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Old 13th October 2013, 01:09 AM   #10581
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Quote:
Originally Posted by nigel pearson View Post
I looked back at a Flying Mole class D amp I tested in 2007. The Hypex is miles better . Still troubles me to see the junk coming out of it . If it was harmonics we would say no way . When class D residuals it is OK .
Did you use a passive LPF between the amp and your measurement box? I ask because Audio Precision say their kit is next to useless (in terms of getting realistic measurements) if you don't have one. The high level of HF clobbers the opamps inside.

http://www.ap.com/products/accessories/aux0100
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Last edited by abraxalito; 13th October 2013 at 01:25 AM.
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Old 13th October 2013, 08:47 AM   #10582
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Quote:
Originally Posted by nigel pearson View Post
Play real music via CD . Hook up a scope . I'm happy . There comes a point where the reactive component is important . 2 R plus 100 uF might work as a test ?
When I transported my speakers (OB) the copper foil coil in the series filter had shorted.. Then one channel of my amplifiers was loaded with three 8" drivers in parallel (between 2 and 3 ohm) with 70uF in parallel again..

When I connected up I did not listen, but put the system on repeat playing at 90 - 95dB average and more than 105dB peak and let in "burn in" for several days..
The first time I sat dow to listen I observed that the left channel was sounding dull and that it was caused by the short.

Removed the short and it played OK again.

It is balanced class A JFET SIT amplifiers with a 20F PSU that have been powered on and have played for close to 10 years. There is no PCB and it is used only silver wires with air as insulation.
Earlier this year I "killed" one amplifier for the first time as I by accident connected 9VDC to one of the balanced inputs.
However the only problem was the JFET regulator transistor that got so hot that the soldering melted. Replaced that and everything was OK again.

The 1 watt class A JFET SIT amplifiers was "benchmarked" (3 - 4 years ago) against the McIntosh MC1.2KW mono amplifiers driving JBL K2 S9800 speakers and McIntosh tube preamplifier.
The only issue the McIntosh MC1.2KW was superior in was playing loud, but playing at normal listening levels even bass control was better with the JFET SIT amplifiers.
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Old 13th October 2013, 08:58 AM   #10583
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Quote:
Originally Posted by gootee View Post
This is in Watts, right? dB = 10log(ratio). 3 dB is a factor 2. To get a factor of 3 (18 Watts), it would have to have been off by about 4.8 dB, not 3 dB. Also, 2 dB is a factor of about 1.6. So your 6 Watts, when higher by 2 dB or 3 dB, could have been 9.5 to 12 Watts, not 15 to 18 Watts. If it was 15 to 18 Watts, i.e. a factor of 2.5 to 3, to then your meter would have been reading low by 4 dB to 4.8 dB.

Sorry. The 3 dB caught my eye so I knew it couldn't be more than 12 Watts instead of 6 Watts.
That peak meter was a Swiss product, a 1 height 19" rack pack, I don't remember the company's name, something like ACR or some such. It was swiped from a studio owned by a friend, who didn't much like it, and was with me for a few months. I did like it, it had a 40 dB dynamic range (which is very handy), a switch for 8/4 Ohms, another for VU/Peak, another for peak hold and yet another for dot/bar mode. Very complete, I'd say.

Take a wild guess what I did with it the first time it got to me? I grabbed my screwdriver and opened it up, naturally. And lo and behold, inside I saw mostly discrete components, two TI TLO op ams and a few three point regulators. The manufacturer obviously felt that the usual LM 3915/3916 setup, typically used when you want an extended dynamic range, wasn't good enough.

I have a project on stock doing the same. One of these days, I will complete it, depending on time.
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Old 13th October 2013, 10:24 AM   #10584
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Quote:
Originally Posted by dvv View Post
No, actually that was a 20 LED peak meter, with some solid response times. By no means the best there is, but much better than one sees in your typical home product range.

Nevertheless, I agree it probably underreads at least a bit, something like -2 or -3 dB in peak mode, so what was shown as 6 Watts was probably more like 15-18 Watts or so. But nowhere near 120W, I guarantee that, simply because the amp it was reading won't do more than 70W/8 Ohms in peaks.
In that case it sounds like what you have is a (quasi) Peak Program Meter.

These also under-read but less than a VU.

A tone burst of 10ms under-reads by 1dB, 3ms by 4dB and 0.4ms by 15dB.
(Numbers are for IEC 60268-10 Type I or DIN meters and from wiki)
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Old 13th October 2013, 11:11 AM   #10585
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Quote:
Originally Posted by Charles Darwin View Post
................A tone burst of 10ms under-reads by 1dB, 3ms by 4dB and 0.4ms by 15dB............
Could this be a reason why so many commentators assume the the HF peak signals are very much lower than all the other frequencies in music samples?
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Old 13th October 2013, 11:24 AM   #10586
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I don't know but they are probably the same people who speak of 'low frequency transients' which makes no sense since all transients are HF by their very nature.

Btw German broadcasters (the 'D' in DIN) use -9dB as the highest level when recording digitally using Peak Program Meters to avoid clipping (reaching 0dBFS).
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Old 13th October 2013, 04:59 PM   #10587
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Quote:
Originally Posted by Charles Darwin View Post
In that case it sounds like what you have is a (quasi) Peak Program Meter.

These also under-read but less than a VU.

A tone burst of 10ms under-reads by 1dB, 3ms by 4dB and 0.4ms by 15dB.
(Numbers are for IEC 60268-10 Type I or DIN meters and from wiki)
Very possibly so, and I did say it probably underreads.
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Old 15th October 2013, 08:05 AM   #10588
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Looking for opinions and experience here.

To my ears, generally Japanese capacitors in the PSU tend to make amps sound bright to overbright. German caps tend to make them sound mightier in the bass, and tend to shift the tonal balance; sometimes, they can be bass heavy, other times they are simply better balanced than Japanese ones.

So, I suppose the ideal might be to use in parallel one Japanese and one German cap. This MIGHT allow for an ideal balance.

My question is: has anyone tried this, and if so, what were the results? Improved balance, or not? Given the prices I need to pay for quality caps, I wouldn't want to try it just for the hell of it.
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Old 15th October 2013, 09:28 AM   #10589
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I think that solves itself . Panasonic decouplers ( FC ) and Mundorf for the main PSU . Aerovox BBH of the UK are cheap and good .
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Old 15th October 2013, 11:27 AM   #10590
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Quote:
Originally Posted by nigel pearson View Post
I think that solves itself . Panasonic decouplers ( FC ) and Mundorf for the main PSU . Aerovox BBH of the UK are cheap and good .
I actually have a stock of Panasonic caps, although for decoupling, I prefer to use Nichicon. In part, no doubt, because I have a solid supplier for them.

For the PSU, which is what I referred to, I have not tried Mundorf, so that is an idea. But, aren't they sort of very expensive?

I have tried Aerovox BBH and didn't like them, I had a feeling they were sort of deadening the sound, as if they were slowing it down. Could be wrong, of course.
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