Asteroid unpleasing distortion

[arjepsen]

Hey guys.
A little while ago, I built an asteroid/Komet 60 type amp.
The circuit is the same apart from an "upgraded" fast/gradual switch, and a LarMar type ppimv.
I really wanted to love this amp, particularly since I built it after having heard the demos by Simon Gotthelf:
https://www.youtube.com/watch?v=bEGgqxAyKNk

Unfotunately I can't quite get those tones. I can hear it's in the right direction, but definately not there yet.
The thing that annoys me the most, is an "effect" I'm not quite sure what is. (blocking distortion? Crossover?)
Let me try to describe it:
I've tried to set up the amp the way Simon shows in his video. When I hit a note, there some distortion on it - not bad in itself, but it doesn't fade away gradually - instead, as the note slowly gets quieter, the distortion ends rather abruptly, often in a kind of "grainy" way. The distortion also has a kind of buzziness to it, that I wonder whether is part of the same thing.
Anyways, anyone got any good tips from these descriptions?

Regards
Anders

[Reeltarded]

What you described could very well be blocking distortion.

Could you post even a 10 second clip of it?

Also, what are you using for grid stoppers?

[arjepsen]

Gridstoppers on the powertubes are 820R, as in the schematic. Currently I'm using SED 6l6. I've tried various other tubes (JJel34, JJel34II, JJkt77, SED EL34, EH 6ca7), and all have the same problem, with the 6l6's being the least "offensive".
I'll see if I can make a clip tonight.

[Stevem]

If the amp has a feedback circuit then try totally disconnecting it or limiting its voltage feed back to the PI section.
Either way after doing this you may need to cut back on the drive level into the PI ,or reduce some unneeded gain in the preamp section.
Distortion issues like this and how fast a amp with feedback goes in and out of clipping when driven hard enough is why I hate amps with a feedback circuit other then amps for pristine clean sounds that have tons of reserve wattage!!

[Reeltarded]

stopping the early stages (maybe more than you'd want) does lots of good in some situations

I have used anything from 18k-220k on drive stages

[arjepsen]

Here's a quick noodling - hoping it shows what I mean.
https://www.dropbox.com/s/wuq3tc6wu806t ... p.wav?dl=0

Amp settings:
Gain, treble, mid, presence: 1 o'clock
Bass: 11 o'clock
HiCut: between 2-3 o'clock.
Biasing: 32,2 & 37,8 mA @ about 485V on the plates

It's a strat type guitar, neck+middle pickup (fralin vintage hots)

Here's a couple of gutshots:
https://www.dropbox.com/s/crojr1c4q4x9q ... 8.JPG?dl=0
https://www.dropbox.com/s/nsazy6bxk9mw6 ... 9.JPG?dl=0

[Roe]

Try grid resistors on the phase inverter

[arjepsen]

ok, tried putting a 10k stopper on the PI. (between the 1m, 220K/330K junction and the grid pin.)
Couldn't really tell the difference - the harsh raspy fade-out is still there.

[Reeltarded]

Yeah, that is tiny.. not much expected but a little cleanup if any

Try like 33-68K on the second stage

[Reeltarded]

Does almost soound like raw dump on a middle stage.. hmmm

[arjepsen]

Not sure I understand what that is - can you elaborate?

[Reeltarded]

Driven stages just need a little mediation from the preceding stage(s).

I would stop all drive stages up to the PI with a 33k on each and see if that totally fixes it. Input stage included..

If that works, we can back out of it with lower values working from the PI toward the input until you are happy.

The frequencies affected should never never be heard anyhow with little stoppers. Those amps have a ton of face. We are just knocking a little bit of the surprise out of the eyebrows.



I really need to build my Asteroid.

Do your voltages match closely with the expected ones from whatever your source was? I can't wait to hear it when it gets sweet like the example you posted from youtube. That is the very vid that made me want one.

[arjepsen]

I just put together a spreadsheet with my voltages, and the voltages that others have reported, in the package documents I recieved in here.
Here's a link for my spreadsheet:
https://www.dropbox.com/s/xeysvdeitkjr6 ... .xlsx?dl=0

[arjepsen]

I have to confess, I'm a little worried about loosing the "chime" I hear in Simons demo, but I'll try the stoppers and see.

[Stevem]

While your playing around you might try adding a 350K 1/2 watt resistor from the plate of the output tube back to the plate of the PI.
This will cut back on the saw Tooth nature of the clipped output wave and make if far more square wave.
You will loose a tad of output power though!
You can go Down to about 200K with this resistors , or up to 470K if you like.