Burson "Preamp"

mgalusha · « **on:** 10 Sep 2007, 02:30 am »

A few months back I posted about a test combo of a Burson Buffer and a remote control stepped attenuator in this thread: http://www.audiocircle.com/index.php?topic=42545.0

We ended up picking up one of the stepped attenuator kits from Jos VanEijndhoven in the Netherlands as it seemed considerably better engineered than the LITE Audio from China. In June I had the opportunity to compare it to Wayne's (BOLDER Cable) prototype Bent/Burson/BOLDER combo and my test rig was not quite as smooth or dynamic as the BOLDER unit. There were several obvious differences, the most obvious being the I had the Burson connected to the attenuator via IC's and the premium S102 nude Vishay resistors in Wayne's unit.

An order was placed for a set of Vishay VTA-55 resistors. These have a tempco of 4ppm, while not as good as the nude S102's at 2ppm it is still quite a bit better than the 25 to 50ppm for the existing Dale-Vishay RN65's.

Well the parts arrived several months ago and while the resistors were installed right away I just didn't have a chance to machine the chassis to get it all in one box and eliminate the inter connects. IMO the new resistors were quieter and provided a perception of greater richness and increased transparency in comparison to the RN65's. I expect this is because they are quieter due to the lower tempco.

Anyway, I finally had some time to get the chassis machined and assembled and I'm happy to say it was totally worth the effort. Getting the attenuator right next to the Burson modules and eliminating the 4 RCA jacks and 4 plugs made a significant improvement. It also allowed me to tie all the grounds to single point, further reducing noise. I was also able to keep the transformer a significant distance from the gain modules and I'm sure this helps reduce noise as well. Wideband noise output is .02mV for a 100dB S/N referenced to 2 volts.

I have no idea how it would compare to anything else other than what I've heard in the past but in my system it's sounding very nice indeed. I'm really going to hate turning this over to Jerry. On the bright side, I can build one for myself.

More photos here: http://www.audiocircle.com/index.php?action=gallery;area=browse;album=1197

Mike

And before anyone hammers me... I know it doesn't have fuses yet, I still need to pick up some fuse holders.

edit: fixed typo on noise voltage.

JoshK · « **Reply #1 on:** 10 Sep 2007, 02:55 am »

What size chassis is that? looks like 12 x 8 x 2-3...Looks like a good size case for quite a number of potential projects.

mgalusha · « **Reply #2 on:** 10 Sep 2007, 03:12 am »

Josh, it's a Par metal, 16x12x3. Pretty much standard rack size without mounting ears

TomS · « **Reply #3 on:** 10 Sep 2007, 11:04 am »

Mike - Very nice! Are you using stock 6db gain on the Burson or did you step it up to 12 or 18? Tom

JoshK · « **Reply #4 on:** 10 Sep 2007, 01:36 pm »

Thanks Mike. It looked like it was smaller in comparison to your rack.

mgalusha · « **Reply #5 on:** 10 Sep 2007, 01:40 pm »

Quote from: TomS on 10 Sep 2007, 11:04 am

Mike - Very nice! Are you using stock 6db gain on the Burson or did you step it up to 12 or 18? Tom

Hi Tom, it's the standard 6dB of gain. In my system and the one it's going into that is plenty. I tried it with my vinyl setup last night as well and have more than enough gain.

ebag4 · « **Reply #6 on:** 10 Sep 2007, 01:54 pm »

Mike:
Are you saying that your Burson Buffer is stock? If so, are you seeing an improvement when using it with your modded Squeezebox?

Thanks,
Ed

mgalusha · « **Reply #7 on:** 10 Sep 2007, 03:21 pm »

Quote from: ebag4 on 10 Sep 2007, 01:54 pm

Are you saying that your Burson Buffer is stock? If so, are you seeing an improvement when using it with your modded Squeezebox?

Ed,

Not quite, the amount of gain is stock. It does have Black Gate caps in the power supply and the gain modules. They are otherwise unchanged.

In my system the Burson sits between the modded SB and the Marchand XM44 crossover. The improvement with the Burson in place is not subtle. The other difference between this and a stock Burson (besides the volume control) is the physical distance between the transformer and the power supply & modules. The original unit has a piece of aluminum "shielding" between the transformer / power supply module and the gain modules. Unfortunately aluminum doesn't provide any magnetic shielding so the added distance will reduce the opportunity for magnetic field induction in the power supply and gain modules.

Mike

Occam · « **Reply #8 on:** 10 Sep 2007, 03:44 pm »

Hey Mike,

It looks like a very nice implementation. A trivial point - actually, a non ferrous material can make an effective shield of magnetic flux if it is thick enough as it has to do with the 'skin depth' which decreases with frequency. For aluminum, you need about 1/2" of thickness at 50/60Hz.

