Pass B1

[Hari Iyer]

I think I am gonna try the above mod as I will get "Buffer (Yaqin) -> Volume Control -> Buffer (B1)" configuration.

I am looking at this post from Om as reference : http://www.hifivision.com/diy/21036-pass-b1-148.html#post498322

I used i/p op-amp buffer --> Op-Amp + class A o/p stage (Voltage Gain 3) ---> DCB1 with excellent results. Volume control is at the input of the DCB1. I am using 300B tubes as power amp in SET mode.

Op-Amp used is LM4562.

 

[sachu888]

Many people have used SSP for gain with good result. It won't be required if you don't need additional gain.

Regards
Sachin

 

[sachu888]

Locally available? Is it log or linear?

@Sachin, do you have a spare that I can buy?

Hi Joshua
I have only one pot. It's from eBay. I am going to order few more again. I will keep one for you.

Regards
Sachin

 

[anilva]

I bought a Alps blue velvet pot from theaudiocrafts

I am extremely happy with the purchase. They are genuine and priced reasonably. Highly recommended.

Cheers.

 

[mbhangui]

Hi Joshua
I have only one pot. It's from eBay. I am going to order few more again. I will keep one for you.

Regards
Sachin

Sachin, I also need one. Can you order one for me. Will transfer the amount right away.

 

[sachu888]

Sachin, I also need one. Can you order one for me. Will transfer the amount right away.

Sure.

Regards
Sachin

 

[spirovious]

A good thread for B1 user-
Nelson Pass B-1 preamp kit

How to check JFETS if they are matched or not?

 

[Hari Iyer]

A good thread for B1 user-
Nelson Pass B-1 preamp kit

How to check JFETS if they are matched or not?

You can check the drain current by connecting the jfet in series with a 9. Volt battery. Ideally drain currents should be same but are also considered matched if I'd is within 10% of the value..

 

[omishra]

You can check the drain current by connecting the jfet in series with a 9. Volt battery. Ideally drain currents should be same but are also considered matched if I'd is within 10% of the value..

With battery, I use CCS (Constant current source made from 2 transistors) to check current Idss and we buy with matching of 0.1mA with <10mA current.

 

[Hari Iyer]

With battery, I use CCS (Constant current source made from 2 transistors) to check current Idss and we buy with matching of 0.1mA with <10mA current.

You need to measure the drain current quick within 5 sec else will risk overheating the jfet with this method, but is again very safe if done properly. I have matched many jfet till date with this method with zero issues. If you mess up with the battery polarity then the jfet will blow instantly, hence caution should be exercised.

In my current DCB1 i used one pair with an Idss = 8.06mA and 8.07mA and second pair with exactly Idss = 9.25mA.

My offset voltage after the class A settles is 0.2mV. Till the time the class A settles (around 10 minutes) the offset varies between +/- 25mV with no major issues to the power amp.

 

[sachu888]

All the jfets are tightly matched. They don't actually blow even if someone accidentally reverse the polarity.

Regards
Sachin

 

[Hari Iyer]

Reverse drain current will blow them if connected without any source resistance.

 

[mbhangui]

Some surprising result with B1. I have 50K volume control before SSP. The output of SSP was connected to LSA. I removed the LSA and now the output of SSP directly goes to the 1M resistors R100 and R200. My setup is like this.

Cadence VA 1 tube 20+20 watts amp
Asus Xonar Essence one DAC. Output of this goes to volume control of SSP
Output of SSP directly goes to Pass B1 resistors R100 and R200 (capacitor coupled version)
Output of Pass B1 goes to a volume control of another Preamp (Elliots Preamp - Kit from Bibin) - High Quality Audio Preamp


Following is the result

1. The soundstage has improved dramatically and for the first time I am getting a 3D effect. I can clearly hear the placement of the vocals, drums and instruments in the room (both X and Y axis).
2. Music now has lot of punch and attack. Listened to few Jazz tracks and A.R. Rehman tracks.
3. For few of the MP3 songs, the sound gets distorted (music comes with warbling sound). However if the volume control connected to SSP is reduced, the distortion disappears. This warbling does not disappear if I reduce the Elliot's preamp volume and keep the SSP volume at full.

