| marcus7601 |
I am looking into a way to add a 6N1P (6922) tube into a already finished Audiosector 3875 gainclone. I have very little knowledge of tubes and i dont want to break up the gainclone pcb i already have assembled.
Is there and easy way to add a tube on the input of the GC?
To be honest i dont care much about improving the sound quality, i just want to fiddle around with my first tube project.
I am using 35V rails to my GC and i now that there are projects that uses this with LM3875 and 6922 tubes but i want to use the audiosector kit i already have.
Please help a newbie! |
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| ionomolo |
Yes, there is:
http://www.customanalogue.com/diytu...clone/index.htm
If the amp is AC-Coupled noninverting connect the cathode of the tube directly at the input and check if placing something like the 1n5 cap removes some noise.
The 1n5 cap is imprescindible in the inverting amp as it is to make the noise gain of the amplifier independent of the source impedance. |
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| marcus7601 |
Hmm...can you be more specific? :clown:
Which part of the schematic from the link should i use to then connect to the input of my gainclone? |
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| ionomolo |
The tube, the input (resistor + pot) network and the cathode resistor (4 parts).
If your amplifier is DC coupled (does not have a resistor and a cap at the input) you should use a capacitor and a resistor to connect the tube |
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| leadbelly |
| A 6N1P is NOT equivalent to a 6922, no matter what the eBay sellers say. If you want to use low voltage rails I recommend you use a ECC88, 6922, or 6N23P. |
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| Nordic |
add 6DJ8
A nice High voltage supply can be made with a 2x24V PCB mount transformer and a greinacher voltage doubler useing caps from a dead PC PSU... |
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| flubug |
| What's the problem with using the 6N1P? |
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| leadbelly |
| quote: | Originally posted by flubug
What's the problem with using the 6N1P? |
It's not a low voltage tube and will add lots of distortion with the suggested +/-35V rails. |
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| flubug |
QUOTE: It's not a low voltage tube and will add lots of distortion with the suggested +/-35V rails.
Thanks for the warning! You probably saved me a lot of grief. |
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| marcus7601 |
Thanks for the tips but i will use my 6N1P for testing and maybe later change to better tube.
I cant seem to find schematic to audiosectors gc to check the ac-coupling. Anyone knows where to find it? |
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| hidetogil |
Hello,
If you're interested, I'm also trying to add a tube buffer on my LM3875 GC. I hope to test it next week.
Bye |
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| marcus7601 |
| Interesting.. :D how will you do it and which tube do you use? |
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| h@kan |
I'm lazy and purchased a tube buffer kit from ebay ($58). Just mounted it in my box and pressed play. Hard to describe what it did to the sound but the words "air" and "warmness" feels relevant. I'm really glad I added it to my gainclone.
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| Nuuk |
| Nice work! Sometimes Ebay makes even DIY seem expensive! ;) |
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| marcus7601 |
Very nice! Yes, for that money it almost seems stupid not to buy readymade pcb. Is that buffer from Diygene on ebay?
Nice enclosure by the way! |
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| h@kan |
| Yes it's the ls-29 from diygene. |
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| neutron7 |
| quote: | Originally posted by h@kan
I'm lazy and purchased a tube buffer kit from ebay ($58). Just mounted it in my box and pressed play. Hard to describe what it did to the sound but the words "air" and "warmness" feels relevant. I'm really glad I added it to my gainclone.
image
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thats a beauty. but whats all that scrumpled up foil for?
and is the transformer you have there just for the tube high voltage or is that for the whole thing? |
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| h@kan |
| The aluminium foil is not there anymore it was just a desperate attempt to get rid of some hum. The hum disappeared when I connected the input rca's. There is a torroid transformer 300VA 22x2 for the chipamp (placed under the tube buffer board) and one 14V AC for the tube buffer. |
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| skidave |
H@kan,
Nice job. Do you have any more pics? Did you connect the output of the tube buffer to the gainclone boards? Any info would be great.
Dave |
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| h@kan |
Yes thats right. Connect the signal inputs to the buffer and connect the output from the buffer to the inputs on the lm3875 boards.
If you wish to have just one power button for the system I strongly recommend some kind of delay on the chipamp part. This is because when power up the buffer strange things happens to the outputs before the tube warms up.
