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Old 27th April 2015, 10:04 PM   #1
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Default Orange and Other Amp Design Features

My son mentioned Orange amps to me about 8 years ago and since most guitar amps more or less copy the usual stuff I found it interesting that there were a few different features:
Here is the Orange 120, note the FAC control, and the dual Master volume pot right before the power tubes, interesting that it is inside the feedback loop:
http://www.orangefieldguide.com/OFG_...geotrschem.gif

The FAC control makes a lot of sense to high pass the signal and protect speakers that cannot handle much bass, or just to reject out of band garbage.

Is overdriving the output stage driver a good thing for distorted tone, it should only provide odd distortion if it is well balanced.

Thoughts?
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Old 27th April 2015, 10:29 PM   #2
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Here in the Tiny Terror is another interesting feature, the main input gain is done with a dual pot at the input and output of the second stage:
http://elektrotanya.com/PREVIEWS/634...rror.pdf_1.png

This is talked about in system design, do you put a volume control at the input, output, or both? If it is at the input you get the best resistance to overload, for a given Master gain setting, but the worst signal to noise ratio since all of the stages noise is wide open to the output.

If the pot is at the output you get the worst overload margin since the amp stage sees all the signal, but the best reduction of noise because turning that volume down also attenuates the noise in that stage.

A better performing option is to put pots at the input and output, if you just crack the volume open, you get lots of dynamic range because of the input attenuation AND low noise because the output pot is attenuating much of the stage noise. This is perfect for a clean channel and if you just crank it full, and turn down the Master volume then it is no different than any other pot arrangement.
You would use a dual linear pot in this situation since the combination approximates an audio taper.

This amp also has Master gain right in front of the power tubes.
Neither has feedback around the power amp.
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Last edited by PB2; 27th April 2015 at 10:58 PM.
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Old 27th April 2015, 10:53 PM   #3
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I seem to remember seeing the odd biasing arrangement shown here in the Soldano SLO-100 in V2b with 100K plate and 39K cathode load:
http://www.4tubes.com/SCHEMATICS/Mus...0/slo100_1.gif

That is a very odd value for the cathode resistor, it is a highly imbalanced phase splitter.
I seem to remember seeing those exact values in a Marshall amp but can't find it now.

Anyone know if this provides some good distortion? It is in the dirty channel.
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Old 28th April 2015, 01:55 AM   #4
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Yeah talking about the Post phase inverter Master Volume, been wanting to do it, but need order the dual ganged Pot/resistors. With that said I, heard some amps with them, sounded pretty good while others sounded really weird with it, like all bloated...
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Old 28th April 2015, 01:58 AM   #5
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Quote:
Originally Posted by PB2 View Post
I seem to remember seeing the odd biasing arrangement shown here in the Soldano SLO-100 in V2b with 100K plate and 39K cathode load:
http://www.4tubes.com/SCHEMATICS/Mus...0/slo100_1.gif

That is a very odd value for the cathode resistor, it is a highly imbalanced phase splitter.
I seem to remember seeing those exact values in a Marshall amp but can't find it now.

Anyone know if this provides some good distortion? It is in the dirty channel.
220k plates and that plate bypass is the real deal, telling you haha, as far cathode and if bypass or not, mess around with it to what you like I guess.

Last edited by AudioFreak88; 28th April 2015 at 02:01 AM.
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Old 28th April 2015, 04:08 AM   #6
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Quote:
Originally Posted by PB2 View Post
This amp also has Master gain right in front of the power tubes.
Neither has feedback around the power amp.
Not sure why I wrote that, the 120 DOES have feedback around the power amp.
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Old 28th April 2015, 04:57 AM   #7
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Quote:
Originally Posted by PB2 View Post
Not sure why I wrote that, the 120 DOES have feedback around the power amp.
It has way too much Feedback for my Taste, I would change that real quick. and wow all them 68nF couplings 150k feeds, thing has to be bloated/overly bassey/sluggish.

Last edited by AudioFreak88; 28th April 2015 at 05:15 AM.
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Old 28th April 2015, 01:22 PM   #8
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Quote:
Originally Posted by PB2 View Post
My son mentioned Orange amps to me about 8 years ago and since most guitar amps more or less copy the usual stuff I found it interesting that there were a few different features:
Here is the Orange 120, note the FAC control, and the dual Master volume pot right before the power tubes, interesting that it is inside the feedback loop:
http://www.orangefieldguide.com/OFG_...geotrschem.gif

The FAC control makes a lot of sense to high pass the signal and protect speakers that cannot handle much bass, or just to reject out of band garbage.

Is overdriving the output stage driver a good thing for distorted tone, it should only provide odd distortion if it is well balanced.

Thoughts?
Another interesting feature is that they chose the cathodyne PI. They usually use this type for lower powered amps where the power tubes don't need as large a signal to drive them, like EL84 amps
The cathodyne tends to produce different signals from the outputs since one almost is like a cathode follower and one is like a normal gain stage. This will give the power tube pairs different drive signals and produce more even order harmonics with the tubes operating at different drive conditions. I think they did that by design. This way, they can get pleasant overdrive without blowing out your eardrums and then if you want over the top sounds, then dime the volume. Also, it is interesting that they didn't use a grid stopper on the cathodyne input.
I rebuild old Hammond organ amps and this is the same place they use to inject the feedback, although it doesn't come stock with any contols, so I can choose what I want for them. I add changeable FB values for different sounds.
One question, aren't almost all post PI MVs inside the FB loop? You say it is interesting that it is there.

Last edited by boobtube; 28th April 2015 at 01:29 PM.
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Old 28th April 2015, 01:52 PM   #9
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Originally Posted by boobtube View Post
One question, aren't almost all post PI MVs inside the FB loop? You say it is interesting that it is there.
Well, yes if there is feedback and there is a post PI MV then it would be inside but do you know of any other amps that do this?
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Old 28th April 2015, 03:09 PM   #10
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Triode Elecrtonics,Ceriatone, MetroAmp and Trinity all offer an add on mod or sell it with their kit. I don't have the time to pour over the thousands of older schematics to see who did this. Not sure why it is important. But it seems as though most of the older amps used the pre PI MV. Much less work and don't have to use a double-gang pot. When it comes down to saving production costs, many decisions are made by the bean counters, especially 1965-1985, the CBS years at Fender and the Rose-Morris years at Marshall. Cliff Cooper and the rest at Orange didn't have these constraints.

Last edited by boobtube; 28th April 2015 at 03:19 PM.
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