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Author Topic: can i swap a resistor for a speaker in a cabinet?  (Read 14710 times)

rjd2

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can i swap a resistor for a speaker in a cabinet?
« on: October 19, 2006, 09:43:53 pm »

i was considering bypassing one speaker in an AC30 for the purpose of making it less loud. amp runs at 16 ohms. 2 8 ohm speakers. can i "swap" one speaker for a resistor of the proper value? or is this a generally bad idea? thanks.
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Sin x/x

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #1 on: October 19, 2006, 10:13:28 pm »

It should work, but you will get just 6dB of reduction.

I use a bridged -T attenuator.

It does change the tone of the amp, but not much.

I've heard great things about Weber, but have no experience with them.


Here's a link:http://amps.zugster.net/articles/attenuation
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Tom C

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #2 on: October 20, 2006, 08:36:00 am »

rjd2 wrote on Fri, 20 October 2006 03:43

i was considering bypassing one speaker in an AC30 for the purpose of making it less loud. amp runs at 16 ohms. 2 8 ohm speakers. can i "swap" one speaker for a resistor of the proper value? or is this a generally bad idea? thanks.



Why don't you use a (high power) potentiometer to control the
loudness of both?
You'd have much more control this way.

[Edit because of speeeliing]
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Andy Peters

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #3 on: October 20, 2006, 04:36:32 pm »

rjd2 wrote on Thu, 19 October 2006 18:43

i was considering bypassing one speaker in an AC30 for the purpose of making it less loud. amp runs at 16 ohms. 2 8 ohm speakers. can i "swap" one speaker for a resistor of the proper value? or is this a generally bad idea? thanks.



You'd be better off getting an AC15.

-a
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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #4 on: October 23, 2006, 04:15:14 pm »

rjd2 wrote on Fri, 20 October 2006 02:43

i was considering bypassing one speaker in an AC30 for the purpose of making it less loud. amp runs at 16 ohms. 2 8 ohm speakers. can i "swap" one speaker for a resistor of the proper value? or is this a generally bad idea? thanks.


I would not rush to assuming that it would work. Speakers are NOT resistors, and the design of a speaker (a very complex device) is not optimized for such a practice. Typically, a driver is low impedance source, and most often there is some series resistance paralleled with an inductor in series, for a good reason. That "network" is near short at low frequencies.

But if you insist doing is with a series resistor, it will have to be a very high power device, rather large, and it will run hot when the signal is high. So be careful not to get burned.

And given that many high power resistors are "wire wound", many such resistors may have too much inductance at the higher audio frequencies, which may further muck with the response...
Will it? At say 10KHz, it only takes 16uH inductance to have 1 Ohm or reactance. I do not know of the top of my head how much inductance to expect, but I would be carfull to be sure that inductance is not a problem...

Some of us pay a lot of attention to matching source and load (amp and speaker in this case). Others view all speakers as being "about the same load". But replacing 2 speakers with a resistor and a speaker? I am not sure it is such a great idea....

Regards
http://www.lavryengineering.com
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Transcending Music

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #5 on: October 26, 2006, 12:43:52 pm »

rjd2,

did you consider a power soak or "hot plate" or even the attentuator suggested by sin x/x ? they work fairly well and keep the loads safe.
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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #6 on: October 26, 2006, 12:58:45 pm »

Transcending Music wrote on Thu, 26 October 2006 17:43

rjd2,

did you consider a power soak or "hot plate" or even the attentuator suggested by sin x/x ? they work fairly well and keep the loads safe.


That would answer only one aspect of the problem, the heat. It still falls short in the area of impeadance matching, and potential inductance issues when using wire wound power resistor.

Regards
Dan Lavry
http://www.lavryengineering.com
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Teddy G.

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #7 on: October 27, 2006, 12:22:11 am »

I must stumble in, here - these kinds of posts and replies hurt my head. I just can't NOT look at them - sorry.

I know I'm not getting it, but, I guess that's what these forums are for - to learn.