I burned one of the lm3875 chips caused (i think) by this.
I solved it with 2 power buttons, one for the chipamp and one for the buffer. I power up the buffer first and after 1 min I power up the chipamp.
Can anyone confirm that my theory about this have any relevance?
pics |
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| Nuuk |
| quote: | | If you wish to have just one power button for the system I strongly recommend some kind of delay on the chipamp part. This is because when power up the buffer strange things happens to the outputs before the tube warms up. |
I think what you mean is a delay on the output of the buffer section, ie before the amp.
You need to mute the output of the buffer while it powers up. I have found at least a minute is about right for tube circuits. My valve pre amplifier uses the circuit shown here but with a 1M resistor in series with the trimmer (you could just use a 1M in series with a 470K resistor as there is much to gain from being able to adjust the delay).
The alternative is to use some sort of speaker protection with a built-in power on delay (as used in this project ). |
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| h@kan |
| Yes I suppose thats what I mean but if there is no power on the amp boards while the buffer heats up there is nothing that could be damaged, right? |
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| Nuuk |
| quote: | Originally posted by h@kan
Yes I suppose thats what I mean but if there is no power on the amp boards while the buffer heats up there is nothing that could be damaged, right? |
Yes, but (providing there is no problem with the amp circuit) it is not the output from the amp that is likely to cause the nasty sounds and/or damage to the speakers.
You can of course power up each section in order using two switches. The problem arises if you, or somebody else, forgets which order to power them up. :att'n: |
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| lineup |
| quote: | Originally posted by marcus7601
Thanks for the tips but i will use my 6N1P for testing
and maybe later change to better tube. |
this is perfectly alright to do
6N1P likes higher voltage, even more than 6DJ8 (6922, E88CC)
but question is how much more distortion this will give you.
I say the diffrence may not be too big.
But later, as you intend to, you should upgrade to 6DJ8 or some real low voltage triode.
It should be noted, that even if 6DJ8 has been shown to work reasonably well at say 50-70 Volt DC,
this one too, will perform better audio at 100-120 VDC.
Nordic suggestion of doubling the power supply voltage
from you Gainclone transformer, is one good idea.
Will save you one extra transformer.
The circuit to get double voltage power supply output is not very complicated.
You can get schematics for this from people here.
If we want use some low 'solide state voltage' for the tube part
there are some other more dedicated low voltage tubes.
Like 6GM8 / ECC86 = Max 30 Volt anode.
http://tdsl.duncanamps.com/show.php?des=ECC86
And you can get even further & better advices on this
in the Tube forum of www.diyaudio.com
Regards Lineup |
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| marcus7601 |
Thank you all for your comments. All are deeply appreciated.
As i see it i will start (when i find time) with my original tube. Later on the voltage doubler and better tube sounds like a good idea. |
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| h@kan |
| quote: | | You can of course power up each section in order using two switches. The problem arises if you, or somebody else, forgets which order to power them up. |
You're absoluely right about that. For my upcoming project, that will involve a tube buffer in some way, I will look into the "buffer power on delay". It seems like the proper way to do it. |
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| hidetogil |
Well done, you did a great job! I was a bit late for my tube buffer, but I finished it three days ago. It's not as beautiful as yours but here's a picture :
Originally it's a gainclone from audiosector (LM3875). I added an unregulated snubberized PSU (from Carlos FM) and Velleman k4700. The buffer schematics are the one you find on Joe Rasmussen site (site )
I think (or it's seems to me) that the sound improves a lot, the difference between every instrument is more perceptible and accurate. I really don't regret this modification and I really advise it to every gainclone's builders! |
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| h@kan |
Nice work hidetogil!
I will definitly try to build a tube buffer from scratch but there is some basic electronics knowledge missing for me but I guess thats the beaty of it, trial and error until you got something that actually working. Do you have more pictures, especially of the tube buffer?
What is the black box on top of the main toroid? |
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| lineup |
black box
can be some mains filter
before the 230 VAC primary of trafos
but maybe it is some extra pcb transformer
those tubes need some heater supply, too
let us see what he say
if i am right in something
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| hidetogil |
Lineup is right, the black box is the transformer for the heater. You need two transformer for the buffer and one for the LM3875. Don't worry about building it, it's really simple, I've done many mistakes before getting it functionnal.
