Pass B1

[grubyhalo]

I did not understand how it won't need light speed kind of pot. May be I missed something while reading? Can you please point out?

The reference build on that guide states this:

"VALAB 23 Step Attenuator Potentiometer 20K Stereo Log (ebay) I think it is just a series resisistor setup, but it performs nicely, small 2db steps. Before I was using a 20 or 25K precision instruments, or whatever Nelson used on origial B1."

I take it that the choice of pot for the DCB1 is upto the builder and does not limit other kind of pots. Please let me know if my understanding is wrong.

 

[omishra]

In the example he linked, it is a resistor ladder based pot ...

~G0bble

Ohh.. I kept reading DCB1 again, thought some line may give another hint. Thanks.

 

[omishra]

The reference build on that guide states this:

"VALAB 23 Step Attenuator Potentiometer 20K Stereo Log (ebay) I think it is just a series resisistor setup, but it performs nicely, small 2db steps. Before I was using a 20 or 25K precision instruments, or whatever Nelson used on origial B1."

I take it that the choice of pot for the DCB1 is upto the builder and does not limit other kind of pots. Please let me know if my understanding is wrong.

Yes stepped attenuator is better but it's not series resistance setup, it's made of multiple voltage dividers fixed on 4 pole rotary switch (in case of stereo). Also double buffer setup make life easy for LSA.

 

[gobble]

It just occured to me, with a single board and the LSP inline in the signal path, the input imedance was a problem. But is it possible to position/connect the LSP such that the single board and its input load is seen by the source device and the LSP comes in the signal path only on the output side? I.e as in the case of the double buffered B1 but without a second board?

I didnt think this in terms of electronics or review the circuit, just thought it in plain logic of before and after, so please pardon me if it sounds stupid and clarify why a practical implementation like this was not attempted.
~G0bble

 

[omishra]

This is the reason we need buffer at output side towards Power Amp. Any Volume control made of dividing signal to ground resistance of itself into 2 parts - one series to signal and other shunt to ground. If you add any Volume Control (including LSA) then wipers position (variable terminal's) vary wrt singal and ground depending upon volume level position. This changes value of resistance in series of signal and its ground position wrt shunted resistance value. In turn PowerAmp see variable impedance. So problem of impedance mismatch still there and still more than standard impedance required by Power Amp. Buffer shows constant impedance at output irrespective of volume. Though LSA Volume Control shows less impedance to source still its constant.

 

[rikhav]

I want to thank forum members sachin, Raghu and Joshua for helping me build the b1 pre for me

For a non DIY guy it's a blessing in disguise.

As we all know sachin imports the whole kit and on top of that he populated the boards for me and sent it to Raghu for final assembly

Raghu went out of the way even with his tight work schedule and did the final assembly for me, testing and ordering the transformer. He did take special care of packing it very well for me and even sending the finished pre to me by courier

Thanks to mishra ji for designing a very good power supply which is powering the b1

Joshua is of immense help to me and coordinated things for me and also got me the fuse which was needed for b1. It was Joshua who suggested me that I should give b1 a shot

Now about the b1 and how it sounds
I have not done extensive hearing but one thing that strikes immediately with few days of listening is that it's got a very very clean sound and it's very transparent. Negative side to it is that it exposes the weak link in your setup.
But then rewards you with a very good natural, balanced sound with good recordings and sorted out setup

I am not sure how to compare the b1 with other pres but it surely can beat or be a tough competition to other reasonable solid state pre amps

Of course it has it limitations that it does not have any kind of gain but I guess there is a tweak for that to increase the gain. Not sure if it's recommended or not

But in its stock avatar it has little more gain then my promethius passive pre

I am sure it can be improved more with using very exotic parts wherever needed.

This kit is nonetheless is using quiet good parts like new Russian caps

Again thank you all

 

[mpw]

rikhav,

photoos please !!

mpw

 

[rikhav]

rikhav,

photoos please !!

mpw

I am yet to receive the front panel. Once I get that will surely post pictures

 

[shafic]

I want to thank forum members sachin, Raghu and Joshua for helping me build the b1 pre for me

For a non DIY guy it's a blessing in disguise.

