenever I touch the case, so I am guessing it is ground related. I am not sure how to fix this, as it is not a short or anything. It just seems to want much more grounding resource. Where would I even start? thanks, Nkk

Based on the prototypes, the PCB may not be big enough to provide a sufficient ground plane by itself. I'd carefully check to make certain that you have the case scraped and full contact is being made between the RCA jacks and the case, and the center standoff and the case. Make sure you use two wires, each connected to the respective RCA jack - for signal ground. You probably don't want to take the shortcut of using a single ground wire simultaneously connected to both jacks for this amp.

 

[nkk]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Based on the prototypes, the PCB may not be big enough to provide a sufficient ground plane by itself. I'd carefully check to make certain that you have the case scraped and full contact is being made between the RCA jacks and the case, and the center standoff and the case. Make sure you use two wires, each connected to the respective RCA jack - for signal ground. You probably don't want to take the shortcut of using a single ground wire simultaneously connected to both jacks for this amp.

Will do. I though I was pretty meticulous about that, but it seems perhaps I was mistaken.

Thanks,
Nkk

 

[tomb]

Quote:

Originally Posted by nkk /img/forum/go_quote.gif Will do. I though I was pretty meticulous about that, but it seems perhaps I was mistaken. Thanks, Nkk

Well, it's only a guess after all.

You might check the pot, too. Did you solder that ground wire to the pot body? That can give hum as well, but it's usually in reverse - hum when you touch, none if you don't.

 

[choka]

I have finished building the amp, and was testing it with my computer as source. There are two things I noticed:
1. Tonally it is very dark with my k702, compared to other amps I am using. All the voices (midrange) I hear, it is almost like they are singing with a slightly lower frequency. I don't know if this is what you call the "tube sound". I have the Bravo tube amp as well but that one doesn't act like this. However, this works pretty nicely with my darth beyer. Almost feels like the bass is covering up all the details so I don't care anymore.
2. There seems to be a shielding problem. You know how your computer speakers sometimes make a sequence of low beeping noise before/during your mobile phone rings? I can occassionally hear it on this amp. Is there anything that can be done about this?

 

[tomb]

Quote:

Originally Posted by choka /img/forum/go_quote.gif I have finished building the amp, and was testing it with my computer as source. There are two things I noticed: 1. Tonally it is very dark with my k702, compared to other amps I am using. All the voices (midrange) I hear, it is almost like they are singing with a slightly lower frequency. I don't know if this is what you call the "tube sound". I have the Bravo tube amp as well but that one doesn't act like this. However, this works pretty nicely with my darth beyer. Almost feels like the bass is covering up all the details so I don't care anymore.

This is a perfect symptom of not burning it in enough. (Yes, I know that's a controversial topic - please read the SSMH PCB Build thread!) Both the Nichicon KW's and the Wima's will have a prominent "bass fog" the first few hours that you run the amp. Let it run for a day or so and it will open up enough to surprise you.

Quote:

2. There seems to be a shielding problem. You know how your computer speakers sometimes make a sequence of low beeping noise before/during your mobile phone rings? I can occassionally hear it on this amp. Is there anything that can be done about this?

Keep it away from the mobile phone.

(Translated: "What shielding?")

 

[choka]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Keep it away from the mobile phone. (Translated: "What shielding?")

Actually my phone is at least 15 feet away from me most of the time and it still happens.

I've always thought metal cases would be enough of a shield for low energy waves. I am probably wrong.

 

[Juaquin]

Depends on how the case is connected (or not) to the circuit and earth ground. FWIW pretty much all of my audio equipment gets hosed by my iPhone within a couple feet, which extends to 5+ feet when it's actively transmitting.

 

[choka]

the case should be well grounded, i checked with a meter before. let me make sure again tonight.
i understand it if the phone is right next to it, but i almost always never put the phone close to me.

 

[tomb]

Quote:

Originally Posted by choka /img/forum/go_quote.gif the case should be well grounded, i checked with a meter before. let me make sure again tonight. i understand it if the phone is right next to it, but i almost always never put the phone close to me.

Unlike magnetic shielding, with RF or microwave shielding, it's possible that additional grounding may help. It may also be in your cables - you can try different pairs that may be shielded. You might try some reflective material in the general vicinity of the amp - try putting up a metal screen between your amp and where you think the source of the radiation might be. Do you have a microwave tower in the general vicinity? Could be that's causing it. Anyway, conductive metal of some sort is best. Aluminum foil may work in a pinch or at least for testing. I'd try the shielded cables, first though - you might even try wrapping the aluminum foil around them.

 

[choka]

i doubt it is the cable because i was using the same cable with another amp. i actually moved the original amp out of the way and put the ssmh in that location and connected with the same cables.

anyway i'll try some more grounding and other stuff and see what works.