BeePre2 and the mainline

[phatfish]

I currently have a topping dx9 as a DAC for digital signals and an Eros2 feeding into the mainline and I don't anticipate additional inputs.  Very happy with this setup, but what can I say, I have the bug for another project.  8)

I think my main question is if I would lose anything adding a stock BeePre2 in the mix before the mainline in terms of (noticeable) noise or resolution?  What about a fully upgraded one? 

I know I would gain some...well gain of course, the balance control which I do really want, the sweet sweet look of some 300b's, and of course a fun new project.  Anything to gain on the sound front with this in the mix?

Thanks for looking and your thoughts.

 

[Doc B]

The Mainline is a more neutral leaning amp, and the BeePre2 is a little more weighty and warm. So if you would like to add some weight and warmth that could be a nice combo.

 

[phatfish]

Thanks Doc!  What about the noise floor compared to the mainline only especially with digital sources?  I'm assuming I'd be looking at some increase with at least the standard kit, perhaps not after upgrade(s).  Not a dealbreaker but just trying to know what to expect.  The improved noise floor was noticeable moving from a speedball'd crack to the mainline to me for example. 

 

[Doc B]

While I well may have heard a BeePre2 running into a Mainline I don't recall a specific event. That kind of connection would usually happen when we were doing quick checks on things and plugging them into the system for a brief time. I can say that I don't recall feeding any of our headphone amps from a BeePre2 creating a problem in terms of noise floor. The revamp from the original BeePre to Beepre 2 was done with a very low noise floor in mind. I would not expect there to be much of an issue.

 

[phatfish]

Cool.  Thank you.

 

[Jameson]

I ran a BeePre 1 into a Mainline driving HD800s and I don’t recall there being noticeable amount of noise unless either amp was cranked all the way up. My setup didn’t require the BeePre to be set higher than a step or two up on the coarse setting.

 

[Doc B]

Just a little tip - generally you want the upstream device (BeePre2) to have the volume set higher so the downstream device (Mainline) volume can be set lower. The higher signal level coming from the upstream device will improve the signal to noise ratio of the signal coming into the downstream device.

 

[Jameson]

Yeah, I'd typically set the BeePre high enough that I was never turning up at the Mainline, but I had the Mainline next to my chair and the BeePre was out of reach so sometimes laziness beats signal chain best practice.

 

[phatfish]

Well gentlemen, I just placed my order for one. ;D 

 

[Jameson]

Nice, thank you and congrats! We’re waiting on wood bases at the moment and will get it shipped out as soon as we get them in from the supplier.

 

[phatfish]

Been doing more reading getting excited for my build.  I saw the sticky about noise reduction for sensitive systems (adding 27 ohm resistors).  But also caught this thread about swapping 130 with 22 ohm resistors which I guess accomplishes the same thing?
https://forum.bottlehead.com/index.php?topic=14922.0

Posts are a few years old now so i was wondering if the mod is included in the base kit now?  If not, it seems like I would just want to go with using 22 ohm resistors in place of the 130 from the get go given my headphone use.  Is there a recommended part number and/or more guidance on this?  Thanks for the help as always.

 

[Paul Birkeland]

If you're not planning to install the upgrade modules, then this is a good idea. 
https://www.mouser.com/ProductDetail/Vishay-BC-Components/PR02000202209JR500?qs=LCMWAU1DZcy7Q8Qj0JD37Q%3D%3D
That's a perfectly reasonable choice for the resistors.

 

[phatfish]

Thanks PB, to confirm I would simply use 4 of the suggested 2W 22 Ohm resistors instead of the stock 2w 130 ohm ones (page 51 and 53)?  (which I assume does the same thing as adding in the 27 ohm ones in the sticky).

I am planning on doing the upgrades and recently added them to my order.  I'm planning to drill another hole into the top plate and retain the balance pot (I have confirmed asymmetrical hearing loss  ).  It looked like this was possible:
https://forum.bottlehead.com/index.php?topic=15718.0

With that background in mind, I have the following questions:
Is the replacement 22 Ohm mod the same as the additional 27 Ohm mod in terms of still working with the upgrades? 
Any downsides to the 22/27 Ohm mod if I'm planning to do the upgrades down the line?  If not, I would think the kit would be simply updated to use 22 Ohm ones?
Any benefit (even small) to performing both the 22/27 Ohm mod and doing the upgrades down the line?

Finally (and I'm getting ahead of myself here), what would be the best way to wire in the balance pot alongside the attenuators in the 1st upgrade?

Thanks, and sorry about all these questions. 

 

[Paul Birkeland]

Yes, you just substitute the 22 ohm resistors for the 130 ohm resistors.  This is what I wrote in the thread you linked to:

"If you don't have the second upgrade installed, the noise floor will drop a fair amount once you get there.  Otherwise if you decrease the value of the 130 ohm resistors on the 5 lug strips by the 4 pin sockets to more like 22 ohms, that will also drop the noise floor."

If you're going to be using the base level kit and the noise is bothersome, then change out the resistors.  If you're going to install the upgrade modules, then you don't need to bother with that.

I don't have a whole lot to offer in terms of where to put the balance pot if you decide to retain it.  You'll have to move it to a different spot so it's not in the way of the stepped attenuators.  If your hearing is off by a certain fixed amount, then this could be built into the preamp with some fixed resistors rather than keeping the balance pot.