As we all know sachin imports the whole kit and on top of that he populated the boards for me and sent it to Raghu for final assembly

Raghu went out of the way even with his tight work schedule and did the final assembly for me, testing and ordering the transformer. He did take special care of packing it very well for me and even sending the finished pre to me by courier

Thanks to mishra ji for designing a very good power supply which is powering the b1

Joshua is of immense help to me and coordinated things for me and also got me the fuse which was needed for b1. It was Joshua who suggested me that I should give b1 a shot

Now about the b1 and how it sounds
I have not done extensive hearing but one thing that strikes immediately with few days of listening is that it's got a very very clean sound and it's very transparent. Negative side to it is that it exposes the weak link in your setup.
But then rewards you with a very good natural, balanced sound with good recordings and sorted out setup

I am not sure how to compare the b1 with other pres but it surely can beat or be a tough competition to other reasonable solid state pre amps

Of course it has it limitations that it does not have any kind of gain but I guess there is a tweak for that to increase the gain. Not sure if it's recommended or not

But in its stock avatar it has little more gain then my promethius passive pre

I am sure it can be improved more with using very exotic parts wherever needed.

This kit is nonetheless is using quiet good parts like new Russian caps

Again thank you all

Hi,

I had opportunity to listen to the B1 pre amp with my McIntosh power amp this Friday.

I agree it is giving clean sound.

At the same time we also listened to 'LYRITA' tube pre amp (old version).
regds,
shafic

 

[rikhav]

Hi,

I had opportunity to listen to the B1 pre amp with my McIntosh power amp this Friday.

I agree it is giving clean sound.

At the same time we also listened to 'LYRITA' tube pre amp (old version).
regds,
shafic

Hi Shafic

Tube pres are different beasts all together. Best part about them is very good holographic imaging

Of course they do have their pros and cons like any other design

B1 does a very good job as what it is and does it the way the designer wanted it to i.e. to sound very clean

 

[omishra]

Rikhav, congrats. Btw I am paying for r-core Trafo to Raghu. Please keep it in mind.

More update -
Some update for the people who felt Pass B1 is ultra clean but lifeless. Today I tried replacing R102, 104, 202 and 204 all are 1K ohm with 221 ohms. Yes it made huge difference for low end and vocals felt coming from throat. Still sweetness of HF excellent. Cleanness still maintained. :thumbsup: I suggest use above mod for further kit building.

Also I tried adding small 0.1uF parallel to output 10uF cap C100, 101, 200 and 201. Thought theoretically it would not make much different but sound was turned too sharp. FM svaze also listened with me. So,I reverted this quickly.

 

[gobble]

Rikhav, congrats. Btw I am paying for r-core Trafo to Raghu. Please keep it in mind.

More update -
Some update for the people who felt Pass B1 is clean and lifeless. Today I tried replacing R102, 104, 202 and 204 all are 1K ohm with 221 ohms. Yes it made huge difference for low end and vocals felt coming from throat. Still sweetness of HF excellent. :thumbsup: I suggest use above mod for further kit building.

Also I tried adding small 0.1uF parallel to output 10uF cap C100, 101, 200 and 201. Thought theoretically it would not make much different but sound was turned too sharp. FM svaze also listened with me. So,I reverted this quickly.

Hi OMishra
What does changing the R values acheive in terms of electronics in the circuit? What was the logic behind the move?

Also why do you think adding a bypass cap changed the sound the way it did?

G0bble

 

[omishra]

What does changing the R values acheive in terms of electronics in the circuit? What was the logic behind the move?

This was discussed on DIYA forum and I see it does not affect as filter at input or output. But it's look like something to do from current in JFET gate and output.

Also why do you think adding a bypass cap changed the sound the way it did?

There are many theories on bypassing bigger caps with smaller make audible difference to audio band. I and Swapnil witnessed one.
Topic "bypassing output cap with smaller"- generally says bigger caps also has some inductance inbuilt due to foil/film winding. Smaller bypass cap make lesser inductance path available for signal and hence enhance upper mid to HF. Though total capacitance value it changed with tolerance limit.

