I tried 4.7uf and there is too much hum. I picked 22uf as a "it's won't kill the rectifier like a 150uf will but also doesn't have too much hum" compromise.
Nobsound 6p1 Amp flaws/mods
- Thread starter StepheK
- Start date
I tried 4.7uf and there is too much hum. I picked 22uf as a "it's won't kill the rectifier like a 150uf will but also doesn't have too much hum" compromise.
Monty Gibbon
New Member
Yeah, originally I was searching for something sub-$100 that'd be a trainwreck in hifi terms, but potentially useful to colour the guitar frequency range.
You know how things go; just got sucked-in and it's more like a $300 investment now. That said, I've had a fair few China products die on me and cannot rule out my 250v UK mains is killing things. So, I suspect the APC Line-R will prove to be a prudent long-term investment.
Toggle switches on guitar gear can be a distraction; too many available settings which draw your attention away from playing ~ and towards toggling about for yonks, straining to perceive any difference. So, your response has served as a timely reminder of that. Cheers.
If long runs of wire are needed ~ as well as a rubber mallet to bash additional components into the small chassis, I can see my inexperience carries a risk of inducing significant noise problems. Thanks for helping me out with some clarity of thought there.
For my purposes, VU removal to free up some interior space is a brilliant idea I'd never have thought of. So, that's definitely a useful consideration.
My understanding of the reservoir cap situation is that there's a window of acceptable capacitor values; 4uf being the datasheet spec ~ StepheK's de-hummer 22uf recommendation in light of her experimentation ~ and I see one owner has gone for 47uf in order to reduce hum further. My thought process here had been an option to toggle between safe bet / less hum cap values; dependant on the nature of usage (volume+proximity) once fired up.
Off (my tresspassing) topic, the pre-purchase process was quite entertaining. I have assurances from the AliE' seller that their particular variant has an upgraded transformer so my 250v mains will be okay ~ plus their component improvements render the reservoir cap mod unnecessary. The seller invited me to stop being troublesome when I raised my figurative eyebrows. That's me told.
Hopefully I'll be able to meaningfully contribute to the thread at some point in the future. The best I can do right now is to confirm in the UK, Nobsound is pronounced "Knobsound".
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Definitely go with the 22uf as StepheK recommended.
It'll be interesting if they actually did do "component improvements" and a more appropriate transformer. Share some interior pics when you get it.
FlaCharlie
Super Member
The 5Y3GT is a drop in replacement for the Chinese 5Z4P. It draws the same heater current and the data sheet lists 20uf for the first cap. It is directly heated, so you will lose the slow start of the 5Z4P, but that's not a big deal. If you want to keep the slow start there is a 5Y3 variant, the 6087, which is indirectly heated like the 5Z4P. It's first cap value is listed as 10uf.
How much more? Some data sheets include a series of 3 charts which can be used to determine this. You must measure your amp and use those measurements to make calculations. If the results are acceptable on all three of the charts, your cap value is OK. Not surprisingly, the Chinese data sheets don't have charts, though. And, while a somewhat higher cap value might pass the 3 tests, I don't think the limit will be anywhere close to the stock value, which is way too high.
Here are the data sheets for the 5Y3GT and 6087, which include the charts:
https://tubedata.edebris.com/sheets/093/5/5Y3GT.pdf
https://tubedata.edebris.com/sheets/083/6/6087.pdf
Unless they're making a version with a different rectifier tube that allows a larger first cap value, or they have reduced the value of the cap, then the value of the first cap is still an issue. It may still be an issue even if they are using a different rectifier tube. Sellers rarely know anything about the technical requirements of tube electronics. He's just trying to make a sale.
Most of the Chinese amps don't actually run the tubes all that hard, in terms of operating points. So the problem caused by the higher voltage that's produced by the PTs is mostly the heater voltages. I say "mostly" because Stephe has also pointed out that, in some cases, the reason they don't push the tubes that hard is because the transformers can't handle the increased current.
