DIY Audio Projects Forum

Pass B1 Buffer, Tony van Roon RIAA, Preamp
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Author:  roggom [ 06 Feb 2010, 20:36 ]
Post subject:  Pass B1 Buffer, Tony van Roon RIAA, Preamp

Hi all,
I am putting together a bedroom system and wanted to build a pre from scratch. I have seen may passive pre's out there, but impedance matching can be an issue sometimes. So I decided on the Nelson Pass B1 buffered pre The schematic looked very straight forward, and the good thing is that it can be built on any budget. Mr Pass had the cad files on his website, so I downloaded and etched the board at 85% size (to fit on a radio shack board). I used all metal film 1% resistors, 2SK170 fets, Solon and some other caps from Futurlec. I soldered all of my connections under the board, and I am using a Compaq 18.5 2.7A wallwart. The sound is very transparent, with my source on pause and I crank up the volume -silence-.

Now I plan to use an AM/FM tuner and TT, so for the TT section I went with a solid discrete gem. Tony van Roon has many wonderful circuits for DIY folks and his RIAA circuit brings out great detail form my Grado Green. The circuit provides "1-volt output from a 6-millivolt input at 1KHz, and provides equalization that is within 1 dB of the RIAA standard between 40 Hz and 12KHz." (Tony van Roon, 1994) ... xtor5.html.

I drafted the circuit up in Eagle and have provided the files for those who want to download and etch the boards. Thanks to Tony for a great design.

The third part of my pre is one of my hybrid headamp builds. It is actually the prototype I made, the new project is much smaller and will fit in a radio shack project box. Since the power supply is 18.5, I threw a 7812 between B+ and the filaments. Since the final stage of the headamp is Class A, it will crank out a bit of heat, but the sound is wonderful.

With all DIY circuits there tends to be some turn on thump, I have a mitigated this issue with two delay circuits, the first is of Pass Labs and can be found on page 5 of the Zen light build The delay will turn the headlamp on 3 seconds after the B1. Further, I wanted to protect my headphones from thump of the MOSFETS, so there is another delay circuit for low voltage signals..

Now all of this is enclosed in an old Dynaco tuner chassis. I used the existing switches and 20k linear pot. It will fit nicely in my room. Will post pics of the rack when it is totally up and running.


Author:  roggom [ 06 Feb 2010, 20:42 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp

Here are the files for the RIAA stage. You may have to order the parts from mouser as there are some non standard value components. I used BC337 bjt's for amplification. The whole circuit uses only 10mA @ 18volts. So you can use 2 9volts in series for power.

Author:  roggom [ 06 Feb 2010, 20:49 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp

The delay circuit is an extract from Ti Kan's (Amb) e12 circuit. It can be used for voltages from 12-24. Best to sink the trannies over 18. All credit to Ti for the design. Again some files to buid a single rail power version.

Author:  obe1 [ 08 Feb 2010, 20:09 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp

Hello Roggom,

A nice buffet of "best of breed" circuits / topologies. Still looking forward to seeing your next generation hybrid headphone design.

Best regards,


Author:  Gio [ 08 Feb 2010, 20:14 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp

Very nice work Rogers and I like the re-use of the enclosure.

Obe1, I've got Rogers' article and it is in queue to go on the site but it will be a couple more weeks before I get a chance to pull the page together. Sorry for the delay.
Cheers, Gio

Author:  soundsgreat [ 11 Feb 2010, 12:41 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp


Very nice indeed Rogers :D , couple of questions tough,Hope you don't mind me asking them !

First is when you say you shrunk the PCB size, you did the components changes to necessitate the shrinkage ? or changed the placements to manage the changed size (as in vertical to horizontal or opposite) ??? Although I've studied that circuit and the tracks have generous space between and such to play around but aren't they supposed be that way ? So Am just curious...........

Second you've mentioned bout the RIAA and the Pre but whats that Tube PCB Thingy present there in the Cabinet :confused: ??


Author:  Gio [ 11 Feb 2010, 23:03 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp

Damn those pesky tubes, they pop up everywhere - even in the solid state forum! ;)

That looks like Rogers new tube/mosfet headphone amp, similar to this one: ... phone-Amp/

Author:  roggom [ 12 Feb 2010, 01:32 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp


I shrank the B1 pcb, just to fit on a standard 4.5 x 6.125 inch Radio Shack card, they are readily available for about $4 US and I can pick them up in store. The original board is just over 7" in length. All of the traces are fine, I had to fold the leads under for the film caps and dremmel out a little room for the 10,000 uF electrolytic leads, but the pads were plenty large to accommodate.

As Gio has mentioned, the tube is part of a tube hybrid headphone amp. I have been working on for a couple of years. The one in the pic was the first proto that I etched. The newer design will be out soon, and can be built as a stand alone headphone amp (12vdc) . Just give Gio a few weeks to put get it online.

Author:  roggom [ 12 Feb 2010, 23:41 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp

Here is the current setup, from top to bottom, Minimus 7's - a real "sleeper" speaker, one would be surprised at the sound. Pioneer DT-400 digital timer (my fancy clock), my B1 pre-amp, Maggie 185 6V6 PP amp, Pioneer tuner, and Last but not least Sony Linear track TT.

Now for another cool item, I found this cool power strip online, the Belkin BG108000-04 ... B001GQ2W6W, it runs by a wireless remote, with 2 "always on" and 8 switched outlets. The remote sits nicely in a cradle; with 4 stick-on rubber feet the remote sits nicely on my nightstand. The strip is hidden under the ladder.

I would like to say I bought it to save energy, but more like save my energy :mrgreen:


Author:  Gio [ 13 Feb 2010, 10:56 ]
Post subject:  Re: Pass B1 Buffer, Tony van Roon RIAA, Preamp

Nice clean setup and Dianna is good too! ;)

So what is the pioneer unit? an external clock?

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