Here we go for more pictures :
(:xeye: I know, I printed a reverse circuit, so I had to solder on the component side... I made a lot of mistake!!!!)
I still have a little bug, maybe someone could help me here :
when power is on, the velleman k4700 display an error (red led is on) during 5-10 sec. After that, the red led turn off and the normal temporisation starts, that lead me to wait about 28 sec before the amp works. (I follow Nuuk's advises about temporisation by changing a capacitor on the velleman kit)
see you |
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| marcus7601 |
| Nice job! Do you have pcb layout available for the buffer? |
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| h@kan |
| quote: | Originally posted by marcus7601
Nice job! Do you have pcb layout available for the buffer? |
You just stole my next question :) |
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| Will |
do you find the hiss level is higher after adding the tube buffer?
cheers. |
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| h@kan |
| I think its a matter of the definition of "hiss level". The tube buffer gives, naturally, the character of tube sound. I'm sure some would say the "hiss level" is higher. I would probably call it something else since I think the tube buffer turned my allready great gainclone into something I would describe as excellent. |
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| Zigis |
Nice build, hidetogil,
what schematic you use? Joe Rasmussen buffered gainclone use 1 tube for amp (half for channal) , I see 2 boards with 1 tube on each.
Have you Rasmussen comercial amp schematic ?
I have gainclone with high voltage 6N1P cathode follower buffer.
Zigis. |
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| KT |
Is it better to use a tube buffer or to put something like a Foreplay preamp in the chassis with the chipamp to make an integrated?
I've been using chipamps with tube preamps and like the combo alot, so I'm wondering if a buffer would sound as good as a stand alone preamp circuit.
I know the buffer is by definition a unity gain stage, but does the stand-alone power supply design of an outboard preamp give it the leg up? Any experiences comparing the two?
Thanks,
KT |
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| Will |
| quote: | Originally posted by h@kan
I think its a matter of the definition of "hiss level". The tube buffer gives, naturally, the character of tube sound. I'm sure some would say the "hiss level" is higher. I would probably call it something else since I think the tube buffer turned my allready great gainclone into something I would describe as excellent. |
I know what you mean by the tube turning the amp into an excellent one; been there, done that with JoeR's first IGC then later upgrading to a VBIGC status.
Using normal standard efficiency speaker i.e. 86-90dB are of course a joy, all the excellent musical tunes churning out from a relatively low cost amp; but I've graduated from those and went on to higher efficiency now, and this amp 'hisses' even at the seating position at 10 feet away. I'm using 2 VBIGC to power my high efficiency active dipole (used in the mids - double B200 and highs - Fountek JP3 ribbons). They have the qualities of a good SET, almost edgeless treble and very good projecting emotions from the singer, excellent transparency, just that the hiss level takes some joy away during softer passage.
Another thing to note is that on both my VBIGC, the first was done point to point wiring and the second was done mostly on an experimenter's pcb. Guess which amp sounded better?? PTP of course.
Nevertheless enjoy our amp for now ;) |
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| Will |
| quote: | Originally posted by Zigis
Nice build, hidetogil,
what schematic you use? Joe Rasmussen buffered gainclone use 1 tube for amp (half for channal) , I see 2 boards with 1 tube on each.
Have you Rasmussen comercial amp schematic ?
I have gainclone with high voltage 6N1P cathode follower buffer.
Zigis. |
Zigis can you please describe in more detain on the schematic of the 6n1p stage? I've just discovered lately that despite all the hype in ebay, 6n1p is NOT equivalent to 6922.
cheers. |
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| Nuuk |
| Will do you use a NOS DAC? :att'n: |
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| Will |
| quote: | Originally posted by Nuuk
Will do you use a NOS DAC? :att'n: |
Processing is done via a DCX2496 with passive output. The problem is entirely coming from the VBIGC because previously I used a Rotel 6 channel amp and it's very quiet - but the typical solid state sound put me off.
cheers. |
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| Nuuk |
I asked because you can get a hiss from most NOS DACs and the better the rest of the system, the more you will notice it.
My VBIGC is absolutely quiet, and I also use efficient OB speakers. So you can get rid of the hiss- the $64000 question of course is "how?". |
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| Zigis |
Hi Will, I build Decware ZSLA-1 clone and chipamp in one box, PS for both in other box.