Why don't you just turn the thing down? Tone not the same?

Have you tried the little foam widgets you stick in your ears?

Are you using it mic'ed in the studio and can't get the mic far enough away? Can't turn the pre down far enough?

So loud at good tone level it interferes with other instruments in the room? Neighbors can't hear their own lawnmowers running?

Seems like a bit of a pricey gadget to tear into to mess with, anyway, even if it would "work"?

If a non-inductive resistor is the largest stumbling block(I know, it's not, but in the interest of more goofy thoughts, maybe useable in the future...), no reason to look for a single, perfect, resistor is there? One should, with a bit of head scratching and paper and pencil be able to figure out a non-inductive resistor network(Several/many resistors correctly wired together) even if all of the 2 watt variety(1/4 watt if you enjoy soldering.). Hams do this quite often with success, for power levels of hundreds of watts - even drowning the poor little resistors in cans of oil, to absorb the heat. Messy, but....?

Sometimes our questions are a bit goofy in the first place(That's fine, I ask LOTS of goofy ones!) -- and while it is interesting to see everyone jumping in with highly technical talk of the if's and's and but's, sometimes the simple answer is "best", I think.

I must go with "-a" --- go to the store and get the smaller amp.

Move on......


TG

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Transcending Music

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #8 on: October 27, 2006, 05:56:18 pm »

Hi Dan, correct me if I'm mistaken...

The THD hot plate for example dissipates the heat but are also manufactured to match impedance.
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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #9 on: October 27, 2006, 07:47:07 pm »

Transcending Music wrote on Fri, 27 October 2006 22:56

Hi Dan, correct me if I'm mistaken...

The THD hot plate for example dissipates the heat but are also manufactured to match impedance.



Hi,

I do not know that much about it. But looking at their site it says:

"How do I use it?
The THD Hot Plate
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maxdimario

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #10 on: October 28, 2006, 07:15:28 am »

leave it as it is, it won't get much quieter and you won't have the phase cancellation and distortion which comes from running two speakers instead of one (side-by-side).

both acoustically and electronically.
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GoobAudio

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #11 on: October 30, 2006, 05:43:49 pm »

[quote title=danlavry wrote on Fri, 27 October 2006 21:47]
Transcending Music wrote on Fri, 27 October 2006 22:56



Built-in Noise Reduction
The THD Hot Plate
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Spock

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #12 on: October 30, 2006, 10:25:50 pm »

It's been a very long time, but I know it can be done without added too much inductance.  A 100 to 200 watt resistive dummy load for an RF transmitter for 30Mhz or lower would be put in a paint can with mineral oil to help with the heat transfer.
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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #13 on: October 31, 2006, 01:00:12 pm »

[quote title=GoobAudio wrote on Mon, 30 October 2006 22:43]
danlavry wrote on Fri, 27 October 2006 21:47

Transcending Music wrote on Fri, 27 October 2006 22:56



Built-in Noise Reduction
The THD Hot Plate
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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #14 on: November 01, 2006, 03:07:20 pm »

More about wire wound power resistors:

The type of wire itself is much more resistive then say copper, and that is how one gets to build resistance. Say one wants to have 8 Ohms, and the resistive wire used is the type of 4 Ohm per foot. That would call for 2 feet length for 8 Ohms.

But, given that we would not wish to just have 2 feet of wire, it is often being wound around a cylinder made of an insulating material. The standard way to wing is one layer (single row), and that works great for some applications such as DC power, or 60Hz AC line and more.  

The inductance of wire wound resistors in a single row depends on the a "form factor" (it has to do with ratio of length to diameter), the inductance is proportional to the diameter of the windings and most of all on the number of turns (proportional to number of turns square).

Say we have 1 inch diameter, and 5 inch winding length.  
That would yield form factor F=.003.
Say we have 20 turns (windings), then the inductance will be around .003*1*30^2 = 2.7uH

That would yield .339 Ohms of reactance at 20KHz. Such reactance against say 8 Ohms resistive load resistance means a loss of nearly .01dB. So the example above shows a resistance construction that has little effect on audio.

