OT wire routing under board

[matt h]

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[gingertube]

Matt,
I think you are correct about the first loop and the high end "dullness". I modeled the feedback on that first stage to see what it did.
Basically the "naked" circuit has a small (1.5dB) drop in gain from about 1kHz upward till it hits the "real" HF roll off. That feedback elminated that and maintained flat response out to greater than 10kHz.

Haven't investigated the other loops in any detail but since I think you nailed it with your explaination of the 1st loop I should look closely at what you say about the other 2.

Cheers,
Ian

[Alan0354]

I finally print out the schematic of SSS and read the preamp, actually there are two negative feedback, the first one is from plate of 1b back to cathode of 1a as mentioned already. there is another from cathode of 2b ( CF stage) back to the cathode of 1b. The second NFB is a little funny as there is a filter section in the middle. This might create extra phase shift and affect stability. Also, since the filter is inside the forward gain, the NFB should negate some of the effect of the filter.

Also, if you look at the negative feedback, the division is so large compare to the forward gain of the two stages, you really don't have much of the NFB effect. ie. on the second stage, the feedback divider is 470K/1K, but the forward gain of the two tube stages is 50X50=2500 at best, you really don't have NFB.

Anyway, this is off the subject of the wiring discussion. I am more interested in making sure people don't use lead dressing to create positive feedback to create some special sound of the guitar amp. That all the talk about lead dressing is just to minimize cross talk between later stages back to the previous stages.

[matt h]

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[Gaz]

Yeah, probably more wise words on this in the Dumble section.