Not sure what is happening? Does the 13K impedance of LSA cause issue for SSP? Apart from removing the volume control, I also replaced all input and output wiring with twisted pairs harvested from an ethernet cable and also kept the L & R channels apart separated by air. Earlier I was using a ribbon cable and I suspect, due to capacitance, L&R channels were getting mixed. The new wiring scheme has solved mixing of L&R channels, but I don't believe that's the reason for the dramatic increase in volume and soundstage. I will try connecting two 47k resistors across the output of SSP and see what happens.

 

[lifewater]

Hi,

Got in touch with Sachin for a DCB1 kit, but since it was not available with him, he very kindly sent me a B1 fully populated and tested. Thanks sachin...
Now I would eventually use it with my myref V1.3, but till such time want to use it with a NORGE 2060 which my brother gave me after burning out its output transistors which was eventually repaired by me. (I also have an unmolested piece of the same amp in storage hyeah. Could I recieve your valuable suggestions where should the B1 come in my audio chain. SOURCE --> B1--> Norge or Source --> Norge Pre --> B1--> Norge power (In this case I will have to do surgery on the Norge, which I am prepared for.) Also what about the Volume control of the Norge should I keep it at full or midway. I prefer to control sound output using the B1's volume control (Pot)

Thanks for reading such a long query,

Regards,

Lifewater

 

[omishra]

Try to avoid Norge pre from chain. It clutters the sound. If you want to keep norge volume control then keep it at max level and control volume from B1.

 

[lifewater]

Try to avoid Norge pre from chain. It clutters the sound. If you want to keep norge volume control then keep it at max level and control volume from B1.

Thanks Om ji. So you suggest I go ahead with the surgery of removing the NORGE pre and couple the B1 directly to its power amp ... Should be easy given the modular construction of the NORGE amp.

Thanks again,

Lifewater

 

[omishra]

Thanks Om ji. So you suggest I go ahead with the surgery of removing the NORGE pre and couple the B1 directly to its power amp ... Should be easy given the modular construction of the NORGE amp.

Thanks again,

Lifewater

Yes, I have done it simply disconnecting power supply to preamp and removing those 4 - 1 source selecting push switches. you can fit any 4-1 selector board from online stores.

You can try step by step. First avoid pre then further.

Other thought -
Simply from backside, add L/R RCA pair for preamp out and two RCA inputs for power section. Just loop them for normal use. Otherwise feed power section directly. Avoiding all remaining stuff.

 

[lifewater]

Yes, I have done it simply disconnecting power supply to preamp and removing those 4 - 1 source selecting push switches. you can fit any 4-1 selector board from online stores.

You can try step by step. First avoid pre then further.

Other thought -
Simply from backside, add L/R RCA pair for preamp out and two RCA inputs for power section. Just loop them for normal use. Otherwise feed power section directly. Avoiding all remaining stuff.

Great idea NAD types...

 

[anilva]

TO me it looks like something around on board power supply of B1. Please check if it has 18-24V from regulated PS. There is 10K? + 10K? voltage divider on B1 board with charges two big capacitors. Something related to charging of second 15000F cap from this divider. This divided voltage goes to jFET input terminal on both channel through 1M?.

Also if you are using inductors in 24V line of PS then please short them with wires.

I had this intermittent problem crop up now and then (i.e. one channel does not work) and I had to restart the B1 preamp powersuppy everytime and it would more often than not become alright.

Finally yesterday opened the preamp and shortned all the inductors on the power supply as suggested. So far it has been working fine. There seems to be nothing wrong with CDE 15000 uF, 25v caps. If it happens again, I need to change the caps.

Wanted to update.

Cheers.

 

[vikoma]

I have completed my Raspberry Pi --> PCM5102A based i2S DAC from DIYINHK --> SSP --> Arduino based remote control LDR --> Pass B1 (with its pot volume control) --> Norge 1000 Power amp --> PSB T6 speakers.

However, I am quite unhappy with the LDR output. The quality degrades beyond limit, particularly for lower volumes. I am able to control the voltages across both pairs of LEDs using arduino. But I have not been able to tune it properly. At full volume however, there is no problem from this LDR.

(I ended up using Atmega8 chip directly on general purpose PCB.)