But say we have 2 inch diameter and 5 inch length. That would yield a form factor of around .006.
Say we have 40 turns (windings), then the inductance will be around .006*2*40^2 = 19.2uH
 
That would yield 2.4 Ohms of reactance at 20KHz. Such reactance against say 8 Ohms resistive load resistance means a loss of nearly .38dB. The loss at 10KHz is around .1dB. That may be  audible.

As a rule, the large single winding power resistor can work, but for lowering inductance, one needs to watch for a few factors:

1. Stay with single winding. Multiple winding may increase inductance exponentially.

2. Look for a wire wound resistor with fewer winding.

3. Go for a long resistor, with as small diameter as you can find

Also, consider paralleling wire wound resistors. Say you parallel 2 resistors of 16 Ohms each to get 8 Ohms. The inductance will be also cut by half. The purist may wish to mount the resistors in such a way that the winding directions of the 2 resistors is opposing each other. It should not matter here, but it is a good thing to keep in mind for higher frequency signal applications.

I am still not convinced that a series resistor to a speaker is a good idea. This post is a follow up of the inductance comment of wire wound resistor inductance.

Regards
Dan Lavry
http://www.lavryenginering.com
 
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Jon Hodgson

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #15 on: November 04, 2006, 06:29:14 pm »

[quote title=danlavry wrote on Tue, 31 October 2006 18:00]
GoobAudio wrote on Mon, 30 October 2006 22:43

danlavry wrote on Fri, 27 October 2006 21:47

Transcending Music wrote on Fri, 27 October 2006 22:56



Built-in Noise Reduction
The THD Hot Plate
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iCombs

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #16 on: November 08, 2006, 12:11:38 am »

danlavry wrote on Fri, 27 October 2006 18:47

Transcending Music wrote on Fri, 27 October 2006 22:56

Hi Dan, correct me if I'm mistaken...

The THD hot plate for example dissipates the heat but are also manufactured to match impedance.



Hi,

I do not know that much about it. But looking at their site it says:

"How do I use it?
The THD Hot Plate
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Ronny

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #17 on: November 09, 2006, 02:27:30 pm »



Whatever happened to those 100 watt guitar amps that had the switch that defeated two of the four power tubes to run at 50 watts?

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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #18 on: November 09, 2006, 06:42:23 pm »

iCombs wrote on Wed, 08 November 2006 05:11

danlavry wrote on Fri, 27 October 2006 18:47

Transcending Music wrote on Fri, 27 October 2006 22:56

Hi Dan, correct me if I'm mistaken...

The THD hot plate for example dissipates the heat but are also manufactured to match impedance.



Hi,

I do not know that much about it. But looking at their site it says:

"How do I use it?
The THD Hot Plate
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Jon Hodgson

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #19 on: November 09, 2006, 08:17:03 pm »

From the THD website (my bold)
Quote:

The THD Hot Plate
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iCombs

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #20 on: November 10, 2006, 05:57:26 pm »

danlavry wrote on Thu, 09 November 2006 17:42

iCombs wrote on Wed, 08 November 2006 05:11

danlavry wrote on Fri, 27 October 2006 18:47

Transcending Music wrote on Fri, 27 October 2006 22:56

Hi Dan, correct me if I'm mistaken...

The THD hot plate for example dissipates the heat but are also manufactured to match impedance.



Hi,

I do not know that much about it. But looking at their site it says:

"How do I use it?
The THD Hot Plate
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Lightspeed Group, Inc.
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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #21 on: November 10, 2006, 07:40:49 pm »

iCombs wrote on Fri, 10 November 2006 22:57

My bad...I was talking 110-115+ dB SPL...stage volume.  Loud.  As I said before, I CAN'T speak to the noise reduction...but I don't give a rat's ass, either.  If I want to make my amp less noisy, I'll pick tubes carefully, make sure my cables are good, and make sure my signal chain is properly grounded.  Or I wouldn't turn my gain knob up so damn much.  I wouldn't buy a Hotplate for that purpose.  I've never even so much as looked at THD's lit on the thing...the guys at my local guitar shop (not GC...good high-end/vintage crazy shop...[url

http://www.solidbodyguitar.com[/url]) swear by them, and I've come to trust their opinions on a practical level as they have the time and resources to shake this kind of gear down.    

