Can I connect balanced output straight to Quad 405?

[HarryCrumb]

Hi,

I posted this question over on Pinkfish but it was a much longer post, possibly too long (I was just trying to add context) and no one has replied, so I’m trying the short version here. I’m new to hifi and do not yet understand the relationship between output voltages and input sensitivity. I’m rushing this a bit, trying to set something up for someone who’s health has taken a turn for the worse, and I don’t want to damage our speakers through my ignorance.

So, short version; is it ok to take the x2 stereo xlr output from a 'Behringer Monitor2usb' which I assume is a balanced signal (I can’t find any more detail than that) straight in to a Quad 405 power amp (modded input sensitivity 1.5v) ?

https://www.behringer.com/product.html?modelCode=P0BK8

I feel like it would work but isn’t the best idea, and I’m not sure if it would be a case of “not enough to drive the amp” or “you’re going to blow your speakers”. I have a NAD1000 pre amp so I thought perhaps that could go in between. Then I would be concerned about having too many volume knobs, or is it just a case of balancing them?

For what it's worth, these will be used by a responsible adult and never driven too hard.

I appreciate any advice here…

Thank you!

[Ali Tait]

Yes it will be fine. I do the same, albeit the other way round- I run my Behringer bass amp from my passive pre, so feed into XLR from RCA.

[HarryCrumb]

Thanks Ali!

[Light Dependant Resistor]

If your Behringer has a balanced output it is comprised of a negative waveform called COLD, a positive waveform called HOT and ground. the three conductors are explained here:
https://www.boxcast.com/blog/balanced-vs.-unbalanced-audio-whats-the-difference You would need to arrange either the behringer to output unbalanced audio, or use a conversion
of balanced to unbalanced - usually done with a transformer, but other methods are a operational amplifier explained here: https://www.jensen-transformers.com/wp-content/uploads/2014/08/an003.pdf

Your Quad 405 is designed for unbalanced audio - not balanced as such. You are better designing your attenuation as unbalanced, rather than dwelling between the two
Opto coupling offers great advantage over balanced in terms of noise immunity explained here: https://lunainc.com/product/optocouplers/

[Puffin]

I have used balanced to unbalanced op-amp based converters, transformer based converters and by joining 2 of the internal connections of the XLR plug.

Wiring diagrams here https://www.ranecommercial.com/kb_article.php?article=2107

[Barry]

I have used balanced to unbalanced op-amp based converters, transformer based converters and by joining 2 of the internal connections of the XLR plug.

Wiring diagrams here https://www.ranecommercial.com/kb_article.php?article=2107

The Quad 405 uses an unbalanced input, so the best way of connecting it to a source with a balanced output is to use the wiring arrangement Fig 4 in the above-mentioned link. This is the best and safest way to do it. You will suffer a 6dB loss, which given the high sensitivity of the Quad 405 (500mV) will not be a problem

You can buy off-the-shelf XLR balanced to un-balanced RCA interconnects, but be aware in these the pins 1 and 3 of the XLR connector are connected together, thereby shorting out the 'COLD' connection. Depending on the actual item used having a balanced output, this may not matter, but it could cause damage to some items. I would strongly recommend you follow the advice discussed in the link above.

[Pharos]

I think figure 2 is best.

[Barry]

I think figure 2 is best.

The Quad 405 does not use a stereo (BTR) 1/4" jack socket, so Fig 2 is inappropriate. Figure 4 is the one to follow.

[Ali Tait]

I use these to connect my Behringer to passive pre. Works fine. Did the same with my miniDSP which again worked fine.

https://www.ebay.co.uk/itm/Neo-Oyaide-d-XFR-Class-B-XLR-female-To-RCA-male-Audio-Cable-2m/164062837789?hash=item2632e83c1d:g:QkgAAOSwwgVeOEG r

[Pharos]

The Quad 405 does not use a stereo (BTR) 1/4" jack socket, so Fig 2 is inappropriate. Figure 4 is the one to follow.

