B1 Preamp - Help Me!

[Nelson Pass]

I'm sure it would be fine.

 

[udailey]

That will work fine. You need only a tiny amount of power so this will more than do it.
To match your 170's just stick them in a DMM that has a HFE measurement option. You will know if it does because it will have a little circle with about 6 holes in it.
Stick your 170 in the holes until you start getting measurements that make sense. Leave the 170 in there for about 5 minutes. Thats your measurement. The HFE measurement varies with heat. Thats why you leave it, cuz your fingers will raise the temp. This is what I have heard anyway. I bought mine matched.
Then stick another one in and measure. Write it down and tape the 170 to the piece of paper you just wrote on. This way you know which one has which value.
You have to test dozens of these to get a decent match so really if you can find them matched this is the best solution. I bought mine on ebay from China.... so you can to.
Here you go
http://cgi.ebay.com/8-X-MATCHED-2SK...VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247
You only need 2 🙂
Lucky thing is that you are going to build this and it will be easy. And then it will work well. And then its going to sound fantastic. And then you will want to build more Nelson Pass DIYs and since a lot of them use 2sk170 you will have 6 more matched 🙂 and thats half the battle anyway.
Just get any caps and try it. Its super cheap to try regular caps. Buy the specified DN55 Dale resistors since they are cheap and Papa recommended. You can swap caps and play for a few days and see how it sounds. Then, settle on some caps and you have it quick, easy, and beautiful.

Uriah

 

[Professor smith]

could you please tell me how to match them?

I have a cheap multimeter. Will it work?

 

[udailey]

I was wrong about the multimeter part.
Read this article on matching them.
Uriah

http://www.diyaudio.com/forums/showthread.php?postid=1601638#post1601638

 

[udailey]

I dont know whats recommended, but I can tell you that mine sounds very good with +/-3% as advertised on the ebay auction I bought them from.
Sorry I cant help more than that. Dont worry so much though. This is an easy build and you can do it. Even Nelson has said that matching is not a necessity. So you can either bite the bullet and buy prematched or buy a dozen and pick the two best ones then ebay the other 10.
Really, its super easy and I am almost as newb as they get.
Uriah

Yeah, 9V.

 

[Professor smith]

for caps c200 and c201 can I use these>?

http://www.cricklewoodelectronics.com/Cricklewood/home.php?cat=155

 

[Professor smith]

for caps c200 and c201 can I use these>?

http://www.cricklewoodelectronics.com/Cricklewood/home.php?cat=155

 

[Professor smith]

I dont understand whether I should use a dc blocking cap even though the source output has one fitted?

same with if the power amp has one on the input then do I need it?

 

[AndrewT]

If one side of the interconnect has a DC blocking cap then the other side does not need another DC block.
i.e. one DC blocking cap between the source and pre-amp and another DC blocking cap between pre-amp and power amp.

 

[udailey]

for caps c200 and c201 can I use these>?

http://www.cricklewoodelectronics.com/Cricklewood/home.php?cat=155

You can use those caps. They will work fine. If you want to spend any less money you can try to find some that have a lower voltage rating. The higher the voltage the bigger the cap the more material they used in manufacturing.
Uriah

 

[Professor smith]

can someone help me ? Ive spent hours on this and soldered it point to point. But it doesnt work. Just a distorted quiet sound coming through.

I have followed the circuit except I have omitted the input dc blocking cap and the LED.

What could be wrong? Ive checked my wiring..

 

[udailey]

take a picture of it and post the picture. Make sure the resolution/focus/lighting is good so we can see what we are looking at.
Why eliminate the LED?
Uriah

edit: Make sure you have your pots wired right.
Check here about 2/3 down the page
http://sound.westhost.com/pots.htm

 

[Nelson Pass]

Unless you have extensively modified the power supply arrangements, you
still need the input blocking cap.

 

[Professor smith]

I have got it working. I am using a 2.2Uf cap instead of 1Uf at the input. What is the effect of this?

But my impression is very good so far. I have tried all kinds of devices between cd and amp and it just goes to show how important the 'interface' is.

 

[Nelson Pass]

but would that missing 1Uf capacitor account for what im experiencing?

What would happen when I omit the 10µF cap?

If you are using a single supply, you can only omit these caps if the
attached equipment is cap coupled and without any resistor to ground
on the B1 side of the cap. Otherwise you will have trouble.

 

[Professor smith]

But after listening for longer I'm not terribly happy with the sound.

The dynamics seems to be there but the highs are harsh and the bass seemed rolled off it doesnt have that deep sound.

I am taking the vout from the pcm1716 chip through a 10Uf cap into the B1.

In the B1 I am using 2.2Uf instead of 1Uf at the input and 4.7 Uf at the output instead of 10Uf. Can somebody work out what effect this will have?

perhaps the lack of low pass filter after the dac is causing problems?

 

[Professor smith]

The choice of capacitors is unlikely to have that much effect. Assuming that
the DC voltage at the output before the cap is 1/2 the supply voltage,
it is likely that the issue is switching noise from the DAC.

Ok, well can I ask what difference would a first order passive filter make? It only seems to lower the noise by a few db.

 

[Professor smith]

could someone tell me what values to use for the low pass filter after the dac?

Nelson suggested 25khz cutoff.

 

[Nelson Pass]

Try 2.2 Kohm in series with the output of the DAC followed by .0033 uF to ground,
and see what you get.

 

[Professor smith]

after the 10Uf dc blocker of the dac?

and can i ask, how is the phase shift determined?


and given that we can vary both R and C to obtain the desired cut off, do we go for a high value of C or R?