I cannot speak to the noise reduction issue, but I'd say that it's safe to say that no one thinks "noise spressor" and buys a Hotplate.  That said, perhaps a better look at the circuitry of the Hotplate is in order?


You seem to like the product and that is fine. With electric guitars I expect that people go for a lot of analog type of distortions, nothing new here. In fact, the amp distortion is part of the sound of an electric guitar, and I have no problem with that.

If no one cares about the "noise reduction" aspect, then why do the sellers of the product promote it as a noise reduction tool?

Personally, for me, I do have a problem with 110+spl. I know it is "part of a culture" to go to a rock concert, to a high
school dance and similar, where people blast their ears real bad. The long term outcome for such a short term "pleasure" is pretty sad. It really does not take much time at 110 spl to have permanent hearing loss.

Sadly, I know that my comment will do little good. People like fat food and loud music, and it is often not until after the damage is done that they realize it. This is not a top down lecture. I too did some real dumb things in my life, I was a heavy smoker and I did not eat well. It is sad to see a whole generation of Ipod users be exposed to such loud music.

Regards
Dan Lavry
http://www.lavryengineering.com

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Jon Hodgson

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #22 on: November 11, 2006, 06:22:29 am »

danlavry wrote on Sat, 11 November 2006 00:40

iCombs wrote on Fri, 10 November 2006 22:57

My bad...I was talking 110-115+ dB SPL...stage volume.  Loud.  As I said before, I CAN'T speak to the noise reduction...but I don't give a rat's ass, either.  If I want to make my amp less noisy, I'll pick tubes carefully, make sure my cables are good, and make sure my signal chain is properly grounded.  Or I wouldn't turn my gain knob up so damn much.  I wouldn't buy a Hotplate for that purpose.  I've never even so much as looked at THD's lit on the thing...the guys at my local guitar shop (not GC...good high-end/vintage crazy shop...[url

http://www.solidbodyguitar.com[/url]) swear by them, and I've come to trust their opinions on a practical level as they have the time and resources to shake this kind of gear down.    

I cannot speak to the noise reduction issue, but I'd say that it's safe to say that no one thinks "noise spressor" and buys a Hotplate.  That said, perhaps a better look at the circuitry of the Hotplate is in order?


You seem to like the product and that is fine. With electric guitars I expect that people go for a lot of analog type of distortions, nothing new here. In fact, the amp distortion is part of the sound of an electric guitar, and I have no problem with that.

If no one cares about the "noise reduction" aspect, then why do the sellers of the product promote it as a noise reduction tool?

Personally, for me, I do have a problem with 110+spl. I know it is "part of a culture" to go to a rock concert, to a high
school dance and similar, where people blast their ears real bad. The long term outcome for such a short term "pleasure" is pretty sad. It really does not take much time at 110 spl to have permanent hearing loss.

Sadly, I know that my comment will do little good. People like fat food and loud music, and it is often not until after the damage is done that they realize it. This is not a top down lecture. I too did some real dumb things in my life, I was a heavy smoker and I did not eat well. It is sad to see a whole generation of Ipod users be exposed to such loud music.

Regards
Dan Lavry
http://www.lavryengineering.com




Dan,

I think you're missing the point a little.

Firstly with regard to levels, iCombs was talking about getting the desired tones WITHOUT those levels. The thing is that guitar amps tend to give the best sounds when they are being driven hard, but driving them hard usually means high volumes. One of the aims of units like the hot plate is to attempt to achieve those tones without deafening the guitarist.

