As I await my delivery of a bare board pre from Tortuga (single ended unbalanced LDR) I will be encasing it ans wiring it up to input and out sockets. I would rather not use RCA phono, because I am feeding the pre with a DAC that has balanced out XLR, and a phono set from my turntable phono amp. The pre then outputs to a DBX Venu360 (also XLR) to do digital crossover into two sets of power amps to drive a pair of hybrid ESLs.
I also like XLR plugs from an engineering standpoint and have all the necessary balanced quad core cables, so don’t really want to rip them apart to make a balanced to RCA cable.
So my plan is to wire the XLR sockets and plugs in the amp to treat them as single ended.
There are many views on how best to achieve a balanced out to unbalanced in and unbalanced out to balanced in. My research based on this site Dealing with unbalanced gear in the studio - Crookwood leads me to the following plan, though I have to confess the more I think about, this more confused I get. Especially as what I am doing is a little different, in that I am trying to preserve standard XLR cables and get the right result by correctly wiring up internally. The DAC is a Chord Hugo TT, metal chassis with wallwart DC power (not sure if that makes it a floating or mains earth, I am guessing floating) The DBX is a pro unit with earthed mains in, so I am assuming this is a mains earthed unit. It also has a pin lift that can help with earth loops)
Please let me know if you agree or have a better suggestion.
For the input from the balance cables from the DAC
Internally within the amp, wire the hot pin 2 to the board, connect pin 1 and 3 together and earth on the chassis, or should the earth be taken from pin 1 and 3? The earth to be chassis earthed in a star.
For the output from the pre to my DBX, wire the signal +ve out to pin 2 again, and again connect pin 1 and 3, wire this to the -ve output signal.
Any help would be gratefully received
I also like XLR plugs from an engineering standpoint and have all the necessary balanced quad core cables, so don’t really want to rip them apart to make a balanced to RCA cable.
So my plan is to wire the XLR sockets and plugs in the amp to treat them as single ended.
There are many views on how best to achieve a balanced out to unbalanced in and unbalanced out to balanced in. My research based on this site Dealing with unbalanced gear in the studio - Crookwood leads me to the following plan, though I have to confess the more I think about, this more confused I get. Especially as what I am doing is a little different, in that I am trying to preserve standard XLR cables and get the right result by correctly wiring up internally. The DAC is a Chord Hugo TT, metal chassis with wallwart DC power (not sure if that makes it a floating or mains earth, I am guessing floating) The DBX is a pro unit with earthed mains in, so I am assuming this is a mains earthed unit. It also has a pin lift that can help with earth loops)
Please let me know if you agree or have a better suggestion.
For the input from the balance cables from the DAC
Internally within the amp, wire the hot pin 2 to the board, connect pin 1 and 3 together and earth on the chassis, or should the earth be taken from pin 1 and 3? The earth to be chassis earthed in a star.
For the output from the pre to my DBX, wire the signal +ve out to pin 2 again, and again connect pin 1 and 3, wire this to the -ve output signal.
Any help would be gratefully received
nearly a 100 views and no thoughts on best way to do...i thought I would get a quick answer to this. Hope someone has some thoughts.
Hi David,
From what I understand you've got an unbalanced Premp, Balanced DAC + SE Phono PrePre as sources, balanced DBX XOver/Compressor and I guess balanced Amps.
I am right ?
Cheers
From what I understand you've got an unbalanced Premp, Balanced DAC + SE Phono PrePre as sources, balanced DBX XOver/Compressor and I guess balanced Amps.
I am right ?
Cheers
All understandable, save the phone part... is that a balanced output too?
This is most confusing: using balanced plugs and quad core cables for single ended use.
Can you make a draft with all the 'blocks' and interconnections between them and the grounds? And if unsure if a 'block' is on the mains protective earth, measure it!
Yes, so...?
If pin 3 is driven by the source, it is shorted. Might damage things, so check that.
Most earthings are in 'starconfiguration', distributed stars are more difficult.
Same as above, make sure pin 3 is not driven by the pro DBX.
Yes all balanced components apart from phono from TT, so would have RCA phono in pre for TT and XLR in and XLR out for DAC and feeding DBX.
Phono from TT is std RCA phono cables, into RCA sockets, plan is to use XLR for DAC in and XLR out to DBX, to retain XLR end to end cables between those devices, but cable internally within the pre to handle the signal as unbalanced, so really a question of how best to assign the pin/earth options of XLR internally in the pre amp. only other alternative is to make up XLR to RCA phono cables to do the same thing, seems pointless given i am in complete control of the pin assignments of the XLR sockets on the pre.
I've read a number of your posts over time, but I had never seen this article. For a person with no formal electronics training, it was extremely enlightening. As I learn more, I will continue to come back to it as a reference. The simple graphics made the material easily digestible, even though I have no clue (yet) how the circuits function, with the exception of the Wheatstone bridge 😀
Once I gain a bit more knowledge, your pre-amp will be on the list of "must build".
Thank you for all you contribute to this community!
Also, for converting BAL to SE, Google 'superbal circuit'.
