Nelson Pass B-1 preamp DIY kit

[Finleyville]

Anyway...

I may need a very simple preamp soon. The Finalist speakers I just finished building are very power hungry that requires more power than my older receiver can comfortably provide. Therefore, I will probably purchase an Adcom GFA-555 or an Emotiva XPA for power. I do not want a large, old receiver acting like a preamp so I am looking for a smaller option. While researching I came across a simple DIY design and wanted to know if anyone here built/uses one of these.

[Face]

They sound fine. Just consult with whatever amp manufacturer you use and ensure a passive preamp will work with their amp. Just curious, what source will you be using?

[wkhanna]

I wish I could find the time & $.........

Used kits can often be found V cheap, but then often, you end up trouble shooting someone else's mistakes....

Passives are becoming chic these days, especially in the computer audio niche.
But be careful, as sometimes, depending on the other equipment in the system, they are not always the best match.
Since there can a wide variation in the output voltage from DAC's, its effect can vary greatly depending on the input impedance of the amp.
I have heard both extremes, DAC's run straight to the amp that sounded fantastic, & some that sounded flat, dull & vague with a totally collapsed sound stage & zero imaging (in one case in a system using B&W 802d's.)

I have done some research on my own (a while back).....
This is what I came up with:



passive pre-amp options:

Goldpoint

Music First - Baby Reference

Pre-Amp kits:

Bottlehead

Hagerman

[PewterTA]

Problem solved: Devialet

New Problem: Money.

[Johnloudb]

. While researching I came across a simple DIY design and wanted to know if anyone here built/uses one of these.

My current DIY preamp is basically a B-1 buffer preamp. Mine runs on sealed lead acid batteries and has no coupling caps. I love it! It's very smooth, detailed, with no brightness to speak of in the HF to my ears.

Yeah, yeah the B-1 Pass kit is a great deal for $40.00. Of course you still need a box, and the other parts that aren't included with the B-1 preamp kit (just PCB and 4 matched JFETS). Have you ever built any electronics projects?

As mentioned in the previous replies, you do need to have enough voltage gain in your system, since a buffer provides no voltage gain. Speakers with a high sensitivity help too!

[Finleyville]

Yeah, yeah the B-1 Pass kit is a great deal for $40.00. Of course you still need a box, and the other parts that aren't included with the B-1 preamp kit (just PCB and 4 matched JFETS). Have you ever built any electronics projects?

As mentioned in the previous replies, you do need to have enough voltage gain in your system, since a buffer provides no voltage gain. Speakers with a high sensitivity help too!

Thanks for all the replies!


I have built three headphone amps and three sets of speakers. The two sources I plan on using are a Onyko CD player and a laptop using a Schiit Modi DAC. I have no idea if those two sources have enough gain. My speakers are NOT sensitive; they eat power. Otherwise, I would be content using my current dated Denon receiver.

If I am using a DAC it doesn't sound like that would be enough voltage gain for a pure passive preamp. Thoughts?

EDIT: I just checked the Modi DAC. The specs state that its maximum output is 1.5V. I have no idea what the CD player output is....

[wkhanna]

Typically, output used to be ~ 2V, give or take .5V.

[Finleyville]

Billy,

Those linked preamp designs are nice. I especially like the Goldpoint designs; they are simple, small, elegant. They are out of my budget unfortunately. That is why a DIY or a great deal on audiogon was my intention.

The input sensitivity on the Adcom GFA-555 is 130mV and on the Emotiva 1100mV. So it seems like the Adcom would be a better choice with a passive preamp than the Emotiva (if I understand the definition of input sensitivity, that is...)


Of course, I could always buy the amp that I want THEN directly plug in the rcas from the cdp or Modi DAC to see if the amp likes an unamped signal. If they both work then a simple passive preamp would work.

[wkhanna]

I forgot to link to John Broskie's 'GlassWare' site:

Glassware scroll down to see some attenuator kits...

And John's journal which I always enjoy reading

[Johnloudb]

Billy,

Those linked preamp designs are nice. I especially like the Goldpoint designs; they are simple, small, elegant. They are out of my budget unfortunately. That is why a DIY or a great deal on audiogon was my intention.

The input sensitivity on the Adcom GFA-555 is 130mV and on the Emotiva 1100mV. So it seems like the Adcom would be a better choice with a passive preamp than the Emotiva (if I understand the definition of input sensitivity, that is...)


Of course, I could always buy the amp that I want THEN directly plug in the rcas from the cdp or Modi DAC to see if the amp likes an unamped signal. If they both work then a simple passive preamp would work.

Looks like the Emotiva amps of have a gain of 29dB which is pretty good. If you use 2 emotiva amps in bridged mode it nets you 6dB more gain for 35dB. That would probably do it for ya, but that is two amps.

The input sensitivity of the FDA-555 looks wrong as it is listed as 1.7v in the user manual. It has 27dB of gain.

Do you know the sensitivity of your speakers?

John

[Finleyville]

The input sensitivity of the FDA-555 looks wrong as it is listed as 1.7v in the user manual. It has 27dB of gain.

Do you know the sensitivity of your speakers?

Thank you for the correction on the GFA555.

The Finalist speaker design is measured to be approximately 84 dB.

I do not need a dual Emotiva solution. I think a single Emotiva or that Adcom will be fine. They seem to really like the Rotel RB-1090 currently powering them. Too bad I don't own that amp....

[Johnloudb]

Thank you for the correction on the GFA555.

The Finalist speaker design is measured to be approximately 84 dB.

I do not need a dual Emotiva solution. I think a single Emotiva or that Adcom will be fine. They seem to really like the Rotel RB-1090 currently powering them. Too bad I don't own that amp....

That's fairly low speaker sensitivity, but a buffer preamp still might work. Also depends on the size of your room and how loud you play the speakers.

Yeah, better to get a preamp with gain than to buy two amps.

[Hdale85]

I've got a few PassLabs projects in my closet that I need to work on at some point.

[Finleyville]

I've got a few PassLabs projects in my closet that I need to work on at some point.

Have a B1?

[Finleyville]

So I am now undecided.

I thought I wanted a B-1 until I looked at the PCB and saw that it only has 2 inputs. I would like at least 3 with NONE of them being a turntable input.

So now I am thinking of a PGA-2310 project (passive) or an Adcom GFP-555 or better yet the GFP-565 if I can swing the money.

[Hdale85]

You can add an offboard input selector from somebody like Twisted Pear Audio, could even do digital selector and all sorts of stuff, and make it like a real pre-amp.

[Face]

You can add an offboard input selector from somebody like Twisted Pear Audio, could even do digital selector and all sorts of stuff, and make it like a real pre-amp.

+1.

Goldpoint has a really nice selector switch, but there are many other more affordable choices out there.

[Finleyville]

So after all the searching and researching I have picked up an Adcom GFP-565.



I understand that their latest preamp, the GFP-575, is fantastic and that the 565 isn't far behind. I am looking forward to hearing it for the first time.

[wkhanna]

Nice find, Michael!

Are you bringing it over to Dan's (PewterTA) tomorrow so we hear it?

[Finleyville]

nah, sorry....

I just won it on eBay today.

It is not a great unit but I got it at a great price.