Secondly as regards the "noise reduction", the problem with driving guitar amps really hard is that you end up with a lot of noise, this isn't really a problem when you're playing (since it's being masked by a signal that's choc full of harmonics), but is a problem in between notes. Given the choice between two otherwise equally good units, where one can reduce this problem and one cannot, you go for the one which reduces it, hence the feature and hence it goes in the advertising.

The information on THD's site is pretty clear on this, they say it reduces noise BETWEEN notes. It doesn't claim to improve signal to noise ration, because by definition there is no signal when there's nothing being played.

You might argue that their claim of noise reduction is incorrect with regards to engineering terminology, but it is NOT incorrect with regards to the English Language. Noise Reduction is by definition something which reduces noise, and cutting it during periods of silence, even if you do nothing anywhere else, is reducing it.
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Sin x/x

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #23 on: November 11, 2006, 11:28:55 pm »

Jon Hodgson wrote on Sat, 11 November 2006 05:22


The information on THD's site is pretty clear on this, they say it reduces noise BETWEEN notes. It doesn't claim to improve signal to noise ration, because by definition there is no signal when there's nothing being played.

You might argue that their claim of noise reduction is incorrect with regards to engineering terminology, but it is NOT incorrect with regards to the English Language. Noise Reduction is by definition something which reduces noise, and cutting it during periods of silence, even if you do nothing anywhere else, is reducing it.


Just nitpicking:
I think it should be "noise gate", if it reduces noise between notes.


You can also get more output stage (penthode) distortion if the amp has output tubes in parallel. Simply remove 1 half of the tubes and instead of the 8 Ohm trafo output you must use the 16 Ohm output.
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Jon Hodgson

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #24 on: November 12, 2006, 05:45:50 am »

Sin x/x wrote on Sun, 12 November 2006 04:28

Just nitpicking:
I think it should be "noise gate", if it reduces noise between notes.



Well it seems to be a low level expander rather than a gate, but let's face it, most of the target market wouldn't even understand what that meant!

It's not like they're the only ones using this terminology, the Rocktron Hush Pedal appears from the documentation to only be a low level expander (as opposed to the rack system which has a dynamic filter aswell), and they call it noise reduction.

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Andy Peters

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #25 on: November 12, 2006, 11:19:22 pm »

Sin x/x wrote on Sat, 11 November 2006 21:28

You can also get more output stage (penthode) distortion if the amp has output tubes in parallel. Simply remove 1 half of the tubes and instead of the 8 Ohm trafo output you must use the 16 Ohm output.


... or you could just use an AC15.

Surprised

-a
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danlavry

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #26 on: November 13, 2006, 03:15:48 pm »

Jon Hodgson wrote on Sat, 11 November 2006 11:22

danlavry wrote on Sat, 11 November 2006 00:40

iCombs wrote on Fri, 10 November 2006 22:57

My bad...I was talking 110-115+ dB SPL...stage volume.  Loud.  As I said before, I CAN'T speak to the noise reduction...but I don't give a rat's ass, either.  If I want to make my amp less noisy, I'll pick tubes carefully, make sure my cables are good, and make sure my signal chain is properly grounded.  Or I wouldn't turn my gain knob up so damn much.  I wouldn't buy a Hotplate for that purpose.  I've never even so much as looked at THD's lit on the thing...the guys at my local guitar shop (not GC...good high-end/vintage crazy shop...[url

http://www.solidbodyguitar.com[/url]) swear by them, and I've come to trust their opinions on a practical level as they have the time and resources to shake this kind of gear down.    

I cannot speak to the noise reduction issue, but I'd say that it's safe to say that no one thinks "noise spressor" and buys a Hotplate.  That said, perhaps a better look at the circuitry of the Hotplate is in order?


You seem to like the product and that is fine. With electric guitars I expect that people go for a lot of analog type of distortions, nothing new here. In fact, the amp distortion is part of the sound of an electric guitar, and I have no problem with that.

