How to go from RCA to XLR?


I've got an Aragon Stage One processor with RCA outputs and two Aragon Palladium 1K monoblocks with XLR inputs. I know there are a lot of RCA-XLR cables available, but a fabricator told me you have to know which XLR pins are "hot" and these have to match the amps' input circuitry or you will damage the amp.
So how do you know which pins to make hot when you order the cables? When you buy these cables "off the shelf" are you just hoping you get lucky and they match up with your equipment?
Thanks
noslop
Although unfortunately there are variations, the most common xlr pin connection arrangement is:

Pin 2 -- hot (the positive waveform if differential [balanced] signals are being sent from xlr outputs)
Pin 3 -- cold (the negative or inverse waveform if differential signals are being sent from xlr outputs)
Pin 1 -- ground

If that is the configuration of your monoblock inputs, the center pin of the rca connector at the other end should be wired to pin 2, and the rca shell (ground) at the other end should be wired to pins 1 and 3.

To verify the pinouts used on the xlr's on the amps, you could either try to obtain a schematic, or perhaps some Googling would lead you to the answer, or else use a multimeter to check for continuity between pin 1 and signal ground on the amp (probably the chassis).

Verifying the ground pin is key. Reversing hot and cold (usually pins 2 and 3) will reverse absolute phase but will not hurt anything. The sonic effects of absolute phase reversal would be subtle, and would be correctable by changing plus and minus connections to the speakers, as well as by having correspondingly reversed connections in the xlr to rca cable.

Regards,
-- Al
Great answer, Al. Thank you very much.
Could I use the "ground prong" (the round "3rd" prong) on the power cord's plug to check for continuity with the ground pin on the XLR input?
Scott
I'd suspect so, but I'm not sure that would necessarily be true with all equipment. Try it and see. If you get continuity to one of the xlr pins, you've verified that that pin is ground. If you don't get continuity to any pins, then that approach won't provide you with an answer. Same goes for measuring to chassis.

By "continuity" I mean something very close to 0 ohms (or at most say 1 or 2 ohms), as measured on an ohmmeter, not just an indication from a buzzer or other rough continuity checker which could indicate continuity even if a significant resistance is present.

Also, when you measure it would be prudent to have all signal cables from other pieces of equipment disconnected from the amp, so that your measurement is not confused by any possible paths to ground through the other equipment.

Regards,
-- Al
The standard for US equipment is pin 2 hot. Europe and most japanese brands use pin 3 as hot. It really doesn't do anything but reverse phase if it is not same, as Al stated.
Got some really bad news from Aragon tech support. Changing the XLR to XLR cable to an RCA to XLR cable, will cause the amp to run at only half power. Said half the input signal is grounded out so the amp, so the amp only puts out half power. Great.
Sounds like you need a single ended to balanced transformer like the Jensen model.
With designs that I am familiar with, feeding a balanced differential amplifier input with a single-ended signal will only mean that you have to turn the volume control on the preamp up a bit higher, by 6 db. It will not affect the maximum power output of the amp, only the volume control setting on the preamp that is required to reach that maximum output.

I suspect that the person you spoke to at Aragon doesn't know what he is talking about. Or else their design is very unusual in some respect.

A transformer such as Rwwear suggests will get you back most of the 6db, if that matters, but a quality transformer is likely to cost significant $, and even a good one may still have subtle sonic effects.

Regards,
-- Al
Noslop, the news you got is erroneous! If one of the phases is not present, the gain of the amp may be reduced by 6 db, but there will be no loss in power! Whoever told you that really has no idea how this stuff works.
Yes, I suppose any circuitry added will have a sonic signature but the Jensen transformers are the same one's Audio Research and Rowland use to make their products balanced. They claim the sound is better than truly balanced but I don't know. It's certainly much cheaper at around 200.00.
Atmasphere, isn't losing 6db of gain the same as losing half the output of the amp or more?
Atmasphere, isn't losing 6db of gain the same as losing half the output of the amp or more?

No. That's the basic point that both Atmasphere and I were making, which the person at Aragon apparently doesn't understand. Losing 6db of gain just means that the volume control on the preamp has to be turned up a little bit higher (6 db), to drive the power amplifier to the same maximum output power level that it would otherwise have reached at a 6 db lower setting of the volume control.

There is absolutely no difference either way in the amplifier's maximum power output. The only difference is in the volume control setting at which that maximum happens to be reached, which is a completely inconsequential difference, except perhaps in an extremely rare situation in which the preamp and power amp are severely mismatched in terms of gains and levels.

