D'Lite presence wiring question

[dogears]

Henry, you are backwards. 8K/1K has much more negative feedback than 4.7K/390ohm. Combined with the 40% higher voltage on the 8 ohm tap, you will have much deader amp. Don't touch the tail but increase the feedback resistor. You also increased the tail....

Henry, the 8 ohm tap has 40% more voltage, not double. You multiply the resistor by 1.4 to get the scaled size.

Having said that, if you use the 8k/1K pair, you have a hell of a lot more NFB with an 8 ohm tap. That is only 8 to 1 ratio. A Dumble I saw with only an 8 ohm tap actually had an 8.2K over a 390ohm tail! About 21 to 1 ratio.

Keep in mind that changing the tail has a big effect on the knee of the presence circuit. If you want traditional Dumble presence, then you have to stick to the 390ohm tail. Or scale the cap...

Thanks for catching that - the 8k2/1k recommendation is correct as it is almost exactly 1.4 times larger than what he has now. The amount of actual feedback voltage available to the presence control does work out to be a little higher. When I've played with this in the past I really couldn't hear much of a difference in actual response although I've never used 6k2. My experimentation was trading 4k7/390 on the 4ohm tap to 8k2/1k on the 8 ohm tap. My current favorite is 9k1/1k on the 8 ohm tap.

[heisthl]

2 ways to lower B+5, the easy way is to add the "Fet simulator" resistor to ground at the end of the string - start with 150k and see what the plate voltages on v1 are - you may have to raise this resistor if the plates are too low, but if plates are 2 high I wouldn't go lower than 100k.
If you already have this resistor or it doesn't lower the voltage enough you need to adjust the dropping string, if you followed the D'lite spec I believe you have a 15k(B+4) followed by a 10k(B+5) you need to decide if you like your existing B+4 (plate voltages on V2 less than 210?) if so just adjust the 10k to 12k or even 15K if required, else change the 15k to 22k to lower both V1 and V2 plates. Feel free to play with these values, you'll be amazed at the difference in "roundness" of tone when you lower the voltages.

[heisthl]

Henry, you are backwards. 8K/1K has much more negative feedback than 4.7K/390ohm. Combined with the 40% higher voltage on the 8 ohm tap, you will have much deader amp. Don't touch the tail but increase the feedback resistor. You also increased the tail....

Am I missing something here? wouldn't an exact doubling (on the same tap) be functionally equivalent? i.e. 4k7/390 is the same as 9k4/780.
OH - I just got it, 8k2/1k is roughly 25% higher to the PPot and to make it worse we're going to connect it to a 40% higher tap = a lot more feeding the PPot and the coressponding gain reduction.
So are you of the opinion that the correct answer to switching 6k2/390 from the 4 ohm to the 8 ohm tap should be roughly 8k7/390?

[DaveBo32]

2 ways to lower B+5, the easy way is to add the "Fet simulator" resistor to ground at the end of the string - start with 150k and see what the plate voltages on v1 are - you may have to raise this resistor if the plates are too low, but if plates are 2 high I wouldn't go lower than 100k.
If you already have this resistor or it doesn't lower the voltage enough you need to adjust the dropping string, if you followed the D'lite spec I believe you have a 15k(B+4) followed by a 10k(B+5) you need to decide if you like your existing B+4 (plate voltages on V2 less than 210?) if so just adjust the 10k to 12k or even 15K if required, else change the 15k to 22k to lower both V1 and V2 plates. Feel free to play with these values, you'll be amazed at the difference in "roundness" of tone when you lower the voltages.

Heisthl,
I think your refering to the ODS-101 schem. I'm using the Dlite schem. I'm not to great with electronic theory, but are you just calculating the voltage drop (ohms law) across the resistor to tweak the voltage? I play around with some of the values.

Thanks

[heisthl]

Forget Ohm's law in this case - lift one end of the resistor and use clipleads to sub in alternates. The problem with Ohm's law here is you don't know what you want til you hear it.

[DaveBo32]

That's cool, I'll give it a shot. By the way I changed those silver mica caps to mallory ceramic disks, that seem to improve the sound a little. Thanks for that tip.