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Old 31st August 2013, 07:05 PM   #1
oshifis is offline oshifis  Hungary
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Default Sweet distortion

Distortion gives the spice to many instruments, and there are distortion pedals around. I never heard of a real Leslie rotary speaker but I read tubes and moderate overdrive gives its characteristic sound. Overdrive and distortion was also used by Jon Lord through Marshall speakers, and I always admired its magnificient sound.
Now I have a small guitar combo and a rotary speaker emulator, both having an ECC88 (12AX7) tube for the overdrive effect, but neither satisfies my taste. The overdrive on both devices becomes harsh and roughly distorted at a given point, not so sweet and soft as I expected. I expect musical, enriched harmonic content.
Is there any way to reach that desired sweet, soft distortion with some simple trick with the tube?
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Old 1st September 2013, 01:31 AM   #2
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The ECC88 (6922) is not a 12AX7 (ECC83). Two totally different tubes with different characteristics. Which one is it?
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Old 1st September 2013, 05:18 PM   #3
oshifis is offline oshifis  Hungary
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Sorry, I made a typo. I mean ECC83 that is most frequently used in guitar amplifiers. The typo came from the fact that I use ECC88 (6DJ8) in my hifi gear overall.

I also heard that the PSU of guitar amplifiers is undersized and this contributes to the typical distortion.
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Old 1st September 2013, 06:06 PM   #4
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Quote:
Originally Posted by oshifis View Post
The typo came from the fact that I use ECC88 (6DJ8) in my hifi gear overall.
Interesting?, the ECC88 was an RF (VHF) double triode, where as the ECC83 is a high quality audio double triode, specifically made for HiFi systems.
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Old 1st September 2013, 08:41 PM   #5
tinitus is offline tinitus  Europe
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Originally Posted by oshifis View Post
Overdrive and distortion was also used by Jon Lord through Marshall speakers, and I always admired its magnificient sound.
ahh, Jon Lord ... he happens to always be pulling that big funny organ around everywhere he go

what is your instrument ?
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Old 1st September 2013, 09:49 PM   #6
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The type of speaker that you are using can also greatly attribute to the kind of sound that you are getting.

For instance I have a little (Marshall) Park practice amp (solid state) and it can distort rather harshly when the output (TDA2030) starts to go into clipping.

With the original 8" speaker it is hardly noticeable and has a nice smooth creamy sound and even when it is driven very hard in to clipping and it is still not as noticeable.

But when I hook it to a pair of some really old Jensen special design 12's that I have, The harshness really comes out and changes the whole feel of how the distortion sounds.

They are quite bright and that particular model that I have has been noted as such from what I have read.
Sorry, I don't have the model number of them handy at the moment.

Maybe you can change the gain of the preamp stages as well.
I have an old Knight P.A. unit that has EL34's for outputs and it is a very clean sounding amp and when I drive it hard it becomes very harsh sounding as well.

It uses the very same 12AX7's that my Marshal 8100 Valvestate used.
Only that the Marshall only had one tube in it and to this day it was best sounding distortion I have ever heard through my speakers.

I was curious to find out why this was.

So, I got my scope out and I found out that the Marshall's tube circuit gave a completely different type of waveform than what I was expecting.

It was not your typical flattop clipping that I had found in my overdriven Knight amp that I had used a Fender Vibro Champ preamp to drive it with.

It was completely different and resembled more like the signal was run through a half wave rectifier with a rounded peak and square bottom with some spikes leading and lagging the bottom flat part of the waveform.

I totally did not expect to see that this type of waveform was giving me this Ohh Sooo Sweet Sound!!!
I was expecting more of a very clipped and sharp square wave.
Or, at least one with rounded corners!

If you look up the schematic you will find that a lot of designs use basically the same type configuration for the distortion stage.

After that the tone stack makes a big difference in the tone as well.
It is amazing as to how much it changes the waveform as well.

You never mentioned what kind of EQ you are using.
Even a simple muti-band graphic equalizer in line can maybe taylor out some of that harshness.

FWIW

jer
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Old 2nd September 2013, 01:11 PM   #7
oshifis is offline oshifis  Hungary
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Originally Posted by tinitus View Post
what is your instrument ?
I am not a musician, just a beginner playing around at home. I have an AXL/Johnson T-15R guitar amplifier with a tube input stage, and I wonder what is the secret of that nice sound. The answer is probably: money
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Old 2nd September 2013, 02:31 PM   #8
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by oshifis View Post
I have an AXL/Johnson T-15R guitar amplifier...
looks cool

Quote:
Originally Posted by oshifis View Post
......wonder what is the secret of that nice sound. The answer is probably: money
it does not appear to be expencive

but probably more like ... built with experience
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Old 2nd September 2013, 02:55 PM   #9
Jsixis is offline Jsixis  United States
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I had a friend who was a phenomenal guitar player and she had one of the better ears around when it came to guitars and distortion. She had a few marshall amps some peavy's and fenders. I had lots of 12ax7's of various brands and we would spend a few hours each month rolling tubes.
I learned that almost every amp behaves differently. Some of the amps 1 tube would make a large difference, other amps changing tubes made no difference.
Power tubes were the same way. Overall we learned that a smaller amp like her subway rocket which one could crank up was easier to get that fat overdrive sound out of just because it didn't blow your ears off like those 50 watt marshals and 100 watt peavey's.

If I had known then what I know now I would have bought a Peavey Classic 30 head instead of the classic 50.

Speakers as previously stated do make a difference.
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Old 2nd September 2013, 09:32 PM   #10
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The original Peavey Classic was one Awesome amp!!!
I have no idea as to what speaker they put in them back then.

It is mostly all in the preamp though.
When I blew out the output stage of the Valavestate 8100 and would just run the preamp out into on of my other bigger power amps and still got that incredible sound!!

Yes, I tried different tubes too and it sometimes made a big difference!!!
Especially between the different versions of the AU7's,AT7's and AX7's.

Because I was so moved by the sound of the 8100, I am going to build just the preamp stage to use with my rig like I used to do, rather than replacing the whole head like the one that got stolen from me as it is just some TL07x opamps and a tube!!

jer
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Last edited by geraldfryjr; 2nd September 2013 at 09:39 PM.
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