2. amps-preamps
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REL Strata iii connected to Krell KAV-250A

Hi, 

I want to connect a REL Strata iii to a Krell KAV-250A. I need confirmation back on the proper way to do this. I have reached out to REL (no response). However I also do not have confirmation on all the facts either. 

For example :

1.) Relative to the support posting below -  is a Krell KAV-250A a differential amp? Should it be connected as described in the support link below? Note that I am not using the XLR inputs, and I have the jumper connecting pins 1 & 3 so the amp is inverted. 

2.) I have read that when not using the balanced XLR inputs the XLR inputs should be jumped between pins 1 & 3, which makes the amp outputs invert the signal. However, also looking at the specs it appears that jumpering pins 1 & 2 the output is not inverted. I understand the issue of inversion as relates to direct, or inverting preamps. Is there some reason why inverting is the preferred reccomended mode? The docs make no reference to the type of input being used. What I am looking for is a best practice relative to the design of this amp when I am using an inverting, or a non inverting amp. The last part of the equation is potentially to just reverse the polarity relative to the speakers my switching the connection at the amp outputs, or speaker inputs. 

relsupport.zendesk.com/hc/en-us/articles/115004648928-Differential-Amp-Connection-Method

Thanks! 
agdrago
6 responses Add your response
almarg's avatar
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almarg
9,670 posts
 
First and foremost, do NOT connect the jumper between pins 1 and 2. Pin 2 is almost certainly connected directly to the center pin of the RCA input connector within the amp, and therefore doing so would short the signal provided to the amp’s RCA input to ground. Resulting in no audio and even the possibility of damage to the preamp.

I took a look at the manual for the KAV-250a, and ***assuming that you are not using it in bridged mode*** its outputs are not differential, and the sub should be connected in the normal manner that would be used to connect it to the outputs of a stereo amp that does not have differential (i.e., balanced or bridged) outputs.

I don’t know if that amp or the components that are "ahead" of it in the signal path in your system invert polarity. But in any event selecting between the 0 degree and 180 degree settings of the mode switch on the sub, as described on page 8 of the sub’s manual, would be the proper way to align the polarity of the sub with the polarity of the main speakers.

Regards,
-- Al

almarg's avatar
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almarg
9,670 posts
 
I have read that when not using the balanced XLR inputs the XLR inputs should be jumped between pins 1 & 3, which makes the amp outputs invert the signal.
That is not a correct interpretation.

When the amp is provided with balanced inputs via the XLR connectors, the two signals in the balanced signal pair for each channel (which have opposite polarities) are applied to XLR pins 2 and 3, with ground being pin 1. And the amp responds to the difference in voltage that exists at any instant of time between pins 2 and 3.

When the RCA inputs are used, the input signal that is provided on the RCA center pin for each channel is almost certainly connected directly to pin 2 of the corresponding XLR connector, as I had mentioned. And that signal is presumably sent into the same differential receiver circuit that is used to receive balanced XLR inputs. So the jumper is used to provide zero volts (i.e., ground) to the input of that circuit which would receive the signal from XLR pin 3 if the XLR input was being used. Otherwise that input would be in an uncontrolled state, and prone to noise issues.

That has no direct relation to whether or not the output of the amp is inverted relative to the input.

Regards,
-- Al


noromance's avatar
noromance
9,766 posts
 
I connect my REL Strata 3 to my monos using the high level SpeakOn connection. 3 wire - right ground/right hot and left hot.

mattmiller's avatar
mattmiller
1,497 posts
 
Wow are you trying to blow your amp up? I 2nd the Spkon connection from the amps output! Two positive one negative and your good!


Matt M
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
Wow are you trying to blow your amp up?
Matt, the OP's misinterpretation of the information provided in the amp's manual about the function of the XLR jumpers is understandable, IMO.

Also, as I mentioned the damage that could conceivably occur if the jumper was connected between pins 1 and 2 on the amp's XLR input would be to the preamp, not to the amp.

Regards,
-- Al
 
agdrago OP
2 posts
 
Hi all, 

Thanks for the clarification, almarg. I am not running the amp bridged - that would be an experience. I initially connected it correctly and saw no ill effects. However, I became unsure if it should be done as described for a differential amp.

The docs seem to imply there is an option between inverting and non-inverting output based on the jumper. I was suspicious, which is why I asked the knowledgeble members of this forum. 

I have an inverting and a non-inverting preamp. I have always resolved the phase issue by reversing the output to the speakers. 

Thanks for everyone's help and concern that I might damage the equipment. 


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