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Old 3rd February 2011, 04:20 PM   #1
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Default SET amp/speaker issue.

I have a separo se88i that I have upgraded with mundorf sio and nichicon muze caps. All the power caps have been upgrade to audio grade nichicon. Self biasing is handled my mills wire wound resistors. My amp is supposed to be 10wpc, but I am not sue if that is running at 240v or 220v or is the voltage makes a difference on the output. This is due to lack of knowledge. I am running my amp through a APC line R power unit so that my amp is running on 220v as I am not convinced that running this amp at the limits of component tolerance is a great idea. It runs quite cool for a valve amp I guess. Tubes are telefunken smooth plate MKI 12ax7, RCA clear top grey plate 12au7a and a pair of GL re-issue kt88. CD is a rotel RCD965BXLE which has done about 2 years worth of work only. Speakers are klispch RB61 on apollo Z sand filled stands.
The problem is that when get past the 12-1pm position on the volume control the music starts to get a bit harsh/bright. If I play heavy metal at this volume or louder the sound gets very harsh, the amp seems to loose timing/composition - the sound is sort of a bit jumbled. If I play Fleetwood Mac or something less complex the sound is not jumbled at the 12-1pm position but still a bit harsh on occasion. Volume control range is from 7 to 5 if one was looking at a clock face. Am I expecting too much from my amp or is it to do with the speakers? The tweeters are 1 inch titanium horn loaded type. If it is the speakers, would the tekton design 8.1se full range bookshelf speakers be a better choice for my amp or are these a bit harsh when pushed as well?
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Old 3rd February 2011, 04:39 PM   #2
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Yes, yes you are asking too much of your "little" Klipschs'. At 95 Db sensitivity a foray into Rock music brings out the limits of your amp. The Cornwalls, Klipschorn or the RF-7 would be more suitable (102Db) , leaving your ten watts to get the SPL levels your trying to attain.

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Old 3rd February 2011, 04:44 PM   #3
kevinkr is offline kevinkr  United States
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Sounds to me like the amplifier could be starting to clip at this volume level, the amount of available undistorted power is not that great at probably much less than 10W per channel. You haven't stated how loud this actually is, but I suspect from your comments that your expectation is that it would play more loudly with an acceptable level of distortion.

You may need either a more powerful amplifier (unlikely to be SE in that case) or more efficient speakers.

The other possibility is that the tweeter in those Klipsch speakers just sounds harsh at higher SPLs. I'm not really a fan of Klipsch, but am not directly familiar with your specific model.
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Old 3rd February 2011, 04:55 PM   #4
chrisb is offline chrisb  Canada
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Before concluding the amp is at fault, you might want to taste test it with some other speakers. I you don't already have a posse of like-minded audionuts, I wouldn't be surprised if a query posted here on or the AudioTalk forum could find you a (number of ) DIYer(s) close enough to you eager to provide the opportunity. Offers of "bribes" of their favorite beverage always help, and you could consider the expenses as investment in your system.

I'd imagine the amp is transportable enough that you could make a day trip of it.

But as Kevinkr noted, be prepared to accept that at least part of what you're hearing might well be the speakers -( a titanium diaphram horn loaded mid/tweeter would certainly be on my suspect list ) if so, increasing the power won't guarantee mitigation the harshness.
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Last edited by chrisb; 3rd February 2011 at 04:58 PM.
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Old 3rd February 2011, 05:00 PM   #5
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I am not sure how loud the sound level is. It is quite loud, you could not hold a conversation in the room for example. I do not have a meter to test it with. I can only guess a comparison and that is not very accurate for sure. Perhaps like a 75 watt amp at just over half volume using 86db sensitivity 2 and a half way speakers. But that is just a guess.
It would seem that I need more sensitive speakers so as not to start the amp clipping so soon. For example if I got 102dB sensitivity speakers as suggested would the amp start to clip later on IE at say the three o'clock position on the volume control? have I understood this correctly?
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Old 3rd February 2011, 05:05 PM   #6
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Originally Posted by bottletop View Post
My amp is supposed to be 10wpc, but I am not sue if that is running at 240v or 220v or is the voltage makes a difference on the output.
I couldn't come up with a schemo for this. There's no tellin' what's causing the problem. If the KT88 final isn't being used as a psuedotriode, then this sounds like normal pentode operation without gNFB or inadequate gNFB -- starts to sound harsh and aggressive as you play it louder and/or with more difficult program material. Ran into the same problem with 807 finals. These needed help from local and global NFB to tame the beasts. Once that was done, they sounded just fine. Seen the same problem with 6BQ6s and 6V6s: in pentode operation, they sound just fine at low levels, but cranking it brings out that characteristic pentode nastiness.

It could also be running into clipping and/or blocking distortion. Really hard to determine without seeing a scheme for it.
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Old 3rd February 2011, 05:29 PM   #7
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I am pretty sure the amp uses no negative feedback. Yes I have a schematic, but funnily enough it bares a passing resemblance to what is really under the hood.
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Old 3rd February 2011, 05:34 PM   #8
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The "accepted" SPL level for a "Rock concert" is 115 DB or so....with your Klipschs that would make for a 64 Watts of input power (113 Db). Now mind you, posted sensitivities are usually measured with a single frequency 1K. That said, the frequencies roll-off rather severely approaching 100 Hz. Given that your 6 1/2" driver will roll-off sooner than say a twelve incher. Also, there will be an outright upper limit of SPL of any given speaker.....& your Klipsch may not even be able to physically attain RC levels. I won't even get into dynamics of SPL levels as they get rather involved.........
So......a 102 DB level speaker will attain 114 Db at a mere 16 Watts of power.........much closer to your 10 Watts available.

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Old 3rd February 2011, 06:03 PM   #9
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Rewind a little.

95dB is loud. That's 101dB for both speakers driven at 1 watt, which is getting silly. In the workplace, you have to (legally) wear ear protection at anything above 90dB, which is also much too loud to have a conversation.

I think I'd question the speakers first - 95dB@1w, from a single 6" woofer in a bookshelf-size box, down to an f3 of 43Hz... Seems unlikely. I mean, some PA drivers (from Eminence and the like) are at ~95dB at 1w, and they need huge boxes to get close to 40Hz...

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Old 3rd February 2011, 06:46 PM   #10
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Well yes it is loud, like I said perhaps I am asking too much from my amp and indeed it is starting to clip. I had a look at the klipschorn and RF7 speakers as suggested. Might get away with the RF7 one day but those horns are serious and serious money I suspect. That would certainly increase the wife's nostril diameter if she came back from work and those were sitting in the corners of the room.
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