Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on October 18, 2013, 03:37:47 am

Title: Keeping it clean
Post by: TIMBO on October 18, 2013, 03:37:47 am

Hi guys, I need to make some adjustments to the Hudson SJ. I'm wanting to keep the clean channel clean at higher volume.

This is what I have .......
The required sound is a BOSS DS1 into the clean channel but to keep it from sounding crap the clean gain has to be kept at a low volume, this then is robbing the overall volume of the amp with the master turned up.
I suggested that he turn down the volume a bit on his guitar to clean up the signal.

Looking at the circuit, is there away to keep the clean, clean even with the gain turned up. Thanks

Title: Re: Keeping it clean
Post by: stratele52 on October 18, 2013, 04:01:14 am

Can't open your schematic.

Title: Re: Keeping it clean
Post by: tubenit on October 18, 2013, 04:46:11 am

I indicated where I would experiment to increase clean.

Starting place for me would be to use a 5751 or 12AY7 in V1

with respect, Tubenit

Title: Re: Keeping it clean
Post by: ac427v on October 18, 2013, 08:10:02 am

I notice that V2b has a 220k plate resistor and a 470 cathode resistor. Would more traditional values clean up that stage?
Craig

Title: Re: Keeping it clean
Post by: jjasilli on October 18, 2013, 09:11:15 am

The first place I start is at the 1st gain stage.  It sets-up the performance of the rest of the amp.  Still, prior posts are all good points, and may get you where you want to go.  Back to the 1st stage, it's is set for pretty hi gain.  What we want is a production of a taller sine wave that doesn't clip or go non-linear.  This can be achieved by changing the operating point of that stage.  Some suggestions:

*  If the plate voltage is high, drop it to around 150 - 180 VDC.
*  maybe eliminate the cathode bypass cap.
*  drop the value of the cathode R to 1500 or even 820 ohms.  The latter value should allow the stage to accept a signal voltage of up to about 1VAC without distorting.  See, "Dave Funk's Tube Amp Workbook".

If modding the 1st stage is insufficient, then I'd follow-up with other options downstream. 

But, modding the 1st stage may reduce overdrive production in the gain channel.  This might be cured with higher gain mods there, or a 12BZ7 tube in a slot after the first position.

Title: Re: Keeping it clean
Post by: sluckey on October 18, 2013, 09:33:44 am

Quote from: stratele52 on October 18, 2013, 04:01:14 am

Can't open your schematic.

Read this...

http://www.el34world.com/Forum/index.php?topic=11457.0 (http://www.el34world.com/Forum/index.php?topic=11457.0)

Title: Re: Keeping it clean
Post by: PRR on October 18, 2013, 01:14:08 pm

 Re: Keeping it clean
 
I don't see any "clean" path through that amp? It always has diodes hanging off it.

Snip the diodes, see if that suits your Clean needs.

Title: Re: Keeping it clean
Post by: TIMBO on October 18, 2013, 05:23:15 pm

Thanks guys, some good things to try.

PRR, this is the circuit, I added a bypass sw. as I am not a great fan of the clipping circuit. Thanks