Regards,
-- Al
Al.
But because the amps are mono, they were probably converted from stereo by inverting the left or right channels thus making the amps differentialy balanced and increasing the power by a factor of four. By using only the positve half of the signal, you are losing the much of the power the amp would be capable of.
Hi Rwwear,

First, I would not assume that the monoblock amps are designed internally as bridged stereo amps, unless you know that to be true for the specific model.

But in order to answer your question, let's assume they are. I'm pretty certain that the design of a mono amp which is internally a bridged stereo amp, and has a balanced differential input, would NOT have one of its two amplifier sections driven off of the positive-going input line, and the other off of the negative-going input line, which I think is what you are envisioning.

If it were done that way, that would defeat the fundamental noise reduction advantage of having balanced interconnect cables and interfaces. As you probably realize, by feeding both the positive and negative signal inputs into a differential receiver device, common mode noise that can be expected to be present equally on both lines gets cancelled.

I believe that what would be done in the design of a mono amplifier that was internally bridged and had differential inputs is something conceptually similar to the following diagram. Note that the second diagram, in fact, shows a single ended input and a differential output, from the same circuit that can also be used to receive a differential input:

http://www.edn.com/contents/images/84302f4.pdf

The op amp that is used in this case (the same concepts would apply to an amplifier stage made up of discrete transistors) receives either a balanced differential input, or a single-ended input referenced to ground, then amplifies the difference between the two inputs, and then in either case outputs an out-of-phase (balanced differential) pair of signals that in turn would then branch off to the two amplifier sections as you envisioned.

So both output amplifier sections would still be driven, and therefore the result would be no reduction in output power capability, just a 6db reduction in gain as I and Atmasphere indicated. Perhaps Atmasphere or someone else can confirm that I am envisioning the design correctly.

Thanks for your good question!

Regards,
-- Al
Thanks Al. The reason I suspect the amps are converted from a stereo design is because the tech sort of alludes to the theory. There's many high end mono amps out there that are done the same. I look back at Audio Research's Classic 60 and Classic 120s as an example. I'm not sure but I suspect the 60s were converted in a like manner. Krell's KSA 300 can be converted to mono in a similar fashion.
BAL-TX1 from space-tech-lab dot com.
Al, your descriptions and explanations are dead on.
Al, if truly balanced is achieved best with mirror imaged circuits, what better way is there than taking a stereo amp and letting one channel drive the positive signal and the other drive the negative? I know this seems like a simplistic approach but it should work maybe at the cost of low impedence drive.
Rww -- I'm not certain I understand your question, but I think you are asking why shouldn't all monoblock amps, at least the better ones that have balanced topologies, be designed as bridged amps.

I'm probably not the best person to give you a comprehensive answer on that, because although I am an experienced EE my professional background is primarily digital, not analog, and is unrelated to audio. But the basic point to bridging is, as I'm sure you realize, to increase output power capability. But that comes at the cost of the ability to drive low impedances, as you alluded to, and I'd imagine at the cost of a number of other conceivable distortion mechanisms. Off the top of my head that would include difficulty matching the two amplifier sections precisely in terms of many different parameters (gain, linearity, phase and frequency response), delay offsets between the inverted-polarity path and the non-inverted polarity path, etc.

And whatever the reasons may be, I think the conventional anecdotal wisdom is that more often than not bridged stereo amps often just don't sound as good as when those same amps are used in normal stereo mode.

Let me know if I misunderstood your question.

Regards,
-- Al
Al, thanks again for your answer and I see your point. But a stereo amp should also be closely matched as well. I am certainly no expert which is obvious. But an example of such an animal is MBL whom offers some of their most costly designs as either stereo single or a mono pair that simply uses the XLR input to make them balanced mono only. Such a design cannot be used in single ended mode as a mono amp. It could be used as a single channel amp in single ended mode but only with one channel which would be half as much power or less.
http://www.mbl-germany.de/Reference_html/9007.html
So both output amplifier sections would still be driven, and therefore the result would be no reduction in output power capability, just a 6db reduction in gain as I and Atmasphere indicated.

This is correct. The problem of using RCA to XLR (apart from figuring out what is + and -) is that you are grounding one side of a balanced circuit. It will make your setup much more susceptible to ground loops and ruin its immunity to noise. Balanced means just what it says - everything is balanced with respect to ground and noise of ground loops (from power supply leakage, different ground points etc.) become irrelevant as they affect both line level signals equally.
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MBL whom offers some of their most costly designs as either stereo single or a mono pair that simply uses the XLR input to make them balanced mono only.

