Pass B1

[captrajesh]

@Sachu888 / Omishra, As you may remember, I've sourced an additional LDR which I intend to incorporate in the Class D power amp.

Is there a simpler way to power up the LDR than using the elaborate power supply?

The guy who is helping me to solder the components is suggesting that it is possible to wind copper wire of specified gauge and length on to the existing trafo so that voltage is induced into the circuit. Is it possible?

He is also saying that the LDR circuit has a power limiter and even if the voltage exceeds by a couple of volts, it would not matter. Is it true?

Please guide me on this.

 

[quad]

Capt,

Yes, the LDR board has a 7805 voltage regulator IC on board.
But please note that it takes DC voltage input - between 8V to 15V
would be ideal.
If any such DC supply is available in your chassis, you can use it.
You can also use a single 9V battery, but not sure about the life.

It is possible to derive the supply voltage by winding
some turns around an existing transformer (esp easy to do
for toroids), but some experimenting may be required to
find out the numbers of turns.
The transformer winding will give AC voltage, which has to be
rectified and filtered (using capacitors etc) before connecting to
the LDR board. In short, you will be making a supply board anyway.
Om's supply is a very high quality board with excellent filtering - will give best sonics.

 

[omishra]

That is correct! One turn gives approx 0.4V. So for 6V, you must be winding 15 turns. That gives AC output and you need to supply DC for LSA. So rectifier and filter needs to be added after turns.

Other way is use existing DC PS, put appropriate resistor of 2-3W inline, value depend upon voltage diff.

 

[bhaskarcan]

Re: Pass B1 Audition

Yesterday auditioned Kroyin's Pass B1/LDR/PSU combo with my system (Garrard301/CNC phono/Sansui AU-719/Bose). First & foremost thanks to Kroyin for making time & bringing his equipment to my house (And also presenting me the double vinyl album of Lata-live at london Paladium, from his father's collection). We really had a nice evening.

We listened to various LP's for around 2.5 hours(Pink Floyd's 'The Wall' LP being reference). I must say that B1's performance is quite impressive. Most important observation is the quietness of the system even at high volume. Soundstage improved a lot. Instruments became more defined & very very clear. Overall music sounded sweeter. Both of us liked the sound very much.

Now on the 'con'-side - the bass almost vanished with B1 in the chain. Normally I listen to music with the bass & treble in neutral position(which gives enough power & clarity for my liking). But with B1, bass was not enough even in max. position. Though it(the bass) sounded more defined & tight, the Bass-power was reduced drastically, lowering satisfaction quotient. I would like to ask other FM using B1 regarding their experience on reduction of bass.

Best regards,

Bhaskar

 

[sachu888]

Re: Pass B1 Audition

Yesterday auditioned Kroyin's Pass B1/LDR/PSU combo with my system (Garrard301/CNC phono/Sansui AU-719/Bose). First & foremost thanks to Kroyin for making time & bringing his equipment to my house (And also presenting me the double vinyl album of Lata-live at london Paladium, from his father's collection). We really had a nice evening.

We listened to various LP's for around 2.5 hours(Pink Floyd's 'The Wall' LP being reference). I must say that B1's performance is quite impressive. Most important observation is the quietness of the system even at high volume. Soundstage improved a lot. Instruments became more defined & very very clear. Overall music sounded sweeter. Both of us liked the sound very much.

Now on the 'con'-side - the bass almost vanished with B1 in the chain. Normally I listen to music with the bass & treble in neutral position(which gives enough power & clarity for my liking). But with B1, bass was not enough even in max. position. Though it(the bass) sounded more defined & tight, the Bass-power was reduced drastically, lowering satisfaction quotient. I would like to ask other FM using B1 regarding their experience on reduction of bass.

Best regards,

Bhaskar

I have discussed the same thing with Omishra,yesterday regarding Bass response of b1.I am getting very good bass and more details if I turn Pass volume at full and control it from my integrated Technics Amp.I also read this Nelson Pass B-1 preamp kit where a member sondale suggested to use LSA into input of B1 and baypass the pot.
According to him we should get a good bass response from B1 if use it as a pure buffer.
http://www.audiocircle.com/index.php?topic=78312.120

Regards,
Sachin

 

[captrajesh]

Re: Pass B1 Audition

Now on the 'con'-side - the bass almost vanished with B1 in the chain. Normally I listen to music with the bass & treble in neutral position(which gives enough power & clarity for my liking). But with B1, bass was not enough even in max. position. Though it(the bass) sounded more defined & tight, the Bass-power was reduced drastically, lowering satisfaction quotient. I would like to ask other FM using B1 regarding their experience on reduction of bass.

I have paired the B1 with AP Power amp as well as Class D amp. I did not face any such issues with either of them. The bass was just fine.

 

[omishra]

Re: Pass B1 Audition

I have paired the B1 with AP Power amp as well as Class D amp. I did not face any such issues with either of them. The bass was just fine.

