bcowen
Headphoneus Supremus
Thanks! Greatly appreciated!
The DIY'rs Cookbook
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Thanks! Greatly appreciated!
Tjj226 Angel
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John informs me that this amp has way too much gain for you. Please understand that using a CCS on the 6SN7 is going to significantly RAISE the gain. This amp will basically have an input sensitivity of half a volt peak to peak or less than 0.25v rms.
I would probably add in a voltage divider on the input to the amp to lower the volume. At this point the ccs is really only helping with noise and cross talk. The big improvement to be made is the output capacitor. I believe the stock output cap is only 30uf. This is way too small. I would bump it up to 100uf at least. In the schematic below I have 300uf and the phase shift still isn't all that great. As you can see its 15 degrees off at 20hz. With the stock cap in the simulation it is closer to 50 degrees off.
johnjen
Headphoneus Supremus
Ok so I lied, but only sorta… 
Today as I type this the SQ is almost on par with what I heard yesterday before the the first case of component infant mortality I've had in decades, which required new FETS to replace the 2 that 'died'.
And there are hrs yet to go before shut down tonight.
And I have a single word that describes what the 'NOT subtle', as in at all, lifting of the unsuspected veil (but aren't they all?) has resulted in.
Immersive.
It's a close cousin to CNST (Central Nervous System Tap) where the music surrounds me with precision in 4d space (3d location and thru time).
The bigly difference between Immersive and CNST is, I'm IN the music, as I hear more of it's inner structure and the 'fabric' of the harmonics and it's acoustic presence, as there is less of the created acoustic pressure wave which was out of synch with its true waveform shape.
Thus less of this acoustic waveform is smeared in and thru time, and thus more acoustic energy is 'concentrated' properly in the now as the music plays in that ongoing 4th dimension.
IOW, Since the acoustic waveform is more 'concentrated', there is better coupling of the driver to the air, to re-create the original waveform, for me to hear deeper and with greater focus and definition into the all of the individual 'voices' and the music as a whole.
I've finally reached a point where I have a reference of such an alluring nature, that I can use it to compare it to the aspiring upcoming amps, and try other circuit combinations to selected portions of this amp.
Like the input xfmrs.
And perhaps I'll haul out my set of HD700's and see about fussing with them and take the info I've learned about improving the 800's and apply it to the 700's.
Just to see what happens, 'cause I think the 700's are vastly underrated what with the same reputation of those hi-freq peaks as the 800's.
But if I can dial back the overshoot just a smidge, I figure they could be 'a contendah'.
JJ
ps during the course of writing this post the SQ has risen still further and now is about on par with just before the amp went sideways, which is a quicker recovery than I expected for the SQ to return, and of course there is tomorrow to push the bar still higher yet.
Today as I type this the SQ is almost on par with what I heard yesterday before the the first case of component infant mortality I've had in decades, which required new FETS to replace the 2 that 'died'.
And there are hrs yet to go before shut down tonight.
And I have a single word that describes what the 'NOT subtle', as in at all, lifting of the unsuspected veil (but aren't they all?) has resulted in.
Immersive.
It's a close cousin to CNST (Central Nervous System Tap) where the music surrounds me with precision in 4d space (3d location and thru time).
The bigly difference between Immersive and CNST is, I'm IN the music, as I hear more of it's inner structure and the 'fabric' of the harmonics and it's acoustic presence, as there is less of the created acoustic pressure wave which was out of synch with its true waveform shape.
Thus less of this acoustic waveform is smeared in and thru time, and thus more acoustic energy is 'concentrated' properly in the now as the music plays in that ongoing 4th dimension.
IOW, Since the acoustic waveform is more 'concentrated', there is better coupling of the driver to the air, to re-create the original waveform, for me to hear deeper and with greater focus and definition into the all of the individual 'voices' and the music as a whole.
I've finally reached a point where I have a reference of such an alluring nature, that I can use it to compare it to the aspiring upcoming amps, and try other circuit combinations to selected portions of this amp.
Like the input xfmrs.
And perhaps I'll haul out my set of HD700's and see about fussing with them and take the info I've learned about improving the 800's and apply it to the 700's.
Just to see what happens, 'cause I think the 700's are vastly underrated what with the same reputation of those hi-freq peaks as the 800's.
But if I can dial back the overshoot just a smidge, I figure they could be 'a contendah'.
