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Nobsound 6p1 Amp flaws/mods

So as everyone reading these can tell, I'm new to alot of this. Here is what I'm trying to do. Maybe by explaining this, it'll keep me from buying all the wrong stuff. So here is what I have.

Pro-ject T1 turntable and a Fluance RB82 with orotofon cartridge.

Nobsound JP1 amp with mods listed in this thread.

Klipsch RB51 II bookshelf speakers
Klipsch R-12SW powered subwoofer

Nobsound T3 MM preamp


Originally I wanted to go from either turntable to the amp to my klipsch bookshelf speakers. Well the sound was very clear and sounded great. However I wanted more bass. So I purchased the subwoofer to add bass. However I wanted to be able to control the volume of both the subwoofer and bookshelf speakers from one place. As of now I can change the volume on the amp for the bookshelf speakers. But I have to go to the back of the subwoofer to turn volume up and down. Pain in the rear.

Hopefully this helps. Maybe there is something else I need, or maybe the nobsound T3 MM is bad.
 
Oh, if the turntable has a built in preamp, you need to connect this new one directly to the cartridge output. Most have 2 sets of RCA jacks so you can do this.
 
@StepheK , As someone with zero soldering experience, let alone working inside an amp, I finally got the guts to try out the mods and I am happy to report that it was a big success. Ironically, I actually spent more time trying to figure out the polarity of the Coupling and Grid caps from your videos than struggling with anything else. The amp sounds far better with negligible distortion at full volumes. I am enjoying with the Sound Artist LS3/5a which at 11ohm is a bit hard to drive and after this mod, I am able to significantly crank up the volume. They are a terrific pair. Thank you so much!!!

I just noticed that you have other videos on the A50 and your own (?) designs? How would you say the modded Nobsound compare to them? It is surprising that all the more expensive models are still only in the 6~8 watt range. Is all that added cost only of value if you want specific tube sounds like the 300B? Or are you paying more better power transformers?
 
The A50 as delivered puts out less power than the modded 6P1 lol. But the modded A50 does put out more power before heavy distortion sets in so that is the reasson. My design with the big Edcor OT has a LOT more bass and better midrange smoothness, but I wouldn't say it's night and day. Fiscally, just adding a small powered sub to the 6P1 is probably a great setup.
 
StepheK said:
Fiscally, just adding a small powered sub to the 6P1 is probably a great setup.
Click to expand...

This is exactly what I have with an external cross over (MiniDSP) set to 100Hz to reduce the load on the amp.

Another question - what are the two 22uf 450v capacitors above the PCB on either side of the rectifier tube socket for? I don't see that showing up in the original or your final schema? Worth upgrading them to something decent?
https://imgur.com/X7TdHld
 
vvume said:
This is exactly what I have with an external cross over (MiniDSP) set to 100Hz to reduce the load on the amp.

Another question - what are the two 22uf 450v capacitors above the PCB on either side of the rectifier tube socket for? I don't see that showing up in the original or your final schema? Worth upgrading them to something decent?
https://imgur.com/X7TdHld
Click to expand...

Those caps are part of the power supply for each channel. You can see them on all the schematics after the 1.5KOhms resistors. Yes, I replaced them by the same cap I used for the oversized 150uF "big blue cap" replacement.
 
StepheK said:
Hi all.

I wanted to post about my first tube amp and some issues I discovered reading online after I purchased it. This is a made in China, off Amazon, Nobsound 6P1, which has a major design flaw: the first cap after the rectifier tube being 150uf. This severely overworks the rectifier tube, causing them to fail and also possible arc if short cycled before this cap has drained down, which could take a while.

[...]

The other issue, for use in the US, is a 110 mains tap which makes everything over-volt. I see in the Amazon reviews people saying they quit working after a few months and I have to believe this, along with the super oversized rectifier cap, is probably why. I put a 12.5V 3a transformer in a bucking configuration inline to resolve this voltage issue. The power trans also runs much cooler now.



View attachment 2051686
Click to expand...

Hi @StepheK,

many thanks for providing all the info and supporting us 6p1 owners. May I ask whether the design flaws you identified apply to us here in the UK as well, where we have (circa) 230V?

Again, top marks for your invaluable insights.
 
There shouldn't be any difference to the circuit mods, but I honestly can't speak to the supplied power transformer vs your line voltage. You could compare the B+ I measured VS what you see? Do be careful, these are lethal voltages!
 
