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B4 Buffer Preamp Group Buy round 2...

I've finally had a chance to start putting together my B4. Looking at the schematic the regulators are set to roughly 18vdc. That means a raw supply feeding it could be anywhere from say 21-33vdc-- following the guidelines that the voltage should not exceed 15v over the LM317 output voltage (doens't Naim feed their LM317s 39vdc to get 24vdc?).

My question is: it looks like everyone is using low voltage raw supplies. Is there any reason not to use a higher voltage raw supply? An 18-0-18 tranny would give about 25v or a 20-0-20 tarnsformer would yield around 28v.

Did I miss something? An important bit in the thread that I overlooked?

Thanks,
John
 
My understanding is that the transformer is more efficient at voltage stepping. If you feed higher voltages to the regulator sections the regulation will involve the loss of more energy /power than is necessary. This is inefficient and also generates heat which is bad for circuit stability and capacitor life.

the designer of the circuit always states that the power supply doesn't need to be oversized or over regulated. The view of others is that huge power supplies and super regulation are needed for good sound quality.

my version uses a medium sized transformer, and an over capacity rectifier with an oversized capacitor set and the results are excellent.
 
A couple more questions for the group while i am waiting for my transormer to arrive:

Has anyone tried their B4 with C6/106 wired out? If the input caps are eliminated does the value of R5/105 need to change?

Also, does the value of the volume pot effect the value of R5/105? For example if one uses a 10k pot should R5 increase, or should it decrease if a 50k pot is used?

Hope these aren't dumb questions.

Cheers,
John
 
force of 1/2 said:
A couple more questions for the group while i am waiting for my transormer to arrive:

Has anyone tried their B4 with C6/106 wired out? If the input caps are eliminated does the value of R5/105 need to change?

Also, does the value of the volume pot effect the value of R5/105? For example if one uses a 10k pot should R5 increase, or should it decrease if a 50k pot is used?

Hope these aren't dumb questions.

Cheers,
John
Click to expand...

They are good questions.

If you omit the input caps, then R5/R105 are no longer strictly needed, but do no harm, so I would just leave them alone, in case you want to put the caps back at a later date.

R5/R105 should be fine for most sane values of volume pot; if you went really high (say 1M) they would alter the taper (the loudness versus pot position curve), and I suppose you would need to raise them to get the taper back.

But really high pot values are not reccomended; you get masses more noise, and have to worry about stray capacitance and interference. All other things being equal, use the lowest value pot that your sources are really happy to drive. Typically this is somewhere between 10K and 50K.
 
I've just upgraded my LP12 by fitting local TRs to the Prefix. I have built a separate ps (not a HiCap) and attached the earth to the case of this, which is earthed to mains. There is mains hum generally, which gets much worse when I turn on the TV.

I have no earth on the B4 yet. The case is not earthed.

The B4 ps case is earthed to the mains supply. Should I earth to this?

Paul
 
Okay, spent a couple hours yesterday wiring things up. Made up a little PS tacked to a scap of plywood (Antek has shielded toroids now for only a couple dollars more, nice to have a little electrostatic shielding. Earthed the shield to the PS ground rather than mains ground).

First impressions: Nice! More oomph and a tad more edge than my B1. Much more full sounding. Sounds much like a really good preamp with a gain stage in this respect. Everything is extremely well defined and it even has the added bonus of sounding very good at low volume!

If I had a gripe about the way it sounds as it is now, I would say it is a bit too full-- not sluggish, not bloated, but it sounds a bit like a loundness button is engaged somewhere. If I had to guess I would point to the Caddocks I used in in R5/105-- this is what those resistors sound like-- or maybe the 10uf wet tants on the outputs. I've never used wet tants before so, I'm not sure if this is part of their character.

It sounds really very good, though. Leaves me with a solid sense of the tune and even a good measure of PRAT. I'll keep messing around with it a bit while it settles in (is that totally contradictory?) I still would like to try it with no input caps. Using 2.2uf Vishay 1822s and 12k at R5/105 presently.

