My B1 Buffer Build

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#43
Jennifer G said:
I made a mistake and ordered the 2 inch tall preamp chassis instead of the 3" tall one. I haven't yet ordered the 15K uf 25v electrolytic caps (x2) yet. But I know the standard size ones are 2 inches tall and they won't fit into the case I got.

Nelson Pass says the uF value isn't critical and can even be as low as 1000uF at 25V.

Do you know of a short 15K uF electrolytic that would fit on the b1 buffer board? OR a short 10k? What do you think about going smaller size?

If I have to I'll order the 3" case and just save this 2" case for another project later.

I'd order the 3" chassis if the 15K uF sounded better than a 10K uf or lower SHORT height cap.
Click to expand...
Epcos make good, low profile, electrolytic capacitors.
 
#46
The B1 if fed from a noiseless supply performs very well.

Any SMPS is NOT noiseless. But if you filter the output, you can attenuate the noise.

It's the same for a transformer+rectifier+smoothing capacitor. It is not noiseless. Filtering the output attenuates the noise.

Pass shows something like a 20mF capacitor and a low value resistor. That is your FILTER !
 
#47
It's been a while since I updated this thread -- the B1 buffer board with a few components on it has been sitting on the shelf for the past several months.

Now that I have finished my LM3886 amp build, it's time to finish this B1 Buffer.
(Link to LM3886 build: http://www.diyaudio.com/forums/chip-amps/291371-flea-market-bargain-enclosure-my-lm3886.html )

Here is a photo of what I've done so far. The board and 4 matched transistors were purchased from Pass Labs:

2ijqb7m.jpg
 
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#48
I am intending on purchasing the following low profile 10k uF 25V caps (Nichicon) unless someone convinces me otherwise (the board is going into a low profile case 2 inch tall case):

Electronic Components and Parts Search | DigiKey Electronics

For the 1uF Poly caps, I am going to get three of what Nelson Pass mentioned by part number:
Electronic Components and Parts Search | DigiKey Electronics

For some reason, at http://www.audiocircle.com/?topic=78312.0, the person suggested only buying one of the above and purchasing two of the following:

Jantzen Audio 1.0uF 400V Crosscap Capacitor

I just decided to get three of the same, because I didn't want to pay extra shipping and because Nelson Pass says that's what he used.

I haven't place the order yet so I can change anything. Should I go with the other 2 1uf caps?

Also, should I go with the following 24V wall wart or build my own linear regulated power supply? Or does it not matter about the noise from the switching since this circuit ignores that noise? Can that noise get into the signal?

http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=198396257&uq=636001068257477920

EDIT: By the way can I use one of my existing ALPS blue pots? I have 10k and 100k not 20k or 25k (like Pass uses).
 
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#50
Dennis Hui said:
Hi JenniferG,

Just to let you know you digikey links aren't coming up with specific items.

Cheers,
Dennis
Click to expand...

Thanks Dennis. Too bad I can't edit that post now. So here it is again copy and pasted with the link corrections:

I am intending on purchasing the following low profile 10k uF 25V caps (Nichicon) unless someone convinces me otherwise (the board is going into a low profile case 2 inch tall case):

UVR1E103MRD6 Nichicon | Capacitors | DigiKey

For the 1uF Poly caps, I am going to get three of what Nelson Pass mentioned by part number:

BFC241671005 Vishay BC Components | Capacitors | DigiKey

For some reason, at Nelson Pass B-1 preamp kit, the person suggested only buying one of the above and purchasing two of the following:

Jantzen Audio 1.0uF 400V Crosscap Capacitor

I just decided to get three of the same from Digikey, because I didn't want to pay extra shipping and because Nelson Pass says that's what he used.

I haven't place the order yet so I can change anything. Should I go with the other 2 1uf caps?

Also, should I go with the following 24V wall wart or build my own linear regulated power supply? Or does it not matter about the noise from the switching since this circuit ignores that noise? Can that noise get into the signal?

EPS240025-P5P CUI Inc. | Power Supplies - External/Internal (Off-Board) | DigiKey

EDIT: By the way can I use one of my existing ALPS blue pots? I have 10k and 100k not 20k or 25k (like Pass uses).
 
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#51
In the photo below, the top silver enclosure is my passive attenuator preamp for the LM3886 sitting below it. I'll be adding the B1 buffer to this top enclosure using the existing Grayhill switch, ALPS potentiometer (if 10k is ok -- I also have a 100k I am not using), and rca's.

The case is plenty wide enough for the Nelson Pass PCB but the holes on the PCB don't line up where they need to be to be centered then screwed in. So, like for my dc supply board in my reclaimed case for my LM3886, I'll be designing an adapter plate with integrated standoffs in OpenSCAD and printing on my 3D printer. Will be mounted well and centered after the adapter plate.

2mdhtea.jpg
 
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#57
The Nelson Pass DIY board assumes one will have 1 to 2 inputs. As you know, the PCB has 2 inputs on the back of the board, and selection solder points in the front middle of the board for these 2 sources.

I however have a very nice 4 position Grayhill switch on the front and would like to have 4 inputs not 2 (e.g. DAC, turntable, mixer, TV).

My question is, can I just solder a jumper wire to input 1 on the front middle of the board and then run 5 sets of twisted pairs of wire to the back for the 4 inputs ? Will this introduce much noise into the circuit or any distortion, or any lack of clarity? The wires will be going over the left most side of the board (to the left of the left 10uf cap)

I suppose I could add 4 relays to the back if that would help instead of the greyhil up front.
 
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#58
Use your 4way switch.
Ensure you have twisted pairs, or coax for each input.
Ensure you have twisted pairs, or coax for each output.
All the connections connected at BOTH ends.

If you can locate the switch at the input sockets and use a long control shaft, you can reduce the risk of interference, but for line level inputs into a Buffer that has no gain, there is not going to be much interference.
 
#59
AndrewT said:
Use your 4way switch.
Ensure you have twisted pairs, or coax for each input.
Ensure you have twisted pairs, or coax for each output.
All the connections connected at BOTH ends.

If you can locate the switch at the input sockets and use a long control shaft, you can reduce the risk of interference, but for line level inputs into a Buffer that has no gain, there is not going to be much interference.
Click to expand...

Thank you. Should I twist each pair with varying number of turns per inch? 5 pairs of wires -- 5 different turns per inch? To avoid crosstalk? (Like I did with my mains AC input to transformer w/ it's dual primaries?)
 
#60
The switched OFF inputs will have a broken circuit so can't carry current and can't crosstalk.

The switched ON pair of inputs just need a little bit of space between them and the low source impedance limits the crosstalk. Same for the pair of outputs
 
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