Rww -- I took a look at the MBL 9007 via the link you provided. Yes, it pretty obviously is designed to work in a bridged configuration when used as a mono amp, since it can also be used as a stereo amp. Just goes to prove the old saw about the design approach that is chosen being less important than how well the particular approach is implemented. Not sure why they didn't provide balanced inputs for stereo use, though, unless they just felt that from a marketing standpoint those who would buy just one amp and use it in stereo mode would be less likely to be driving it with a balanced preamp than those buying two amps for monoblock use.

Such a design cannot be used in single ended mode as a mono amp.

Not by going in through the single-ended inputs, but I would think you could do just what we have been discussing, namely going in through the xlr connector with an adapter that grounds one of the two polarities.

As Shadorne states, that would of course sacrifice the noise and ground loop-related advantages that the true balanced interface would provide. But I think it is important for the OP to keep in mind that the results he can expect in those respects would not differ dramatically from those that a comparable fully single-ended (unbalanced) system would provide.

Regards,
-- Al
Al the reason they don't offer balanced inputs for stereo is because they are using the two separate channels combined to make the amp balanced. One channel drives the positive and the other the negative. In stereo mode they wouldn't be able to drive the pos/neg legs of the balanced signal and keep a true differential balanced config. That's the reason you probably should not use an RCA adapter to convert an amp to single ended in this type of design. A friend had an ARC amp that only had balanced ins and was warned by a tech at ARC not to use an adapter on his amp. Balanced and bridged are closely related it appears.
Rww -- yes, but they still could have provided balanced xlr inputs for each stereo channel, and then fed those inputs into a pair of differential receivers with single-ended outputs. The single-ended outputs could then have been fed into the same path that the single-ended rca inputs in the actual design are fed into. That would add the benefits of a balanced interface and cabling, without changing the internal architecture significantly (other than the addition of a few components).

they are using the two separate channels combined to make the amp balanced .... That's the reason you probably should not use an RCA adapter to convert an amp to single ended in this type of design.

Well, ok, I don't have sufficient familiarity with this type of design to comment on this.

Regards,
-- Al
See pages 28 and 29 of the following paper for a description of how to feed a single-ended signal into a balanced input without major degradion of noise performance. My thanks to Shadorne for calling this paper to my attention.

http://www.jensen-transformers.com/an/generic%20seminar.pdf

Regards,
-- Al
My thanks to Shadorne for calling this paper to my
attention.

You're welcome - Bill Whitlock used to work at Capitol Records - he is a member
of IEEE and AES. What he says is obviously designed to help raise awareness and
promote Jensen products but he shoots straight! I would not hesitate to use his
products.

Sounds like you need a single ended to balanced transformer like the Jensen model.
Rww -- I get your drift; touche! :)

But the op should note in the reference that he can get a great deal of noise rejection just with the cabling arrangement that Whitlock describes (his diagram labelled "correct" on page 29), without the expense and possible sonic signature of a transformer.

And as I indicated earlier, even if he just uses the adapter as originally envisioned (Whitlock's diagram labelled "wrong" on page 29), he would have noise performance comparable to a fully single-ended arrangement, which may prove to be satisfactory anyway.

Regards,
-- Al
It should be fairly easy to try anyway if he's still here.
I still think that there will be a loss of power if the Palladium amps are using a
bridged balanced scheme which I suspect. From what I've read the Palladiums
are based on either the 4004 or 8008 stereo amps depending on vintage.
Rwwear, if you have only a single-ended source, get a transformer from Jensen to convert from SE to balanced. That will assure that there will be no issues.
I agree Atmo. I value your opinion and would like to ask what you think of a plan I have. I have a Citaion II that has been almost completely updated. It sounds great but would benefit from more power. I would like to find another and convert them to balanced mono by using the two separate channels of each amp for the positive and negative. Do you see any problems with this plan? Simply converting to mono is easy but I feel balanced would be better.
Hi Rww -- I'm having difficulty envisioning how that would work at all. What would the output configuration be, in terms of how the speakers are hooked up? And what would generate the inverted input signal?

Regards,
-- Al
One channel of the amp will be the positive input the other the negative of the XLR. This will bridge the amp but it will be balanced bridged operation. This is what the Pallidiums and MBLs are I believe. It is a pretty common. One of the outputs to the speakers will be the positve and the other positive output will be the negative or ground. Just like with a bridged stereo amp.
That sounds ok to me at the output side. The speaker would be connected between the two positive output terminals of the amp (I think, although I'm not certain offhand, that you would want to use the 16 ohm taps if you have 8 ohm speakers), and the two negative output terminals of the amp would be left unconnected (they are tied together and to signal ground internally).

