Building a symmetrical PSU B1 buffer

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Geofd

Member
Joined 2011
Shunt Reg output voltage

Spent a lot of time reading many thousands of posts but this is my first post as I want to make sure I have this running as it should for this project (also finishing an F5 amp)
I have just about finished my B1 mezmerize, just waiting for my 22K pot to arrive - All powered up perfectly ( tested before putting in the matched 2SK170 ( Idss 9.55 for the quad)
I matached the LEDS using an Peak ATLAS DCA55 - component analysier - all were matched ( I think at 1.71 V red leds) , but I have slight difference in he shunt output voltage +9.453 and -9.196 , is this OK, or do I need to match the LEDS better ?

Also the voltage seems to drop slightly as the system gets warm is this as it should be

Output offset - no signal Left 0.0004V right 0.0012V - is this acceptable ?

Sorry if these are easy questions but its been a hile since I worked on this stuff this level - I am used to just puting kits together from Jaycar ( recently built the 20W class A amp)- no matching etc
 
C

CR500

Member
Joined 2010
Got a basic question, is the resistor from pot wiper to gnd there to change the law of the pot or does it tweak the sound?

I think I'm ready to start a point-to-point build this week. I powered up 30 jfets for about an hour before measuring their currents. Took them a while to stabilize and had to keep them away from any air flow or the current would float around.

Thanks!
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Its safety. If the wiper loses contact when a pot craps out eventually you get 4VDC on output. Res 10-20times bigger than the pot itself it even balances its tracks out better. Smaller do the fake trick on linear pots, another story. Not here. You should get a log pot.
 
C

CR500

Member
Joined 2010
Ah, that wouldn't be good! My mid / tweeter amp has caps on the input so it would be safe. The woofer amp does not. I plan to come off the pot wiper and into to the B1 (mids / tweeters) as well as an opamp (OPA627) for the woofer section (need about 6 dB gain to make up for the difference in amps). I'll put a cap on the output of the opamp. I'll try it all out on a proto-board first.

Thanks!
 
C

CR500

Member
Joined 2010
Damn, turns out my pot is a 20k linear (motorized). If I drop the wiper resistor to 3.3k, will I still have the open pot factor of safety (I'm thinking it will)? Any other adjustments recommended after that change?

Any suggestions for the dc blocking cap value? I have some half decent 1mfd and 10mfd poly caps.

Thanks!
 
C

CR500

Member
Joined 2010
10u it is! Decided to live with the linear pot until I can find a motorized 20k log.

Assembled one channel and gave it a quick test. Seems quiet for not being in a box yet, square wave looks nice and sharp. A short listen didn't show much difference over my old NAD 1130 preamp. I'll solder up the second channel tomorrow and do some serious listening while finding the time to build a box.

Thanks!
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Don't know, only used Toshiba. J111 might also get too hot with so much IDSS it specs. Might need resistors to calm it down, don't know its current gain anyway. If it has gfs below 20mS won't do much for THD especially if it will need resistors to cut IDSS and heat. Will degenerate.
 
T

TheShaman

Member
Joined 2007
I'll be building a new DCB1 on the latest HotRod boards.
Volume control preceding the DCB1 board will be based on an R-2R ladder attenuator (fixed input impedance @ 24k, variable output impedance).

Do I need to tweak that 220k resistor?
My notes only mention R=220k for 10-20k pot, R=22k for no pot.
 
KatieandDad

KatieandDad

Member
Joined 2011
CR500 said:
10u it is! Decided to live with the linear pot until I can find a motorized 20k log.

Assembled one channel and gave it a quick test. Seems quiet for not being in a box yet, square wave looks nice and sharp. A short listen didn't show much difference over my old NAD 1130 preamp. I'll solder up the second channel tomorrow and do some serious listening while finding the time to build a box.

Thanks!
Click to expand...

I'm tending to find the B1 a bit bland too.
 
triode_al

triode_al

Member
Joined 2004
regiregi22 said:
I don't have too much experience for this, but I asked the same for a similar cable on the forum and they told me not to use it because it has STEEL in the conductor core. It gives you bad sound (at least, is what people say about steel)

If you look at the datasheet, it sais:
CONDUCTOR: S.P.C.C.S. (Silver Plated Copper Clad Steel).
What makes me think that the inner of the core conductor is made of, well, steel.

Are my suppositions right? If not, I have some similar cables wich could be able to use.

Thanks
Click to expand...

Indeed iron in de core. The reason: high frequencies will travel anyway on the outer skin ("skineffect") And yes, this is not good for audio frequencies . And these cables are made for MHz frequencies.

BUT . .
If you hold a magnet to most components, then you will find that almost all lead wires of components are magnetic i.e. have an iron core. :eek:
Should we be worried??
 
A

AndrewT

R.I.P.
Joined 2004
DCB1 appears to do nothing in my arrangement.
It is transparent.

That is quite different from bland.

I have stopped using DCB1 until I find a source that cannot drive cables properly.

In the meantime I am developing Mezmerize into a multi-input pre-amp. There are many traces that need to be re-routed to remove errors in the standard PCB. I think I am almost there.
 
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