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Old 18th November 2005, 06:13 PM   #921
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Hi Bob,

I will change the caps as soon as I get some films.

Yes I mean the initial gain. If I unplg the preamp and plug it into the Krell with the same setting on the pre the Krell sounds twice as loud. If I turn the pre up when using the A-X it gets plenty loud.

Blessings, Terry
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Old 18th November 2005, 07:35 PM   #922
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Hi Terry,

the Krell probably has 30dBs of gain (10dB more) wich would sound twice as loud.

Like Bob said you should adjust the absolute offset with the top on the amp (if possible) to get a constant value.

William
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Old 18th November 2005, 08:44 PM   #923
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Hi William,

Yeah, I think it is a gain issue. A good listening level for my Krell is about 8:00 on the pre. For the A-X it is about 10:00. That made me think the A-X was underpowered. However, I could get it plenty loud before distortion by just raising the gain on the Pre.

Adjustilon the offset with the lid on is not an option. I can make adjustments and then replace the lid and watch though. I try that when I have a lot of time.

I played this amp through my nearfield speakers last night. They are 4 ohm and it really sounded nice. Probably sound even better once I get the right input caps installed. The board that I use in my studio for the nearfields is ballanced so I'm looking forward to seeing how that works out as well.

Blessings, Terry
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Old 20th November 2005, 08:17 PM   #924
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Hi Guys,

OK, I've been listening to the A-X all morning. I seem to detect a slight fizzle sound like I'm getting some distortion. I have just purchased a Tektronix 475 scope but don't have a clue how to hook it up. I would like to try that and maybe post some pics of the screen so you guys can maybe help me get to the bottom of this.

Can one or more of you give me some step by step to get my scope hooke up? It came with P6106 probes.

Thanks, Terry
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Old 20th November 2005, 08:52 PM   #925
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The probe is easy: attach the ground clip to an _actual_ ground point somewhere in your amp, near to where you want to measure. Be careful to _not_ attach the ground clip to any non-ground point in your circuit. Aside from that, just be careful to not short anything out with the probe tip.

If you're working with audio signals, it's easiest to trigger the scope from the AC line. This is labelled LINE on the trigger selection on Tektronix scopes.

I'd start by looking at the output, just to get a feel for what's happening. Then you'll want to look at the outputs of the differential, and the current source drive. Of course, you should start by measuring the DC parameters first, to get an idea of what the quiescent point is.
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Old 20th November 2005, 09:03 PM   #926
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Quote:
Originally posted by still4given
Hi Guys,

OK, I've been listening to the A-X all morning. I seem to detect a slight fizzle sound like I'm getting some distortion. ...
Still got those electros on the inputs? You might try bypassing them with a 100nf or two while you await your big film caps.
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Old 20th November 2005, 09:48 PM   #927
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You'll have better results using a differential input to the scope. Otherwise, the scope will only read half the output signal, since the probe is referenced to ground and not to the other side of the amp.
The implication here is that you will also see distortion and noise that would otherwise be cancelled by the "X" action of the circuit.

Grey
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Old 20th November 2005, 10:38 PM   #928
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Quote:
Originally posted by BobEllis


Still got those electros on the inputs? You might try bypassing them with a 100nf or two while you await your big film caps.

I was going to ask how inportant the 10uf was. I have a few 1uf metal film caps and quite a few .1uf. (100nf same?) I'll order some 10uf pp caps if it will make that much of a difference.



Quote:
Of course, you should start by measuring the DC parameters first, to get an idea of what the quiescent point is.
Did I forget to mention I don't know anything about using a scope?

I've finally figured out how to get the line to jump around when music is played through it but don't have a clue what to look for. When you say measure the DC parameters, how would I hook that up and what would I look for. Maybe I should wait until I can meet someone who can walk me through all of this so I don't take up folks precious time here.

Do you gys know of any stufff on line that can help someone who needs to learn this, like a scopes for dummies of something?

Quote:
You'll have better results using a differential input to the scope.
I though of that when it said to hook up to ground, that it was going to be seeing absolute offset and not really telling the whole story.

Thanks, Terry
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Old 20th November 2005, 10:58 PM   #929
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use a couple of those 1 uf film caps in parallel if you have enough - that ought to give you a low enough corner frequency to be useful.

yes, 100 nf = 0.1 uf

you'll be better off using a sine wave to try to find distortion. reduce the time interval until you have a wave or two and look for discontinuities.

Is it a dual trace scope? try one probe on each output terminal, select A-B to view the output waveform.
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Old 21st November 2005, 05:27 AM   #930
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Default I could use some pointers on this one.

Hi guys,
As a fourth amp project I would like to build an Aleph-X. I am pretty cheap so I would like to use what I have on hand. The amp I would like to construct would be the largest,heaviest, and highest power AX I can muster. Before you go on about heat, consumption, and etc I want to say that I really want to build this thing. Here is what I have on hand....

- a few hundred IRFP140
- a lot of capacitance
- too much heatsink
- a pair of Kari and a pair of rev. 1 boards (help me choose)
- an old >3kva transformer +-21.5v or +-23v or +-39v (help me choose)
- a bunch of 1r and .47r power resistors (help me choose)
- plenty of wire of all colors.
- little time


OK, this is going to be a large 2 channel amp (1 chassis) with p2p wiring on the output/ccs section. I need to settle on a rail voltage, source resistor value, and best boards for the app. I have been thru the axe1 spreadsheet but there is no replacement for a little experience. I want to use the 23 v secs with maybe 20 or probably more fets per channel. I wanna do this..any advice?

Thanks in advance,
Marc
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