Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on October 16, 2011, 11:35:21 am

Title: MASTER VOLUME HARSH DISTORTION
Post by: Colas LeGrippa on October 16, 2011, 11:35:21 am

Hi everybody !

In a SE amp ( KT77) I have put a master volume ( 1 meg ) just b4 the power tube control grid ( pin5 ) that works fine. But to my taste, I find that the distortion is not as good as it could be. The ''grain'' of it is too coarse if you see ( hear, rather, hey hey ) what I mean. All the voltages and tubes are good and the amp is noiseless, very stable. I was wondering if something simple could be done to cure the ill or if one of you people have a preamp schem proven to give good distortion , in a SE amplifier.

Cheers !

Colas

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: stratele52 on October 16, 2011, 03:16:38 pm

And with no master vol , how is the distortion ?

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: Colas LeGrippa on October 16, 2011, 04:40:48 pm

no distortion, unless volume at 10 or so.

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: tubenit on October 16, 2011, 04:42:25 pm

Colas LeGrippa,

If you can post a schematic, I think we could offer some suggestions.  

IF you're using 22uf or 25uf cathode caps on 12AX7's, then the first thing I'd do too lessen the coarseness is lower those to 22.uf - 5uf range and also lower the cathode resistor value.

For example,  instead of 100k (plate)/ 1/5k & 22uf ................ I'd use 100k/1.2k & 5uf and then see how that sounds to you?

This may be more complicated than you want, but this is the Carolina SongBird amp that I built. If it sounds smoother than what you have and isn't more complicated than you want to fool with, ........ you could consider it. The schematic is in the SCH library. It has two 12A_7  tubes.   http://www.el34world.com/Forum/index.php?topic=11889.0 (http://www.el34world.com/Forum/index.php?topic=11889.0)

http://www.soundclick.com/player/single_player.cfm?songid=10819072&q=hi&newref=1 (http://www.soundclick.com/player/single_player.cfm?songid=10819072&q=hi&newref=1)

With respect, Tubenit

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: tubenit on October 16, 2011, 05:38:53 pm

I posted this a while back just showing some examples of what I do to increase the smoothness. The soundclip in the above post is an example of what I find to be a reasonably smooth tone for a SE amp.

With respect, Tubenit

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: Colas LeGrippa on October 16, 2011, 06:26:56 pm

Thanks to you, Tubenit, I'll try the mods and get back to you.

best regards

Colas

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: Colas LeGrippa on October 17, 2011, 10:23:47 am

Hi,

I have found that putting a .001uF accross the cathode follower 100K plate resistor combined with reducing V1 cathode bypass cap from 25uF to 4.7uF helped  A LOT in reducing harsh distortion that my amp suffered from. In fact, now, I play my amp straight , no pedal, the tone being so pleasant to hear. With the preamp vol to 10 and the MASTER to taste ( taste to my neighbour, I mean hey hey ), I get just the right crunch tone I was after.
 :worthy1:

Regards

Colas LeGrippa

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: tubenit on October 17, 2011, 11:49:12 am

You're a fantastic guitarist & I'm glad you've got it closer to what you are wanting!  Very cool.  Thanks for sharing the results.

With respect, Tubenit

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: Colas LeGrippa on October 17, 2011, 12:32:34 pm

Thanks for the compliment and for the tips

Regards

Colas

Title: Re: MASTER VOLUME HARSH DISTORTION
Post by: stratele52 on October 17, 2011, 05:15:09 pm

tubenit , your amp Carolina songbird, sound very good, congrat.