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11-28-2018 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 177
Joined on 06-12-2009
Post #: 1
Post ID: 25172
Reply to: 25172
The need for a balanced buffer stage
In my situation there is a missing link between my single ended phono stage and my balanced active crossover. Between them is 35ft. of interconnect. The missing link is indicated with "?" in the sketch.

What I need is one single-ended input, some attenuation, the ability to drive 35ft. interconnects and have transparent sound. My question is this: is it best to find a buffer stage that has single ended outputs or true balanced outputs? Or is this the wrong question and should I just look for a good buffer without regard to it's type of outputs? What qualifies as a good buffer?

Buffer_needed.jpg

Thank you.
11-28-2018 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,656
Joined on 10-12-2006
Post #: 2
Post ID: 25173
Reply to: 25172
Combine Functions?
Gera, what sort of active X/O are you using there, for what sort of music/expectations? Doesn't your X/O have a buffer already? There are plenty of pro solutions that combine the X/O with pre-amp functions, including the ability to drive long IC runs.  Today, these "boards" are mostly digital, but there are still analog boards out there, as well, if that's what you want.  While pros typically use balanced connectors/cables, I have seen SE inputs, anyway.



Best regards,
Paul S
11-28-2018 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 177
Joined on 06-12-2009
Post #: 3
Post ID: 25174
Reply to: 25173
Future proofing
Paul,
My current active crossover is a DSP unit which likely has low enough input impedance and single ended inputs. I added BAL inputs by using input transformers. By no means do I want to use this combination as a representation of my crossover! I intend to replace this DSP unit with either analogue active crossover such as Pass Labs B4 or ultimately convert to all passive line-level crossover as Romy uses. So with that in mind, I am looking for a solution that will be: 1. an attenuator 2. have the power to properly drive 35' of interconnect 3. drive a passive line level crossover that is 35' away.

Still, my sketch holds true and represents the general layout now and in the near future.

This buffer stage will be my first step in moving towards a system that is free of DSP processor and also future proof enough to accommodate the above listed goals down the road.

It may be an active Placette, as Romy uses, or perhaps it is a better idea to have balanced outputs with those 35' in interconnects. That is the point of my post here. Should this buffer have SE outputs or have BAL outputs...
Gera  
11-29-2018 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,656
Joined on 10-12-2006
Post #: 4
Post ID: 25175
Reply to: 25174
Long Runs
Well, the pros always say, all balanced, and ground everything, and this is the usual short cut to quiet, long cable runs in complex systems.  I think Guy H will make something for you if you can explain to him what you want. Again, while one buffer is essential here, it seems to make sense to avoid two buffers, if possible.  Likewise, the attenuators.  I understand that you want to find your X/O values without spending too much, just not sure how to wind up with acceptable results with the constraints you've imposed.  Are the long runs essential even for "mocking up" the X/Os?



Paul S
11-29-2018 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,656
Joined on 10-12-2006
Post #: 5
Post ID: 25176
Reply to: 25175
Rent-A-Board?
Not sure where you live, but near large cities one can rent "pro" sound equipment.  Once you have your end game figured out in terms of architecture you can just plug in the Board, find and note your X/O configurations and values, then make up and install your putative ultimate solution.  Based on my own experiences, I recommend you allow for DIY/on the fly changes in your ultimate solution, not rotary knobs, rather easy ways to swap resistors, caps, and inductors, also the leads between them, for fine tuning over time.


Best regards,
Paul S
11-29-2018 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,155
Joined on 05-28-2004
Post #: 6
Post ID: 25177
Reply to: 25172
The less you "buy" is better.
I do not think you need anything in your current configuration. If you use the only one sources and all the you need is to manage volume then you can put an attenuator in your phonostage before the output stage, presuming the phonostage has enough current to drive you 35’ cable. If you are looking to get rid of the active crossover and go all the way passing, if you do not use high order filter then you can do it but you would need a strong current source in your phonostage’s output stage. If you phonostage has 100-200R and you have the only 3 amps then you can make the amp to have let say >300kR input impedance and you should be able to live with it. There is no need to create complexity and to buy boxes if you do not need them. Talk to the guy who build your phonostage. I do not know what it is. if it is SS then you can run it much harder with high idle current, perhaps beefing the radiators and you can have much stronger output. If it tube then you can use other tube in output stage. It is all deepens what it is and how playable the phonostage topology is.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
11-30-2018 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 177
Joined on 06-12-2009
Post #: 7
Post ID: 25178
Reply to: 25177
Okay
It's certainly worth trying. How do I choose the proper value of the attenuator? 10K or...?
12-01-2018 Post does not mapped to Knowledge Tree
gurevise
Posts 2
Joined on 01-23-2006
Post #: 8
Post ID: 25181
Reply to: 25178
The need for a balanced buffer stage
Ideally, you'd want to drive 35 feet of balanced interconnect with the low impedance source ( say below 150 ohms or so). How low depends upon interconnect capacitance. You can try Jensen output transformer to convert SE to Balanced at the phono-stage output, if phono output is SE.
I'd try SE/Balanced transformer into 35' balanced cable first. Add low output Z buffer later if there are some HF losses.   

You don't want to put volume control on the source (phono) end. If you do, you push very low level (attenuated) signal through the long lossy interconnect. Hence, some signal integrity issues. You'd want to go into long interconnect with strong signal.
Good place to place volume control is at the crossover input. Or even better to have separate linked volume controls for each amp (all 6 of them). This way you get maximum S/N ratio.
Sergey  
12-02-2018 Post does not mapped to Knowledge Tree
rowuk


Germany
Posts 454
Joined on 07-05-2012
Post #: 9
Post ID: 25183
Reply to: 25181
Problematic at best
 gurevise wrote:
Ideally, you'd want to drive 35 feet of balanced interconnect with the low impedance source ( say below 150 ohms or so). How low depends upon interconnect capacitance. You can try Jensen output transformer to convert SE to Balanced at the phono-stage output, if phono output is SE.
I'd try SE/Balanced transformer into 35' balanced cable first. Add low output Z buffer later if there are some HF losses.   

You don't want to put volume control on the source (phono) end. If you do, you push very low level (attenuated) signal through the long lossy interconnect. Hence, some signal integrity issues. You'd want to go into long interconnect with strong signal.
Good place to place volume control is at the crossover input. Or even better to have separate linked volume controls for each amp (all 6 of them). This way you get maximum S/N ratio.
Sergey  

Sergey, we know that the thread owner is using a DSP as a crossover. Putting a volume control at the input means that you lose even more bit depth. It is the very WORST place to put one.
Why spend serious money on a line level transformer when electronics cost far less and give better performance?

Whenever I feel blue, I start breathing again.
12-02-2018 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 177
Joined on 06-12-2009
Post #: 10
Post ID: 25184
Reply to: 25183
THAT driver
Rowuk,
When you say "electronics with better performance" are you referring to something like this IC driver board?
https://www.neurochrome.com/that-driver/
12-03-2018 Post does not mapped to Knowledge Tree
rowuk


Germany
Posts 454
Joined on 07-05-2012
Post #: 11
Post ID: 25185
Reply to: 25184
No specific circuit out of context
My point was that a volume control on the input of a DSP is the worst of all solutions. Either lose the DSP (best solution) or create a multichannel attenuator for the output. It will need low impedance to drive long cables - that means an active buffer.

Whenever I feel blue, I start breathing again.
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