Bottlehead Forum
Bottlehead Kits => Moreplay => Topic started by: mmwwhats on March 30, 2024, 07:25:46 PM
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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!
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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.
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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.
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One 100K resistor per 6V6.
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roger that PB. Need a grid load.
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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?
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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.
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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.
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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).
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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?
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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.
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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?
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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.
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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?
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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.
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You may find it's a lot easier to just put the 100K resistors across the input jacks.
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I'm doing work with the inputs, how would I go about running the resistor across the input jacks? One end to hot and one ground on each RCA input?
Also relooking at the volume pot wiring, am I seeing the input grounds running to the output grounds? Connecting on the same pin of the of the chassis side terminal of the volume pot? Without the selector and balance pot, wouldn't I need to wire the grounds of the input and output jacks together at the jacks? Any chance I could use the 4 input jacks that are tied 4 grounds together at the same L bracket with little yellow resistors or diodes? Use 2 jacks for input 2 for output?
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wouldn't I need to wire the grounds of the input and output jacks together at the jacks?
I don't really recommend doing this. You have better control over the signal current running through the ground wires if all that is separated, and you may end up inadvertently creating ground loops if you deviate too far from the stock layout (which is tested).
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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.
No, the 100K goes from A6 to terminal 2 and B6 to terminal 12. The grid stopper is already wired A5-A6 and B5-B6. A6 and B6 are not used by the tube so it's effectively just another terminal. Remember, "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."
The photo in the manual of the completed preamp shows red/black twisted pairs, with reds going to A6 and B6 and blacks going to 2 and 12. The other end of the twisted pairs is connected to the balance controls. Unsolder those twisted pairs from the balance control and connect them to whichever input RCA jacks you want to use. (Obviously you'll have to remove the existing wires from those chosen RCAs!) You can then put the 100K resistors at either end of the twisted pairs, whichever is easiest.
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This has been greatly helpful and informative. Thank you guys! Feel like I've gained more understanding in the last day than the last few months combined.
If reducing inputs and working on them already it's the space already being worked on so that's where they'll be added in mine.
Last question...for now. What are the purpose of the little yellow caps at the intake jack grounds? Assuming I should be leaving them in when installing the 100k resistor from input RCA hot to ground? Would an output jack be able to use the yellow .01uf cap if I swapped a couple of the input jacks to output? Or would a different resistor or just bare RCA ground to ground for output jacks? As I'm rewiring the inputs and outputs, they're already tied to a ground and looking appealing to reuse if tieing all the grounds together, input and output, at the jacks.
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The yellow caps present a very low impedance between audio ground and the chassis but only at very high frequencies. This is a way to drain off high frequency gunk off the audio ground before it gets into the circuit. These are not necessary, nor useful on the output jacks.
We have about three decades of preamp kits that never used these, so don't fuss too hard over them.
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Live in the mix! Functional, sweet sounding preamp is back! Was a lot of changes at once, output cap change happened, also heavy duty on/off switch too. Been listening without it for 3 to 4 weeks. Immediately could tell it's going to be a lot of fun having it back. Engaging. Completely black at very high levels when music goes quiet, not that it wasn't before, just probably a good sign?!
A few things I think the next iteration could end up with: using the same red & black wire as sent with the kit, parts express wire coating is minimal. Probably add an on light. Not sure what chassis changes yet but probably stay the same external dimensions, finish the base. Reposition RCA jacks and iec power cord to the back.
Thanks again guys! Rockstars!