JJ
ps during the course of writing this post the SQ has risen still further and now is about on par with just before the amp went sideways, which is a quicker recovery than I expected for the SQ to return, and of course there is tomorrow to push the bar still higher yet.
bcowen
Headphoneus Supremus
John informs me that this amp has way too much gain for you. Please understand that using a CCS on the 6SN7 is going to significantly RAISE the gain. This amp will basically have an input sensitivity of half a volt peak to peak or less than 0.25v rms.
I would probably add in a voltage divider on the input to the amp to lower the volume. At this point the ccs is really only helping with noise and cross talk. The big improvement to be made is the output capacitor. I believe the stock output cap is only 30uf. This is way too small. I would bump it up to 100uf at least. In the schematic below I have 300uf and the phase shift still isn't all that great. As you can see its 15 degrees off at 20hz. With the stock cap in the simulation it is closer to 50 degrees off.
Thanks very much for taking a look at this. Really appreciated. You are correct on both the gain issue and the 30 uF output capacitance -- there are three 10 uF caps/channel that appear to be film. As you can see there's not a lot of room in there as it currently sits, so getting 100 uF (or more) of film caps in there isn't going to be easy if it's possible at all (but I haven't really looked to see what's currently available either). I think what I need to do next is get the volume pot swapped out and see if that helps with the gain issue. I have an Alps to put in, and it probably goes without saying that the pot that's in there isn't much to speak of in a $200 retail amp.
johnjen
Headphoneus Supremus
So today my experiment with new input xfmrs will commence later this evening, after the amp gets another operational thermal cycle.
Mostly to see what happened to the SQ before the new parts go in.
Yep more fun…
JJ
Mostly to see what happened to the SQ before the new parts go in.
Yep more fun…
JJ
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johnjen
Headphoneus Supremus
Just an additional note about that volume pot.snip
I think what I need to do next is get the volume pot swapped out and see if that helps with the gain issue. I have an Alps to put in, and it probably goes without saying that the pot that's in there isn't much to speak of in a $200 retail amp.
You already have a 200KΩ pot (according to the schematic) and changing it to a lower Ω one isn't going to help.
And finding a higher value pot might help but you really should to go with the voltage divider that Tjj mentioned in his previous post.
And while a better quality pot is a good idea, the voltage divider will lower the input signal level so the pot will be usable in it's sweet spot (9-3)…
And it would be WAY easier to implement since it only involves 2 resistors, or you could add a stereo pot and 'dial in' the amount of signal attenuation and then just leave it alone.
The other 'option' would be to lower the overall gain of the amp, which is a MUCH more involved process and kinda asks the question of why, based on the complexity of trying to improve a $200 amp.
Just a passing thought or 2.
JJ
bcowen
Headphoneus Supremus
200k? Do you mean 100k x 2? If so, cool. If not, you're confusing me (which isn't hard).
Changing the volume pot will require a little more, um, balls than I originally thought.
What's in there has an 8 pin connection so I can't use the existing circuit board as the Alps has 6 pins and the spacing wouldn't line up even if the pin assignment did. I'll have to don my big boy pants and solder the wires directly to the Alps pins. And I'm a bit mystified with the readings I get on the existing pot. Pins 1, 3 and 4 are wiper, signal, and ground, but I can't figure out exactly what pin 2 is doing. Referenced off of any of the other 3 pins, it reads the same at 47k full CCW rotation, and 49.5k at full CW rotation. I haven't pulled the 'assembly' out yet, so maybe it will become obvious when I can better see the board traces.But tell me about this voltage divider thing. Sounds like a great solution. Easy enough to explain here? I have a box full of resistors, and only $200 at risk. LOL!
JKDJedi
Headphoneus Supremus
Take one for the team!200k? Do you mean 100k x 2? If so, cool. If not, you're confusing me (which isn't hard).
Changing the volume pot will require a little more, um, balls than I originally thought.
But tell me about this voltage divider thing. Sounds like a great solution. Easy enough to explain here? I have a box full of resistors, and only $200 at risk. LOL!
Tjj226 Angel
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200k? Do you mean 100k x 2? If so, cool. If not, you're confusing me (which isn't hard).
Changing the volume pot will require a little more, um, balls than I originally thought.
But tell me about this voltage divider thing. Sounds like a great solution. Easy enough to explain here? I have a box full of resistors, and only $200 at risk. LOL!
A voltage divider is just two resistors in series. You put your audio input at the top and you take your output from the middle of the two resistors. Two resistors of the same value (say 50K) will reduce your volume by half.
