Bogner Shiva 20th, raise the mids?

sonofmickel · Post by **sonofmickel** » Wed Jan 09, 2013 11:43 pm

Hi all.
Can't find schematics for the Shiva 20th. I like higher mids and was wondering if anyone had traced the circuit and found the appropriate tone stack parts. This amp would be awesome if it were a bit more "open" sounding.

sonofmickel · Post by **sonofmickel** » Thu Jan 10, 2013 5:35 am

More specifically:
The circuit boards are double sided and blue printing isn't my forte. I can trouble shoot a plexi/fender circuit but this is quite different in there!

Bogner is probably sending highs to ground somewhere, I would like to reverse that. Coupling caps would be a good place to start.

Gaz · Post by **Gaz** » Thu Jan 10, 2013 9:09 am

Here is a partial schem, which I did not do. It seems like they got rid of one low-pass filter in this incarnation, but clearly it doesn't have the crunch you're looking for yet. One obvious place to start is lowering the 1000p anode bypass cap to see if that gives you what you're looking for. I honestly wouldn't go to low or you'll just get fizz. Try adding a bypass/bright cap across the top leg of one of the interstage dividers. Try 470pf-100pf over the 498k after the 2nd stage.

roberto · Post by **roberto** » Thu Jan 10, 2013 6:48 pm

Do you notice this problem on all channels?
If so, I would mod the power amp.

Gaz · Post by **Gaz** » Thu Jan 10, 2013 7:52 pm

Damn, forget my post I thought it was for the xtc not the shiva. Roberto's right if it's on all channels. Maybe too much NFB, or perhaps you could lower the presence pot value.

thejaf · Post by **thejaf** » Thu Jan 10, 2013 8:22 pm

What cabinet/speakers are you using with it? My circa 1999 Shiva was a huge midrange monster when wired through the Bogner 4x12 w/V30s. On the other hand, it sounded rather dark and "Voxy" through the Shiva sized ported 1x12 with Lead-80 speaker.

sonofmickel · Post by **sonofmickel** » Thu Jan 10, 2013 9:00 pm

Using a Fender Tonemaster 4x12, V30 x G1275t.

I do not typically have the presence turned on. I have Mids and Bass up high treble to taste. The amp sounds pretty compressed. I would like it to have more Plexi-like attributes.

roberto · Post by **roberto** » Thu Jan 10, 2013 9:08 pm

I won't set the bass control so high with your problems.
What about other controls?

http://www.bogneramplification.com/shiva

sonofmickel · Post by **sonofmickel** » Thu Jan 10, 2013 9:14 pm

I like the master as high as the room can stand it. The Bass control does not really add much, we should call it a "girth" control. The Excursion control on the back of the amp is off. The Treble control really adds "ice pick" to the tone.

I typically use the "Vintage" channel with the boost off. Gain is at 12:00.

Gaz · Post by **Gaz** » Fri Jan 11, 2013 3:49 am

If you really wanna mod this bad boy, you should really just try to draw up some of the preamp using the old schematics as a guide. Otherwise, it's anyone's guess as to what's going on. If that's just too daunting, you could try to increase the size of the presence cap, which is probably .1uf as is, so maybe up to .47 or .68. for some extra high mids.

thejaf · Post by **thejaf** » Mon Jan 14, 2013 3:55 pm

Have you tried turning the lead channel volume up, and reducing the master? The Shiva uses a post FX loop master volume, and the lead channel volume is placed in the "master volume" spot same as a JCM800 (immediatley after tone stack).

sonofmickel · Post by **sonofmickel** » Mon Jan 14, 2013 7:47 pm

Yes, I have the Lead channel volume at 2-3:00 usually.
Hmm...so the Shiva has a Pre PI master and PPIMV.

What I have been doing for the past few months is using the clean channel and some dirt boxes up front. Just more dynamic than the lead channel. I will say the the lead channel seems more Dumble-ish then Marshall-ish to me anyway.
I suppose an EQ up front and in the loop would get me where I want the amp to be.

Gaz · Post by **Gaz** » Mon Jan 14, 2013 8:38 pm

No, just a pre-PI master. If you're not up for modding, I agree an EQ in the loop would work wonders.

sonofmickel · Post by **sonofmickel** » Mon Jan 14, 2013 8:59 pm

Are you sure just a pre-pi master?

The clean channel has gain
The Rhythm channel has gain and a volume.
The Lead channel has gain and a volume.
Then an overall master volume. Your sure it is a Pre PI master?

thejaf · Post by **thejaf** » Tue Jan 15, 2013 2:14 pm

The Shiva has separate volumes for each channel, (clean volume, lead volume), very much like two separate preamps (Fender channel and modded JCM800 2204) that are then mixed together at the input of the series FX loop, which is a cathode follower loop akin to the Dumbleator. The FX loop return signal passes through the Master Volume pot, then to the PI.

So, not PPIMV, but also not traditional master volume either.

Therefore, yes an EQ in the FX loop would be a good idea to add the frequencies you're missing

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