 

[rikhav]

I think the gentleman here has done the same mods to the stock b1 as mentioned by mishraji and has achieved good results

Nelson Pass B1 Buffer | DMS Audio


Tweaks

Thanks to Val for the 0.01uF Russian Silver Mica which I used to by-pass the input audio coupling caps. I also by-passed the output caps with some 0.22uF Obbligato I had spare. I also managed to replace some of the copper in Teflon with silver in Teflon. I also lowered the value of R102, R202, R104 and R204 from 1K to 220R. I later removed the Silver Mica by-pass caps and used some Tin Foil caps with much better results.


One thing I want to know from all you diyers. As it is doing diy of electronics is such a complex process. On top of that how do you come up with such mods like changing part values and achiving a better sound. Its not an easy job as changing a cable or a connector

 

[quad]

More update -
Some update for the people who felt Pass B1 is clean and lifeless. Today I tried replacing R102, 104, 202 and 204 all are 1K ohm with 221 ohms. Yes it made huge difference for low end and vocals felt coming from throat. Still sweetness of HF excellent. Cleanness still maintained. :thumbsup: I suggest use above mod for further kit building.

If someone wants to test this mod temporarily, you can solder 270 ohms in
parallel with the existing 1K resistors at the given locations.

 

[rikhav]

If someone wants to test this mod temporarily, you can solder 270 ohms in
parallel with the existing 1K resistors at the given locations.

I tried the mod suggested by mishraji. Thanks to quad for providing a way to try it temporarily. It was more helpful as i dont know how to solder

Joshua got me some resistors and some clips by which i put the 270 ohms resistors in parallel to the existing 1k resistors


Changes are very positive but i feel its through out the spectrum. For me the top end got much more smoother and maybe the pre is extracting tad more details

Mid range has become much more resolving and maybe due to that vocals have better focus. Overall the sound has a certain richness with very smooth top end

Right now I have used some ordinary resistors. Later on, joshua will solder the resistors for me which sachin will send me soon. Thanks a ton for that

Mishraji, glad you tried this mod. This has taken the B1 to another level

 

[omishra]

Yes Rikhav, that improvement is through out the band. It's like opening the doors wider than before. You rightly said pre is like extracting more-n-more details. Sound is open and airy as well as deep bass.

 

[sann]

Too significant a mod to be ignored. I am overwhelmed since I changed the regs last weekend.
Beware, it strips bare the source. I am not able to listen to a couple of FM transmissions and LP's which are in bad condition.
But otherwise it feels like the vocals are rendered near your ears and all the instruments are easier to follow and discern. It is cleanness, purity and openness at its peak.
I would suggest B1 owners to give it a try.
-sann'

 

[TheCoolestOne]

I too managed to upgrade R102/104/202/204 yesterday with the values recommended by Om. No expensive / exotic parts used only simple 220R's used. The difference was noticed immediately. I have been using the B1 for over a year but at times found it to be a tad flat and lifeless to my liking (though it is very clean and dark). The recommended mod changed this and I now find my setup more dynamic and lively.

As mentioned by others the vocals seem more refined, smooth and open. There is a change in the bass. It is deep but i somehow preferred the earlier bass for some reason. Maybe some more listening will change my perception. The most important difference I noticed that the soundstage opened up more on my setup and sounds a bit wider now. Just the way I like it.

Thanks as usual to Om for sharing his constant updates on the B1 and also to other FM's who did the mod and shared their experiences.

 

[jls001]

It's unbelievable what four resistors can do to change the sound of the B1. I have read the testimonials of omishra, sann, thecoolestone, and Rikhav, but didn't think it could be such a huge difference. Till I heard Rikhav's system this evening.

The mids have become beguilingly sweet. The bass weight too has improved substantially. The highs which was a bit strident before has been tamed. But the most dramatic improvement is in the improved resolution and the much improved tonality.

It's like Rikhav has a new, much improved, setup.

It is so worth the effort and the inconsequential amount of money spent. I'm now motivated to complete my B1 build.

Addendum: I totally forgot the most positive improvement in Rikhav's setup - the soundstage has migrated from the plane of the speaker's front baffle to well behind it. In fact this was the biggest gripe he had against the sound of his setup. Another positive outcome of this is that voices are dead center and instruments have a near-pinpoint location in the lateral space and have acquired depth and layering. It's truly amazing what this small tweak did.