Balanced Input Options

[Mike Hanson]

I'm building another amp for a friend, and he's requested that I add XLR inputs. I've explained that it's a short run from his pre-amp to the power-amp that I'm building, negating the benefit of balanced for long runs. He countered that he noticed his pre-amp's balanced inputs sound better than the unbalanced, so he's assuming that its balanced output is better too. So here we go!

I have one option on hand: a Neurochrome Universal Buffer with their associated Preamp Power Supply. This is an acceptable solution, but rather expensive and probably overkill.

Any other suggestions for possible approaches that are cheaper and sonically invisible? If it's active, then I need to provide the necessary power supply. This amp has both 70VDC and 60VDC rails for the amps themselves, so I could potentially make use of that.

 

[ramona]

I had a similar thought but only as an option. My solution was from VZAudio but unfortunately Vallery passed away (RIP) and it's not available now.
It was based on THAT1206 chip from THAT corportation and it requires minimum parts, can easily implemented on a breadboard.
I can send you the building guide for VZAudio implementation (no gerber files though).

 

[Mike Hanson]

I found these from Audiophonics, which has the benefit of switching between XLR and RCA. It requires a 15-0-15V transformer. I'm not sure if I'll be able to get all that stuff to fit (especially on the back panel), and the resulting cost isn't much cheaper.

 

[Mr_Sukebe]

Can the amp you’re building operate in balanced mode? If not, it’s a bit pointless adding XLR connections.
If the amp can operate in balanced mode, it wouldn’t seem unreasonable of him to ask to have it wired to genuinely support that mode, as long as he’s happy to pay for any required component changes.

 

[Mike Hanson]

Can the amp you’re building operate in balanced mode? If not, it’s a bit pointless adding XLR connections.
If the amp can operate in balanced mode, it wouldn’t seem unreasonable of him to ask to have it wired to genuinely support that mode, as long as he’s happy to pay for any required component changes.

The amp is unbalanced, so I agree with you. However, my friend contends that his preamp's unbalanced output isn't as good as its balanced. Therefore, it's worthwhile doing that conversion inside of my box (using a superior method) rather than in his preamp.

 

[john.luckins]

The simplest solution would be a line input transformer such as the Lundahl LL1540, set up for an asymmetric amplifier input as per the Lundahl datasheet with 2 X 12k loading. Will work with both balanced and unbalanced sources and you do get a 70kHz low pass filter thrown in! I used them on my Hackernaps for many years. Good if the pre is a long way away. Also very small at 38 X 25 X 17 mm They do pop up on ebay from time to time. I got a pair there for £50 (half price).

John

 

[Mike Hanson]

The simplest solution would be a line input transformer such as the Lundahl LL1540, set up for an asymmetric amplifier input as per the Lundahl datasheet with 2 X 12k loading. Will work with both balanced and unbalanced sources and you do get a 70kHz low pass filter thrown in! I used them on my Hackernaps for many years. Good if the pre is a long way away. Also very small at 38 X 25 X 17 mm They do pop up on ebay from time to time. I got a pair there for £50 (half price).

John

Thanks, I'll ponder that possibility, and let you know if I want to buy yours. (I'm in Canada, so shipping could inflate the overall cost significantly.)

 

[337alant]

Mike
It depends if your friend has a pre amp with balanced outputs ? and how & where is the signal ground is connected to chassis ground in his system? RANE do some good papers on various scenario's https://www.ranecommercial.com/kb_article.php?article=2107

Grounding and Shielding Audio Devices

Since the Audio Engineering Society has adopted the "pin 2 is hot" standard, what is the correct use for pin 1?

www.ranecommercial.com

I do like XLR connectors and use them as unbalance inputs on my pre amp for my R2R inputs

If your friend is using a pre amp with XLR unbalanced outputs then you could use XLR inputs to the Power amp with matching pin outs, normally pin 2 hot Signal+, pin3 cold ground-, pin 1 cable screen to chassis ground, it may be wise to fit a ground lift switch where it can switch between connecting pins 3 to 1 and open

Alan

 

[Dan K]

I think you'll need to add a pair of Cinemags

CMLI-10/600 is the transformer that you'd want.



