Krell Help


Hi Guys
A few questions regarding my Krell Power amp. 
I have a pair of Krell KRS 200 Monoblocks paired to the Krell KRC3 pre amp running B&W 800D. Due to some electric issue one XLR channel on the pre has stopped working though the RCA outputs work fine. The way my pre and power are wired at the moment is that the pre XLR out goes into a convertor into the back of the power. As I bought these used I never really gave this connection much thought, but at the back of the power this convertor becomes 2 RCA into the power. The RCA inputs on the power are labelled inverted/non inverted. 
Firstly I don't even understand how the connections on the power amp even work. Secondly is there a way to get RCA to split the same way? 
Also along the way due to the same electrical issue one of the monoblocks has now become direct in that the power button on the front of the amp does not work. The amp has to be shut of from the back main power button. When i do shut it from the back the amp will play music distorted for a few seconds as oppossed to the other one which shuts off when either the front or back power buttons are used. Any suggestions as to what could be causing this. The amp works absolutely fine and sounds fantastic. 
At the moment I am using a a ML 38s as a pre which was in another system. I have noticed that though the ML produces far less bass at similar volume the sound in my opinion is better and the imaging is just fantastic. I may just leave the ML in this system but would still like to get to the bottom of this issue. 

Thanks 

srafi
I don't know the amplifier so am guessing the reason you hear music playing and fading out when the power is turned off is because there is a fault with the speaker protection circuit. The front button probably controls power to a relay that opens and closes contacts at the output from the speaker terminals. The main power switch breaks the mains power to the transformer, which also de-energizes the speaker protection relay. If this circuit is stuck in the closed position, the giant power supply capacitors maintain voltage for a few seconds after power is cut and you are hearing the fade out as they discharge. 

Even though the amp may sound fine, that protection circuit guards against DC offset, thermal overload and short circuits. Most important, it is the only thing protecting the output stage devices -- I doubt there are fuses protecting the output rails. It should be checked out by a tech. The amplifier is a 30-year old design and some things inside that amp are way past due for replacement.
srafi-

hopefully, Audiolabrynth (Keith) will see this post. He knows Krell amps very well. You can also send him an email.

srafi,

Is this what the back of each of your mono's look like?

http://www.highperformancestereo.com/krell-krs200-monos.html


srafi said:

"Due to some electric issue one XLR channel on the pre has stopped working though the RCA outputs work fine. The way my pre and power are wired at the moment is that the pre XLR out goes into a convertor into the back of the power."

Why did it need a converter? Don't the amps have balanced input jacks?

Have you tried hooking the preamp to the amps using single ended RCA interconnects? (You will need to install the shorting pins on the XLR input jacks)


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srafi said:

"Also along the way due to the same electrical issue one of the monoblocks has now become direct in that the power button on the front of the amp does not work. The amp has to be shut of from the back main power button. When i do shut it from the back the amp will play music distorted for a few seconds as oppossed to the other one which shuts off when either the front or back power buttons are used."


Mute the preamp first before turning off the amps. If no mute turn the volume all the way down. Or just stop playing the front end source.


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Quote from Link below:

"Description of On/Off and Standby Operation

When powering up any system, amplifiers should always be turned on  last and

turned off first.

1. Locate the power breaker on the rear panel of the amplifier. Move the switch

to the ON position. The power LED, labeled P, will illuminate on the from

panel. This engages the input circuitry and sets the amplifier to the Standby

position.

2. Press the silver power button on the front panel of the amplifier. The

regulator LED, labeled R, will illuminate. Once the regulator secures control -

of the output stage, the bias LED, labeled B, will illuminate. The Sustained

Plateau Bias II system is now engaged After the protection circuits have

confirmed that safe operating conditions exist, the input relays will engage.

You will hear a click. The amplifier is now ready for operation.

3. With the preamplifier in the Mute position, or volume control fully attenuated,

select a source. Turn the volume control up to your desired listening level.

4. When turning the system off, lower the volume of the preamplifier completely

or place it into the mute or stand-by position. Switch the amplifier to Standby

by pressingth e silver powebr utton.I t is nows afe to turn off the rest of the

system.

NOTE For optimal performance the rear panel power breaker should be left in

the ON position at all times."

http://krellonline.com/assets/support/FPB_ORIGINAL_SERIES_MANUAL_V982.pdf


The back of the amplifier looks similar but not exactly the same. It does not have a balanced input. Just 2 RCA jacks labelled inverted and non inverted. Is there a way I could link a picture?
I did leave the amps powered up from the back and just turn of the button on the front until it became direct. 
Thanks everyone for the comments. 
Jim (Jea48), some rear panel photos I found confirm that as Srafi said just above SOME versions of the KRS200 did not provide an XLR connector, but instead provided two RCA connectors, one designated as inverting and one as non-inverting. Lettering on the rear of those amps indicates that they are designed to be driven with a balanced pair of signals, so the "converter" Srafi referred to presumably just routes each of the two signals it receives via an XLR connector into a corresponding RCA plug.
Srafi 7-2-2016 2:22 am
...is there a way to get RCA to split the same way?
No, since the RCA outputs of the preamp do not provide both an inverted and a non-inverted signal.

What may be worth trying, though, is connecting the left channel RCA output of the preamp to the non-inverted input of the left channel amp, and connecting the right channel RCA output of the preamp to the non-inverted input of the right channel amp, and inserting an RCA shorting plug into the inverted input of both amps. Depending on the design of the amp that may work fine, although with a 6 db reduction in gain. Or, again depending on the specific design, it may result in a large reduction in power capability, as well as some degree of sonic compromise. Without being familiar with the design of the amp, my guess is that the odds are in favor of it working well, with just the gain reduction I mentioned.

The only other approach I can think of, besides having the preamp repaired, would be to connect the RCA outputs of the preamp to a pair of single-channel Jensen Transformers, one for each amp, that would convert each of the unbalanced signals from the preamp to a balanced pair of signals. It would provide those signals on an XLR connector, which would then be connected to the existing "converter."

Regards,
-- Al

Lose the KRC-3 and get a KRC-HR.