While heater voltage specs say +/- 10% is acceptable, once you get past 5% tube life drops much more rapidly. This issue can be solved without dropping the overall (B+) voltage by adding a couple of low value wirewound resistors to drop the heater voltage. Take the heater specs of all the tubes on the winding and use Ohm's Law to calculate the proper resistor values that are needed to drop the voltage to the correct level.
In some cases that's true. The cap value shown in tube data sheets assumes that the tube is being operated at its maximum voltage and current specs. If it's being run easier it's permissible to use more capacitance.
How much more? Some data sheets include a series of 3 charts which can be used to determine this. You must measure your amp and use those measurements to make calculations. If the results are acceptable on all three of the charts, your cap value is OK. Not surprisingly, the Chinese data sheets don't have charts, though. And, while a somewhat higher cap value might pass the 3 tests, I don't think the limit will be anywhere close to the stock value, which is way too high.
Here are the data sheets for the 5Y3GT and 6087, which include the charts:
https://tubedata.edebris.com/sheets/093/5/5Y3GT.pdf
https://tubedata.edebris.com/sheets/083/6/6087.pdf
I'd say there is an 99.99% chance that the seller's claims are total BS.
Unless they're making a version with a different rectifier tube that allows a larger first cap value, or they have reduced the value of the cap, then the value of the first cap is still an issue. It may still be an issue even if they are using a different rectifier tube. Sellers rarely know anything about the technical requirements of tube electronics. He's just trying to make a sale.
Most of the Chinese amps don't actually run the tubes all that hard, in terms of operating points. So the problem caused by the higher voltage that's produced by the PTs is mostly the heater voltages. I say "mostly" because Stephe has also pointed out that, in some cases, the reason they don't push the tubes that hard is because the transformers can't handle the increased current.
While heater voltage specs say +/- 10% is acceptable, once you get past 5% tube life drops much more rapidly. This issue can be solved without dropping the overall (B+) voltage by adding a couple of low value wirewound resistors to drop the heater voltage. Take the heater specs of all the tubes on the winding and use Ohm's Law to calculate the proper resistor values that are needed to drop the voltage to the correct level.
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Hi, yes. And I remember you told me months ago we need to use 2 resistors (1/2 resistance each). One for each winding from transformer. There is no 0v and 6.3v(which in that case there would be no problem using a single resistor). But instead there is a -3.15v and 3.15v windings. Hence we need a resistor on each one. Is that correct?
I would like to try this approach instead of decreasing input voltage a 10% by the APC voltage regulator. Keeping a higher B and B+ voltage provides better performance, right? More gain?
FlaCharlie
Super Member
It's my understanding that a pair of dropping resistors is preferable but one can be used if you can't find the right values. Unless the heater winding is being used to heat a rectifier tube, it's best to have a ground reference on the heater supply. Typically this is done with a center tap. If it's not you might want to add a hum pot with its wiper to ground or construct an artificial center tap using a pair of fixed resistors. I don't recall if @StepheK addressed this in her mod videos or not.
I doubt that the slightly higher B+ voltage will make any appreciable difference in performance. As Stephe has pointed out, this amp is pretty seriously compromised by a variety of factors. I know she has been quite frustrated by it and I think she now plans on reworking it using a totally different circuit.
Ok. So, if there is no benefit of having a higher B+ voltage, I'll stick to the APC then.
FlaCharlie
Super Member
Generally, running the output tubes at a higher dissipation level will produce more power but the slightly higher B+ will not alter the operating point / power output significantly.
I think Stephe found that the transformers are the limiting factor. Watch her video series, if you haven't. She was able to get a little more power out of the amp as I recall. But it takes 2x the power to produce a 3db increase in volume, which is the same as moving 39" closer to your speakers. It takes 10x the power output to make something subjectively sound "twice as loud". The relationship between power output and volume is not linear.
If you already have the APC you can use it to keep the heater voltage in check. If you don't already own one, though, it's a lot cheaper to just use dropping resistors on the heaters and ignore the slightly higher B+.
