[Polaris111688]

Oh $&@$.... I just realized that one of my buffers is in reverse... I didn't realized that the the BUF634P pads for each BUF634P are in opposite direction relative to the pads for the other BUF634P.

 

[gsteinb88]

Ive fried 2 or 3 like that. Dont feel bad.

 

[Polaris111688]

Oook. Put a pair of BUF634Ps in correctly, and there's music! However, there's this weird hum that accompanies the music. I'm not sure, but I thought the Sony EX71SL's attached were getting warm too. I checked DC offset and verified it to be 0.00V.

*Edit* I'm dumb. I forgot to solder ALPS to ground pad.

 

[tomb]

Quote:

Originally Posted by Polaris111688 Oook. Put a pair of BUF634Ps in correctly, and there's music! However, there's this weird hum that accompanies the music. I'm not sure, but I thought the Sony EX71SL's attached were getting warm too. I checked DC offset and verified it to be 0.00V.

I've read that a less-than-perfect tube can cause biasing problems. It might be the source of the hum, too - particularly if you have a high gain on those Sony buds.

P.S. I've done a lot of work on that thing in your avatar.

 

[NeilR]

Quote:

Originally Posted by Polaris111688 Oook. Put a pair of BUF634Ps in correctly, and there's music! However, there's this weird hum that accompanies the music. I'm not sure, but I thought the Sony EX71SL's attached were getting warm too. I checked DC offset and verified it to be 0.00V. *Edit* I'm dumb. I forgot to solder ALPS to ground pad.

Just out of curiosity, was the hum present even when you were not touching the ALPS knob/shaft? Reason I ask is that I only get hum when I touch it (before I ground it), and I think that is most people's experience here, based on the comments I've read over time.

 

[n_maher]

Even a properly grounded alps pot can still hum/buzz whatever. In the quietest Millett's I've built I've tied the alps pot directly to the input ground. This amp pcb would appear to love to cause ground loops.

 

[NeilR]

Quote:

Originally Posted by n_maher Even a properly grounded alps pot can still hum/buzz whatever. In the quietest Millett's I've built I've tied the alps pot directly to the input ground. This amp pcb would appear to love to cause ground loops.

Nate- are you saying you ran a wire from the Alps screw all the way back to the input ground pad or the jack grounds?

 

[Polaris111688]

There's humming when we don't touch it. When my friend touches it, it goes nearly silent. When I touch it, it doesn't go silent, but the humming is somewhat reduced.

 

[NeilR]

Quote:

Originally Posted by Polaris111688 There's humming when we don't touch it. When my friend touches it, it goes nearly silent. When I touch it, it doesn't go silent, but the humming is somewhat reduced.

I think you have the polarity of one of your grounds reversed.

(that's a joke)

Interesting how that pot reacts differently in the same circuit in different builds.

 

[n_maher]

Quote:

Originally Posted by NeilR Nate- are you saying you ran a wire from the Alps screw all the way back to the input ground pad or the jack grounds?

Yup, all the way back to the RCA's and tied it directly to one of the grounds back there. It silenced the amp and is really no different than doing some sort of star or central ground, right?

 

[NeilR]

Quote:

Originally Posted by n_maher Yup, all the way back to the RCA's and tied it directly to one of the grounds back there. It silenced the amp and is really no different than doing some sort of star or central ground, right?

Well, I guess that is a lower impedence path than to the ground pad, through the ground plane, and up the input ground wires. I don't have a 4 wire meter so I don't think about those things too much unless my ears complain

Were you trying to solve a specific hum problem or were you just maxxing out the build?

(Curious minds want to have a peek into the inner soul of a demented DIYer and I can't think of a better subject

)

 

[n_maher]

Quote:

Originally Posted by NeilR Well, I guess that is a lower impedence path than to the ground pad, through the ground plane, and up the input ground wires. I don't have a 4 wire meter so I don't think about those things too much unless my ears complain

This technique has been used with great success on more than one amp.

Quote:

Were you trying to solve a specific hum problem or were you just maxxing out the build?

In this case, a specific hum. It's happened with each of the 3 milletts that I've built in little hammond square cases. At first I thought it was the TREAD, then the unshielded off-board mounted pot, then the metal end panels. I tried everything then finally decided to have a go at redoing the grounding scheme. Worked like a charm.

Quote:

(Curious minds want to have a peek into the inner soul of a demented DIYer and I can't think of a better subject )

Demented, surely you jest. If I were demented I might build something like this...

That'd be the first public picture of my Millett

. All blackgate caps, Riken and PRP resistors, stepped attenuator, Jung super regulator power supply, and not to worry, diamond buffers have already been installed. I was just testing it with the BUF634s. I have no idea what I'll use for a case, but at this point the parts cost alone is hovering well above what I'd consider advisable.

 

[Polaris111688]

Hmm! Thanks, n_maher. I'm definitely going to try tapping the Alps' ground screw directly to ground input.

 

[NeilR]

All blackgates? I see a couple of Cerafines in there.... You know that you inspired me to do something demented like that. Plus the SA of course, which is winging it's way from Australia as we speak. I might use all Rikens but only match the output pair. I don't think matching the the others really matters since the tubes themselves aren't exactly precision devices (but then I don't know if any of this boutique stuff matters, which is why I got inspired to do it).

Just egging you on, you know. After all, that build isn't my money

Thanks for the sneak preview! For some strange reason, all the sudden we're inundated with GBs and I don't know what to do next. I don't multi-thread these projects very well.

Regards,
Neil


Quote:

Originally Posted by n_maher This technique has been used with great success on more than one amp. In this case, a specific hum. It's happened with each of the 3 milletts that I've built in little hammond square cases. At first I thought it was the TREAD, then the unshielded off-board mounted pot, then the metal end panels. I tried everything then finally decided to have a go at redoing the grounding scheme. Worked like a charm. Demented, surely you jest. If I were demented I might build something like this... That'd be the first public picture of my Millett . All blackgate caps, Riken and PRP resistors, stepped attenuator, Jung super regulator power supply, and not to worry, diamond buffers have already been installed. I was just testing it with the BUF634s. I have no idea what I'll use for a case, but at this point the parts cost alone is hovering well above what I'd consider advisable.

 

[n_maher]

Quote:

Originally Posted by Polaris111688 Hmm! Thanks, n_maher. I'm definitely going to try tapping the Alps' ground screw directly to ground input.

No problem and I don't see how it could hurt. Another Head-Fier was kind enough to suggest it to me way back so I figured I'd pass it along.