blackface mod to a Gibson GA-5 Reissue...

[lookah]

Hi. I am very new to amp tweaking and have basic knowledge which i've acquired by having bought/rented/borrowed books and videos by dave hunter and gerald weber as well as reading many online forums. I own a reissue Gibson GA5 Les Paul Junior and successfully (drained the filter caps ) and performed 2 of the trinity mods discussed in much detail on a lengthy tdpri forum. (lifting the 1M /22pf tone filter as well as the 25uf bypass cap).

http://www.thegearpage.net/board/sho...&postcount=173

i liked the mod but, given my newly acquired obsession, i figured i'd try a blackface filter mod that Gerald Weber mentioned in one of his books. a mod i realized would be easily performed in the GA5 since the circuit board is already layed out for it. i attached a picture of the components i swapped and what their current values are. basically, the mod replaces the .022 cap with a .1uf/400v (i used an orange drop .1uf/600v), it replaces the 1M resistor with a 220k 1/2 watt, and it replaces the 22pf cap with a 250pf (i used a silver mica).



well, other than a crappy soldering job (i'm getting intermittent signal...i need to resolder!) i think it sounds pretty cool! it definitely scooped the mids and added some blackface grainy highs. my questions are:

1) does anyone predict any long term problems with this mod?

2) will there be too much bass and blow my speaker? i actually haven't gone past 5 on the volume because it sounds like my amp is now much louder and may damage the 8 inch speaker. i have changed the weber sig8 (15 watts) to a jensen c8q which is rated for 25 watts.

3) will adding the 47k negative feedback resistor be advisable?

4) any other comments?

thanks so much!

luca

[jeefberky]

Hi lookah,

Glad to hear the mod worked out for you. I've never tried it, but I plan to do it to one of the channels on a tweed I'm building. To answer your questions:

1. I don't forsee any long term problems with it. If it sounds good, rock on.
2. I'm not sure what the wattage of the amp is, but this mod will definitely not change the amount of power going to the speaker. I don't think it's going to increase bass response that drastically. Its seems like tons more bass because of the mids being cut, but the .1 mfd cap shouldn't give you enough boom to destroy a speaker. However, being 8" it may fart out/not sound good when cranked. Woudn't hurt to try a .047 mfd in that position instead and see what you like at your normal volume level.
3. The 47k feedback resistor will mellow things out, definitely. It will decrease apparent loudness by a few dB and take some edge off of the highs (less presence). This is not a drastic amount of NFB. You could try 10k, 22k, and 47k . See what you like.

Have you resoldered the connections yet? Did the intermittent signal problem get resolved? How has the mod affected the usability of the tone control?

Jeff

[jeefberky]

oops, i meant to say volume control

[lookah]

Hi Jeff. Thanks for answering my question. I don't know if you noticed but my post was actually from March last year

But, yes, i solved all the issues and ended up just performing the much discussed trinity mod but without adding the negative feedback loop. Amp sounds nice!

Anyway, good luck with you tweed build...

Luca