Some questions before I finish my first clone!

[Tdale]

There are a couple of things I need som help on before I finish the last few solder joints in my Hybrid-A build.

1. The output jack: I'm using the black plastic, insulated ones.

I have the 2-4-8 ohm secondaries going to a 3-way impedance switch, and then from the switch-common on to the tip of the output jack.

The common wire from the secondary goes to the "sleeve" of the jack.

Is that enough, or does the "sleeve" have to be connected to gruound too?



2. The global negative feedback... On the schematic it connects to the hot side of the OT secondary. But what about when I use a impedance switch? Can I connect it to the common-lug of the switch, to make it work with all speaker-impedances, or does it have to be just one of them?

3. Presence. Does presence and global negative feedback have anything to do with each other, or is it possible to have presence withouth GNF, or have GNF without a presence control?

I have for some reason alwayst thought of the two as parts of the same thing, bur realise that might not be so....

4. Ground bus. I plan to run a thick copper wire along the pots, using it for grounding. All the pots, input jack and the cathode resistors/bypass caps will be grounded here. But where do I connect to the chassis, at the input end or the other? I planned to connect at the other end, near the PT, and also ground the power supply etc. at the same point. Is this a good idea?

I hope some of the experienced builders will take the time to answer, because this is all I have left on this amp now. Can't wait to fire it up!!!

Tommy


3. Bias pot(s). I have two bias pots, one for each tube. Do I use the same resistor-to-ground value for them as I would If I had only one bias pot (15K) ?

[Normster]

There are a couple of things I need som help on before I finish the last few solder joints in my Hybrid-A build.

1. The output jack: I'm using the black plastic, insulated ones.

I have the 2-4-8 ohm secondaries going to a 3-way impedance switch, and then from the switch-common on to the tip of the output jack.

The common wire from the secondary goes to the "sleeve" of the jack.

Is that enough, or does the "sleeve" have to be connected to gruound too?

The sleeve must be grounded to provide a reference for the OPT.

2. The global negative feedback... On the schematic it connects to the hot side of the OT secondary. But what about when I use a impedance switch? Can I connect it to the common-lug of the switch, to make it work with all speaker-impedances, or does it have to be just one of them?

Connect to the 4 Ohm tap of the impedance switch.

3. Presence. Does presence and global negative feedback have anything to do with each other, or is it possible to have presence withouth GNF, or have GNF without a presence control?

I have for some reason alwayst thought of the two as parts of the same thing, bur realise that might not be so....

The presence control merely controls the amount of NFB sent to ground, so yes, they're part of the same circuit.

4. Ground bus. I plan to run a thick copper wire along the pots, using it for grounding. All the pots, input jack and the cathode resistors/bypass caps will be grounded here. But where do I connect to the chassis, at the input end or the other? I planned to connect at the other end, near the PT, and also ground the power supply etc. at the same point. Is this a good idea?

Dumble grounds the bus to the chassis at the input end of the chassis. I've been doing it that way and never had a problem.

I hope some of the experienced builders will take the time to answer, because this is all I have left on this amp now. Can't wait to fire it up!!!

Tommy

Well, not very experienced, but hopefully I'm not too far off the mark with my answers.

3. Bias pot(s). I have two bias pots, one for each tube. Do I use the same resistor-to-ground value for them as I would If I had only one bias pot (15K) ?

Sorry, can't help with that one, but you could always just try it and see. If it doesn't work out, just change the resistor values. (I always end up adjusting my bias resistors anyway.)

[Darkbluemurder]

Hi Tommy,

1. Output must be grounded.

2. Even with an impedance switch you can use either tap (not the common). I would use the 4 ohms tap.

3. The Presence control decouples the global negative feedback at high freqs. Without GNF you need a "cut" control a la AC 30.

4. I was told that I should not ground the preamp grounds to the same point as the power supply grounds. Close to the input should work well.

5. The bias pot resistors should be halved with two pots.

Hope that helps. Good luck!
Stephan

[Tdale]

Thanks!

I talked on the phone with a friend, and he said that when there s GNF, that grounds the output jack, and a ground from the sleeve of the output jack could give you hum..and is not necessery, since it's already grounded through the GNF resistor.....

Does that make sense?

[Normster]

Thanks!

I talked on the phone with a friend, and he said that when there s GNF, that grounds the output jack, and a ground from the sleeve of the output jack could give you hum..and is not necessery, since it's already grounded through the GNF resistor.....

Does that make sense?

No.

[Tdale]

Ok..

I looked at my DC30 clone, and I was wrong. I thought I didn't ground the sleeve, but a closer look revealed that it's grounded.

I'll do it that way then.

It's my first time with a ground bus...so I'm a bit anxious about how that's going to work out.. I guess I'll just have to try, and then listen.

You guys use more than one grounding point in the chassis I guess..since you ground the bus at the imput jack, and the power supply/PT center tap in the area around the PT..?

Tommy