B1 Buffer Preamp

[Professor smith]

Do the LSK 170s have to be matched or not?

Either way, I cannot seem to find them anywhere?

please help me

 

[Salas]

They did not have inexpensive smaller ones over 12V unfortunately. You may order it online. Maplin is UK, so you gonna get it 2nd day. What can you do if you can't find a decent smaller 18V easily? That supply can make do for many applications. Any laptop that burned its PSU, other stuff from 15-24V. Use 20V setting if you get it. My B1 proved better for 10V on each FET than 9V.

 

[sonidos]

Is matching with 10 volts a hard and fast rule? Can I just set up the jfets on a breadboard and use a 9 volt battery or a set of batteries in series that measure around 10V?

I don't want to go to all the trouble of putting together an adjustable supply..i know..lazy..hehe

 

[Salas]

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.

Uriah

HFE for JFETS? Are you sure? Idss with a battery is all I ever knew.

 

[udailey]

Well, like I said I hadnt tried it but I thought that was how it was done.
Hopefully I can rectify that with this link
http://www.diamondstar.de/transistor_matching_jfet.html
And look, this one is with 9V
Sorry about the wrong info.
Uriah

 

[sonidos]

Great! Looks like I'm in bizness! Thanks, Gents!

 

[sonidos]

Great! Looks like I'm in bizness! Thanks, Gents!

 

[Nelson Pass]

Is matching with 10 volts a hard and fast rule? Can I just set up the jfets on a breadboard and use a 9 volt battery or a set of batteries in series that measure around 10V?

9 V is fine. You only want to match - you don't need absolute measurements.

 

[Professor smith]

so i just use a 9v battery in my case ?

and what sort of matching tolerance am I looking for if my meter is say 1mA?

what can I realistically achieve? because I dont want to buy dozens of them and find that none of them match.

 

[twitchie]

Count me in

Thanks to Papa Pass for the B1 and to ZM for redrawing it with the split rail psu - I've thrown together a protoboard B1 using 2 9V batteries and a total of 15 components (including the pot) - I forgot the 1M resistor on the input, but I'm not switching sources at this point.

I'll have to get pictures up later, but I did use dip-8 sockets to hold the jfets as I haven't had a chance to do any matching yet.

Maybe I'll get a chance to use those 2SK108GR I picked up last year

Testing with my F4, the pedal really is to the metal right now, but it sounds quite nice

Now, anyone have any recommendations for audiophile boutique batteries?

Just kidding of course (although I'm sure someone will have some recommendations)

Now where did I put those unfinished F5 boards ???

 

[noelectrix]

I have a twistedpear Joshua relay attenuator in my aleph-P clone. Ithought about using this for a B1 attempt.
I was told by Brian that it´s ratings are roughly 2.2K input imp.(varying) and about 740 Ohm output impedance
(me gruenschnabel thought it´s the same impedance from "both sides").

But the question is, can you recommend this attenuator in the input of B1
greets
stefan

 

[Tea-Bag]

Re: Count me in

Testing with my F4, the pedal really is to the metal right now, but it sounds quite nice

Now, anyone have any recommendations for audiophile boutique batteries?

Twitchie,
How are you achieving any gain here with the F4? What sound does two no gain devices produce?

On the battery side, it may be overkill for this design, but I use camcorder batteries wired in series for my tube pre.

 

[pinco]

Is this layout OK for B1, I use PSU from P1.7, with different value of resistor and zener for 24V output, is it beter to live big capacitors, 15mF, if I have regulated PSU?

An externally hosted image should be here but it was not working when we last tested it.

 

[twitchie]

Re: Re: Count me in

Twitchie,
How are you achieving any gain here with the F4? What sound does two no gain devices produce?

On the battery side, it may be overkill for this design, but I use camcorder batteries wired in series for my tube pre.

It sounds like a tree falling in a vacuum with no listening device around to register it

With the pot maxed out on my 85db (in)sensitive speakers, it's at low-moderate listening levels. I test with the F4 because it has zero noise/hiss/hum, especially compared to my chipamps which have a light buzz. I'm too lazy to rewire the psu for now, but it's very low - not audible at normal distances.

WRT to the PSU from the P1.7 - is that what you call a fet regulator with zener string?

 

[pinco]

Re: Re: Re: Count me in

WRT to the PSU from the P1.7 - is that what you call a fet regulator with zener string?

Yes, from Pass P1.7 preamp....

http://www.kk-pcb.com/a17-pwr.html

 

[Professor smith]

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

(I ommited the LED because I dont need a light)

 

[Tolu]

What would happen when I omit the 10µF cap?

 

[Nelson Pass]

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?

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.

 

[7thsense]

Is this layout OK for B1, I use PSU from P1.7, with different value of resistor and zener for 24V output, is it beter to live big capacitors, 15mF, if I have regulated PSU?

I'm interested in this, too. Is it necessary to use 15mF with a regulated PSU like this one?

 

[udailey]

I'm interested in this, too. Is it necessary to use 15mF with a regulated PSU like this one?

It is not necessary. In the owners manual Nelson Pass states that anything as low as 1000uf is fine. I am using 4700uf because thats what I had on the bench.

ProfSmith,
I think you should give it a few days. I probably ran mine about 15-20 hours before I said anything great about it. Remember, this is not supposed to "ADD" anything to the sound. You should not even know it is there unless what you removed to put in the B1 was coloring the sound somehow.
Caps, I know it sounds crazy, have a burn in period. I used Paper in Oil caps. For me the burn in period was short. A few days is no biggie. I have heard that electrolytics take from a moderate amount of time to over 100hours.
Now, I used to think this was a bunch of bull until I tested a few different caps in an amp and hated the sound. REALLY hated the sound until days later. Its not as drastic as speakers burning in but its definitely a factor and I would guess thats what you are dealing with.
Uriah