[JamesL]

fixed

 

[smeggy]

The one used in the min3 is decent, I have one in my CTH and it works nicely. Bit small and fiddly but works fine.

 

[gurusan]

I found the one in the BOM to be terrible as well. I am using an inexpensive RK09 and it's great.

 

[JamesL]

nvm

 

[cms5423]

I'm sure this has been explained, but really quickly, why are people upping the value of the capacitors to 470uF? What does this do to the audio/circuitry

 

[JamesL]

Of the PS or output?

It lowers the frequency cutoff at the output, lowers esr, and stabilizes the power supply.

 

[cms5423]

I guess just in general, why are the cap values being tweaked? Like why would the original MSSH use 150uF and then now they are being upped to 470?

 

[cms5423]

and for the PSU, is .38amps enough, or where would i find the PSU that is the cisco 48v one that had a 1.5, or even 1 amp output?

 

[tomb]

Quote:

Originally Posted by cms5423 /img/forum/go_quote.gif I guess just in general, why are the cap values being tweaked? Like why would the original MSSH use 150uF and then now they are being upped to 470?

I can't speak for Pete Millett, but perhaps his "regular" headphones are Sennheisers or other high-impedance phones. 150uf provides plenty of bass for a 300ohm load. Cutoff is down into the single digits with 300ohms, but the -3dB response starts as high as 33Hz with 32ohm Grados. 470uf gives you -3dB at 10Hz, so it's well below audibility.

As for the other two electrolytics, 680uf has been found to prevent startup "stuttering" in every case.

Quote:

and for the PSU, is .38amps enough, or where would i find the PSU that is the cisco 48v one that had a 1.5, or even 1 amp output?

0.38A is enough - it only pulls 0.3A in the standard configuration, perhaps 0.32 with a couple of tube LED's. I think someone once said that switching supplies don't like to be lightly loaded, anyway.

 

[cms5423]

thanks a bunch tom. That leads me to my next question: If I want to add some tube LED's, I can just implement them, plus a resistor (RLED) preceding them, anywhere in the circuit right? Is that because adding a resistor+led into the circuit will just pull more energy out of the power supply?

Also, how big of a volume is a reasonable amount of space to build this in? So that I can narrow down my enclosure options. I'm trying to pick some sort of metal case from mouser to enclose this in, but am not sure how big of one that I need to choose.

Thanks

 

[kuroguy]

Yes, an LED with a series resistor across power and ground will work fine. 50v=0.01*R. R=5k should be a good starting place.

I built mine in a 4.5" wide x 3.5" deep x 2" tall hammond enclosure. In retrospect, I could have made it fit in a case that was 1" tall with some squeezing. I could have certainly used a 1.25" tall chassis without a problem.

 

[cms5423]

Great, thanks for the help. And as far as the pot goes for this project: I see people are using many different options, some go 50k, others 100k, and many say the one in the original BOM is awful. What is a good pot that I can purchase through mouser, that I can implement in the original schematic? Thanks again guys

 

[tomb]

Quote:

Originally Posted by cms5423 /img/forum/go_quote.gif Great, thanks for the help. And as far as the pot goes for this project: I see people are using many different options, some go 50k, others 100k, and many say the one in the original BOM is awful. What is a good pot that I can purchase through mouser, that I can implement in the original schematic? Thanks again guys

Just remember that suggested 5K resistor will need to be 1W.

As for the pots, the Alpha is fine if used with the input-resistor-scheme. The production PCB version I just built seems to work fine with a 10K Alpha and ~40K input resistors. That makes the total input impedance ~50K, so it's in the mid-range of things. For typical volume levels and loads, the pot travel is pushed out far enough in its range that the tracking is OK.

 

[cms5423]

Ok, but is there a pot option that mouser sells, that I can use without input resistors? Like just get a 50k pot from alps? But which one?

Can someone post a mouser part number for a good pot for this project?

Thanks everyone

 

[cms5423]

Ok, but is there a pot option that mouser sells, that I can use without input resistors? Like just get a 50k pot from alps? But which one?

Can someone post a mouser part number for a good pot for this project?

Thanks everyone