StepheK said:
There shouldn't be any difference to the circuit mods, but I honestly can't speak to the supplied power transformer vs your line voltage. You could compare the B+ I measured VS what you see? Do be careful, these are lethal voltages!
Click to expand...

Ah. Being rather unskilled in electronics, I rather not. I might have a go at changing the capacitor as you suggested, though.

Again, many thanks for your help.
 
Yes, changing that first cap will ensure a long rectifier life. Do let the amp sit for a couple of days and then to ensure there is no voltage stored, short across the cap with a well insulated screwdriver. You might also consider adding the bleeder resistor to drain the voltage when you turn the amp off. those are both very simple to do.
 
Chemdawg said:
Originally I wanted to go from either turntable to the amp to my klipsch bookshelf speakers. Well the sound was very clear and sounded great. However I wanted more bass. So I purchased the subwoofer to add bass. However I wanted to be able to control the volume of both the subwoofer and bookshelf speakers from one place. As of now I can change the volume on the amp for the bookshelf speakers. But I have to go to the back of the subwoofer to turn volume up and down. Pain in the rear.
Click to expand...
Does the sub have speaker level inputs? Just run a set of lines from speaker out to sub input.
No speaker inputs?
Several adapters found from a quick Google search that take speaker level input and give you RCA out.
 
@StepheK . What is the reason for the 10uF 50V capacitors at the speaker output between both speaker posts? Can those be replaced by a better quality ones? Does it worth it?
 
Would I get better bass (less tubby) by going ahead and installing a pair of Edcore output transformers? I love the way the amp sounds except for the soft bass.
 
@StepheK , I see that you are doing a reboot of Nobsound 6P1 and enjoyed seeing it. Any chance you might also cover potentially replacing the output transformers on this thing as you seem to suggest that they might be holding back some potential. Something like the GXSE10-8-3.5K might provide a decent upgrade?
 
vvume said:
@StepheK , I see that you are doing a reboot of Nobsound 6P1 and enjoyed seeing it. Any chance you might also cover potentially replacing the output transformers on this thing as you seem to suggest that they might be holding back some potential. Something like the GXSE10-8-3.5K might provide a decent upgrade?
Click to expand...

I think there is more to be had from the iron it comes with. Hope to get some stuff sorted out today!
 
@StepheK , saw you latest video on the NP1, but it wasn't clear to me what the advantage of a solid state rectifier (with a thermister) was to using a tube rectifier? Does it allow for more current to pass through? Also I found the SS Rectifier on ebay, but it seems to need some construction/mods given that it has 8 pins?

You also seem to suggest that the power transformer was the main limiting factor in the original design that prevents us from extracting more out of the 6P1 tubes. I understand that an exact replacement transformer with more power delivery is hard to find, but could one technically use 2 of them (say move the 6.3vac and 5vac rails to the 2nd one) and feed more power into the circuitry? I know it will need to be an externally mounted transformer that would be butt ugly, but wondering if that will allow the upgrade of the output transformers to 2.5/3.5K ohm tube side input impedence.

The 6P1 is still a very compact tube amp for the desktop which to me is the biggest part of its appeal. Almost everything else eats up a lot of space. Your original mods actually allows me to crank up the volume to max and it still sounds beautiful with a 90Hz active crossover and my Sound Artist LS3/5a + RSL Speedwoofer 10s. I guess I must be using less than 2 watts in this configuration as the distortion is not distracting at all (except for an occasional song like Spanish Harlem by Rebecca Pidgeon that seem to push it over its limits).
 
I'm still evaluating this option but a SS rectifier has less voltage drop across it and also doesn't need the 2 amps of current for the heater the tube has, which lightens to load on the power transformer. As far as the 8 pins, a normal tube rectifier only uses 4 of the pins. And yes the one I linked is a kit, but doesn't need any mods, just assemble it. There are also dozens of premade ones out there.

Yes the power transformer is the main limiting factor, but possibly the output transformers are too. If you are going to externally mount a transformer that costs 1/2 the price of this amp, plus replace the output transformers that are another $100+, to me you are getting way outside of what is reasonable. And honestly, this amp's design isn't that great to warrant spending this much effort and money on.

I'm still working on this so be patient, I think running the output tubes as pentodes might unleash some more power. If you want a small amp, my little 6BM8 amp is 1/4 the size of this one at the same power output :)
 
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