Latest krell saga

[Ronm1]

Your a better man than I am, Mark. As I have mentioned in other threads Noise of any kind is a particular pet peeve. It would have been toast early on for me.

 

[treitz3]

Mep, I know you aren't mad with me. I'm not to blame. I do, however, feel bad for being the one responsible for making you mad today. That was purely not my intent. Hopefully some positive can come out of this and it seems that only time will tell. Surely you can not be the only one who notices this issue throughout the history of the company and that amplifier. I would try to contact them again, explain what a hassle it is for you to return said amp and that after the repair, a rather big issue for you remains. In other words, perhaps they did not fix all that was wrong with it to begin with.

I do not have a spare amplifier with balanced outputs/inputs but if you would like an amp to use [with no hum] while you figure this out, let me know. Regardless, try to enjoy the rest of the weekend.

Tom

 

[microstrip]

I have a similar issue with my Rowland 8, hums all the time. I knew this problem going in, as it was mentioned by listeners in the Far East as a problem. The issue was traced to the choke power supply that Jeff used in the amp. Unfortunately, when Jeff caved into the pressure and changed the power supply to accommodate the Far East market, he succeeded in removing the hum, but also threw away a lot of the inner resolution that the amp is capable of. Now why amp designers cannot get this hum issue resolved in this day and age is a real question to me? Seems that any amp designer worth his salt should be able to get these basics right from the get go. The integrated amps from Japan from the seventies never illicit this problem! Couldn't Jeff Rowland or Dan D'Agastino get this seemingly MAJOR issue under control.
Okay, that's it for the rant, I still love the amp, but come on guys!!!

DaveyF
Are you referring to mechanical hum or hum in the speakers? Is it an 8 or 8Ti?

 

[mep]

Your a better man than I am, Mark. As I have mentioned in other threads Noise of any kind is a particular pet peeve. It would have been toast early on for me.

I understand completely. I used to have a much higher tolerance for noise than I do now. I came to understand that phono sections don't have to sound noisy and nor do preamps. I always expected amps to be quiet. I have been on a mission to drive down the noise floor of my gear and the KSA-250 was/is a setback on that journey. It kind of reminds me of the ET-2 arm that Sparky is in love with. The damn thing has no true ground and it's a never ending battle to try and keep it from humming.

 

[microstrip]

Mep,

You can measure the power supply ripple very easily - just connect the negative probe of the AC voltmeter (black) to the speaker negative or RCA ground and measure the AC at each of the four terminals if the diode bridges using the red probe. The measurements with the higher value are the AC of the transformer, the smaller ones are the ripple.

See this video:
http://www.youtube.com/watch?v=Ng3RlJb1SsU&context=C479900aADvjVQa1PpcFMa9syZf2Ph3qtH7khB4KMKqZolbSs_Peg=

 

[mep]

Interesting video. Typical engineer in that he can't spell worth a damn.

 

[DaveyF]

DaveyF
Are you referring to mechanical hum or hum in the speakers? Is it an 8 or 8Ti?

Microstrip, the hum is in the speakers ( well through them actually). I have an 8, the later versions including the 8Ti did away with the choke power supply. The dreaded hum was vanquished in those models, but so was the inner detail.

 

[fas42]

Mark, something worth trying is aiming to get maximum twisting of the conductors of the cables, especially the power cables. This is something I pursue quite rigorously, to minimise interference pickup, and it may be worth giving a go. Aim to determine what the natural twist, if any, is in the cable and then enhance it by manually increasing the twist. So, for a power cord, pull the plug, and start winding it up by turning the plug in whichever direction is right: I take it up to the point where the cable is getting quite "stressed", will want to coil up if you release the plug.

Obviously, if you have a speciality cord which is possibly a bit fragile in construction you may want to think hard before doing this, but a conventional run of cable can easily take this treatment.

Plus, there may be other benefits from doing this: it stabilises the materials in the cable, gets rid of floppiness, which may cause other problems ...

Frank

 

[Orb]

I have talked with other people who claimed they have owned the KSA-250 and all of them said they didn't have this problem which surprises me. I know my listening room has a very low noise level which makes issues like this worse than someone who has a noiser background than I do. But if this really was a problem that affected all KSA-250 amps, that tells you there was a design flaw in the power supply. I'm sure it is low levels of 60 Hz hum coming through.

Also, I just read the measurements that were taken as part of the review and they never mentioned any hum which I find quite curious given that Lewis Lipstick mentioned it in his review.

Have you tried to borrow a good mains conditioner?
Sorry to ask again but I cannot remember what you said when I asked quite awhile ago on this.
Although Micro's suggestion makes sense 1st.

Cheers
Orb

 

[Gregadd]

As I have said before there is a big difference betwee malpractice and fraud.
In either case you are due a refund.

 

[mep]

Mep,

You can measure the power supply ripple very easily - just connect the negative probe of the AC voltmeter (black) to the speaker negative or RCA ground and measure the AC at each of the four terminals if the diode bridges using the red probe. The measurements with the higher value are the AC of the transformer, the smaller ones are the ripple.