If no one cares about the "noise reduction" aspect, then why do the sellers of the product promote it as a noise reduction tool?

Personally, for me, I do have a problem with 110+spl. I know it is "part of a culture" to go to a rock concert, to a high
school dance and similar, where people blast their ears real bad. The long term outcome for such a short term "pleasure" is pretty sad. It really does not take much time at 110 spl to have permanent hearing loss.

Sadly, I know that my comment will do little good. People like fat food and loud music, and it is often not until after the damage is done that they realize it. This is not a top down lecture. I too did some real dumb things in my life, I was a heavy smoker and I did not eat well. It is sad to see a whole generation of Ipod users be exposed to such loud music.

Regards
Dan Lavry
http://www.lavryengineering.com




Dan,

I think you're missing the point a little.

Firstly with regard to levels, iCombs was talking about getting the desired tones WITHOUT those levels. The thing is that guitar amps tend to give the best sounds when they are being driven hard, but driving them hard usually means high volumes. One of the aims of units like the hot plate is to attempt to achieve those tones without deafening the guitarist.

Secondly as regards the "noise reduction", the problem with driving guitar amps really hard is that you end up with a lot of noise, this isn't really a problem when you're playing (since it's being masked by a signal that's choc full of harmonics), but is a problem in between notes. Given the choice between two otherwise equally good units, where one can reduce this problem and one cannot, you go for the one which reduces it, hence the feature and hence it goes in the advertising.

The information on THD's site is pretty clear on this, they say it reduces noise BETWEEN notes. It doesn't claim to improve signal to noise ration, because by definition there is no signal when there's nothing being played.

You might argue that their claim of noise reduction is incorrect with regards to engineering terminology, but it is NOT incorrect with regards to the English Language. Noise Reduction is by definition something which reduces noise, and cutting it during periods of silence, even if you do nothing anywhere else, is reducing it.


OK, you are correct that they are talking about "reduce the noise between notes". But reduce noise compared to what? The other leading product? It is very unclear to say the least.
Of course as an engineer I would prefer some noise figure or a plot for the unit between notes.  

Clearly, it is not engineering terminology. But it is also poor English description. It took you coming in here to explain to me that someone is trying to do their best to make sure that the tradoff between "tube saturation" (or whatever they use it could be a transformer or even a transistorized circuit) provides an acceptable balanced between saturation when the note is played, and noise between notes.  

You are in fact describing "less noise increase", not noise reduction, and even that is without a referance.

I can see that marketing would rather not say "less noise increase" when they can say "noise reduction". There is no noise reduction between notes. There is possibly "less noise increase" compared to some other product, which may have a lot of value to a user. I do not know all the products on the market. I do think it should be stated in a clearer way.

Regards
Dan Lavry  
http://www.lavryengineering.com
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Ronny

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Re: can i swap a resistor for a speaker in a cabinet?
« Reply #27 on: November 15, 2006, 09:45:52 pm »


Where I come from a basic gate removes noise and is a noise remover, not a reducer as the noise isn't removed but eliminated below threshold. However it only works when there isn't any keeper material, so it's effective at removing 60 cycle hum and the higher noise floor that amps exhibit in between notes where John correctly stated the noise is typically masked by the loud keeper notes, but the gate is never activated when the keeper notes are present, so noise removal does not take place while the guitar notes are sounding, otherwise it would remove the keeper notes. Modern gates have range settings which allow the gates to act like a low level expander. They attenuate the signal relative to range setting and thus are not true gates which mute the total signal route. Technically the Hot Plate folks are not gating if they are attenating the signal in between notes and I agree it points to a downward expander, which pushes low level signals down while leaving the main levels intact. Typically noise removal is a gate, whereas noise reduction can be based on various parameters from narrow band eq cuts where the noise range resides, to dynamic expanders that reduce noise on the broadband by attenuating lower levels at all frequencies. If the circuit has an expander involved that attenuates low levels by -10dB, than it qualifies as noise reduction.
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