Wow! I never realized how difficult it would be to add tubes with a KRELL amp. I'm no engineer, and, I don't pretend to be into the "technical" side of the audio world. So I'll try to explain.
It seems that tube Preamps create DC. I've been told that DC will dammage my Krell amp (FPB400cx), and possibly my speakers(Tyler Acoustics Linbrook Sig, System 1 piece). UNLESS, I open the amp up and do something to the "jumpers on the digital board" . This puts some protection into the signal path. The Bad thing is, I'm told, - it also colors or degrades the audible signal coming thru the speakers. So, if I want to use my SS set up, say for SACD or DVD-V/DVD-A, I would have to open the amp up again and reverse the proceedure. This would remove the "blockage" in the signal path. :-( This of course, would have to be re-done when I want to go back to the tube setup. WHAT A PAIN!
Needless to say, this has thrown the proverbial 'wet blanket' on my tube enthusiasm. Is this problem common to ALL SS amps? Or is it just a KRELL thing?
Any thoughts would be helpful. (This is part of a thread i started on the speaker threads, but i thought i might have more luck here on the "amp' Threads) Thanks
I use a BAT Rex preamp (all tubes, power supply and output stages) with a Krell EVO 402e amp. I did nothing but set up the components. Everything sounds glorious with the best of both worlds: big, rich, sound that is also tight, detailed, dynamic.
Well I learned quite a bit from every one regarding Krells and tubes..Thanks to all for the input...
Any idea what would make my amps have a loud electrical discharge, as heard through the speakers, when switching to standby from being on? The tweeters are taking a kicking when this happens. Yes the amp gets switched to standby first as it is turned on last when system is powered on..
hi Dave - NO! I was tracking the delivery from ups. (scares me to begin with) and the Pre was "rescheduled" for delivery to 3/24! Six days past the original delivery date! What's up with that? How does that happen? Emmanuel Ships the unit - it has a delivery date - then suddenly the date is move back 6 days. I don't understand. Any ideas? Thanks for asking Dave. Now I'm keeping my fingers crossed for a safe arrival. I'll let you know.
Well gang. I figured I might add some thoughts to this thing I started. There are, after all, several tube preamps which, by design, do not leak DC. (Yay!!!! For all the Krell owners out there.) I am one day away from taking delivery on a new First Sound, Presence Deluxe MkII. It doesn't leak DC. The designer, Emmanuel Go, through his own experience with krell amps, says that Krell and his preamps are a match made in heaven. Who am I to dispute him :-) Tomorrow we'll see. Thanks to all who contributed.
Oldpet, the bass is just fine. The preamp is transformer coupled; it can't leak DC. Also, since it is a differential parafeed design, there is no DC at the input of the output transformer. That is how they are able to use a high quality mike input trannie wired in reverse for that job. These transformers will not tolerate any DC on their input.
Oldpet - I purchased the RA line stage as a kit which requires doing all the soldering. Most of that is to PC boards and the instructions are very complete. If this is a problem, it is available already built. I now have over 350 hours on mine and the sound has continued to improve. My experience with the Lundahl transformers in my K&K phono preamp is that they will continue to "sweeten up" over several hundred hours.
Oldpet - log on to: www.kandkaudio.com or check out the K&K Audio sponsored forum over on the AudioAsylum. There was also a series of articles published in AudioXpress by Dave Davenport under the title "A Line Stage Odessy". A very complete kit is available for $1799 which is what I purchased and built. The kit has 6 inputs (one XLR, 5 RCAs with one of the RCAs a fixed volume one for HT cinema use), remote volume and mute and two outputs, XLR and RCA. The only change that I made was to substitute Cardas caps for the supplied Kimber parafeed blocking caps.
Rwwear It's funny that you have an FPB 600c. In my continuing research on Tube preamps, Tvad, on this thread mentioned the First Sound Presence Deluxe II. So, I contacted Emmanuel Go. He (Emmanuel) LOVES his Presence Deluxe II design with Krell amps. He had personal experience with the 600c and his design and absoluteley RAVED about the combination! So, his designs are safe to use with Krells. I'm looking for one, but I'm trying to wait to see If I can get one used before I would spring for a new one. Here's hoping. :-)
I have been reading that the VAC preamps use output transformers and really sound great. I would like to hear one with my Krell 600c but they are quite expensive if you want the top model.
John_tracy I don't know anything about the amorphous core transformers, but if they work that's the only thing that matters. I'm curious as to where you got the pre amp, and the approx. price range. Thanks
I just finished building and "burning-in" a Raleigh Audio line stage kit that was featured in a series of articles in AudioeXpress magazine. The circuit was in part inspired by an article on parallel feed circuit topology by Lynn Olson that appeared in Vacuum Tube Valley. The relevance to this thread is this: it is transformer coupled on the input and output with Lundahl amorphous core transformers. If you haven't heard these trannies, don't let any pregedices you may have for transformers close your mind to this option. These amorphous core transformers have "magic" in them. And more to the point, no DC in output. Also, all your components will be galvanically isolated from each other. Since I have inserted this component into my system I have noticed a real lowering of the noise floor. This is one of the most open, realistic and revealing preamps I have ever heard. If you are looking for "natural presense" and "holographic" imaging check this preamp out.
I asked Audio Research if I can use a Refr 2 mk2 pre to my Krell 450monos. They answered: Teh ref2 mk2 has 4+MFD output capacitors, ie it is NOT direct coupling. We use it with our solid state power amps and have experinced no DC problems. They have direct coupling like the Krell amps" So I can assume that it OK to use the Ref 2 without connect Coupling Capacitor in my Krells?