See this video:
http://www.youtube.com/watch?v=Ng3RlJb1SsU&context=C479900aADvjVQa1PpcFMa9syZf2Ph3qtH7khB4KMKqZolbSs_Peg=

I watched the video. Are you talking about the diode bridges that sit on top of the power supply caps? Do you have to test all of the bridges?

As for using any type of power conditioner, the answer is no. I plug the amp straight into a dedicated 20A circuit. Joe Abrams was kind enough to send me a Z-trap to try out and see if it would kill the hum and it didn't. Here is the deal people, either Lewis Lipstick was the only one honest enough to admit that the KSA-250 has low level hum through both speakers and they all have that problem because Krell didn't have enough capacitance to filter out the supply hum or me and Louie are just some unlucky guys and we have the only two KSA-250s to have this problem. It was interesting that when Harley took the measurements for the KSA-250 that he did not mention any hum issues. I wonder why. If Louie could hear the hum, it should have shown up in the measurements.

 

[RBFC]

I think it's much more likely that you and Lewis have the same grounding issues, or the same capacitor issues. If there was a global hum problem, it would show up in measurements. I will reiterate, stay after it with Krell.

Lee

 

[treitz3]

Lee, I am forced to think that's the only things it can be as well. Either a PS issue that is upstream somewhere or an issue within the unit itself. I'm leaning towards the issue being with the unit itself based upon the evidence being presented but as always, it can be difficult troubleshooting over the web. I would second the advice to stay after Krell as I believe it's good advice, mep.

Good luck with whatever you decide to do.

 

[mep]

Lee-I don't know how it could possibly be a grounding issue. I have a new dedicated 20A circuit that I have verfied that it is wired properly. I have tried lifting the ground and that didn't matter. What other grounding scheme can I come up with? And I will stay on Krell, but I don't see how I'm not going to feel pain in this fix.

 

[Phelonious Ponk]

I'd be seriously pissed by now, and the only way I'd stay after it with Krell would be if they were sending someone to my house to pack the damn things up and ship them back at their expense. Stay with Krell for a couple of more rounds at your own expense and you could have bought a better amp with the shipping costs.

Tim

 

[mep]

I'd be seriously pissed by now, and the only way I'd stay after it with Krell would be if they were sending someone to my house to pack the damn things up and ship them back at their expense. Stay with Krell for a couple of more rounds at your own expense and you could have bought a better amp with the shipping costs.

Tim

Kind of my point Tim. Let's say Krell says they will fix my amp for free and let's take another leap of faith and say that Krell will pay for shipping both ways (which I doubt). The amp still has to be packed up and carried upstairs and loaded into my vehicle. I have to drive to Indy to drop it off at the freight forwarder. That's 3 hours round trip. Ditto for the return of the amp. If I pay shipping both ways, now I'm in for over $600 more.

 

[microstrip]

Mep,

The voltmeter weights less than one pound. Can you borrow one having a full-scale sensitivity of 200mV AC locally? If you can provide us (and Krell) with measurements maybe we (they) can help better.

BTW, what type of shorting plugs do you use at the input?

 

[mep]

Micro-I have a Fluke multimeter so I can take the measurements. I just need to know exactly where in the amp I'm measuring. As for shorting plugs, I inserted the U connectors from Krell into the XLR connectors and I used RCA shorting plugs into the RCA input jacks.

 

[microstrip]

Micro-I have a Fluke multimeter so I can take the measurements. I just need to know exactly where in the amp I'm measuring. As for shorting plugs, I inserted the U connectors from Krell into the XLR connectors and I used RCA shorting plugs into the RCA input jacks.

Very good - I also own a Fluke 77 - original model bought 30 years ago, looking worn but still working as well as the day I got it. Please check the DC and AC voltage in the four points of each bridge.
Register also the AC reading of the output of the amplifier with the shorts.

 

[mep]

Very good - I also own a Fluke 77 - original model bought 30 years ago, looking worn but still working as well as the day I got it. Please check the DC and AC voltage in the four points of each bridge.
Register also the AC reading of the output of the amplifier with the shorts.

Mine is a Fluke 77 also and is the same age. I have built lots of tube gear over the years with that meter. Mine still looks real good too. Are the diode bridges all on top of the main cap banks? Does anyone have a schematic for this amp?

By the way, my new issue of SP showed up yesterday and they had a review of the new Krell SACD/CD player that costs $12K. The review sample didn't work right as it wouldn't read some disks and just sat there grinding away. It was sent back to Krell and the techs couldn't find anything wrong with it. They went ahead and replaced the laser assembly and sent it back. It still didn't work upon its return and SP had to ask for a new machine to review. The second machine garnered a rave review. At least a CD player isn't hard to pack up and ship off multiple times when Krell can't fix it. Not so for a KSA-250.