To much bass on Normal channel

[Kesi on guitar]

Hi,

The maintenance on the Hohner amplifier is almost finished.
New filter caps, a few resistors, clean potentiometers and a few new 6p14p ev.

It's a shame someone ever removed the reverb driver to make room for 12 inch speakers. But the sound is fantastic and I'm falling more and more in love with it.
Except for one thing and that is that the normal channel has a lot of bass. Boomy. I set the pot between 1/2 and 1. More is too much. The vibrato channel gives a normal response with bass.
Does anyone have an idea to improve this?

 

[Paul G.]

Did you read the first stage coupling cap as 6.7nf (.0067uf)? With a 500k volume pot, this value should roll off at 100Hz.

 

[Kesi on guitar]

Did you read the first stage coupling cap as 6.7nf (.0067uf)? With a 500k volume pot, this value should roll off at 100Hz.

Hi Paul,

Do you mean that 4,7 nf cap?
I allready replaced one of them. They are oke

 

[Paul G.]

Hi Paul,

Do you mean that 4,7 nf cap?
I allready replaced one of them. They are oke

Yup that's the one. I got nothing else.

 

[tubeToaster]

try reducing the V4 cathode bypass cap from 25uf to 2.2uf or 1uf.
also try completely removing the V5 25uf cathode bypass cap.

 

[Lynxtrap]

Partly, it's the way that Vox tonestack works. Frequencies around 200-400Hz are pretty much unaffected by the bass pot down to about 2 on the dial.

You best bet is probably the V4 cathode bypass cap as suggested, but you can play around with the tonestack values:

TSC in the web

For instance, a higher value C3 will shift the mid dip down into bass territory.

 

[Kesi on guitar]

I tried a 10uf on v4 tonight as you suggested.
It was a small improvement, but against that the vibrato channel was now completely empty and sounding in the background. So I put the original back.

Later I was thinking, the reverb dimension pot is not in function anymore, it is an idea to place a middle pot on that spot. Would improve that something? Or is that difficult with a vox like tone control?

 

[Sea Devil]

I would be very tempted to recreate the reverb circuit in a separate box and stick it and the reverb pan wherever they fit. It seems to come before everything else, and the rest of the circuit is presumably designed with that in mind. Maybe a pan that can sit vertically would be required, depending on the available real estate in your cab. (I don't read schematics very well, but wouldn't that affect the Normal channel even if it doesn't have reverb? I know my old BF 6G15, designed as a front-loader, sucked out a lot of bass. Even if it doesn't affect the normal channel, it would be a good idea to get the amp sounding the way it was meant to, and it was meant to have reverb! And of course, if it did, you'd never play the normal channel anyway.)

 

[2L man]

Test a bypass capacitor for V1. It increase highs so you must turn guitar volume down and then in practice it decrease lows. Typical marshall 0,68uF could be first test?

 

[Kesi on guitar]

I would be very tempted to recreate the reverb circuit in a separate box and stick it and the reverb pan wherever they fit. It seems to come before everything else, and the rest of the circuit is presumably designed with that in mind. Maybe a pan that can sit vertically would be required, depending on the available real estate in your cab. (I don't read schematics very well, but wouldn't that affect the Normal channel even if it doesn't have reverb? I know my old BF 6G15, designed as a front-loader, sucked out a lot of bass. Even if it doesn't affect the normal channel, it would be a good idea to get the amp sounding the way it was meant to, and it was meant to have reverb! And of course, if it did, you'd never play the normal channel anyway.)

I would like to have a reverb and have been walking around with the idea of trying to copy the reverb unit or another model for some time. The knowledge to make a design visually from a schematic is still lacking at the moment. I'm still learning. I can work with a layout.

 

[Kesi on guitar]

Test a bypass capacitor for V1. It increase highs so you must turn guitar volume down and then in practice it decrease lows. Typical marshall 0,68uF could be first test?

That is interesting. Because the amplifier is very clean, I wanted to experiment once to get more gain. But I was hesitant to try it out. Now I'm definitely going to try it

 

[Sea Devil]

Perhaps some helpful member will volunteer to draw up a layout for that reverb circuit. Stranger things have happened here!

 

[Kesi on guitar]

Perhaps some helpful member will volunteer to draw up a layout for that reverb circuit. Stranger things have happened here!

That would be awesome

 

[2L man]

That is interesting. Because the amplifier is very clean, I wanted to experiment once to get more gain. But I was hesitant to try it out. Now I'm definitely going to try it

Good explanations and instructions come searching "bypass capacitor local negative feedback"

 

[Kesi on guitar]

update.
I finally had time to replace the 0.68 bypass cap.
This gave a small increase in gain and the reduction of the bass was now moved from 2 to 3 on the pot.
Since this didn't make much of a difference I returned it to the old situation.
And what Lynxtrap mentioned earlier is that a vox tone circuit works just like that.
So I leave it like that.
As far as the reverb is concerned, I will first look for a reverb pedal. After all, I also need it for my champ silverface.

 

[Lynxtrap]

You could always experiment with the coupling caps, like the 22nf from the treble pot. Lower value will cut some bass.

 

[Kesi on guitar]

You could always experiment with the coupling caps, like the 22nf from the treble pot. Lower value will cut some bass.

You mean this one

 

[Lynxtrap]

You mean this one

That one yes. You could also try a lower value for the 47nF going from V5 to the phase inverter.
Try them one at a time.

 

[Kesi on guitar]

Today finally time to open the amplifier again and to locate the 22 nf cap from the treble pot to the phase inverter.
I think I have it.
In the picture you see 3x 22nf in a row. Marked in red on the printed circuit board. The blue line runs from the treble signal to the cap.
Is this the cap I need Lynxtrap?

 

[Lynxtrap]

It's hard to tell from the pics. The cap is connected to the wiper (middle lug) of the treble pot, so just follow the lead from the wiper and the first component you encounter should be the 22nF cap. The 220K grid leak may or may not be connected to the same point, and then the signal goes on to the grid of the next tube.