I have no complaints regarding this amplifiers. It provides more power than what I normally need(10 o'clock on the pot is very loud and the VU meters barely move), and after all the mods suggested by @StepheK plus my own mods: bypass capacitors, Miflex KPCU coupling caps, Aucharm Golden IEC socket replacement and Aucharm fuse and upgraded power cord. It sounds fabulous, even if many people consider these upgrades as snake oil.
Vince Ligget
New Member
@StepheK I can’t thank you enough for taking the time to answer all my questions, I plan to fix the power supply issue with your suggestions and the new bias for the signal tubes. I can’t promise that this is my last question but here goes. Do you think that changing the capacitors in the signal path had much of a change to the sound, I’m looking for better bottom end on the Khorns?
Thanks again, I’m having fun watching your videos and learning about these SET amps, thankfully I didn’t spend twice as much and have one of those amps you mentioned that have a hum and don’t sound as nice! You’re the BEST !!!
Monty Gibbon
New Member
Ooh, in light of some rummaging, I have another question I'd be really grateful for some help with.
I've a few pairs of old/cheap hifi speakers and have been looking up their spec sheets to ascertain their ohm and dB ratings; in the hope a set will be Nobsound 6P1 friendly.
Along the way, I've come across a pair of 10" guitar speakers. My instinct is the Nobsound isn't powerful enough to drive them. But, before discounting them, thought I'd ask for some educated guidance.
Here's their spec sheet. What do you think?
Cheers.
I've a few pairs of old/cheap hifi speakers and have been looking up their spec sheets to ascertain their ohm and dB ratings; in the hope a set will be Nobsound 6P1 friendly.
Along the way, I've come across a pair of 10" guitar speakers. My instinct is the Nobsound isn't powerful enough to drive them. But, before discounting them, thought I'd ask for some educated guidance.
Here's their spec sheet. What do you think?
Cheers.
With a 100db/mW sensitivity speakers you only need 1 Watt to be screaming loud.
I use 88dB/mW sensitivity speakers with this amp and they sound very loud.
I don't see why you cannot use those speakers.
FlaCharlie
Super Member
You should have no problem getting plenty of volume from them.
But their "usable frequency range" of 100Hz to 5.8kHz is very limited, even for use as a guitar speaker. The lowest note on a guitar is 82Hz so they're saying it won't even reproduce the full range of a guitar yet they're selling them for use in a guitar amp?
What brand / model speaker is this?
For stereo use you would need to construct a 3-way speaker system if you want any bass or treble. Any decent bookshelf speakers that are designed to reproduce recorded music would be a better choice.
As far as published speaker specs go, take them with a grain of salt. Sensitivity / efficiency claims are often inflated. The impedance rating is the "nominal" impedance but in reality impedance varies with frequency. Speakers that work best with tube amps have impedance curves that don't vary wildly. Problem is that many (most?) manufacturers don't publish impedance curves, only the "nominal" value.
Monty Gibbon
New Member
Yep. I've got a few sets of hifi speakers I can try...and a couple of EPOS subs from an old AV system.
Fundamentally though, I got the 6p1 to see if it'd 'colourize' a very sterile digital guitar modeller:
https://www.mooeraudio.com/product/GE150-228.html
FlaCharlie
Super Member
I'd suggest that you not try to mix components designed for stereo with those designed for guitar.
Though I haven't kept up with guitar effects / modellers the ones I've heard all sound sterile and processed to me. If you want tube guitar sound, buy or build a tube guitar amp. Something like a Champ clone maybe. If you want to explore that path please start a new thread since this one is about use of these 6p1 amps for stereo reproduction, as they were intended to be used.
There are many folks on AK who have lots of experience with tube guitar amps and I'm sure they can help you. But, start a new thread.
Monty Gibbon
New Member
Wow. That's proper GearPage type stuff right there.
Humour me for five minutes and have a quick read through the thread so as to (a) appreciate the context in which I have sought the kind assistance of the community in this specific thread and (b) the gracious help I have received from it.
