Pass B1

[jls001]

In the end final resistance value matters, whatever combinations you do. You are free to create resistance network to yield specific value.

Using standard resistor values makes life much simpler

 

[rikhav]

With nothing better to do on a Sunday evening, Rikhav and me monkeyed around with the Spiro mod at my place.

In my setup, there is a definite change. Most noticeable is the bass weight, which went up a notch.

I think the mids recessed a bit with the mod, and this led to vocals to be pushed back in the mix, and gave a sense of deeper soundstage than before.

The highs were airier.

We did many rounds of (sighted, btw) A/B of all 220 Ohms v/s

R102, R202 = 1K
R104, R204 = 306 ohms.

The Spiro Mod (TM of Spiro) sounded better to me in my setup, though the changes were mostly subtle, except for the fairly obvious improved bass weight and texture.

I hope Rikhav will write his impression and preference in my setup as well as his when he has some time to give it a listen.

As already mentioned by jls001 we did try the Spiro mod. We had 2 B1's so a quick A/B was possible

My views are almost similar to what Jls001 has but still with every track played I could not confidently make up my mind as to what the changes were and if it was preferred

So it was decided that I listen to the mods on my setup , so I can have a beter idea as its the most known environment for me

I did listen to 7 or 8 tracks which I have listened to many times. It was mix of Bollywood old , Bollywood new, some jazz

The bass has improved but I feel not that much in quantity as it has in detail and texture, which for me is still a a good improvement

Now I sort of can make out the details in the lows, sort of bass has more character. The mids have recessed by a little bit which surely takes the stage more deep. The difference is more apparent in Joshuas setup as his setup has this trait of creating a superb ambience and you actually feel you are in a concert
Initially I did mistake this for lack of resolution in the mids but listening to the mod in my setup did help

I will listen to some vocal centric tracks maybe tomorrow or day after and that will make things absolutely clear

So overall the SPIRO MOD did bring out subtle changes but it improved the character of the sound and I think makes the sound more natural

For me the 220 ohm mod had done all what it was suppose to do, so I would not have even thought of doing such an experiment so thanks Spiro for trying it out. Also since I am non DIY guy I never expected such changes with changing values by little bit

Now I understand how difficult it would be for audio components manufacturing companies to come to a final list of what components to be used and what values

It would surely involve lot of experimentation as the partnering equipment will also play its part


Overall a very good exercise and I again thank Spiro for coming up with this mod and as always thanks to Jls001 for helping me out

 

[spirovious]

Nicely written by Jls00i and rikhav.Thanks for review.
With slight difference in part,the whole character of sound changes.e.g with my DAC,if I try different type of capacitor with same value,sound changes are notable. That's why audiophiles prefer parts from better make.Here in B1,I noticed that only output resisters changes the sound signature.So tried few changes and found this one more balanced.Like said earlier,increasing resister value will improve Bass further,but I feel tonal balance can be at risk.Details may not be the best.Not tried yet,but will see later if I can.Currently enjoying the mod.

 

[keith_correa]

From NP's write up of the B1:

R102 and R202 are there to prevent parasitic oscillation with the very wide bandwidth JFETs.

The Source DC voltage of the JFETs Q100 and Q200 is about the same as the Gate DC voltage (1/2 the supply voltage), and the output from the Source needs to have the DC voltage removed by C101 or C201, leaving the AC output signal, which passes through another safety resistor R104 or R204.

And from an article about the B1:

The actual output impedance is dominated by a 1 kOhm resistor (R104 and R204 in the schematic). That's fairly low, but Nelson says that this value can be arbitrarily lowered down to say 200 Ohm, though he cautions that could cause problems with wideband equipment.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Edit: So, going by the above, I would not touch R102 & R202 at all and just muck with R104 & R204 (^_-)

 

[rikhav]

So keith as we all thought its mainly system matching
Different power amps prefer different output impedance from pre
That expalains why I felt the bass was very less with all 1k resistors

 

[keith_correa]

Noob alert: I think, what is really cool is that one can do the aural matching with just a handful of resistors, 2 leads and clips. Bingo, tailored matching!

 

[rikhav]

Noob alert: I think, what is really cool is that one can do the aural matching with just a handful of resistors, 2 leads and clips. Bingo, tailored matching!

True , exactly as the spec of the power amp.

It will be custom made for ones setup

I have really liked all what I have learnt after having the b1

Is there any calculation to determine what will be the output impedance at a said resistor value

 

[keith_correa]

Impedance question [Archive] - AudioKarma.org Home Audio Stereo Discussion Forums.

Interesting. So, now we have cables in the equation too!!!

 

[rikhav]

Impedance question [Archive] - AudioKarma.org Home Audio Stereo Discussion Forums.

Interesting. So, now we have cables in the equation too!!!

hyeah:
I am not going to experiment anymore and mainly with cables because frankly I dont have many to try and also with the specs of the cables its not easy to know how it will sound

Also I think I have hit the right balance now so I will stay with it

 

[jls001]

Is there any calculation to determine what will be the output impedance at a said resistor value

If I understand right, the B1 (stock) output impedance is about 1KOhms (see here).

Your amp's input impedance is 22 KOhms.

The generally accepted wisdom is that output impedance of pre must be 10 times less than the input impedance of the power amp, and that anything more doesn't bring benefits, though some say 1:50 is better.