I cant really see what difference the plugs and sockets make, it is the cct configuration which matters.

[Mr.Ian]

I have a range of custom built leads but to be honest the cheap xkr to rca adapter plugs from ebay have always worked well for me apart from the space needed to fit them

[Ali Tait]

Yes agreed Ian, have used those also, never had a problem.

[Barry]

I cant really see what difference the plugs and sockets make, it is the cct configuration which matters.

Agreed, Figures 3 and 4 are equivalent and show the correct way to do it.

Depending on whether the balanced output of the source has a series resistors fitted, you may be able to use the cables available on eBay, Amazon etc., but if series resistors are not fitted, then connecting pin 1 and 3 together will short one half of the output, with possible damage.

[HarryCrumb]

Thank you to all of you for this advice, it is such a massive help. I've got tonight and tomorrow free to ingest it all. It's not an ideal setup but it's serving a purpose.

...one day audio will make sense to me, perhaps.

[Ali Tait]

Agreed, Figures 3 and 4 are equivalent and show the correct way to do it.

Depending on whether the balanced output of the source has a series resistors fitted, you may be able to use the cables available on eBay, Amazon etc., but if series resistors are not fitted, then connecting pin 1 and 3 together will short one half of the output, with possible damage.

How would that damage anything?

[Barry]

How would that damage anything?

Because if a series resistor is not fitted, there will be a direct short across one half of the output. That could well damage the output driver.

But several, if not most, sources having a balanced output are fitted with such resistors so the cables from Amazon et al. are sufficient (I have used similar cables between the balanced output of my Levinson preamp and a Quad 405-2). However there are some units which do not have output protection, so to be on the safe side I would recommend connection as shown in Figure 4 of the above cited reference.

Without looking at the circuit diagram of the OP's Behringer amplifier, I can't say if that is necessary.

[Pharos]

I am not familiar with your feeding device, but;

In general signal sources IME are not in danger when shorting their O/P because there is sufficient O/P impedance to prevent damage, but this is certainly not the case when power is involved.

Examples IME, O/P of a preamp, O/P of a tape recorder, O/P from a preamp to a tape recorder.

[Barry]

The user manual of my dual-mono balanced output preamplifier, says that if one wishes to connect it to a power amplifier having an un-balanced input, then pins 1 and 3 of the XLR connector can be connected together. This is because the output impedance of the preamp is finite at 10 Ohm. I have used such a preamp with a Quad 405, using the above arrangement, without incident.

But I have other balanced output devices which use a transformer on the output, and I would not like to short out one half of the secondary winding. In fact the instructions state that the minimum load is 600 Ohm.

[HarryCrumb]

Without looking at the circuit diagram of the OP's Behringer amplifier, I can't say if that is necessary.

I’m struggling to find a cable diagram of the unit. Best I can find is a quick-start guide with the specs in. There is a sister unit which is similar but with a different layout and the outputs are labelled as balanced/un-balanced. The unit I’m working with though is balanced only.

I’ve been reading though all the links that have been posted. I struggle with the finer detail but essentially I can see what I need for the job. If I make myself a cable with no connection/cold to pin 3, having hot on pin 2 and shield on pin 1, I should be ok. I have some nice Van Damme RCA to XLR cables at a good length but they are too nice to butcher and the XLR is male. I wondered about making up some short sex-change cables wired as per diagram 4b so I could utilise the Van Damme cable, but I think it might be better to just make the cables up in one piece. Out of interest, would that idea work? The van dammes are wired - pin 2 - hot to tip; pin1 + 3 shorted to sleeve.


