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B4 Buffer Preamp Group Buy round 2...

337alant said:
Those NOS polystyrenes are fantastic on first listening and changing to 1uf / 25K RC55y has also introduced a lower bass and sounds more balanced overall.
Now I am thinking about changing those output caps which are good WIMA MK4P 2.2uf.
I could parallel up a couple more of those styrene’s on either channel or I could stick in some 10uf or 6.8uf wet tants?, would I need to change the 100r resistor ?

Alan
Click to expand...

No, the 100r can be left alone; it just isolates the active circuit from the cable afterwards, and has nothing to do with coupling cap values.
 
Thanks PD
Q, Do you think a 1uf cap on the B4 output will be sufficient seen as I have 10uf on the input of my power amps, I know I can do away with one or the other but I am a bit nervous about doing that at the moment.



Alan
 
337alant said:
Thanks PD
Q, Do you think a 1uf cap on the B4 output will be sufficient seen as I have 10uf on the input of my power amps, I know I can do away with one or the other but I am a bit nervous about doing that at the moment.



Alan
Click to expand...

What is the power amp input impedance? 1uF will be OK provided the load is about 20K or above (e.g. a Naim input looks like about 22K, and would be fine).

If you have unusual power amps with lower input impedance, like say some Deltec designs, you might need a bigger cap.
 
Thanks again PD
I am using 2 x Avondale NCC-200 amps which is 20 -25K as far as I remember and are based on the old RCA circuit.
Ill try it and report back;)

Alan
 
Finally got around to installing my Valab 10k stepped attenuator into my B4 last night, tested it very quietly (as it was late) and it seemed to work. Trying it this morning and the sparkle has gone.. Gonna give it a week of playing 24/7 (with power amp off for some of that) and see if it evolves. First impressions are poor though.

The Alps blue I removed was 50k, dont know if that has any bearing on the change to the sound.

Sam
 
sam_cat said:
Finally got around to installing my Valab 10k stepped attenuator into my B4 last night, tested it very quietly (as it was late) and it seemed to work. Trying it this morning and the sparkle has gone.. Gonna give it a week of playing 24/7 (with power amp off for some of that) and see if it evolves. First impressions are poor though.

The Alps blue I removed was 50k, dont know if that has any bearing on the change to the sound.

Sam
Click to expand...

If you source was unhappy driving 10K, it might explain it, but I would wait a bit and see if my impressions changed.
 
:)

Left it playing all week (with power amp off), having a proper listen today and it has changed drastically, for the better.. Sounds very good now!

Guess they take time to break in?

Sam
 
I gave one board a go this week. As I had no diodes available, I replaced them with JFET CCS, using one JFET and a resistor.
There was almost no DC offset in and out, so I omitted the coupling cap.
This was mated with a modified NAP-110 (with a dual NAP140-like PSU).
Results are quite good!
The nice thing about it is that you have unity gain, which means you have more usable range for the volume control - fantastic feature!!
I replaced both input low-pass caps with 390pF, which made the presentation very relaxed and easy going. Great stuff!!
Cheers,
Yair
 
I tried those 1uf Russian NOS polystyrene caps on the output and after a few days I have come to the conclusion that although they give a very brightly lit presentation with a very good 3 dimensional image they have an overall lean dry sound, this may suit some systems but not mine and I could tell there was something missing, they sounded excellent with some discs and very thin with others.
I tried bypassing them with Russian Teflon’s but that just smoothed off the treble. I also tried a 5uf Paper in oil cap which are the size of a building brick but sound excellent and put the overall balance right, the only problem with these is their size when stood upright.
So I finally put a 6.8uf mill spec wet tant in there and this sounds superb. I still have the 1uf polystyrene as the input cap and they seem fine together so I am going to leave it like this for now as swapping multiple types of caps drives you nuts :rolleyes::D
Alan
 
If I remember correctly you need more than 1uF on the output to avoid LF roll-off, which would explain the lean dry sound you're experiencing. I'm using 2.5uF Solen polyprops to good effect with the 1uF polystyrenes on the input.
 
Hi Carl
I actually tried a lot more caps than I stated and I agree that 4 - 10uf on the output just sounds right in my system but I guess it depends on input sensitivity of your power amp or amps.
I also tried no output cap with the 1uf polystyrenes on the input and that sounds "incredible" with some discs but just plain wrong with others :confused: so those caps have some thing special and actually the bass is deep and taught but its the upper bass and mid that seems sucked out in my system.
I could experiment more with a higher value input cap / resistor and no output cap but I am not going to do that right now as its been driving me nuts and I just want to get back to listening to my system as it sound's now.

Alan
 
finally got round to starting the soldering and i've realised that Farnell sent me a couple of 1/4 watt resistors instead of the 1/4 watt i ordered. to late to query it now unfortunately. They are signal path RN60s, will they be OK or do they have to be 1/4 watt?

Also a very basic question, how do i know which way round to solder all of the diodes? I was part of the GB for the diodes and i'm a bit stumped as there are no marking on them for C and A. There aren't any on the LEDs either so how do i know which way round they go?

I've got a DMM but am not sure really what the readings are telling me.

Thanks for your help again.

Stefan
 
Hi Stefan

The signal path resistors could be as low as 1/8 watt and as high as you want. I think Neil allowed space for up to 1 or 2 watt resistors.

Now I didn't get any diodes in the group buy but I'm guessing that they are the same as LED's - Flat side is negative / cathode which is denoted by a line - so flat side to line.

LED's have the short pin as flat side / cathode.

Hope that helps

Rich
 
Stefan,

Just to confirm what LoBo says. Resistor size is not an issue; anything that physically fits will work fine. The current diodes have a band, which should go towards the negative side (cathode).

I don't have the LEDs in front of me, but a flat on one side of the package is a common marking scheme.

PD
 
3mm LED's are a real pain to see the flat side, if they have one at all.

I remember like this: 'short is flat'
 
ok, got the leds in front of me, there is no flat but they do have one short leg so i'll follow Rich's advice there. the hole for the leds on the board have a flat on the circle so that matches up nicely. I'm still confused with the others though. i got the cylindrical e505 in the gb not the j505, they do have a flat bit and although it is closer to one leg than the other it's not right by it. The j501 are in the half moon packaging which has a flat side but this obviously isn't nearer either leg, i can't see the band pd mentioned either. They are the same shape as the silk screen niel has on the board, shall i just assume these match?

I'd like to try and learn somthing here, how would i measure these with the dmm?

thanks lobo and pd

stefan
 
in my view the round ones have a flat on the cathode. You need a hand lens to see this....

The transistor shaped ones appear to fit the board picture with the cathode to the right side of the flat.

PS I haven't applied power to mine yet..
 
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