Its basically a fixed value potentiometer. If you google voltage divider, you will find some really nice write ups about the science of the device.
-------------
Pin 2 might be a second ground for shielding?
I honestly wouldn't screw with any of this. I would put humpty dumpty back together and sell it off while you can still get most of your money back. You just don't have the space in the chassis to fix the problems plaguing this design.
Just build yourself a better amp. If you are willing to solder and get your hands dirty, then why not? If you tell me what you want, I can even put together a schematic for you.
JKDJedi
Headphoneus Supremus
@bcowen if it ain't broke don't fix it!
Tjj226 Angel
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More like if it is so broken that even if you fix it it still won't be worth much, don't fix it.
Im gonna have to get back to that later. Like so many other things I do, I started looking into it and figured out I came up with kind of a neat circuit. I need to test it before I put it up online and risk having someone electrocute themselves.
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johnjen
Headphoneus Supremus
Well, D'Oh…200k? Do you mean 100k x 2? If so, cool. If not, you're confusing me (which isn't hard).
Changing the volume pot will require a little more, um, balls than I originally thought.
But tell me about this voltage divider thing. Sounds like a great solution. Easy enough to explain here? I have a box full of resistors, and only $200 at risk. LOL!
It is a 100KΩ pot (my bad) not a 200KΩ one.
And my guess for that 4th connection on the pot connector board is, it’s a ground connection to the body of the pot itself.
And changing out the pot would (or could) be a pia, but then it might just slip right on in too.
But it will take a fair amount of 'practical experience' to determine either way.
And if you don't mind making an example of a true Frankenstein amp and loosing any and all resale value, heh it could be a learning experience in DIY with indeterminate net results.
But then those are the chances and challenges of 'customizing' audio gear.
Of course if you REALLY want to dive into the DIY swimming pool take Tjj's offer and take this opportunity to dive headfirst into the deep end.
Or you could start out 'easier' by going with one of Nelson Pass's starving student amps or go full tilt and build on from scratch.
I mean ya gotta start somewhere, right?
hahahahahahahahahahahahaha.
JJ
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bcowen
Headphoneus Supremus
Well, D'Oh…
It is a 100KΩ pot (my bad) not a 200KΩ one.
And my guess for that 4th connection on the pot connector board is, it’s a ground connection to the body of the pot itself.
And changing out the pot would (or could) be a pia, but then it might just slip right on in too.
But it will take a fair amount of 'practical experience' to determine either way.
And if you don't mind making an example of a true Frankenstein amp and loosing any and all resale value, heh it could be a learning experience in DIY with indeterminate net results.
But then those are the chances and challenges of 'customizing' audio gear.
Of course if you REALLY want to dive into the DIY swimming pool take Tjj's offer and take this opportunity to dive headfirst into the deep end.
Or you could start out 'easier' by going with one of Nelson Pass's starving student amps or go full tilt and build on from scratch.
I mean ya gotta start somewhere, right?
hahahahahahahahahahahahaha.
JJ
Thanks. Both to you and @Tjj226 Angel . I didn't state my intentions very clearly at the outset, but just to clear that up: I have an OTL that I enjoy tremendously (the Incubus), so my musical fix(es) will not be jeopardized by whatever I do to the Darkvoice. I only bought it because 1) it was cheap, 2) I wanted something to play with, and 3) it was cheap.
It doesn't sound bad at all for what it is, but a foray into the best? Well it's not of course, and almost a certainty that it never will be. But....if I can spend $100 or $200 on parts and significantly elevate its performance, then I'm willing to do that, fully aware that it might never be worthy of the parts put in it. But I probably spend more than that every month on tubes anyway. So I may get up the courage to go after the pot, seeing as I already have one in hand. No pain, no gain. Or less gain. Or something.
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johnjen
Headphoneus Supremus
Ya know…
A little shock here and there, while a bit 'shocking' at first (
) can be sorta like 'blowing the carbon' out of your engine…Of course the after effect is you're now in danger of going to fast…
hahahahahahahahahahahaha
JJ
ps this is not medical advice, this is not a cure for what ails anyone, nor should anyone stick their fingers in the wall socket, just because…
hahahahahahahahahaha
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bcowen
Headphoneus Supremus
ps this is not medical advice, this is not a cure for what ails anyone, nor should anyone stick their fingers in the wall socket, just because…
hahahahahahahahahaha
ROFL! Although I'd rather stick my finger in a wall socket than across the contacts of a fully charged 450v, 1500 uF cap. No need to ask why I know that.
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