0.0047uF in the Bassman 100 bass channel.

[Mark]

I was reading a post by Rooster which caught my eye.

“The schematic posted is missing a .0047 cap on the Bass Channel as I recall? I’m not near a schematic but I believe it was a treble roll-off bridging cap that existed between the volume pot and treble pot. This needs to be removed for guitar work, be advised.”

When I look at the circuit I can’t but help but think a 0.0047uF whole limit bass response.

The cathode bypass caps are 5uF which would seem to limit bass response as well.

What is the general consensus on the purpose of the 0.0047uF?

IMG_8417.png

https://schematicheaven.net/fenderamps/ ... _schem.pdf
https://cdn.shopify.com/s/files/1/2325/ ... 0715640943

https://cdn.shopify.com/s/files/1/2325/ ... 0715640943

https://cdn.shopify.com/s/files/1/2325/ ... 0715640943

https://cdn.shopify.com/s/files/1/2325/ ... 0715640943

[martin manning]

Looks like it's a high-pass with the 1M volume pot, -3dB at 34 Hz.

[Mark]

Hi Martin

Thanks for your reply, good to get your input as always. I rebuilt my brother Bassman 100. I increased the cathode bypass caps from 5uF to 25uF and omitted the 0.0047uF cap.

I thought it unusual that the other channel uses a 0.047uF in place of the 0.0047uF.

Thanks again for your assistance Martin.

[JD0x0]

I thought it unusual that the other channel uses a 0.047uF in place of the 0.0047uF.

Guitar channel can push a bit more bass. They trim up the lows in the bass channel, because you generally don't want a ton of fundamental frequency on your lowest strings, especially on extended range basses. Just sounds muddy, so the bass cut opens up the sound on the lowest strings and keeps the amp from flubbing out with blocking distortion.

[Mark]

On the amp pictured. I was lucky to be able to buy a new front panel and I rebuilt the amp from a chassis, power transformer and choke. The boards had tweed disease and were replaced with blue Garolite boards. The output transformer had blown and it had been replaced with a Twin Reverb Schumaker output transformer. This transformer is inadequate for the job and I managed to get hold of a Hammond output transformer from a good friend at a great price.
I increased the 5uF cathode bypass caps to 22uF and did away with the 0.0047uF and the amp sounds very good for bass with no flubbing out. The amp is very slow to distort and is clean up to at least “7” on the volume pot.

https://ampgarage.com/forum/viewtopic.php?f=8&t=32901

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