B1 Buffer Preamp

[WithTarragon]

Two Boards from One Wall Wart

I am building a four channel B1 buffer using two stereo boards. I am using a single wall wart which has 18 volt and 1.1 amp (HP power adapter for a printer).

Each board will be attached to the same wall wart. Each board will be fully populated. Meaning each board will have its own set of power supply caps and resistors (C1, C2, C3, R1, R2, R3 etc). Ultimately all the grounds will be tied together (IOW, the grounds on each board are linked)

As recommended I will be using 15,000 uF caps for C1 & C2. My naive thought is that since the grounds are all tied together, am I actually gaining more capacitance in the power supply filtering? Would the value of R1 need to be changed (currently it is 1 ohm 3 watt).

Is there something I am forgetting by hooking two boards up to a single power adapter?

What is obvious to some is not obvious to me.

Thanks

 

[crt]

i have finished B-1 buffer Salas version. (picture will follow)

- i have DC output (no load) 3.0mV and 1,2mV. is that fine ?
- is there any way to reduce the DC output ?

Thank's
La Ode

 

[Salas]

Yes, if you have read my presentation back then, you may remember that by adjusting one polarity side of PSUs voltage slightly different to the other when measuring output offset, you can get it down to even zero.

 

[WithTarragon]

Re: Two Boards from One Wall Wart

I am building a four channel B1 buffer using two stereo boards. I am using a single wall wart which has 18 volt and 1.1 amp (HP power adapter for a printer).

Each board will be attached to the same wall wart. Each board will be fully populated. Meaning each board will have its own set of power supply caps and resistors (C1, C2, C3, R1, R2, R3 etc). Ultimately all the grounds will be tied together (IOW, the grounds on each board are linked)

As recommended I will be using 15,000 uF caps for C1 & C2. My naive thought is that since the grounds are all tied together, am I actually gaining more capacitance in the power supply filtering? Would the value of R1 need to be changed (currently it is 1 ohm 3 watt).

Is there something I am forgetting by hooking two boards up to a single power adapter?

What is obvious to some is not obvious to me.

Thanks

Perhaps the lack of input is due to my misarticulation of the question. Let me try another approach. I am using two stereo boards (4 channels).
My first thought was to parallel each board off a single wall wart and each board would be fully populated (both buffer sections and the power supply filtering).

My second thought was that each power supply section currently drives two buffers (left and right channels). So why not use the power supply section on a single board to drive the 2 channels on the first board AND the two additional channels on the second board. IOW, don't populate the power supply section on the second board. Rather, take a wire from the power supply side of R203 (or R103) and connect it to the equivalent Resistors (R103 and R203) on the second board.

I assume there would not be a problem since each channel is drawing fairly little current.

Thoughts or concerns? Am I missing something. I checked the previous threads and I don't think anyone has done something comparable.

Thanks

 

[crt]

i have try to adjust the positive supply a little higher 0,2V, but the DC output just a little.
it will fine if the difference about 1V (negatif to positif rail) ?
now i use +/- 10V.


and with the DC output (3.0 and 1,2mV) if i put to my amp, will make any trouble ?

Thank's
La Ode

 

[jean-paul]

Check if your amp has an input cap. If it has one I would not worry. Those are very good values !

If you have a DC coupled amp ( = without input cap ) the DC could be a minor problem as the amp would amplify the DC component. That is bad for woofers. That is why I told you to include a possibility for an output cap on the PCB.

Most amps have the input cap and most preamps have output caps. So in the real world in much cases you will find that 2 caps are in series when you couple such devices. I have never understood why the industry did not find a standard way of doing things like "always input caps and no output caps" or vice versa. Just one cap really is enough !

 

[Salas]

i have try to adjust the positive supply a little higher 0,2V, but the DC output just a little.
it will fine if the difference about 1V (negatif to positif rail) ?
now i use +/- 10V.


and with the DC output (3.0 and 1,2mV) if i put to my amp, will make any trouble ?

Thank's
La Ode

Yes it will be fine to offset the supplies enough. True symmetry is manifesting in DC offset. You just offset the Jfets differences by doing that. Anyway your offset is negligible even with no trimming. Waiting to see your pictures, and know if you can hear differences over the capacitor coupled B1.

