Clipped the .002uf cap on bassman 10 and got major distortion

[sleepingAwake]

This schematic http://www.webphix.com/schematic%20h...n_10_schem.pdf indicates that the original speakers were 32 ohms each, wired in parallel to achieve a total of 8 ohms.
How did you connect your 8 ohm speakers?

Series parallel

[g1]

Usually an 8 ohm speaker will measure less than 8 ohms on the meter (around 5 to 6 ohms DC resistance). A series parallel arrangement of four 8 ohm speakers should read the same. I would expect a 12 ohm meter reading from a 16 ohm impedance load. Check for open or miswired speakers.

[sleepingAwake]

Usually an 8 ohm speaker will measure less than 8 ohms on the meter (around 5 to 6 ohms DC resistance). A series parallel arrangement of four 8 ohm speakers should read the same. I would expect a 12 ohm meter reading from a 16 ohm impedance load. Check for open or miswired speakers.

I'm really more concerned with my question from earlier. I'll check my wiring but it may be due to some sort of hybrid of series parallel wiring.
I'm looking at the spec sheet for the speakers I've have and it lists them as 11.4 ohms. Weird I know.


Does anyone have any more input on this?

I just noticed something else. On the Bass channel the "Bass" knob has hardly any effect on the tone. You have to strain to tell the difference between 1 and 10 on the knob.
Maybe that might explain why the Studio channel has so much lower "boom". Like I said the studio channel actually pushes the air around you. The bass channel not at all.

I read somewhere that the bass channel has a LF cut to keep bass players from blowing out speakers back in the days these amps were produced.

[sleepingAwake]

Would raising the value circled give me more low end response? 330pf seems awful small.

[Enzo]

I'm not sure that the brightness cap is the place to look for bottom end.

[sleepingAwake]

I'm not sure that the brightness cap is the place to look for bottom end.

Adding capacitance there with a jumper did give me more lows.
That's the deep switch on the bass channel.
Not the high freq bypass cap on the bright switch.

Is there a better spot on the bass channel to be looking more low freq responses and maybe some high overtones.
The tone stack doesn't look like a typical bassman and I'm still learning so signal path eludes me.

[sleepingAwake]

Well I tried some stuff and got more lows but loss some clean headroom in the process.
Brightened up the channel as well.
I noticed the heater voltage is low as well at 5.89V.

I took out a cap that bypassed the 100k resistor and moved over to the bass pot. Mostly because out of the ones I tried it brought the most lows.
Take a look and please provide input as to how I could do it better.

[sleepingAwake]

I guess I'll respond to my own question.
I've found putting the .001uf cap back in helped regain headroom. It was probably sending some mid and bass freqs to ground.
Replacing one of the caps on the bass pot with a .0047uf cap has given the bass pot some actual adjustment and gives the amp more bass.
There are still some sub-bass freq and mids that I would like to kill as it is causing some muddiness but I'm just not sure how to go about it.
I believe its all a matter of adjusting the signal V1B sees as I think its getting to hot a signal over some frequencies

.

[Tom Phillips]

It's good that you are experimenting but I suggest that, to progress, you will do well at this stage to learn more of the theory behind the design and voicing of pre-amps. A good source would be Merlin Blencowe's book "Designing Tube Preamps for Guitar and Bass" and/or the TUT series from London Power. You can also download "Duncan's Tone Stack Calculator" and use it to get a feel for the effect of value changes to the various components in the tone stack. All these will be easy to Google. I think you will enjoy the modification work you are doing a lot more once you have a better understanding of the theory. Regards, Tom

[sleepingAwake]

I'll check out the reading suggestion Tom.
I'm a bit disappointed with gerald webers book. I found it repeated the same info over and over again.
It could have been half the size it was.

I did download the tone stack calculator the other day but since the bass channel on the bassman 10 differs it isn't helpful to me at this point.

[pdf64]

You may be finding out why that bass channel tone control arrangement isn't popular.
Consider using the regular arrangement as per the studio channel, but tweak a few values, eg 33nF or 68nF for the mid cap, 150 or 330pF for the treble cap.

[sleepingAwake]

You may be finding out why that bass channel tone control arrangement isn't popular.
Consider using the regular arrangement as per the studio channel, but tweak a few values, eg 33nF or 68nF for the mid cap, 150 or 330pF for the treble cap.

Yeah it's completely backwards from a normal fender tone stack.
I thought about changing it to a AA864 tone stack.

[Tom Phillips]

...I'm a bit disappointed with gerald webers book...

Well...suffice it to say that the Weber content in that book is not a bible of correct information.

...I did download the tone stack calculator the other day but since the bass channel on the bassman 10 differs it isn't helpful to me at this point.

Understood. However the calculator will still show you the general effect of value changes of the tone stack components. Did you use the feature that allows you to change the values?

I'm not sure what your level of experience is. There are good free downloads available of old books. The advantage of the recommendations I made is that they are specific to musical instrument amplifier applications. Take a look at the sample articles on the Valve Wizard site ( How to design valve guitar amplifiers )and let us know if the technical level is right for you.

Regards,
Tom

[Enzo]

Weber's book is interesting but not very educational. Too often you get "move this here,and change that there' advice without showing the schematic changes nor explaining why they work. The book is basically a how-to guide to modifying your amp without learning anything. I recommend them as later reading, after you know enough to sort out which parts are baloney.

[sleepingAwake]

I looked through the website Tom and I can say that some of theory is above my head at this point but I can get a grasp on certains function of a valve.

Trouble is I'm a hands on learner. Reading about a subject isn't the best way for me to learn about it.
But it's what I got for now.

The Bassman 10 bass channel seems to employ the reverse of your standard Bassman tone stack. It looks like there is a high pass filter on one side of the bass pot and then a cap to filter more highs on the other side???
Trouble is stock that pot sounded the same no matter what you set it to.