Now, that Rane document that I have been referencing does advise sticking to 3m max length unbalanced cables. I won’t be running these across a busy stage floor so do you think I could get away with 5m? Possibly 4 at a stretch…? They’ll be a good few feet away from any mains cables.

https://i.postimg.cc/R0TZ9xk9/Screen-Shot-2020-07-20-at-17-50-20.png

https://i.postimg.cc/FRssHnvS/Screen-Shot-2020-07-20-at-17-50-54.png

https://i.postimg.cc/SxZw9WnB/Screen-Shot-2020-07-20-at-18-07-27.png

[Barry]

I’m struggling to find a cable diagram of the unit. Best I can find is a quick-start guide with the specs in. There is a sister unit which is similar but with a different layout and the outputs are labelled as balanced/un-balanced. The unit I’m working with though is balanced only.

I’ve been reading though all the links that have been posted. I struggle with the finer detail but essentially I can see what I need for the job. 1 If I make myself a cable with no connection/cold to pin 3, having hot on pin 2 and shield on pin 1, I should be ok. I have some nice Van Damme RCA to XLR cables at a good length but they are too nice to butcher and the XLR is male. I wondered about making up some short sex-change cables wired as per diagram 4b so I could utilise the Van Damme cable, but I think it might be better to just make the cables up in one piece. Out of interest, would that idea work? 2 The van dammes are wired - pin 2 - hot to tip; pin1 + 3 shorted to sleeve.


Now, that Rane document that I have been referencing does advise sticking to 3m max length unbalanced cables. 3 I won’t be running these across a busy stage floor so do you think I could get away with 5m? Possibly 4 at a stretch…? They’ll be a good few feet away from any mains cables.

https://i.postimg.cc/R0TZ9xk9/Screen-Shot-2020-07-20-at-17-50-20.png

https://i.postimg.cc/FRssHnvS/Screen-Shot-2020-07-20-at-17-50-54.png

https://i.postimg.cc/SxZw9WnB/Screen-Shot-2020-07-20-at-18-07-27.png

1 Yes, that should be fine. As shown in Figure 4.

2 I would break the connection between pin 1 and pin 3, so the return/shielding is connected to pin 1 only. Again as Figure 4.

3 You can probably get away with a 4 - 5 metre length, provided the cable has good shielding (i.e. has a good optical coverage). A braided shield is best, or if lapped, has a supplementary foil layer.

[Pharos]

Agree.

[Ali Tait]

I am not familiar with your feeding device, but;

In general signal sources IME are not in danger when shorting their O/P because there is sufficient O/P impedance to prevent damage, but this is certainly not the case when power is involved.

Examples IME, O/P of a preamp, O/P of a tape recorder, O/P from a preamp to a tape recorder.

That was my understanding, worst that would happen is no output as signal is going to ground.

[Barry]

Taken from https://web.archive.org/web/20081227121252/http://www.rane.com/note151.html :



Figure 5 shows recommended wiring for all combinations of balanced and unbalanced I/O interconnections when 2-conductor shielded cable is used. Figure 5 also includes the two most common manufacturer shield-grounding schemes; signal-grounding the shield and chassis-grounding the shield. Identifying these schemes for every unit in a system is essential to debug system hum and buzz. This is no simple task since chassis and signal grounds are connected together. The goal is to find out if the manufacturer connected them together is such a way that shield currents do not affect the audio signal. The dashed lines in Figure 5 represents the units' chassis boundary. Connections between dashed lines are functions of the cable. Connections outside these lines are the manufacturer's choosing, whether conscious or unconscious.

Figure 5 is arranged such that the top and left most figure (5a) is the theoretical "best" way to connect equipment with optimal results. The "best" way being, everything completely balanced with all shields (pin 1s) connected to chassis ground at the point of entry. As one moves down or to the right, degradation in performance is expected. Whether a system operates acceptably or obeys these theoretical predictions is too system-specific to predict accurately. However, one must start somewhere.

The quality and configuration of the input and output circuits are omitted from Figure 5 and the ensuing discussion, to focus on cable wiring and the internal wiring of the units. The I/O circuitry is assumed ideal.

