[Trevor Wilson[_3_]]

On 6/05/2019 11:37 pm, Howard Stone wrote:
This may be of interest

https://www.pinkfishmedia.net/forum/...heater.227491/

(Still not heard it yet -- the latest info is slightly worrying in fact, I got an email saying:

"There is a slight hum from the transformers which is pretty quiet most of the time but at peak TV time last night with some DC on the mains it did hum quite badly so you may want to use it with a DC blocker. To be clear, this is from the amp chassis itself and mechanical hum from the transformers and not hum through the speakers. It is silent from the speakers in background noise." )


**Pretty normal with many toroidal transformers. They can become noisy
when subjected to excessive DC on the mains supply. It is location
dependent. You may not have a problem in your location. As suggested, a
DC blocker is a simple, inexpensive possible solution.

A few comments on the repair:

* Your tech appears to have done an excellent and thoroughly
professional job.
* See if you can arrange to have the fan suck air UP, rather than
blowing it down. Those idiots at Krell made a huge mistake with early
KSA50 amps, by forcing air down, rather than up. (Hot air rises, after
all). This insanity was rectified in later variants.

--
Trevor Wilson
www.rageaudio.com.au

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[Howard Stone]

Oh the other thing Jez said to me which maybe he of interest was this

€œThere are speaker fuses at the output which are supposed to be 4A, 5A was found to be fitted. Such high values are unlikely to offer any real protection (2A is more common as a speaker fuse... and does sound bad!) to the speakers but could cause a slight reduction in sound quality. I will be opening it up again to check bias and offset after a couple of days use so if you wish I can bypass them altogether. let me know.€�

[Trevor Wilson[_3_]]

On 7/05/2019 7:47 pm, Howard Stone wrote:
Oh the other thing Jez said to me which maybe he of interest was this

€œThere are speaker fuses at the output which are supposed to be 4A, 5A was found to be fitted. Such high values are unlikely to offer any real protection (2A is more common as a speaker fuse... and does sound bad!) to the speakers but could cause a slight reduction in sound quality. I will be opening it up again to check bias and offset after a couple of days use so if you wish I can bypass them altogether. let me know.€�


**Fuses are a really bad idea on speaker lines, as a fuse is, in
reality, a non-linear resistor. Therefore, a fuse (any fuse) will
introduce distortion. The lower the value of the fuse, the higher the
distortion.

--
Trevor Wilson
www.rageaudio.com.au

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[Howard Stone]

Brilliant, thanks for your advice.

[Trevor Wilson[_3_]]

On 8/05/2019 5:33 pm, Howard Stone wrote:
Brilliant, thanks for your advice.


**I should add, that, if the fuses are bypassed, then another means of
speaker protection should be considered.

--
Trevor Wilson
www.rageaudio.com.au

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[Peter Wieck[_2_]]

On Tuesday, May 7, 2019 at 5:44:53 PM UTC-4, Trevor Wilson wrote:

**Fuses are a really bad idea on speaker lines, as a fuse is, in
reality, a non-linear resistor. Therefore, a fuse (any fuse) will
introduce distortion. The lower the value of the fuse, the higher the
distortion.

Source: Bob Cordell "Designing Audio Power Amplifies"

Section '13.11 Fuse, Relay and Connector Distortion' page 268.

Conclusion:

"At 20 Hz, amplifier distortion due to the fuse is calculated to be 0.0033 %."

Me: And, of course no harmonics are affected or altered.

How much are your speakers worth that you would put them at risk over the silliness of fuse adding distortion at audible levels?

Peter Wieck
Melrose Park, PA

[Peter Wieck[_2_]]

RANT WARNING!

Guys and gals, there is common sense (which isn't), and then, there is received wisdom (AKA: Religion) when it comes to audio. Typically, but not always, they are mutually exclusive. Also commonly practiced in this hobby/religion are several common fallacies, the most prominent of which a

1. Leaping to conclusions: My cat is grey, therefore all cats are grey.
2. Begging the question: Given that all cats are grey, therefore my cat must be grey.
3. False premises: My cat is wet, therefore it rained last night.

What brought this on was Trevor's post on fuses, which more-or-less encompasses two 1 & 3 of the above, with a glancing blow to 2.

Some Math:

If Output Watts = V^2/Speaker Impedance
Then V = Square Root of output watts x Impedance

OR: If watts =30
Impedance = 8
Voltage = 15.5
Amps = watts/volts
OR: 2 A in this model

Which, of course, will vary as the actual impedance differs from the nominal impedance.

A 4 amp fuse will not even warm up under normal operating conditions - and well-designed speakers will be able to handle a 30-watt input all day and all night as long as there are no/limited DC components. Sources of DC components could be from clipping in an amp with limited protection circuits, or catastrophic failure in one-or-more internal components. At which point the fuse comes into play. Aren't you glad that it was?

Other problematic speaker-damage sources: A user chooses to send a pure sine wave into a speaker at full volume. The fuse WILL NOT protect the speaker in this case, and 30 watts is 30 watts = heat. Even the very best voice coils will not withstand a constant 30 watts at a single frequency. Similar damage may be caused by a feedback loop.

Point being that a fuse is a line of defense that when deployed protects your speakers better than _ANY_OTHER_OPTION_.

That fuses can add distortion at audible frequencies does not mean that they do add distortion.
That a fuse once added distortion does not mean that all fuses add distortion.
That the speaker is distorting does not mean that the fuse is the cause.

And, of course, I could get started on the many types of fuses out there - including an entire cohort based on audiophoolery.

Peter Wieck
Melrose Park, PA

[Howard Stone]

In fact, the Krell did develop a slight problem. The fan would become noisy=
, a sort of rattle noise. If you turned it on and off then it would stop, b=
ut still I thought it was best to get it changed. The new one is almost sil=
ent and, as Trevor recommended, it sucks up. Jez says that the amp runs sli=
ghtly cooler as a result.=20

The amp is wonderful!

[Trevor Wilson[_3_]]

On 27/08/2019 8:38 am, Howard Stone wrote:
In fact, the Krell did develop a slight problem. The fan would become noisy, a sort of rattle noise. If you turned it on and off then it would stop, but still I thought it was best to get it changed. The new one is almost silent and, as Trevor recommended, it sucks up. Jez says that the amp runs slightly cooler as a result.

The amp is wonderful!


**Good to hear. Literally.

--
Trevor Wilson
www.rageaudio.com.au

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