On the input side, I think you are saying that you would take your xlr source (transformer or preamp), and construct a cable that ran xlr pin 2 to the center pin of an rca plug, and xlr pin 1 to the ground of that rca plug, and ran xlr pin 3 to the center pin of another rca plug and xlr pin 1 to the ground of that second rca plug. The two rca plugs would then plug into the amp's two rca inputs. Correct?

Or are you saying that you would replace the rca inputs on the amp with an xlr connector that you would install, with pin 1 wired to amp ground, pin 2 to the single-ended signal path of one channel (wherever the center pin of the rca had been wired to), and pin 3 to the single-ended signal path of the other channel?

I think that everything would function either way, but I'm not sure that you would gain all that much in terms of noise rejection, especially if you don't replace the rca input connectors. Balanced inputs reject noise that is present equally on both polarities, but with the two polarities being physically branched off I'm not sure that noise pickup would be really equal. You will gain a lot of power, though.

Regards,
-- Al
This is from the Citation II manual and Jim Mcshane's site.

((Connecting Citation Amps In Mono (Bridged) Mode
Here's the how-to, right from the original H-K manual:

In order to operate the Citation II as a 120 watt monophonic amplifier it is necessary to fulfill two requirements:

1. The speaker output terminals must be strapped together. Tie the two ground terminals in parallel and then tie either the
two 8 or 16 ohm terminals in parallel depending on the nominal impedance of your speaker. For example, if you are using
an 8 ohm speaker, tie the two 16 ohm terminals together and attach the speaker between either 16 ohm terminal and
ground. If you are using a 16 ohm speaker it is permissible to connect it as described for an 8 ohm speaker, as a
mismatch of as high as 50% will not affect the tone quality.

2. The amplifier input terminals must be tied together if no preamplifier is to be used and the signal is being fed directly
by a tuner. If a monophonic preamplifier is used it is also necessary to tie the inputs together. This can be accomplished in
any of several ways. One method would be to use two patch cords with RCA type phono plugs on one end. The other
end of these patch cords would be tied together in parallel and soldered to another RCA type phono plug. Connect the
two individual RCA plugs to the input receptacles of the amplifier and the other end (which is paralleled) to the output of
your tuner. A more satisfactory method is to purchase a LAB-TRONICS patching plug, Part #A-7 54 to parallel the
inputs of the amplifier. This device would eliminate the need of soldering and would insure perfect connections.

3. If a stereo preamplifier is used input strapping is not required. Merely connect the two outputs of your preamplifier to
the corresponding inputs of the Citation II and connect the speakers as previously discussed.))

Yes, I would install an XLR for the inputs. I think noise rejection would be excellent. This should be the same as any other differentialy balanced amp which is what I should have. I also think the amp should have more than double the power this way. If anyone elso wants to weigh in you are welcome. Sorry to hijack the post though.
What the manual describes is not differential and is not balanced. It just converts the amplifier to mono by paralleling up the channels, resulting in a single-ended amp with twice the power.

-- Al
I know Al, if it were that easy I wouldn't be asking. The amp is 50 years old. I don't suppose they had much balanced audio equipment then. I hope to get more power and noise rejection by doing it in a balanced configuration.
Yes, well as far as I can tell I think you'll succeed in both respects, if you install an xlr jack connected as I described, and connect the speaker between the + outputs as I described and not as the manual describes.

Good luck with it!

-- Al
I have to aquire another amp first. Might take awhile, but thanks for your input.

Robt.
A couple of further thoughts.

It will be important to make the two channels as identical as possible, meaning identical tubes, identical bias settings, etc. Otherwise the positive and negative parts of the waveforms will be treated asymmetrically, which is equivalent to a distortion.

Also, I take back what I said about possibly using the 16 ohm taps. I think that would result in too much current flowing. Perhaps someone else could suggest which taps would be best to use.

-- Al
I suppose I'll just have to try it.
Man you guys really get into it. Its great. I'm an M.D. so my knowledge of electronic design and theory is quite limited. I'll have to read it all again a few times to even begin to understand all that's been said. But in medicine and all science, empiric evidence trumps all. So here's what I found empirically. When I hooked up a balanced Aragon Aurum pre amp to the Palladiums, I couldn't turn the volume to half before my Martin Logans were so loud, it hurt. With the Stage One's gain at max (there's a gain control in the advanced settings), and the volume at max, the speakers were loud,(sort of), but nowhere near as loud or impressive as when the balanced Aurum was hooked up.So I'd have to conclude that the amps were, indeed, being hobbled by the RCA to XLR conversion.
That being said, anyone want to buy a slightly used Stage One, cheap?
Noslop -- Thanks for the witty presentation of your empirical findings! :)

But I don't think that they necessarily support the conclusion that the rca-to-xlr conversion is what is responsible for the huge volume difference that you heard between the two configurations.

