6V6 line preamp

[Salas]

Originally Posted by harlee

Hi, I have completed the 6V6 line amp built, indeed the sound is big!
I have used Salas' standard line circuit with a 6L6GC shunt regulator. Using the parts that I have, B+ is 292V, 18mA through the circuit.
Thanks Salas!

Hi, I would recommend you use a higher load value in these conditions. Try adding 2.7K 3W-5W resistor in series to the 5K anode load one and tell us if it got better or not. Pictures would be nice too.

[Demonkleaner]

Still listening to mine every day. I've since
changed the B+ regulator to a 6V6 shunt
regulator with DC heaters dialed in at 340V with a larger
transformer. My amplifier can reach full
volume without Salas' pre but it sounds
lifeless. Thanks again for this beautiful
design Salas

[Salas]

Nice when something still delivers to taste, standing the test of time. You are welcome, regards.

[disco]

Originally Posted by 6L6

I have been messing with the circuit today and have learned a few things -

I have got some hummm, but I think it's a wiring problem. It goes away when the pot is turned all the way up or down, and worst at the mid-position.

I think I also have some filament hum, as they are AC for now. I will put together a quick and dirty regulator for them tomorrow.

My 6V6 pre works fine AC heated, perhaps you should have a look at the routing of your wiring?

Here's a pic I made for someone else, suffering from grounding issues. Maybe it's to your service.

[6L6]

Yes, I'm quite sure it's a wiring problem!

It's all a bird's nest of wire, strung all over my workbench. However, there is some insight in your diagram, and I will make a few changes. Thanks!!

[RCruz]

Do I see a GND Loop there ?

[tinitus]

signal RCA plugs should be isolated from chassis/case

dont know about grounding the att

[disco]

Tinitus: The RCAs must be isolated from a conductive chassis indeed.
Would you break up the signal ground and take it to the star directly?

Roberto: In reality the lines you made red are one and the same. Starground(s) and chassis connection is made to the capacitor that has the lowest ripple current to keep large loading currents from the ground. Star topology is used to prohibit larger currents to interfere with smaller currents. Exhaustive runs of grounding cables seem to work contra productive, possibly because of the extra inductance.

New scheme:

[tinitus]

Originally Posted by disco

Would you break up the signal ground and take it to the star directly?

I suppose thats the point of having a starr ground, if there is one
though I prefer to look at it like multiple starr gounds, along the same string

often you see tube amp builders have one(and only one) solid core wire going through the whole amp, for all ground connections

and you often see the signal ground isolated from chassis/earth by a small resistor, or maybe a thermistor(look at NelsonPass DIY)

[harlee]

You're Great Salas!
I found 2.2K/3W somewhere and put it in series with the anode resister of 4700K, and it brought the sound back down, it sound more alive. It was a bit floating especially the high.
Just wondering how it sound with 330V B+?