| akersa |
I am working on building a variation of an Antique Sound Lab Tube headphone amp, and I am wanting to get away from using an output transformer, my problem is when I build the circuit without the transformer, I end up with high voltage on the audio outs. What am I doing wrong? Do I need bigger filters than you do if you have the transformer. I have attached the schematic, hopefully somebody can help me with my problems.
Thanks,
Adam Akers |
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| fdegrove |
Hi,
You did what?
Suppressed the OPTs?
Cheers,:scratch: |
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| Colt45 |
When you drop the transformer, there is no real plate load.. so youll need a plate resistor or choke
but this output will be really high Z..
better use a trafo or do a CF. straight r/c-coupled is gonna have a real high Z |
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| fdegrove |
Hi,
From what I can tell there should be a headphone jack behind C11/R?.
That will probably be still quite high impedance but it does bypass the OPT.
Another option, assuming you leave the OPT in place or use a proper plate load, is to take the signal from the cathode of the 6BQ5 using a good quality coupling cap as Colt45 suggested.
Do you happen to know the input impedance of your cans?
Cheers,;) |
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| akersa |
Thanks for the help. My cans have a 600 ohm Z. Can anybody be more specific on the values of coupling caps, or a plate resistor value. I am new to Tubes, and sometimes my experimentation with different values is a shot in the dark.
Thanks again,
Adam Akers |
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| fdegrove |
Hi,
The PSU of that schematic has a really low B+, 160V.:(
If you could make it around 270V you could than easily run the trioded 6BQ5 in class A using a 3K5 anode resistor and a 270R cathode resistor.
The input stage needs revision also to accomodate the higher B+ but I feel it would be much better off that way.
For 600 R cans a 80 uF cap should be ample, you could even use some // filmcaps to reach that value.
Cheers,;) |
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| akersa |
Thanks for all of the suggestions guys. But I am still having problems with my amp. Would anybody be willing to take the attachement that I am posting and draw in the missing parts. I have been playing with a cathode follower circuit, but I do not think that I am doing it correct. My headphones are 600 ohm. Thanks again for all of your help. I am enjoying this project, but finding it difficult to finish. Help!!
Adam Akers |
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| trespasser_guy |
Ok, I took the circuit and made a cathode follower so you could see what was meant... I don't know what to do with the screen grid, so i left it unconnected. Others here who know their stuff moreso than I can help you out more and make fun of my circuit. ;) I admit- I don't know a lot about tubes.BUt, I got the basic topologies down. hehe MGHead as cathode follower: (not totally complete though...)
EDIT: Ignore pin numbers- I threw this circuit together using the objects I had in my schem program, which were 6L6GC and 6SL7. So, pin numbers are wrong. Part numbers and values not shown on purpose. ;) (because I don't know them hehe) |
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| akersa |
Thanks for the help. Can anyone else fill in any more of the missing peices? Values, what to do with the plate etc.
Thanks
Adam Akers |
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| akersa |
I am still having a really hard time trying to incorporate this circuit. I am in need of some one that understands this stuff better than I do to help me. If anyone out there would spend the time to draw the schematic like it should with the Cathode follower circuit in place I would be willing to pay you. This is a project that I am really wanting to finish.
Thanks,
Adam Akers |
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| SY |
If you're going to use a pentode as a cathode follower, you need to have the screen grid be at a positive, fixed potential above the cathode. The simplest way to do that is to put a bypass cap from cathode to screen, then feed the screen through a resistor to B+.
The REAL answer is to not try to adapt a circuit that isn't really designed to do what you want. I'm certain that with a bit of searching you can come up with a finished, tested design for an OTL tube headphone amp. In fact, I think Joe Curcio may have published one.
:att'n: The usual warnings: unlike much solid state gear, tube amps carry potentially LETHAL voltages. If you're unsure of what you're doing, DON'T DO IT. |
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| HDTVman |
Try looking at "tubecad.com". He has done headphone amps a couple of times and if you take the time to do some reading you will get an education.
Later BZ :geezer: |
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| G |
If you are going to build a headphone amp you are doing yourself a disservice by not visiting the Headwize Forums:
http://headwize2.powerpill.org/ubb/...fnum=3&fdays=20
Also you should take a look at this simple and effective headphone amp project:
http://headwize2.powerpill.org/proj...waarde1_prj.htm
This is a good starting point and the sound is purported to be wonderful. Since you are using 600 ohm cans a good 470uF output cap bypassed by a good poly cap should work well. Just register for the forum and you will have all of the help you will need. I hope these links help.
G |
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| fdegrove |
Hi,
| quote: | | This is a good starting point and the sound is purported to be wonderful. |
It is one of the best on that site and I can only recommend it...especially with the Ying Mingyao PSU.
I know this circuit since it first appeared in the now defunct Dutch audio mag Audio & Techniek and it even drove my 92dB speakers to reasonable levels and with great sound.
There's still room for improvement, but as is it won't disappoint.
Cheers,;) |
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