Use a 2K43 Z foil or AN Niobium 0.5w

 

[Mike Hanson]

Mike
It depends if your friend has a pre amp with balanced outputs ? and how & where is the signal ground is connected to chassis ground in his system? RANE do some good papers on various scenario's https://www.ranecommercial.com/kb_article.php?article=2107

Grounding and Shielding Audio Devices

Since the Audio Engineering Society has adopted the "pin 2 is hot" standard, what is the correct use for pin 1?

www.ranecommercial.com

I do like XLR connectors and use them as unbalance inputs on my pre amp for my R2R inputs

If your friend is using a pre amp with XLR unbalanced outputs then you could use XLR inputs to the Power amp with matching pin outs, normally pin 2 hot Signal+, pin3 cold ground-, pin 1 cable screen to chassis ground, it may be wise to fit a ground lift switch where it can switch between connecting pins 3 to 1 and open

Alan

Yes, his preamp is balanced throughout.

 

[Mike Hanson]

I think you'll need to add a pair of Cinemags

CMLI-10/600 is the transformer that you'd want.



Use a 2K43 Z foil or AN Niobium 0.5w

Again, this will cost at much as the Neurochrome gear that I already have.

I'm starting to suspect there isn't another option that's adequate and any less expensive.

 

[gingermrkettle]

KMTech on ebay have some boards that are quite a lot less expensive than the Neurochrome stuff.

2-channel INA134 based Low Distortion Differential Line Receiver PCB ONLY DIY | eBay

PCB Mounting: 4 x 4mm mounting holes. A high performance, 2-channel, low noise balanced-to-unbalanced line adapter by KMTech Design. Total Distortion: 0.0005%. They are fully specified for high performance audio applications and have excellent ac specifications, including low distortion (0.0005%...

www.ebay.co.uk

Mono Balanced to Unbalanced Audio Line Converter ULTRA LOW NOISE PCB DIY | eBay

PCB Mounting: 4 x 4mm mounting holes. 4 x nylon mounting pillars (not included). Common-mode interference on the hot and cold input lines is dealt with by the onboard differential-mode receiver. Total Distortion: 0.00008%.

www.ebay.co.uk

 

[Dan K]

GlassWare Unbalancer

Much better option :-D

 

[Mike Hanson]

KMTech on ebay have some boards that are quite a lot less expensive than the Neurochrome stuff.

2-channel INA134 based Low Distortion Differential Line Receiver PCB ONLY DIY | eBay

PCB Mounting: 4 x 4mm mounting holes. A high performance, 2-channel, low noise balanced-to-unbalanced line adapter by KMTech Design. Total Distortion: 0.0005%. They are fully specified for high performance audio applications and have excellent ac specifications, including low distortion (0.0005%...

www.ebay.co.uk

Mono Balanced to Unbalanced Audio Line Converter ULTRA LOW NOISE PCB DIY | eBay

PCB Mounting: 4 x 4mm mounting holes. 4 x nylon mounting pillars (not included). Common-mode interference on the hot and cold input lines is dealt with by the onboard differential-mode receiver. Total Distortion: 0.00008%.

www.ebay.co.uk

That looks promising! It would arrive in time for my build, but I think I'll order something from them nonetheless.

 

[Mike Hanson]

GlassWare Unbalancer

Much better option :-D

That looks rather cool. I may order one of those just to build a tube-based buffer.

 

[Dan K]

What's the actual amp that you're building?

 

[Mike Hanson]

What's the actual amp that you're building?

It's another Avondale-based amp for a friend, so definitely unbalanced.

He currently uses an Emotiva preamp, which is balanced internally. We've observed that the unbalanced inputs don't sound nearly as good as the balanced ones, so I'm assuming the same shortcoming exists with its unbalanced output. Hence our assumption that it makes more sense to do the balanced-to-unbalanced conversion ourselves.

Just last night I began pondering a standalone balanced to unbalanced convertor. The only downside is the need for another mains outlet, and an extra set of RCA cables (to go from the standalone convertor to the power amp). That could be a useful proof-of-concept, though. If it improves things, then I could proceed with fitting it into the power amp.

That preamp is the weakest component in his chain, so he may be changing that at some point. Consequently, all this effort may be unnecessary going forwards.

And yes, I've explained to him that for his short (2m) run, there's very little benefit to a balanced cable. He likes going all the way, even when it's not really helpful.

 

[Dan K]

If he wants a much better pre amp give me shout, I've still got far too many

 

[PigletsDad]

Transformer is the easy way to do this. Jensen JT 11p-1 would be a very good choice, but about £80, so not cheap. As you only need a 1:1 transformer, lots of problems cancel out, so a cheaper part would only be a mild compromise. Something from Edcor would do, and would be about US$26.

 

[Mike Hanson]

He likes my proof-of-concept idea, building a standalone box. It turns out that I could potentially benefit as well, so I'll be testing it first before sending it to him.

If we like it, we could use it as-is, or build the equivalent into the amp.