[nick n]

This should be the place to post this. Basically I was starting to clean up my Heathkit AA-151 tube amp and what do you know... no headphone out jack anywhere to be found.
 How do I go about grafting in a 1/4" headphone out jack on this beast?
My headphones are all higher ohm ( 600 and 400 )
 I noticed the speaker connections go from 4 - 16 ohm and was thinking I could somehow attach to these using some sort of cable I could make up while speakers were on at the same time, maybe a switch thing.   Anyhow all I am concerned about for the moment is can it be done ( reasonably ) and if so what are the options for doing so.
 
This is the clearest picture of all the connections on these things. My camera is not as good so this obviously is someone else's. I had a schematic lying around somewhere. If I find it I will post.
 

I had hoped by chance that the matching tuner would have had a jack but nothing there either. It would have given me an excuse to buy one
SCHEMATICS  I am useless at this but it may provide some answer to the electro-geniuses in here
 
from my MediaFire Account
Left and right images.
 
http://www.mediafire.com/imgbnc.php/9f790ef0787abe80b43a09ee75dfef21caa6f97e532191c3876321cef76c95216g.jpg  
http://www.mediafire.com/imgbnc.php/afd90ca81ad665690131909981bb7ec7157f512050602a9e05cceb17062befc66g.jpg

 
hopefully they can be expanded when saved.
Thanks for any insight.
 

 

[JadeEast]

http://sound.westhost.com/project100.htm
 
There are also a few outboard devices you can use like the russound TBL-75.

 

[nick n]

Thanks that Russound looks interesting. I would assume there are others in here with similar devices they have some experience with? Nothing too fancy , around $100 or so seems reasonable.
 
I'll have to take that other DIY design to a friend to check out.

 

[scottiebabie]

u dont need any fancy smancy doodads. there are a few ways to skin this particular cat.
 
1.the link resource in post #2 is a great & prolly the best way to do it correctly. u can either
a)build an external adapter box incorporating the appropriate resistor values for your particular amps output or
b)hack into the casing itself, tap the amps output, route to the front of amp, run the correct signal line thru the appropriate resistor values as above & terminate with chassis mount female 1/4 jack.
 
2. either of the above but use a single 100-220ohm resistor for the positive line/wire. because of the simplicity of a single resistor, u can even use a patch cable with a female cable mount 1/4 jack & the appropriate resistor patched in any part of the cable. not as good as #1 but should be decent enuff for your high Z cans.
 
3. try it directly on the speaker taps. cut off the headphone plug & insert the appropriate wires (R+ R- L+ L-) into the same off the amp speaker posts. depending on how sensitive (insensitive is best for this purpose) your cans are, u may have decent or not much vol headroom to play with. NO u wont blow or destroy your cans by hooking it up directly as long as one STARTS OFF AT ZERO VOL & DIAL IT UP SLOWLY.
 
them be your best bet as material costs are like $10-20 with the casing being the largest factor depending on how smancy u go. i personally went with option 1 as its the best for sonics as it allows one to optimize the amp for its output, lowers the amp output Z & last but not least, lowers the voltage output to 5v rms or so. goodluck

 

[nick n]

http://www.head-fi.org/forum/thread/529100/external-headphone-amp
 
I found the above after modifying my search a bit. Sounds pretty much what you mentioned in option #2 above. Going to give this a try first. Looks pretty straight forward

 

[scottiebabie]

 yup tat be it. remember u dont have to stick to 100ohms. the higher u go, the more volume headroom u give your cans. low Z is better for low Z cans but since your cans are btwn 400-600ohms, u can go as high as 470ohm resistors if u like. let me throw u another curve ball in the form of boutique resistors.
 
if u subscribe to the belief of components affecting sonics, remember that this resistor is directly in the signal path. im not sure how aplenty boutique wire wound resistors there are, but there are choices aplenty for carbon films. option #1 allows one to use most any make as a 2watter will do. just a thought.

 

[nick n]

I have to bring this up at least to show my ignorance in the matter.