Same with me. I did not face any issue. Even my B1 is used by another member 'sann' also. There was NORGE amp. Here it might be something which went wrong. Can you guys verify input resistances of 1K are in same place according to schematic?

 

[bhaskarcan]

Re: Pass B1 Audition

I have discussed the same thing with Omishra,yesterday regarding Bass response of b1.I am getting very good bass and more details if I turn Pass volume at full and control it from my integrated Technics Amp.I also read this Nelson Pass B-1 preamp kit where a member sondale suggested to use LSA into input of B1 and baypass the pot.
According to him we should get a good bass response from B1 if use it as a pure buffer.
Nelson Pass B-1 preamp kit

Regards,
Sachin

Should have tried that combination. I think we've discussed it over the phone b4. My bad.

 

[sachu888]

Re: Pass B1 Audition

Should have tried that combination. I think we've discussed it over the phone b4. My bad.

Yes,you directed me to that thread again.

Regards,
Sachin

 

[bhaskarcan]

Re: Pass B1 Audition

Same with me. I did not face any issue. Even my B1 is used by another member 'sann' also. There is was NORGE amp. might be something which might be went wrong. Can you guys verify input resistances of 1K are in same place according to schematic?

Checked with Krishnendu, confirmed everything as per schematic.

 

[sachu888]

Re: Pass B1 Audition

Same with me. I did not face any issue. Even my B1 is used by another member 'sann' also. There is was NORGE amp. might be something which might be went wrong. Can you guys verify input resistances of 1K are in same place according to schematic?

I think I got the answer.Nelson Pass provided some info here
http://www.passdiy.com/pdf/B1 Buffer Preamp.pdf
"Passive volume controls do have to
make a trade-off between input impedance and output impedance. If the
input impedance is high, making the input to the volume control easy for
the source to drive, then the output impedance is also high, possibly
creating difficulty with the input impedance of the power amplifier. And vice
versa: If your amplifier prefers low source impedance, then your signal
source might have to look at low impedance in the volume control.
This suggests the possibility of using a high quality buffer in conjunction
with a volume control. A buffer is still an active circuit using tubes or
transistors, but it has no voltage gain it only interposes itself to make a
low impedance into a high impedance, or vice versa.
If you put a buffer in front of a volume control, the controls 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."

Regards,
Sachin

 

[omishra]

To make input impedance higher than LSA (13K), I added SSP at the input. But before adding that I remember nothing sort of this experienced. SSP at input hides impedance of LSA and exposes 1M input impedance which quite easy for any source to drive.

 

[sachu888]

To make input impedance higher than LSA (13K), I added SSP at the input. But before adding that I remember nothing sort of this experienced. SSP at input hides impedance of LSA and exposes 1M input impedance which quite easy for any source to drive.

Ureiah Daily has suggested a same combination on Diy audio forums
B1 Buffer Preamp - Page 133 - diyAudio

Regards,
Sachin

 

[omishra]

This is how I have done.

I see only one issue here. The OP-AMP in SSP is influencing the sound. If I used AD823 then sounds is clear, transparent and neutral. No change in B1 sound signature. Same time now I swapped it with LME49720NA, now vocal are forward and thick. Though clarity and background silence is always maintained. Everything is as musical as it was always.



You can see signal from source selector coming to SSP and then going to B1 minimum gain of SSP is 2. Hence I added inline 10K to get it halved again before entry to B1. Those 10K MFR resistors replaced jumper in toggle switch position L1 and R1 under "PASS LABS" label.

 

[Audiodoc]

Why don't you try some exotic opamps OPA627 and latter. Opamp swapping can be fun!

 

[msagar]

Hi Sachin / Omishra,

During cellar cleaning up I came across CANARE cables of different lengths (0.5M-2.0M). PM your addresses to me, I will ship them to you. I know they can be more useful to you guys.

 

[captrajesh]

That calls for a question. What cables are you guys using? Someone on the other thread is seeking participation of members for a group buy of VDH I/C cables of which, he has a source who would cut them and terminate them. Could we use it to build a B1? If yes, how much would I need?

 

[sachu888]

That calls for a question. What cables are you guys using? Someone on the other thread is seeking participation of members for a group buy of VDH I/C cables of which, he has a source who would cut them and terminate them. Could we use it to build a B1? If yes, how much would I need?

I have used CAT5 to all my DIY.Its easy to work and of good quality.

Regards,
Sachin

 

[captrajesh]

I have used CAT5 to all my DIY.Its easy to work and of good quality.

I agree on the quality part i.e. purity of copper strands. What about shielding?
Is it required or not?

 

[sachu888]

I agree on the quality part i.e. purity of copper strands. What about shielding?
Is it required or not?

Shielded cables are not required in B1 as it has no gain.You can twist them tightly for high gain amplifications like phonostage etc.Twisting will provide shielding against RF/EMI.One drawback twisting adds capacitance,so keep wire length as short as possible


Regards,
Sachin