 

[WithTarragon]

Re: Re: Two Boards from One Wall Wart

Perhaps the lack of input is due to my misarticulation of the question. Let me try another approach. I am using two stereo boards (4 channels).
My first thought was to parallel each board off a single wall wart and each board would be fully populated (both buffer sections and the power supply filtering).

My second thought was that each power supply section currently drives two buffers (left and right channels). So why not use the power supply section on a single board to drive the 2 channels on the first board AND the two additional channels on the second board. IOW, don't populate the power supply section on the second board. Rather, take a wire from the power supply side of R203 (or R103) and connect it to the equivalent Resistors (R103 and R203) on the second board.

I assume there would not be a problem since each channel is drawing fairly little current.

Thoughts or concerns? Am I missing something. I checked the previous threads and I don't think anyone has done something comparable.

Thanks

BUMP ......

Thoughts and comments.
Am I on the right track or am I completely missing something?

 

[arold19]

Originally posted by Salas
Yes you can use 25k, only make the wiper to ground resistor 270k-330k. Don't omit that resistor! Strong DC will show up at output when switching the step attenuator if without that shunt resistor.

6VRMS input it can handle if with +/- 10VDC PSUs.

Good luck, I hope you will like it. Report your news.
-------------------------------------
Can I run the B1 without this resistor???
Wiper to ground mean what?

 

[Salas]

In capacitor less B1, no, you must use it for safety. Wiper to ground means from that arrow on a potentiometer symbol, to ground. Pot out to ground in other words.

 

[Vigo]

Hi

I am looking to build a B1 and i found i have some parts at home i am trying to use.

I found a pair of good 4,7uF MKP and a pair of even better 2,2uF MKP that i am looking to use.

Would it be ok to use the 4,7uF instead of the 10uF for C101 and C201.
And the 2,2uF for C100 & C200?

How much would this effect that sound and performance of that circuit.

 

[AndrewT]

if you maintain the same Filter frequency then you lose nothing by reducing the input cap value.

10uF and 10k for Rin gives 100ms (F-3dB~1.6Hz, F-1dB~3Hz).

4u7F requires Rin=22k to give the same 100ms.

2u2F requires Rin=46k to give the same 100ms.

 

[Vigo]

Thank you for the answer.

I also plan to lover the input R102 and R202 as i have read some hear that they could improve the sound and make it more dynamic.

I will keep the input caps at 1uF as i found some of them and try with lover both R102, R202, R104 & R204 to 221 Ohm to start with. then ma by lower R104 and R204 even more.

Then i will order some 10uF to but for C out.
Or could i use the 4,7uF for that and use 221 ohm for out put R .

Or could anyone help me with the formula to calculate the frequency curve.

I have some 4700uF caps to use for C1 and C2.
Will i gain anything to put 2 in parallel to get 9400uF.?

 

[AndrewT]

single pole RC filter

F-3dB = 1 / 2 / Pi / R / C
where Pi = 3.142
R = load in ohms
C = capacitance in Farads.

 

[crt]

Ok, Thank's
i have several amp like JLH, Symasym, DX Amp etc.
and all of them have input caps, so i don't have to worry about it right?

This is my B-1 Buffer - Salas Version

I clearly Hear a Different between them.
BUT I WILL NOT LEAVE A COMMENT 😀 😉

Regards
La Ode

 

[Salas]

Good to know.

 

[arold19]

Can I use 18v unregulated plug in power supply for this preamp or I need regulated power supply ?

 

[Melon Head]

Just use something like a notebook switchmode power supply if you want to keep it simple.

 

[Babowana]

Just use something like a notebook switchmode power supply if you want to keep it simple.

I fully support.

I have used the followings for my B1 (just as the original):

- Samsung computer dc adaptor
- Ctoole shunt regulator
- My Type A shunt regulator
- My Type E shunt regulator (current one I'm using happily)

But, I could not detect any particular sonic quality gain among these. Most probably, the shunts might work with their values on applications for other products than B1 tho . . .

It might be due to my ill ears . . .


>🙂<

 

[Melon Head]

I think one of the reasons why it is not sensitive to power supply performance is that the design is unity gain so your not attenuating the input signal as much as you would be with a preamp with gain.
So the signal to noise ratio is quite good with the B1.
I am sure there are other reasons too.