On the picture above I see that there are 2 "C" =COMMON speaker connections for each channel LEFT and RIGHT, but on the RIGHT side there is also an "S"? Is this for a SINGLE CHANNEL or a SHARED ground?  What exactly does this stand for?
 One other thing I noticed was that the black wire protruding from the back of the amp there emerges from a hole that says "IMPEDANCE SELECTOR" and is attached to a corresponding OHM value in the RIGHT channel speaker terminal. Mine came connected to the 8 OHM  but I have seen pictures of other amps online that has this wire attached to the "S" terminal. What is up with this ? Any ideas?.
 If I can avoid buying the manual that would be great , but if I have to then I will.
With the amount of tube geniuses in here there has to be someone who knows this setup. I am a noob to most of this.
I have been holding off on firing up this thing after carefully doing some minor work on it and really want to try my headphone jack setup. Be nice to do it all properly. This "S" business is bugging me.
 
 
any replies appreciated
 
EDIT: Got this fired up and it's absolutely jaw dropping, minus the slight hum on one channel but there's a tube thats got a minor cherryspot. Got some tubes in the mail as I type. Now I remember what all the tube-bias is about, as in tube-appreciation.
 
Nick

 

[nick n]

For anyone browsing Heathkit AA-151 manual in the future here is the complete scan of the original build and instructions. I nearly spent $35 before finding this. If the link happens to be dead at the point of viewing simply message me and I will email it out to you.
 
http://akdatabase.org/AKview/displayimage.php?album=64&pos=0
 
As far as the above issue, simply for interests sake I will post up what i found. If anyone's interested. 
Here's the odd ( to me ) speaker arrangement:
It looks like the right channel has the Impedance Selection contact. I used that Impedance wire contact point as a + for the right channel as well. ( 2 wires to same contact point on the right ). I guess that may not be a good idea? I suppose I should change that . Seemed to work ok but it might mess something up?
I ASSUME THIS PICTURE IS FOR A STEREO SETUP?

The manual also states:
" Normally, the output of both channels of this amplifier are connected to suitable speakers systems.
If you intend to use only one speaker system ( MONO setup or single speaker ????-nick ) connect it to one of the channels,
and connect the other channel to a resistive load. The resistive load will prevent the unused channel from 'running free",
which could damage the circuit parts in the output of the unused channel."
 
which makes sense but the wording is odd/not clear for meaning of" speaker system " which i take to include a single speaker or a mono setup off of one channel either left or right. Let me know if I am stupidly missing any meaning here.
 The speaker outs are an odd setup which I guess i should follow according to the picture above.  I have it slightly different now which also seems to work.
 
Thanks for checking this out hope it helps any fellow 151 owners, The manual link there is pure gold.
 
 
 
 
 

 

[scottiebabie]

dang nick it sure took u long 'nuff to figure all this out! LOL. glads it all coming together for ya. btw, going a tad off topic here but there's a scheduled mini meet for June 4th. mite be at the Headphone Bar on Broadway or somewhere else - not sure. but check this thread if ya interested. would be fun if u can make it with the heathkit 

 

[nick n]

Haha! Yes it took a while. I was finishing up the passive computer project and got sidetracked with real life at the same time.  Still waiting on the replacement tubes. I'll check the link  but I may be tied up with relatives visiting from afar. Bad timing all around. Thanks for looking in on this post.
Here's a shot of the finished product. It's a stripped chrome lamp base with an added handle for wrapping cord  ( I have no idea why it seemed a good idea ) and a pro female jack. The thing in behind it is another headphone stand... I am not too happy with my soldering job from what I recall it was ok though I may do it all again. I think I may be getting too fussy. It would however be an excuse for modifying the signal path with a switch setup to a second set of larger value resistors, and replacing all of the resistors with better quality, if that makes any difference. ( Pretty sure I used 100 ohm ones thereabouts ) Something to look into. I have it pictured in my mind as i type.
 Can't wait to try these latest HP-1's on the new setup.

 
 

 

[scottiebabie]

too bad u cant make if off da island. woulda loved to have a gander at your vintage tubie heathkit to see checkout the bruhaha. bet it sounds sweet! mayb we'll see u at another local meet sometime soon.