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Audio note M7 question.
https://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=6516
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Author:  M. Gregg [ 23 Apr 2019, 11:39 ]
Post subject:  Audio note M7 question.

Hi,
In the original 5687 Audio Note M7.
Does anyone know the real / actual cathode current of each 5687?

I was looking at post 3 in this link showing dual 100K resistors in the anode and 2K in the cathode.
Can anyone confirm this is the first version?
https://www.stereo.net.au/forums/topic/ ... m7-preamp/

Does anyone know the real / actual cathode current?
Has anyone tried AC heaters? Just curious.

Regards
M. Gregg

Author:  Woodo [ 23 Apr 2019, 16:42 ]
Post subject:  Re: Audio note M7 question.

Somebody has posted audionote circuits at this link. I did see one for the m7 but not certain of the authenticity.

https://www.schematicsunlimited.com/a/a ... UwMw%3D%3D

Author:  Woodo [ 24 Apr 2019, 00:55 ]
Post subject:  Re: Audio note M7 question.

Apologies that link after I copied it does not work. Can try searching manually.

Author:  M. Gregg [ 24 Apr 2019, 14:51 ]
Post subject:  Re: Audio note M7 question.

Woodo wrote:
Apologies that link after I copied it does not work. Can try searching manually.


Thank's for trying.
It seems there is a great amount of info on the net about this line buffer, but the detail of the actual operation characteristics seems sparse.
Any input would be appreciated or any direct listening experiences.
On another circuit supposedly drawn from actual equipment the B+ PSU is shown as
(100uF - 5K – 100uF) @350v WKG. This seems like a high value first Cap for a tube Rec. (6x4)

Regards
M. Gregg

Author:  Gab [ 26 Apr 2019, 13:11 ]
Post subject:  Re: Audio note M7 question.

From what I’ve read when I was looking to build a M77 clone, audio note purposely publish multiple schematics over the years. Probably for parts availability reasons, but they almost always miss some informations, or provide contradictory (if not misleading) informations when compared to other schematics. With all the know how of this company, (and all the respect I owe them) I don’t think that they make "mistakes" in their schematics. The difference between the real ones and the clones, besides parts and worksmanship quality, probably is what’s missing in the scematics.

Can we blame them for keeping little secrets ? I don’t think so :D

Author:  M. Gregg [ 27 Apr 2019, 02:55 ]
Post subject:  Re: Audio note M7 question.

Gab wrote:
From what I’ve read when I was looking to build a M77 clone, audio note purposely publish multiple schematics over the years. Probably for parts availability reasons, but they almost always miss some informations, or provide contradictory (if not misleading) informations when compared to other schematics. With all the know how of this company, (and all the respect I owe them) I don’t think that they make "mistakes" in their schematics. The difference between the real ones and the clones, besides parts and worksmanship quality, probably is what’s missing in the scematics.

Can we blame them for keeping little secrets ? I don’t think so :D


Just some more postings about a similar circuit (I have no connection its just for interest)
https://diyparadise.com/w/simple-5687-based-preamp/

I had a look at the supposed original circuit and compared it with some equipment posted for sale on the internet
http://www.astrasuite.com/astrablog/uh- ... kondo-sfz/

and the values seem to match. :| (maybe)

But it is interesting to look at what others have done.
Its interesting to note that the magic wooden boards were not in use at that time, but then again its all just reflective for fun.
If these circuits have any reflection on the original is another possible maybe.
NB the wooden boards are described as "densified wood" but its an interesting thought.

Regards
M. Gregg

Author:  M. Gregg [ 27 Apr 2019, 03:39 ]
Post subject:  Re: Audio note M7 question.

Anyway,

Aside from the other stuff.
I thought it might be interesting to see if I can make a copper chassis (for fun) :D
As expected its a PITA and smells like old copper coins until its sealed.
So with help from a few friends....A blow torch...solder...and some brass...
At this point I exit stage left and have a think about the tube type....

Regards
M. Gregg

Author:  M. Gregg [ 27 Apr 2019, 05:01 ]
Post subject:  Re: Audio note M7 question.

First fit and clean up.

The bottom plate now has slots and the feet have been made using copper pipe end caps.

The end caps are filled with epoxy then a fibre washer with one standard nut and one nyloc nut pushed into the resin then after it sets remove the screws leaving the fibre washer as the isolator for the feet. So the mechanical connection through the feet is via epoxy (not metal to metal)
Before fitting the felt pads the caps were cleaned with solvol autosol cleaned with acetone, then sprayed with lacquer.
This is just a first fit to see if it works....screws etc have to be countersunk.
The aluminium angle on the bottom plate is jointed to the copper front plate and chassis with JB weld to damp the chassis and join the different metals.

Regards
M. Gregg

Author:  M. Gregg [ 27 Apr 2019, 05:10 ]
Post subject:  Re: Audio note M7 question.

The chassis is joined to the aluminium angle using 3mm screws.

Holes drilled for standoffs to bottom plate.
The top plate is then slotted and initial check and fit.
No clean up at this point..

Regards
M. Gregg

Author:  M. Gregg [ 27 Apr 2019, 05:26 ]
Post subject:  Re: Audio note M7 question.

Just looking at potentiometer fitting and types.
So the support bracket is made and corner soldered.
I managed to get some 6mm brass rod and support pass through bearings for the front panel.

Obviously this has been on going for a while so I thought I would post the progress so far.

Regards
M. Gregg

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