So 1:22 is well within the rule. FWIW, my power amp input impedance is 100 kOhms so the ratio with B1 is 1:100.

To be perfectly safe, I think one should consider the worst case scenario of the worst (meaning highest) output impedance (as it can swing quite a bit across the freqs) and the worst (meaning lowest) input impedance of the power amp. We will need the graphs of the impedances to understand it better.

Now that we have lowered the output resistor from 1000R to 221R, I am guessing the output impedance of the B1 changes to lower. So the ratio must improve.

 

[spirovious]

And from an article about the B1:

The actual output impedance is dominated by a 1 kOhm resistor (R104 and R204 in the schematic). That's fairly low, but Nelson says that this value can be arbitrarily lowered down to say 200 Ohm, though he cautions that could cause problems with wideband equipment.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Edit: So, going by the above, I would not touch R102 & R202 at all and just muck with R104 & R204 (^_-)

Reading this it was good that I did not lower the output impedance than 200ohms.Original mod is with 220ohms and mine around 306.5ohms.

 

[keith_correa]

...Also I think I have hit the right balance now so I will stay with it

You THINK, you do not KNOW!!! Just THINK of how much BETTER it COULD be if you experiment and find the ACTUAL right balance.

 

[jls001]

You THINK, you do not KNOW!!! Just THINK of how much BETTER it COULD be if you experiment and find the ACTUAL right balance.

You trying to make him into an audiophile, or something?

 

[rikhav]

You trying to make him into an audiophile, or something?

Are both of you trying to pull my leg or what?

Just that I am genuinely happy with the results after so many tweaks

 

[manniraj]

Are both of you trying to pull my leg or what?

Just that I am genuinely happy with the results after so many tweaks

I think they already did and I hope that you should be content with the tweaks and hope some day I will be in the same boat as yours

 

[keith_correa]

Just that I am genuinely happy with the results after so many tweaks

C'mon Rikhav, where is your spirit of adventure? Or "keeda"

 

[rohitmusic]

You THINK, you do not KNOW!!! Just THINK of how much BETTER it COULD be if you experiment and find the ACTUAL right balance.

Ma Mama says... Stayyyy awaay from bad ("pun intended") company.....!



this is sooooo.... "Audiophile..." :clapping:

On a serious note... you guyz are simply unbelievable and just push the limits.. Who knew the B1 could sound "Better!!!"
You got news... Heck Yeah! U ppl Rock \m/

 

[gobble]

While you guys are on this, Anyone wants to try plugging in a variable BSC circuit in preamp? Its at the bottom of the page.
http://sound.westhost.com/bafflestep.htm

The results would be interesting.

 

[john_k_antony]

Finally I got some time to try out the various mods. I tried the following combinations and here is how it sounded in my setup.

My setup Oppo 105/Project Debug III -> Pass B1 -> Acoustic Portrait old gen Power amp 75w/ch -> KEF iQ7.

I kept R102,R202 to 1K. Now here is what I got for different values for R104, R204

1. 221 ohm. I used 1W rated "bigger" resistor.

- Good and powerful bass
- "Heavy" sound
- Slightly rolled off highs. I felt this sounded pretty warmer compared to higher values of R104, R204. Due to the above phenomenon, for some songs, the sound stage seemed to narrow. The song for which I felt it very evident was "Kandisa" by Indian Ocean.

2. 330 ohm. I used 1/4W rated "smaller" resistor.

- Details improved a lot.
- The sound stage widened.
- Bass is good and powerful.
- Felt that the "warmth" I got with 220 ohm is missing. However the sound was very crisp and detailed.
- For some songs though, I felt that the sound was sounding slightly harsh at higher volumes.
- Sound was very lively.

3. 470 ohm. I used 1/4W rated "smaller" resistor.

- Almost similar to 330 ohm with somewhat recessed bass.

4. 1K ohm. I used 1/4W rated "smaller" resistor.

- Here it was sounding okay and the response was pretty flat.
- This one lacked the sparkle and life that was there with 330 ohm and the warmth I got with 221 ohm.


Now the biggest issues is, for some songs, I loved the 221ohm and for some other songs 330 ohm sounded great.

I have one question though, did the 1W rated "bigger" 221 ohm interfered with sound in a different way than the 1/4W resistors ? Because I was hoping 221 ohm to sound more detailed, but it sounded exactly opposite.

Now I have REW setup, I will take the frequency response measurement with all the 4 mods and let you guys know the results.

Here is the list of some of my test tracks. All are WAV format ripped from original CD.

Piano Man
Hotel California
I Want To Break Free
Chiquitita
Ring Ring
Rasputin
Walk Of Life
Coming Back to Life
What Makes You Beautiful
Knockin' on Heaven's Door
Livin' on a Prayer
Proper Education (Remixed Pink Floyd with some heavy bass).
Deewana Hua Baadal
Beat of Passion (Title Music) (From Taal. Amazing effects)
Yeh Hai Bambai Meri Jaan (From Confluence)
Hosanna (Tamil Movie - Vinnaithandi Varuvaya)
Kandisa
Flute Fantasy (Fusion music DJ Nasha)
Oh! Shanthi Shanthi (Tamil Movie - Vaaranam Aayiram)
Waiting for the world to change - John Mayer
Gravity - John Mayer


Overall a very interesting experiment .

Thanks,
John.

 

[spirovious]

You can try 306.5 ohm mod too.May you get a balanced response.