Even if the power amplifier architecture corresponds to what Rwwear had suggested, which is the worst case in terms of the possible effects of the conversion on the amp's power output, there would only be a 6db loss in maximum output power. That represents a 75% reduction in maximum amp output power, which in subjective terms is not anywhere near the difference you describe, imo.

Putting db losses into perspective, it is commonly said that a 10db loss (which is a loss of 90% of the maximum output power) corresponds to a subjective perception of "half as loud." What you are describing sounds like a greater loss than even that, given that with the balanced preamp you had the volume control at less than 1/2 scale, while with the unbalanced one you had it at max.

So something else is going on, obviously related to the extra variable of having two different preamps in the comparison. Perhaps their gains are different, or perhaps something in the complex set of settings of the Stage One is confusing things.

I think that a better test would be to compare balanced vs. unbalanced outputs of the Aurum, with the unbalanced Aurum output going into the power amp through the adapter.

To summarize what has been discussed as to the different possible effects of the adapter on the power amplifier output, depending on its architecture:

If the power amp architecture is as I and Atmasphere envisioned, there would be no sacrifice in maximum output power by feeding it single ended through the adapter; it would just be necessary to raise the volume control 6db higher to reach that maximum output power (compared to balanced drive).

If the power amp architecture is as Rwwear envisioned, then the maximum output power of the amplifier (the point at which it would clip) would be reduced by 6db (compared to balanced drive), and that reduced clipping point could not be overcome by the volume control.

I think that the fact that you were apparently unable to clip the power amplifier when driving it with the adapter, even with the volume control at max, reinforces my view that your findings so far are inconclusive.

Regards,
-- Al
If as I think the amps are bridged, what happens to the channel that isn't available when using the RCA adapters? It would be half of the amp's power being sent to ground.
If as I think the amps are bridged, what happens to the channel that isn't available when using the RCA adapters? It would be half of the amp's power being sent to ground.

That was what I was addressing in my previous post when I said:

If the power amp architecture is as Rwwear envisioned, then the maximum output power of the amplifier (the point at which it would clip) would be reduced by 6db (compared to balanced drive), and that reduced clipping point could not be overcome by the volume control.

Actually, 3/4 of the amp's maximum power output would be lost (a 6db reduction), not 1/2 (a 3db reduction). One side of the amp would swing to the output voltage it is supposed to. The other side of the amp, instead of swinging to the same voltage but with the opposite polarity (minus instead of plus, or vice versa), would be at 0. So the net voltage difference across the speaker that is connected between the two outputs would be half of what it is supposed to be. Half the voltage = 1/4 of the power = -6db.

If an attempt were made to overcome that loss by turning up the volume control, then on loud peaks of the music, that would cause the amp to have to output more power than that reduced amount, the sound would clip/breakup/distort. Noslop did not report that he heard any distortion, just that the volume was lower, which tells me that something else was going on, such as his unbalanced preamp having less gain than his balanced preamp.

It's important to keep in mind that reduced power capability does not in itself mean reduced volume (although there would be reduced volume as well, by 6db). A moderate loss in volume, such as 6db, can be overcome by turning up the volume control a bit. What a loss of output power capability does is to reduce the volume level at which clipping/breakup/distortion occurs.

Regards,
-- Al
OK. Thanks.
Rwwear, the traditional method of monostrapping a tube amplifier is to put the two channels in parallel, rather than in bridge mode. You put a 'Y' adapter into the inputs, and then parallel the outputs. The output impedance is cut in half, so if you are using an 8 ohm speaker you use the 16 ohm taps.

So whichever output tap you are using, you will need a jumper to go from the left to the right for that value, for example for 8 ohms you put a jumper from one 16 ohm tap to the other, and then the speaker will connect from either 16 ohm tap and Common.

This will not work for transistor amplifiers, which have to be bridged. You could bridge the Citation as well, but at the minimum you would need an input transformer to convert from SE to balanced, or a converter circuit to do the same. Your output connections then would be the taps themselves- C would be ignored, for 8 ohms you would use both 8 ohm taps, one channel would be the 'plus' and the other would be the 'minus'. I think the monostrapping technique is easier.
Thanks Atmas. But why can't I use one channel of the amp for the positive input and the other for the negative of an XLR to convert the amp to balanced? I would use the chassis for ground.
I think his last paragraph confirms that you can.

Regards,
-- Al
I don't see why I would need an input transformer Al.