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Another B4 Thread

DuncanF said:
Hi Tony,

No you don't need one. It is just a neat/tidy mounting solution if you were to use one of this type of PCB mounting transformers for your PSU. It will fit any of their 15VA/25VA transformers. I plan to use a 25VA/15-0-15 I have to hand. for my B4. I think some of us are buying for other projects too.

The 15VA may do just as well, but someone with more knowledge would need to confirm that for you.

Duncan
Click to expand...

Many thanks Duncan.
 
binnie said:
Question to PigletsDad (sorry if this was already treated in another thread as I did not yet read them all ...):
I know that it is a symetrical PSU but I wanted to know if there is a "thumb" when switching ON / OFF the B4 if the B4 is connected to a NAP ?
Thanks :)
Olivier
Click to expand...

Not having a NAP, I can't say myself, but I would expect the turn-on and turn-off thump to be small.

Of course, best practice is always to turn the power amp on last, and turn it off first.
 
binnie said:
Question to PigletsDad (sorry if this was already treated in another thread as I did not yet read them all ...):
I know that it is a symetrical PSU but I wanted to know if there is a "thumb" when switching ON / OFF the B4 if the B4 is connected to a NAP ?
Thanks :)
Olivier
Click to expand...

Hi binne,

I've got a b4 into a nap140. There's a bit of a minor thump when turning the lot on with the wall socket switch. Nothing alarming.

Pulling the power sulead to the b4 no noise. Plugging it the B4 after the 140 on slight thump, but muted. However, my build has the pots in to reduce the DC offset to a minimum.(R3 R104) See parts list.(BOM) I'm guessing, but a low DC offset would reduce any thump. (Please correct this if I am wrong)

Mike
 
mudlark said:
http://www.quasarelectronics.com/3114-25v-2a-dual-polarity-unregulated-power-supply.htm

I used this with centre tapped transformer as the buffer needs dual rail supply.

http://www.pinkfishmedia.net/forum/showthread.php?t=66430&page=8

This was when I asked the same question. +/- 15 Volt 1 amp

It works fine.
Click to expand...

Thanks for the info Mudlark. Just got 2 of the boards from Quasarelectronics. Could they be improved by using Hexfred's instead of the 1N5401 diodes?.

Regards Keith
 
Heaven knows. You will have to ask a clever /knowledgeable person about that. When I built mine I asked if the board was Ok. It is way over specced as they are designed for power amplifiers. Power supply noise rejection is good and if using the on board regulators again I have had comments that they are fine.

ESP audio say that fast diodes aren't needed in 50Hz power supplies.

If you want to go better than the boards then it's ask specific questions of those with super ears rather than me.
 
I am waiting for the Hackercap group buy Pcb's to appear. Carl recommends the use of Qspeed/Hexfred diodes in the build. Just wondered if they could be used in one of these boards too.
I was thinking about the 6A or 8A version. RS stock these too.
 
keithsnaim said:
I am waiting for the Hackercap group buy Pcb's to appear. Carl recommends the use of Qspeed/Hexfred diodes in the build. Just wondered if they could be used in one of these boards too.
I was thinking about the 6A or 8A version. RS stock these too.
Click to expand...

I don't know, but the hacker is a power amp and the B4 draws little power. having said that I am going to try a Qspeed power supply with my headphone amplifier B4.
 
Thats true, Carl informed me that it would be suitable for the B4 using low current Qspeeds because they are quieter.

By the way , the B4 sounds superb in its present form using a salvaged power supply from an old stack system so it can only get better.
 
I'm finally getting round to stuffing the B4 board and am wondering the following:-

1. Is R3 meant for a variable resistor?
2. Has anyone put a volume pot at the output instead of the input of a buffer?
 
Yes, R3 is a trimmer, for adjusting offset to zero, if you don't use output capacitors.

Volume control after B4 is not ideal - the whole point is to give consist drive conditions from variable resistance of the volume control. I suppose if you had some ancient source device that couldn't drive the volume pot, it might make sense to buffer before the pot, but any even vaguely modern source has no problem.
 
Thank you for replying PD.

What I'd like to do is put together a phono preamp with volume control and using the B4 as buffer after the phonostage. Attenuator will be a Dantimax relays-and-resistors type set to 10Kohm input impedance.

This is what Nelson Pass said about building his B1 buffer.

If you put a buffer in front of a volume control, the control’s low impedance looks like high impedance. If you put a buffer after a volume control, it makes the output impedance much lower. You can put buffers before and after a volume control if you want.


Wouldn't it be better for SNR to have the full output of the phonostage sent to the buffer and then attenuate betore sending it out to the poweramp?
 
Which phono stage? Most will drive the 10K attenuator without any problem. SNR is not a big issue as the noise from the front of the phono stage completely dominates.
 
PigletsDad said:
Which phono stage? Most will drive the 10K attenuator without any problem. SNR is not a big issue as the noise from the front of the phono stage completely dominates.
Click to expand...

Its the Phonoclone.
What would be the drawback putting attenuation last in such a chain?
 
The output impedance varies with attenuation. Putting the buffer after the attenuator fixes that.

Phonoclone is op-amp based, and will drive the attenuator without problem. Putting buffer between it and the attenuator will have no benefit.
 
PigletsDad said:
The output impedance varies with attenuation. Putting the buffer after the attenuator fixes that.

Phonoclone is op-amp based, and will drive the attenuator without problem. Putting buffer between it and the attenuator will have no benefit.
Click to expand...

Thanks for the explanation, PD.
 
I am digging up this thread so I can ask: Wouldn't it be a good idea to split the B4 into two separate channels and make it naim motherboard compatible? I was thinking of something like na321's, fed by the power regulation circuit that would sit on the right of the motherboard and would also feed the jumpered ground coming from the power regulation circuit to the signal ground pin of each board and on those boards the star ground scheme would continue? That would save a lot of cable usage and perhaps help minimize the distance that signal has to travel. They could even be designed in a way to follow naim's motherboard pinouts. I understand that B4 is not naim, but I think we all like the naim's looks. But, would it work? And where on earth can we find a good quality naim styled connectors?
 
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