Hiwatt Pre/Marshall PA build

[Gaz]

I like the early 70's Hiwatt EQ/pre a lot, and wanted to mate it with a Marshall output section and PPIMV to get some more crunch...

Success!... but it's super bright. One thing I'm trying to adjust is the amount of NFB. Looking at the Hiwatt, I see a 10K feedback resistor off the 16 Ohm tap, with a 2.2K shunt resistor setting the feedback ratio. Is that correct, or is there something I'm missing with the weird presence arrangement? If not, then that's a hell of a look of feedback, right? Like a crazy amount.

If anyone has any "bright" ideas to tame this preamp without killing the tone then I would appreciate it. Yes, I know a set of Fanes would help, but all I've got here are Celestions

Thanks!

[img2550]http://hiwatt.org/Schematics/DR_PreLinkedInput_v2.gif[/img]

[eddie25]

First thing I would consider is tinkering with a higher value for those 47n cathode bypass caps.

[Structo]

I think the NFB is down there in the right hand corner.
It says the 10K is connected to the 16 ohm tap.

I would experiment with that value.

In my limited experience, the less feedback the more highs or gain will result.

On my Dumble I have a switch on the Presence pot, which kills the NFB.

The amp gets more gainy and brighter when off.

[Gaz]

I should have already mentioned that I removed the 47n cathode caps, and it's still bright as hell.

I saw the 10K off the 16ohm tap, but am confused about the 470R/10n combo, is that sort of a fixed presence at really high frequecies?

[chopstuck]

Structo, are you sure about that statement about highs, gain and feedback ?

My experience is the opposite.

Limited experience as well.

Marc

[Gaz]

I think someone said something backwards somewhere perhaps, but less feedback is more gain, highs, AND more bass.

[chief mushroom cloud]

I would try changing the 1st coupling to 22n and 47n

[bb5000]

I've built a DR201 and I have these values for the first stage :

Brilliant Channel: 1 uF cathode bypass cap, 10 nF coupling cap
Normal Channel: 25 uF cathode bypass cap, 22 nF coupling cap

I'm using it for bass and both channels sound good.

[Structo]

Structo, are you sure about that statement about highs, gain and feedback ?

My experience is the opposite.

Limited experience as well.

Marc

Yes, I had a dyslexic moment there.

With less feedback the amp gets more wild!