Whilst you do that, and tuck it back into your sock, I'll go and crank up my stereo Fender clone valve amps to lovely clipping and compression through their respective, incredibly heavy and cumbersome 2 x12 inch speaker cabs. As you're aware, it was not Leo Fender's intention his lovely circuitry be used in such an anarchic fashion.
That said, he specified input jacks for microphones on guitar amps and was happy enough to encourage musicians to play ~ wait for it ~ keyboards through a Fender Twin Reverb!?
I know, I know; sacrilege.
Honestly, I'm pretty sure that, with the benefit of my money in their pocket, Messrs. Nobsound won't be that concerned about my plans for their shoddy circuitry. If they are outraged enough to sit and write a lengthy post about my intentions, I'm sure they'll reflect and calm down a bit.
I dare say with the passage of time, Leo Fender's rage that his Bassman amplifier was being used by guitarists dissipated. Eh?
Love you.
Monty Gibbon
New Member
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FlaCharlie
Super Member
I'm afraid I don't know what "GearPage type stuff" means. Not sure why, but you seem to be upset.
Huh? Yes, people have offered you their kind assistance. And I am one of the people who responded to your earlier posts and gave you some information about PS cap values, including how to use the charts in the rectifier tube data sheets to determine if the value you want to use is actually safe so that you don't damage the amp.
It should be clear that when I said "as they were intended to be used", I was referring to the Nobsound 6p1 which is clearly intended to be used as a stereo amp, not a musical instrument amp.
My reason for suggesting that you start a new thread is so that you'll get responses that are more useful to you. Simple as that. Not sure why you would find that offensive.
If you go back and read the thread, not just the last page and your own posts, you'll see that it's about mods designed to improve the amp's performance as a stereo amp. Mods designed to make it work in a guitar amp setup are likely to be quite different.
If you have some other use in mind, a new thread, with an appropriate title, will get the attention of those here who have more knowledge of guitar amplification. Chances are not many of them are interested in modding cheap Chi-Fi stereo gear so it's not likely that they would just happen to stumble across your posts here.
And those who bought the Nobsound amp and are interested in improving it are not likely to be interested in playing guitar through it. Most of them are also new to tube gear since tube newbies seem to be the target market for these amps. So they are also unlikely to have expertise in tube amps designed for guitar.
So a separate thread only makes sense. Welcome to AK!
Inerlogic
New Member
I posted back in April of last year. i've been playing my amp (with StepheK's mods and an APC voltage converter) for the last year, and only recently at lower volume, i tried turning it up this weekend and the distortion was BAD.... the VU meters wouldn't budge even with the volume cranked. Sitting at idle, the tubes weren't even hot... just a little warm. I use the thing to give my Amazon Echo Dot a louder voice, and for listening to Amazon Music, so it sits on quite a bit.... hours on end...
The easiest tube to replace was the rectifier, so i started there, and bam.... the thing came back to life.
I picked up a handful of spare tubes from the Ukraine last year, including the 5u4C with shouldered bottles.
IX-61, so, new ANCIENT stock....
Should i expect "only" a year of (near constant) service from a rectifier?
Should i look into a solid state replacement?
I have 3 ukranian tubes and the original it shipped with, so i have some time to decide on solid state...
Is it a normal failure mode for the rectifier to just slowly go bad?
I noticed the distortion a few weeks back, but figured the dot had reset it's volume to max and was beating up the front end... turning the input volume down cleaned it up.
The easiest tube to replace was the rectifier, so i started there, and bam.... the thing came back to life.
I picked up a handful of spare tubes from the Ukraine last year, including the 5u4C with shouldered bottles.
IX-61, so, new ANCIENT stock....
Should i expect "only" a year of (near constant) service from a rectifier?
Should i look into a solid state replacement?
I have 3 ukranian tubes and the original it shipped with, so i have some time to decide on solid state...
Is it a normal failure mode for the rectifier to just slowly go bad?
I noticed the distortion a few weeks back, but figured the dot had reset it's volume to max and was beating up the front end... turning the input volume down cleaned it up.