FWIW,
Paul

ebag4 · « **Reply #9 on:** 10 Sep 2007, 04:38 pm »

Thanks for the clarification Mike. I don't suppose you would like to go into more detail of the mods you did to the Burson would you?? aa

Best,
Ed

mgalusha · « **Reply #10 on:** 10 Sep 2007, 04:40 pm »

Thanks Paul, well in this case the original piece provide by Burson was about .5mm or so. Certainly not close to the 13mm that would be needed at 50/60Hz.

I do appreciate the info as I always heard that AL didn't provide any shielding at those frequencies.

Mike

mgalusha · « **Reply #11 on:** 10 Sep 2007, 04:43 pm »

Quote from: ebag4 on 10 Sep 2007, 04:38 pm

Thanks for the clarification Mike. I don't suppose you would like to go into more detail of the mods you did to the Burson would you??

Exactly what I posted above, they are stock modules other than the Black Gate caps in the PS and gain modules. No other changes aside from layout and perhaps wire as the original wiring provide was too short.

Mike

ebag4 · « **Reply #12 on:** 10 Sep 2007, 04:44 pm »

Thanks again Mike.

Best,
Ed

H2K · « **Reply #13 on:** 10 Sep 2007, 05:29 pm »

Why not put the SB in there too? Eliminate another set of interconnects.
You might even be able to fit the power supply and eliminate another PC.

TomS · « **Reply #14 on:** 10 Sep 2007, 05:33 pm »

Better yet, drop in the Burson and Ultimate PS too and eliminate an "extra" power cord.

mgalusha · « **Reply #15 on:** 10 Sep 2007, 06:13 pm »

Quote

Why not put the SB in there too? Eliminate another set of interconnects.
You might even be able to fit the power supply and eliminate another PC.
...
Better yet, drop in the Burson and Ultimate PS too and eliminate an "extra" power cord.

I've thought about it and will likely not though it's very likely I'll put the SB and it's PS in the same case. In this case the "preamp" is just that, a preamp made to handle additional sources such as vinyl.

I think it would just be too crowded with everything in the same case but maybe not. I'd have to draw up a layout and see.

TomS · « **Reply #16 on:** 10 Sep 2007, 06:29 pm »

Quote from: mgalusha on 10 Sep 2007, 06:13 pm

Quote
Why not put the SB in there too? Eliminate another set of interconnects.
You might even be able to fit the power supply and eliminate another PC.
...
Better yet, drop in the Burson and Ultimate PS too and eliminate an "extra" power cord.

I've thought about it and will likely not though it's very likely I'll put the SB and it's PS in the same case. In this case the "preamp" is just that, a preamp made to handle additional sources such as vinyl. I think it would just be too crowded with everything in the same case but maybe not. I'd have to draw up a layout and see.

It might have to be a pretty big case to get the separation for the transformers too. My bigger concern would be upsetting the fine balance I have now with Wayne's Ultimate PS, Summit DC cable, etc. I do hate that cheezy little coaxial DC connector on the SB2 though.

I'm quite committed to the single SB2 source at this point, so having all of that in there would eliminate at least one expensive Black Sand MK V power cord, a set of Reality IC's, and that DC connector.

I also have a Sonic Euphoria PLC that has switching of 4 inputs if needed but is totally passive (no power cords) and it is extraordinarily transparent. I think I'm usually just hearing the extra interconnects when it is in circuit anyway, so I could easily drop it in after the Burson if I need another input at times.

BRN · « **Reply #17 on:** 18 Oct 2007, 09:11 am »

mgalusha,

I was wondering about the Jos van Eijndhoven Audio Volume Relay Attenuator. From a sound standpoint how does it sound? Did you get a remote for it? The reason I ask is I want to add a gain stage to my Bolder modded SB. I'm thinking of build a preamp kit, so that I bypass the digital volume control on the SB, but the one I'm looking at does not have remote capabilities and I would like to add them. I got spoiled using the SB directly into my amps and don't want to go back to getting off my butt to change the volume.

Thanks,
Brad

mgalusha · « **Reply #18 on:** 18 Oct 2007, 03:24 pm »

Brad,

I think the Van Eijndhoven attenuator works very well. I ended up swapping the supplied resistors (DALE/Vishay RN65's) for some Vishay VTA-55's. IMO these improved the sound in regards to clarity and openness along with giving a slightly warmer presentation. At least this is what I believe I heard.

I used a $4.99 universal remote from Radio Shack, worked great.

I delivered this to it's owner last week and he mentioned posting some additional thoughts once he's had a chance to listen to it a while.

The only negative thing I can say about the attenuator is that the logic circuits seem sensitive to power glitches. It would occasionally reset itself if we were having a lot of lightening, but by that point I was shutting down the system anyway and pulling the plug.

Mike

BRN · « **Reply #19 on:** 18 Oct 2007, 03:50 pm »

Mike,

Thanks for the info. I read that you had changed out the supplied resistors and if I do go down this path I will probably do the same thing. I may try the Caddock TF020.

I have read about another volume relay attenuator that when you turned it off it reset to 0 volume level. Not sure this is the same problem you were having though.

Brad