Tvad - if it sounds the way it is described in the review i read - I'll live with out a remote. :-) Especially if i can grab one in the price range you mentioned. :-) The "wanted" is running.
Tvad - Just a follow up to your First Sound recommendation. Emmanuel designs them so there is NO DC LEAKAGE! YAY!!! I suppose the search/ wait now begins. Thanks again for the recommendation.
Well, sirspeedy. Why don't you give all of us stupid people an exhaustive list of SS and tube gear, which will match well with each other. So then we won't have to exchange ideas with one another any more.
This ongoing subject of tubes vs solid state is so stupid as to be almost laughable.It is the component matching(impedences,capacitance etc.)within our set-ups that determine how effective our stuff is in reproducing a musical signal.That goes along with low distortion and low coloration,as well as non-resonances.I've heard spectacularly performing products(in actual set-ups)that were solid state as well as those that were tube based.If the system was matched well the end result was MUSIC.This is 2005,there is a wide chasm of products to choose from,some of which are great and some not so good.That's it!Regardless of "The grass is always greener on the other side"marketing of either the tube OR ss camp.
I've not had any problems. The only pre-amps I have read about giving Krells problems were BAT pre-amps.
This could have been an isolated problem even at that I would think? I have used my Mantissa with my Ksa-250 and Kav-500 both at one time or another without problems.
Tvad/Sogood51 - Tvad - Good point. I need to be patient. I also need to find out about the DC situation.
Dave - Thanks of the tip. Do you happen to know if they leak DC? If you used one with a Krell they probably don't. Single ended is not an issue; I've had custom cables made. ;-)
The reason Krell doesn't ship it with the jumper engaged is that they feel it will degrade the sound. And they are probably right. According to the Krell service manual "Full Power Balanced amplifiers use unobtrusive direct current(DC) protection circuitry that strips DC from the signal without corrupting sound reproduction. Full Power Balanced amplifiers feature direct coupled circuity from input to output. This topology eliminates all coupling capacitors from the audio signal path. Coupling capacitors block damaging DC but have sonic characteristics that corrupt sound reproduction." It also states that the high DC output of tube preamplifiers MAY exceed the DC protection of the FPB amplifiers. So in my opinion get a meter and measure the outputs of the preamp for DC. I have used various tube preamps with my FBP600c and never had a problem and have never had to insert the jumpers.
Thanks Rooze, will do. I figure, the worst that can happen is, I'll have to change it back if i don't like it. Of course, I'll try it with my SS stuff, BEFORE I buy the tube pre. I was thinking of the ARC LS16.....or maybe a p-12A, H-CAT. If i go the H-CAT route then this all becomes a moot point since the p-12A is a SS design. I Think? hmmm.......
Oldpet, send an email to Krell through their website at www.krellonline.com and include a fax number with the email. They'll fax you a sketch of the internal layout of the amp with arrows pointing to the two jumpers that need to be removed. It's very easy to do. Again, I didn't hear any difference in the sound.
Like Rooze, I used a Krell 200 FPB with a tubed line (AE-3)level pre-amp. I called Krell and they faxed me the instructions and general jumper location.. I am not a technical person and it took all of five minute get it done. The only issue I had was volume distortion. When played really (Megadeth) loud it appeared to get muddy, less defined but I figured it was the tubes not the Krell. Beware tubes can be habit forming.
I used an ARC LS 15 with a Krell FPB200 for a few months. Initially I didn't remove the jumpers in the amp, and I couldn't leave the amp switched on for any length of time, it would get hotter and hotter (without signal) then eventually shut itself down. I then swtched the jumpers and everything worked fine. It did not degrade the sound in any way that I could detect and it took less than 5 minutes to remove the jumpers and replace the lid. I wouldn't let this put you off using FPB's with tubes....the FPB needs all the help it can get in the warmth and tonal balance departments.....go for it, it's a good amp and the LS range made a good match in my system.
I've used a BAT KV-51SE, Calypso, and SF Line3 with a Krell KSA-200s with good results. (Also earlier a AR LS2B witched worked but the combo with THiel 3.6s drilled a hole in your ears.)
Well Newbee you got me on that one. But just because equipment is old doesn't mean it can't sound good. By the way, BAT has probably fixed the DC leakage problem that they had in their earlier preamps. I guess an SS preamp can leak DC but it is not as likely. You can easily measure for leakage with a voltmeter to the outputs of the preamp. I am pretty sure that Krell amps will only shut down when DC is present at the inputs. Once the problem is removed the amp will come back on without damage.
Rwwear, What would you expect from a newbee who still listens to a 20 year old pre-amp and 10 year old amps? :-)
My point was only that while you might be able to hear the capacitor it might not really make any substantive difference sonically speaking, different perhaps but not better or worse, and if it allows an upstream improvement it would be worthwhile.
Wvick - I think dammage DOES occur. I'm not sure what exactly happens, and I don't want to 'experiment' with my Krell.
Newbee - Thanks for the second BTW :-) I might just try a Tubed CDP. I wonder if the (Modded Exemplar, APL) 3910's counts as a tubed cdp?
Nickt - Great Idea. I haven't bought one yet. (good thing I suppose) But I was considering an ARC "LS" or "SP" 16 (not sure of the difference) or a Cary SLP 2002. I'll contact them to see what they say. Thanks
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