Today I see in decware.com , ZSLA-1 is out of production and schematic is not available online now. I have not saved file too, only printed schematic.
If you are really interested, I can try to draw it, maybe someone have saved schematic?
Zigis. |
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| hidetogil |
I have absolutely no hiss or hum with my gainclone, it's very quiet! My DC offset seems a bit high 90mV one channel and about 40 for the other one.
For Zigis :
I use the same schematics as Joe Rasmussen but I use 2 tubes. The pcb layout is not from me, it comes from a guy called Idefixes on another forum. I simply did the same as him, and I didn't ask why he used 2 tubes instead of one. The only thing different is the regulated PSU for the heater.
Of course I've got the PCB layout and I can share it if you're interested! |
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| Zigis |
| hidetogil, do you use only one half of each tube, or both are parallel ? |
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| hidetogil |
| quote: | | hidetogil, do you use only one half of each tube, or both are parallel ? |
One half of each tube! ;) |
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| Will |
| quote: | Originally posted by hidetogil
I have absolutely no hiss or hum with my gainclone, it's very quiet! My DC offset seems a bit high 90mV one channel and about 40 for the other one.
For Zigis :
I use the same schematics as Joe Rasmussen but I use 2 tubes. The pcb layout is not from me, it comes from a guy called Idefixes on another forum. I simply did the same as him, and I didn't ask why he used 2 tubes instead of one. The only thing different is the regulated PSU for the heater.
Of course I've got the PCB layout and I can share it if you're interested! |
Hi,
As I said, if you're using standard efficiency speakers the hiss is hardly noticable. But push it up to about 98-100dB like mine, hell will break loose.
Nuuk,
What's your current rated efficiency for your OB?
cheers. |
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| Nuuk |
| quote: | | What's your current rated efficiency for your OB? |
They are 95db Will. |
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| hidetogil |
I'm going to try it with a 99db+ speaker...
EDIT :
Will was right, when using a 99db+ speaker, you can hear a little hum, but you have to stick your ear on your speaker, so for me it's insignificant.... |
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| marcus7601 |
hidetoqil - can you send me the pcb layout and schematic you used for the buffer? Thankss
marcus7601@gmail.com |
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| MartyM |
Hello h@kan, I looked at the PCB & kit you bought on eBay...what voltages does it require? Also, any way I could look at the schematic to see if I can use it in my car amp (chip amp based)?
marcus7601, do you have a copy of the schematic you personally used and/or the PCB as the guy above requested? How's the sound to you, also....you like it?
I built a +260V preamp for my car to use with the chip amp but it requires much circuitry for the power & time delays, etc. I would prefer to simplify it if possible as you guys did.
Thanks! :) |
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| marcus7601 |
| I have nor built it heard it yet. I am still waiting for comment regarding the pcb layout and schematic. |
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| MartyM |
I'm sorry Marcus, I meant to type "hidetogil" regarding my post asking for info the same as you.
As a side note, what I did for my car tube preamplifier (12AX7) was to use a 555-based timer that switches over DPDT mini relays from a line pass-through to the tube audio signal after about 30s.
That way I never lose audio unlike the commercial hybrid tube-transistor amps I owned long ago (Planet Audio HVT series) that made the listener wait 30+s with no sound while the tubes warmed up.
However in my LM3886 amplifier, I made a Microchip PIC-based (12F629) multiple-output delay timer for similiar purposes. It ends up being almost the same amount of hardware, but can be more flexible, and the software was simple. |
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| h@kan |
| quote: | Originally posted by MartyM
Hello h@kan, I looked at the PCB & kit you bought on eBay...what voltages does it require? Also, any way I could look at the schematic to see if I can use it in my car amp (chip amp based)?
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The tube buffer requires 12VAC. I use a 14 VAC transformer from a cordless drill charger with no problem. I dont know what happens if connecting 12DC. Maybe some where after the rectifiers on the board.
I dont have the schematic of the buffer, I have asked diy gene for it but with no success. The ebay ad claims that a logical schema diagram are included in the package but thats not true, at least not in my package. |
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| MartyM |
| h@kan, I got a response from "DIY Gene": someone named Ken replied that the preamp can be used with 12V DC OR AC, but did not reply to my question regarding schematic info. |
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