There is one funny thing. I have to agree with Neil, it really doesn't seem to like my 322 or 323 boards. I had to go back to my NAD PP2 (which doesn't sound half bad with a proppper PS, caps upgrade and change of OP Amp). Why shouldn't it mate well with the Naim phono boards? The B1 had no problem with them so, I'm not sure it is gain related. Though I could try upping the gain on the cards. Is it the feedback resistors one changes to change the gain? I think it says something about this on Neil McBride's website.

Anyway, Thanks PD and Neil for a great circuit to play around with!

Cheers,
John
 
John
Give a week to run in first before you change to many things.
I have used the wet tants a lot and love the clean fast sound of them but I have never thought of them as bloated or fullsome they are quite the opposite so I would look elsware.
If you know the caddocks can sound like that then try changing them for a good precision resistor such as the wellwen RC55Y.
The input cap and the pot will also effect the sound

Alan
 
Just got round to building my B4 and have got something fundamentally wrong somewhere. Basic output from the LM317 / 337 regs is set to +/- 13V.

Junction of Q1, Q2, Q3 and D1 is +8V instead of +4V.

Junction of Q4, Q5, Q6 and D3 is -8V instead of -4V.

I've checked all of the component values and polarities and everything looks fine except possibly the E5051mA contant current diode from the group buy that lorenz organised. Can't find a datasheet for this item and had assumed the small flat on the case indicated the cathode but a note by Lorenz in the DB suggests it might be the anode. Can anyone who's used these diodes confirm the polarity and advise whether reversing the polarity is likely to cause the symptoms I have.

Paul
 
I used the ones from Lorenz and the lead nearest the (very small) flat is the anode. I'm afraid I have no idea of the symptoms of reversing the anode/cathode. Hope this helps.
 
simeon said:
I used the ones from Lorenz and the lead nearest the (very small) flat is the anode. I'm afraid I have no idea of the symptoms of reversing the anode/cathode. Hope this helps.
Click to expand...

Reversed all four of the E505 diodes and all is well now.:D

Thanks


Paul
 
I'm looking for the actuall schematics for theB4. I've searched and searched but with no luck so can someone please help me out?
/Staffan
 
Sorry to say but it's a dead end, the link points to a shared document at Google that I can't see. Any other link?
/Staffan
 
I have two of these, one permanently in use, the second I used briefly as a headphone amp but didn't really use it so it's been in a box for years. Recently, I started a refurb of a Leak Stereo 20 and thought a B4 would make an ideal preamp for that. Ok, so I found it, dusted it off and switched it on. It worked perfectly. I changed the input caps for 0.1uF Ruskie PIOs and shorted the output caps. I must have done something bad because now LED 101 and 102 are not lit. Anyone got any ideas? I'm sure I saw something years ago about troubleshooting this preamp but I can't find anything with google, so apols if it's blindingly obvious.
 
SimeonJ said:
I have two of these, one permanently in use, the second I used briefly as a headphone amp but didn't really use it so it's been in a box for years. Recently, I started a refurb of a Leak Stereo 20 and thought a B4 would make an ideal preamp for that. Ok, so I found it, dusted it off and switched it on. It worked perfectly. I changed the input caps for 0.1uF Ruskie PIOs and shorted the output caps. I must have done something bad because now LED 101 and 102 are not lit. Anyone got any ideas? I'm sure I saw something years ago about troubleshooting this preamp but I can't find anything with google, so apols if it's blindingly obvious.
Click to expand...
Pinging @PigletsDad
 
Fixed! Well, maybe more of an unbodged situation, actually. I couldn't find any phono sockets so I was using a load of messy, temporary wiring until I pick some up. When I moved the board and its power supply around in its cut-down cardboard box the LEDs came on. I'm not going to fiddle again until I have the sockets and have it wired ready for placement in new Modushop case. I think a 'Phew!' is in order.
 
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