A nice addition is the variable gain one by Merlin Blencowe, a member here:
https://www.edn.com/variable-gain-superbal-circuit-preserves-cmrr/
Jan
A nice addition is the variable gain one by Merlin Blencowe, a member here:
https://www.edn.com/variable-gain-superbal-circuit-preserves-cmrr/
Jan
I do not understand the question. The connection is described on the site; Google found it instantly.
> Tortuga (single ended unbalanced LDR)
"Balanced Audio:
"Two LDR3x boards (each paired with an optional input relay module) can be configured to accommodates up to 3 balanced audio inputs. One board is designated as the Master (the right channel) and the other is designated as the Slave. This is done via the setting of jumpers on the board together with a 3 wire control cable between the 2 boards."
LDR3x.V2.1 Passive Preamp Controller | Tortuga Audio
> Tortuga (single ended unbalanced LDR)
"Balanced Audio:
"Two LDR3x boards (each paired with an optional input relay module) can be configured to accommodates up to 3 balanced audio inputs. One board is designated as the Master (the right channel) and the other is designated as the Slave. This is done via the setting of jumpers on the board together with a 3 wire control cable between the 2 boards."
LDR3x.V2.1 Passive Preamp Controller | Tortuga Audio
As far as I know, LDRs are non linear and noisy.
Isn't it trouble for audio ?
To overcome non linearity, one must use low-level audio signals, then comes in noise giving poor S/N ratio.
I do not know LDRs well enough. Are they figures and measurements available about what I pointed here ?
Isn't it trouble for audio ?
To overcome non linearity, one must use low-level audio signals, then comes in noise giving poor S/N ratio.
I do not know LDRs well enough. Are they figures and measurements available about what I pointed here ?
> LDRs are non linear and noisy.
Everything has noise and nonlinearity.
Yes you can do a fine audio attenuator with LDRs. It is not stupidly simple. It does not help that they became a commodity, then illegal, and much of the old literature is hard to find today.
Everything has noise and nonlinearity.
Yes you can do a fine audio attenuator with LDRs. It is not stupidly simple. It does not help that they became a commodity, then illegal, and much of the old literature is hard to find today.
Thanks, yes I know this is an option, but for cost, complexity and space reasons I want to go single (unbalanced) in this build. So really looking for advice on how best to wire XLR connectors internally to force the balanced in and balanced out requirements of the DAC and DBX. The more I have read on the subject of balanced designs in the domestic environment tell me the 'value' of fully balanced designs is of little or no value anyway - don't want to start a huge debate on that subject, other to say I am happy with the compromise of going unbalanced in this design, just want to decide if it makes sense to tie pin 1 and 3 and where/what to ground to chassis.
Here are the choices in my head for this internal wiring in the single ended pre:
this is the same for DAC input or Output to DBX crossover
both in and out to be XLR male/female mounted sockets on a plastic backplane.
Input or output option 1:
Pin2 (Hot) to the +ve input/output points on the amp. As if it were the middle pin of an RCA phono.
Pin 3 (cold) left disconnected
Pin 1 (shield) routed to the single start earth point in the pre. as close to the socket as possible.
Plug surround not connected to any metal
Option 2
As option 1, but tie Pin 1 and 3 together
Option 3
As option 1, but connect plug metal body to pin 1
Option 4
As option 2, but connect plug metal body to pin 1.
Maybe folk can indicate which of these they would recommended, or if none of the above what have I got wrong (other than attempting to mix unbalanced unit in an otherwise balanced rig!!)
this is the same for DAC input or Output to DBX crossover
both in and out to be XLR male/female mounted sockets on a plastic backplane.
Input or output option 1:
Pin2 (Hot) to the +ve input/output points on the amp. As if it were the middle pin of an RCA phono.
Pin 3 (cold) left disconnected
Pin 1 (shield) routed to the single start earth point in the pre. as close to the socket as possible.
Plug surround not connected to any metal
Option 2
As option 1, but tie Pin 1 and 3 together
Option 3
As option 1, but connect plug metal body to pin 1
Option 4
As option 2, but connect plug metal body to pin 1.
Maybe folk can indicate which of these they would recommended, or if none of the above what have I got wrong (other than attempting to mix unbalanced unit in an otherwise balanced rig!!)
It sure looks like the guys at Tortuga Audio could use a hand, going by the measurements:
Review: Tortuga Audio LDR3 - LDR "passive preamp" – Neurochrome
At typical attenuation settings and 2 Vrms in, the LDR3x develops over 1% of distortion, mostly 3rd harmonic, and it even slightly increases at very low settings.
That's not a volume control, that's an effects box.
a simple option X is all I would like to get from more experts than me if possible. Thank you
I can't decipher your options. Too early and not enough coffee. In the article you linked... option 6 for DAC to Tortuga. Option 2 for Tortuga to whatever balanced thing comes after. That's how I'd start, but I've also been known to make an error or two.
FWIW - Parr and the manufacturer gave you the best option, IMO.
Don't follow up with "Now it hums. What do I do?"
The surest way to get a response is if I'm wrong 😀
FWIW - Parr and the manufacturer gave you the best option, IMO.
Don't follow up with "Now it hums. What do I do?"
The surest way to get a response is if I'm wrong 😀