Can balance knob be bypassed

[mmwwhats]

Hi, I have no use for a balance knob in my system. Is it possible to bypass the balance knob? I'm building my Moreplay into a custom chassis so this would also allow me to have one less knob installed on my unit. If this is possible, can someone provide guidance on how to do this? Thanks!

[Paul Birkeland]

Yes, you can bypass the balance knob.

You will need to substitute a pair of 100K resistors from grid to ground on each 6V6 if you don't use the balance pot.

[Thermioniclife]

Hey PB. are you suggesting a 50k ohm grid load or a 100k grid load. 2 100ohm in parallel which would be 50k ohms or one 100k on each tube,.just to clarify it to him.

[Paul Birkeland]

One 100K resistor per 6V6.

[Thermioniclife]

roger that PB. Need a grid load.

[Finkle]

Howdy, when adding the 100k resistor to the tube socket is this #5 on the diagram? And then the other end is #8 on the tube socket? Or am I way off If so can someone please clarify what terminals the resistor goes?

[Paul Birkeland]

The easy way is to remove each red wire leaving the balance pot from each of the center lugs.  The red wire that left the top deck can be moved to the balance pot terminal with the white wire, and the red wire that left the bottom deck can be moved to the balance pot terminal with the red wire.

[Finkle]

Thanks for your response. I'm actually removing the balance pot and input selector. Also changing to the alps 10k volume pot. So if the balance pot isn't present, what are the best options? Is the tube socket 5 and 8 even correct thinking?

Anything I should look out for removing the input selector? I was able to find 1 post about this and it reads to have less implications than removing the balance pot.

[Paul Birkeland]

Why are you removing the input selector and the balance pot?  The instructions I provided turn the balance pot into a pair of grid to ground resistors with a relatively constant value (I'd still keep the knob about in the middle, but moving isn't going to do a whole lot unless you go all the way to one end or the other).

[Finkle]

I've been staring at the circuit for day and weeks now and I'm not understanding lots of basic information. Hoping to learn more by manipulating something I don't understand. I'm looking to make a stripped down look with a single knob on top. I've read posts on this forum explaining there's no sonic improvement, and I respect the explanation. I'd like a circuit with less splicing, pots, inputs, less things going on. How can I make it happen?

[Paul Birkeland]

I'd recommend building the stock circuit first to get it operating properly and hitting all its voltage marks before doing any modifications.  When you deviate from the design and what's published in the manual, our ability to help you debug the kit is diminished, and it's very likely that we will end up asking you to put things back to stock as the first step in debugging. 

If you are wanting a clean look with one knob instead of three and one set of RCA jacks in and one set out, then you'd need to start with a custom chassis plate.

Do also keep in mind that the Alps pots are not intended to have wires soldered to the pins, so if you have an Alps pot in your Moreplay and you attached the wires directly to the pot, the pins can snap off from the pressure.  If one of the ground connections happens to snap off, then you'll pass DC through the output jacks, and that can have some rather deleterious effects. 

[Finkle]

I've had the stock preamp built for a few months and am intending to build a custom chassis after the mods are functioning, first things first tho. My question is how are the 100k resistors added at the tube socket like what was recommended earlier in the thread? I'm asking specifically what terminals the resistor is connected to, 5 and 8 or 5 and ground? Also asking so I can see if I'm reading the schematic correctly. All the reading, building, staring blankly at the preamp it might be somewhat starting to sink in. I've thoroughly read the Moreplay section of the forum, might not know much still, so I'm wanting to mod the pots and make a custom unit. This is my first build and the first steps moving away from the abc manual steps so I do appreciate the warnings. Without the balance pot, what terminals does the 100k resistor get wired to?

[Paul Joppa]

On the circuit diagram, there is a resistor (Rgs, 220 ohms ) connected to the grid, pin 5. The other end of that resistor would be connected to the "hot" end of the input jack (the center pin) and to one end of the new 100K resistor.

The other end of the 100K resistor would be connected to the signal ground and to the "ground" of the RCA jack.

----

The resistor Rgs is called a grid stopper. In some special circumstances, a tube can oscillate at very high frequencies (think FM or television signals); the grid stopper reduces the chances of that happening. A grid stopper only works if it is the only thing physically connected to the actual grid; all other "grid" connections are actually made to the other end of the grid stopper.

Pin 8 is the cathode of the 6V6. The cathode resistor Rk (619 ohms) drops 8 volts due to the current through the tube, which sets the bias voltage  - the grid is 8v below the cathode. The capacitor Ck bypasses (shorts out) Rk at audio frequencies.

These two resistors are sometimes omitted in introductory discussions of how tubes work, because they have no effect at normal audio frequencies. But in the real world both are usually included.

I hope that helps?

[Finkle]

Very helpful and reading through the lingo as someone explains my exact scenario does help me understand more than just reading. So thank you very much.

Are these terminal #s correct then? A5 to 2, and B5 to 12. Grid stopper is at the end of the chain to ground at 2 & 12 with the other end everything hot starts from there out and the voltage can't pass through the stopper from the hot side is from what it sounds. And it's just this 100k resistor being installed, no other components need to be added?

Again, i greatly appreciate your guidance and time on this.

[Paul Birkeland]

You may find it's a lot easier to just put the 100K resistors across the input jacks.