help with blocking distortion

[joesatch]

is it blocking distortion and how to cure it? i've swapped out all the tubes, cleaned the pots and connectors. Cap cans are new. it's not the speaker i've tried different cabs. noise is on both channels

http://youtu.be/5ABeJEzZaE0

[HotBluePlates]

is it blocking distortion and how to cure it? ...

http://youtu.be/5ABeJEzZaE0

It's distortion.  It's also a Marshall-style amp with the Volume turned up about halfway, which means it's "normal."

If you don't want the amp to distort, turn the Volume control down.  I don't mean to sound snarky, it's just that there's nothing abnormal here, and nothing to "fix."

[Latole]

What about Power Supply voltages ?

[HotBluePlates]

What about Power Supply voltages ?

More specifically, you're not running the amp on a lightbulb-limiter or the like, right?

[joesatch]

no limiter. variac's @120v the EL34 plates read 465v and bias is 37ma per tube. i'm used to 800's more than these old 4 hole marshalls the dist is weird it comes on like a buzz then goes away when the note dies down. the 800's stay distorted throughout. still not sure this is normal

[joesatch]

this was someone's "project amp".  never seen this before. the 1 ohm bias resistor and speaker ground soldered to the bolt tip..

[Ronquest]

And no heater wires (pins 2-7)!  Unless you pulled those off.

[d95err]

is it blocking distortion and how to cure it? ...

http://youtu.be/5ABeJEzZaE0

It's distortion.  It's also a Marshall-style amp with the Volume turned up about halfway, which means it's "normal."

If you don't want the amp to distort, turn the Volume control down.  I don't mean to sound snarky, it's just that there's nothing abnormal here, and nothing to "fix."

I agree with this. I can't hear anything out of the ordinary in the YouTube clip. Nothing harsh or non-musical that I'd expect from blocking distortion. I think it sounds pretty good!

Perhaps the clip doesn't do the problem justice? Could be YouTube compression and artefacts masking the issue.

[Ronquest]

I agree with this. I can't hear anything out of the ordinary in the YouTube clip. Nothing harsh or non-musical that I'd expect from blocking distortion. I think it sounds pretty good!

Perhaps the clip doesn't do the problem justice? Could be YouTube compression and artefacts masking the issue.

Youtube doesn't compress like that, I hear this said all the time.  People say that youtube messes up their recording by compressing.  Most people's recordings are messed up before youtube gets a hold of it.   Test it for yourself, upload a recording then download it and A/B the original and the youtube version with levels matched.   Now if you listen to youtube at 24kb vs 320kb, then of course the quality will suffer, but who listens at 24kb?

I guess I hear things different than others, as I wouldn't except whats going on here with that amp.   Whether the circuit is proper or not, it sounds good, till it's bad.

 

[66Strat]

Sounds good to me.   I don't hear any blocking distortion. Maybe you just miss the JCM 800 fizzzzzzzzzz.

[JPK]

... 

[joesatch]

well i've done all the evh plexi mods to the amp and you folks were right it was fine. Adding a 5500pf treble cap and 50k mid pot really got it close to where it needs to be. Variac'd at 90 volts then rebiased it is sounding really good. http://youtu.be/ZlOVX5328Hw

[Ronquest]

How did we go from is this blocking distortion to 90V EVH mods?

[joesatch]

How did we go from is this blocking distortion to 90V EVH mods?

stayed up late

[Ronquest]

stayed up late

LOL

[HotBluePlates]

... i'm used to 800's more than these old 4 hole marshalls the dist is weird it comes on like a buzz then goes away when the note dies down. the 800's stay distorted throughout. still not sure this is normal

100% normal for a non-master-volume Marshall.

The JCM800 has a lot more gain in the preamp, and it is used to slap a preamp stage silly and make it distort.  The signal form the guitar does down, but not enough to cause that preamp stage to clean up (which only needs a couple-volts of drive signal to distort).

The amp you're messing with is distorting the output tubes first, and they need something like 40-50v of drive signal to cause them to distort.  With the Volume only halfway or so, loud transient of the guitar distorts, and when the signal tapers off the output tubes stop receiving a drive-signal large enough to make them distort.

All this is normal, expected behavior for each of these very-different types of amps.