I just recreated The Hated Bose 901 Sound

Because I’ve been running PS Audio M700’s with an SGCD before and a DirectStream Sr. now, I forgot why people hate the Bose 901. Well I found out today.

I just built a Nelson Pass B1 Buffer/Preamp. I built a dual mono version for true balanced operation. Pin 2 is my male hot pin and pin 1 female hot pin.

Nelson Pass Assembled and Tested B1 Buffer/Preamp :

XLP Pinouts

My friend lent me two Hypex (NCORE) 250W Class D Balanced Amp Kits that he put together. They have been my surround speaker amps for 4 months. I’ve never done any critical listening to them until today when I wanted to see if the NP B1’s can warm up the NCORE amps a bit. They are just a Hypex module with some basic input filtering to remove any unwanted RF from creeping in stuffed inside a box with an LED. Beggars can’t be choosy since I’m still paying off all my PS Audio stuff.

The B1 Buffer Preamp is dead quiet with 2 old 2WIRE 12VDC supplies wired in series. Shocking (get it power/shocking - i’m here all month - quarantined of course) since they are swiitching power supplies. It does warm the input a bit without killing female voice sibilances and the midrange is not harsh at all. Bass is unaffected as well.

The M700’s have nothing to worry about. The NCORE’s somehow recreate the hated Bose Stereo/Mono EVERYWHERE sound. Yuck. Direct out of the DSD Sr. and into the NCORE’s or with the B1 in line with the DAC/Amp’s, it was there. The sound Paul described in his video 2 years ago ! There is NO Phantom Center for vocals, snare hit, etc.

I tried both flipping the phase button on the DSD Sr.'s remote and flipping the speaker wires around. Nothing worked.

As soon as I put everything back to the way it was before, all was good in my audio world once again.

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The buffer amp sounds very interesting, I’ve been looking for something of that ilk here too. Can you recommend any circuit resources please?

Here you go Sir :

Ships only from China since the PCB’s are no longer made in the U.S.A.


PCB’s :

FET’s can be from anywhere but be careful of fakes (although they seem to work just as well ???) :

Resistors and Caps can be anything really. Obviously 1% resistors (I used Surface Mount) but the board is made for thruhole and Capacitors of your liking will work fine. Power Supply can be anything from two 9VDC batteries in series, a transformer/DC rectifier, or VDC as high as 24VDC will work without distorting/damaging things.

Since I junked all the Analog Bose Series 2 EQ’s, I had enough 5uF SoniCaps to build two PCB’s with :slightly_smiling_face:

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Many thanks :slight_smile:
I have wondered if the “fake” jfets are likely to be ok, I may have to invest in some sort of cheapo 'scope, I could adjust voltages/bias for just the right amount of 2nd harmonic distortion then too :wink:

The PSU is already half built - 5 volt dirty for the relays and LEDs, and 12-0-12 clean for buffer amps.

As you may have seen elsewhere on here I’m finally, after 40 years of furtling with electrons, building proper cases for things I am building - photos will eventually follow but I’ve had a good day of drilling making back panels and another (wired) remote control case :slight_smile:

Thq SK for all the info man that’s great!

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I’ve seen a varient of the Pass buffer with cascoded jfets too, eBay of course, I may get one of those too and compare.

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Anytime my friend. We have a Audio Club member here in Phoenix that plugs his Oppo-205 directly onto his Pass XA-25 Amp using the level control on the Oppo as his “Preamp”. He’s also using the DAC built into the Oppo. The Speaker are HUGE Tannoy’s with a 15" (or 12" ?) Concentric Drivers and an identical size Woofer all built into the same Cabinet.

It would be interesting to see if the Pass B1 inserted between the Oppo & Pass Amp improves things.


It probably will :slight_smile:
I used to enjoy tannoy little reds and little gold’s but it’s been a while. I have a pair of DC2000s but they are rather more sedate consumer models
And the tweeters are gummed up. Bloody ferrofluid! So I don’t use the.
They were all about the imaging rather than the soundstage though.
Would love to hear some Westminsters some day :slight_smile:

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My friends Tannoy’s image like crazy but the whole soundstage/front to back is pretty impressive. It’s funny, he doesn’t like to “crank it” but that’s what those things were built to do without making your ears bleed.

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People are strange…
Which reminds me - haven’t played the Doors for a while!



Oh yeah! Nice build! Nelson is the man.


Thanks man !

I hate prototyping or kit building with thruhole stuff (except power resistors and audio path Capacitors of course). Decent SMT Resistors, some wire or thin Copper tape, and a microscope because my eyes are Old, Man !


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SMT? Blimey I can just about manage through hole with a strong light and 2 pairs of reading glasses balanced on my nose!

I buy 2 watt resistors a lot of the time so I can see them and actually read the colour codes :slight_smile:

I gave up on miniaturisation when I hit 40…

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