Figure 5. Interconnectivity using shielded 2-conductor cable only. Asterisks denote usability with off-the-shelf cable.

https://web.archive.org/web/20081227121252im_/http://www.rane.com/n151fig5.gif

Balanced Output Driving Unbalanced Input

The third column in Figure 5 is the most troublesome, balanced outputs driving unbalanced inputs. Since the input stage is not balanced, induced noise on the signal conductors is not rejected. If you must use an unbalanced input, use as short an input cable as possible. This reduces the induced noise. There's a reason it's hard to find and buy unbalanced RCA cables longer than 12 feet. Figure 5i shows both ends of the cable shield connected to units with chassis-grounded shields. If the units are far apart, the chance of the shield currents inducing noise on the signal conductors is greater. Keeping this cable very short reduces the shield current and therefore reduces the noise that is not rejected by the unbalanced input stage. Most systems may require disconnecting one end of the shield for the Figure 5i case. Even a small current in the shield may prove too much for an unbalanced input stage. Again, support your favorite one-end-only political position.

Disconnect the shield at units with signal-grounded shields (Figures 5j & 5k). If both ends have signal-grounded shields, run for your favorite one-end-only political party. (Figure 5l).

This scheme connects the balanced output's negative output to signal ground, rather than a high impedance input. Many balanced output circuits will attempt to drive this signal ground, causing great distortion and potentially damaging the output stage.

Other balanced output stages are termed "floating" balanced. (Analog Devices SSM-2142 Balanced Line Driver chip is one example.) Also called a cross-coupled output, these circuits mimic the performance of fully balanced transformer solutions and are designed so the negative output can short to signal ground. If you find or use this scheme, be sure that the balanced output stage can properly handle signal ground on its negative output.

(My emphasis)

[HarryCrumb]

I've finally got all the bits together after a long wait for an amp, but the cable I've made, as per diagram 4b is introducing noise. I've double checked the source output, and the amp from a different source, and checked the cable for continuity several times.

Currently then the cable (2 core shielded) is wired as so;

Female XLR end;
hot to pin 2
shield to pin 1

RCA end;
hot to tip
shield to sleeve.

I'm following the articles linked to by Barry but my lack of technical know-how is letting me down really. I've no idea if my output stage is cross coupled, for example. I'm going to try the next best looking diagram, no.6 which has the addition of cold connected to pin 3 at the XLR end (short to shield) and to the sleeve at the RCA end, but I'm curious to know whats introducing the noise. The cable is 4m long and as far as I'm concerned it's terminated well. I'm trying to get in touch with Behringer for some proper specs as the only manual I can find is a quick-start guide.

[HarryCrumb]

Well as far as I can tell, the job is done.

Hot > 2
Cold > 3
Shield > 1 (nothing shorted)

Hot > Tip
Cold/Shield > Sleeve

It's clean as a whistle, unless I'm missing something I can't see or hear. Thanks again to everyone for all of your help and all the links provided, i've definitely learnt a few things.

[Puffin]

Good to hear you sorted it.

[Barry]

Well as far as I can tell, the job is done.

Hot > 2
Cold > 3
Shield > 1 (nothing shorted)

Hot > Tip
Cold/Shield > Sleeve

It's clean as a whistle, unless I'm missing something I can't see or hear. Thanks again to everyone for all of your help and all the links provided, i've definitely learnt a few things.

That arrangement is the one that is most often used in the ready-made leads available on-line. But the 'cold' (or negative-going) output is shorted to the shield (connected to pin 1) at the RCA end. Clearly the balanced output of your pre-amp can cope with this.

As all the articles cited have shown, the best way to arrange for a balanced output to feed into an un-balanced input, does depend on the specific items, and a certain amount of trial and error is needed.

I'm delighted it's now all working well, and to add some reassurance, I have fed a (modified) Quad 405-2 amp from a pre-amp having a balanced output using exactly the arrangement you describe (but that was because the manufacturer of the pre-amp advised such arrangement).

Time now to enjoy some music. :)