Blackstar Artisan 15 - warmer tone

[Bernd]

schematics Artisan 15

Thank you for your descrition.

I have just started to draw the schematics of the Artisan 15. As far as I have drawn now I can see that the design is not the usual vintage amp design. It will take a few more days until I have finished the job.
Does anyone know how to publish the schematics for discussion in this forum?

Bernd

[J M Fahey]

How to post your own schematics

Hi Bernd.
To begin with, how are you drawing?
Are you using
1) a general purpose program as AutoCad or similar,
2) an electronics specific one such as Express Schematic (free and easy) or
3) good old hand drawing on a sheet of paper?
In any of three cases, you'll need to turn your work into some graphics file which can be posted.
1) usually you can save or export as .gif or .bmp , then convert to .gif .
Worst case you save into its native format .dxf ; then with some graphics program open the .dxf and save as grayscale .gif.
2) these usually save as as a proprietary .sch file, which only themselves can open; but some offer the possibility of saving or exporting as some general purpose graphics file , such as .bmp.
Excellent quality but *huge*
You can open these in some graphics package such as free and excellent IrfanView and save them as grayscale .gif.
Try to avoid .jpg which is optimized for color pictures, usually smears formerly clean and sharp schematics.
3) hand draw into an A4 sheet, then scan at 150 DPI and save as grayscale .gif .
If you don't own a scanner, usually some Cybercafe or graphics/photocopy shop will.
Worst case take a sharp clean closeup picture with a good camera, in 1600x1200 pixel resolution or the next higher one.
Sharpness and even illumination are essential; avoid flash , the best light source is outside (sunlight) on a cloudy day, or when a cloud covers it; steady your forearms with a chair, some books, etc, push slowly the trigger button, don't shake the camera.
In this case you can't avoid the .jpg.
Open your picture onscreen, check that small text is still readable.
4) in any of 3 cases, post your image into some photo-sharing site, such as Image Shack , they will give you a link to the full image.
Answer here, go advanced, click "insert image" , in the window that opens paste the link to your Image Shack picture, save, submit reply.
In your answer you'll see your schematic in its full glory.
Good luck.

[Bernd]

schematics ready

I have finished the job now, it took me some evenings, longer than I thought. I had to remove the board to be able to follow all those wires. It is much easier on a printed circuit board. I will redraw it now by hand and scan it tomorrow.

I don't have any webspace on a photo sharing site - I thought that I could publish it directly on this site. So if someone could do the publishing for me it would be helpful. Pass me an email address and I will send you the files.

Bernd

[J M Fahey]

ImageShack lets you publish without even registering.
Afterwards they give you 3 or 4 options ; copy the address that points directly to the image, click here "go advanced" and then within the reply, click "add image" and in the little window that opens paste the link they provided.
Just to be sure click "preview" to see what others will see.
If unsure about some step mail the schematic to juanmanuelfahey (at) gmail (dot) com and I'll post them for you.

[guitarmike2107]

wow, great effort Bernd, likewise I have accounts with photobucket and mediafire that I could upload it for you.

[Bernd]

Schematic files are ready

Thank you for your help guys. It's 2 gif files now. I tried the upload on image shack but something in my computer inhibits the upload.

JM Fahey- please check your e-mail, I have sent you the files, maybe you can do the upload better than me.

I have drawn about 90% of the amp, the complete signal path up to the power tubes.

Let's wait for the files to be uploaded and then let us start the discussion.

Bernd

[Bernd]

Maybe I can attach the files:

Bernd

[J M Fahey]

Hi Bernd.
Your attachmentt works fine, but to display these within the response, I posted on Imageshack too and linked them here.
I took the liberty of downsizing your .gifs to 1/4 original size, to better fit a normal screen

and

I guess both EL84 cathodes should be joined on the top side of the 100 r resistor "41"

[guitarmike2107]

So the volume control has a bright cap as well as the tone control bright cap? You haven’t put the bright cap value on the schematic; I assume it because it was not possible to see it.

There’s lots you can do here to change the “high end” response on this amp,

If it’s the very high frequencies that you are finding harsh then you could remove or lower the bright cap.
If it’s the high mids that are too punchy then you could change the tone control 1n cap to a 470p cap.

[beano4ever]

I appreciate you doing this Bernd. I know it was not that easy so thanks so much for taking the time to map and draw it out. Unfortunately I couldn't read a schematic to save my live so thanks for the suggestions on the bright cap guitarmike. I had been waiting to see what Bernd would find on the schematics before I changed anything on the amp so I will I believe I will just leave in the stock heritage g12m speaker and start by having a tech remove the volume bright cap and go from there. Removing the bright cap seems to be a pretty common / successful mod on various amps so I am hopeful that it will alleviate the problem.

[Bernd]

To guitarmike:
The bright cap that bridges the vol. pot of ch. 1 is 1nF. I wrote this on the left side of the vol. pot, it may be hard too see. The drawing is a bit narrow in this area and I didn't want to squeeze the value between the pots so I wrote it outside.

I could imagine that putting some resistors in series could tame the overall response.

Bernd



Bernd

[guitarmike2107]

Ok I can see that now, I plotted the frequency response of the stack earlier, but dont have the file at home to change the bright cap value to see how much it affect it, but the with the tone up full you have a 2n volume bypass cap, I would start by removing the bright cap, but would probably end up putting a 100pf cap or so back in its place. .

AFAICR the Marshall 18watt doesnt have the bright cap at all and the top tone cap is 470p. the bottom tone cap is different too. usefull as a reference anyway

Neds a bit of experimenting anyhow, a decent tech will get it closer to what you want anyway.

Edit: Neds should be needs, wasnt meant to be a reference to my fellow countrymen
http://en.wikipedia.org/wiki/Ned_(Scottish)

[Bernd]

I'd like to have some changes on ch. 2 which has no bright cap across the vol. pot but feels the same as ch. 1. Any suggestions to "marshallize" this channel without completely rebuilding it?

Bernd

[guitarmike2107]

The only Marshall amp I know with a single tone control is the 1974 and derivatives

If you look at the schematics you can see the 18watt trem channel uses the same layout, but different cap values, you if you change the cap values you will get closer to the 18watt Marshall response.

Your C5/C6 and C23/C24 are the caps to change.

For a more “Marshall” tone C5 and C23 could be changed to ~470pf., C6 and C24 could be changed to 4.7n, but it wont change the tone as much as changing C5/C23 so I would just leave it

Another option would be to change the caps to Matchless/Vox type tone controls, for that you need to change the C5 or C23 cap to ~180pf

If you don’t mind drilling the front panel you could put all three options on three way toggle switch and switch between them depending on what you feel like.

I have plotted the response of the different controls discussed here to get a visual of what they sound like. The key area is the 1 – 2 khz area, I think our ears are quite sensitive in this range, normally when its boosted like this the guitar has a great thrusted sound, but may be over bearing too, as you can see the blackstar tone controls boost in this area, I think this may be what you are complaining about, along the with the brightness of the vintage 30 speaker in the back.

http://www.mediafire.com/file/xuqm1p...e-Controls.pdf

If this was my amp build I would add a switch, or have each channel set up differently.

Hope this helps

[guitarmike2107]

oops.. I made an error on the last blackstar plot, I have updated the file now, I had 1n instead on 10n for C6 and C24. from the new plots you can see that those caps affect the low mid roll off point. I would still leave it at 10n.

http://www.mediafire.com/file/xuqm1p...e-Controls.pdf