23.8.08

vox ac15

this amp is based off of the ac30hw (handwired) limited edition amp that was built in the marshall factory in the 90's.

i had previously picked up a an empty ac15cc1 cabinet from north coast music and loaded it with a 30w weber alnico blue dog. this sat under my ac30cch. it looked pretty impressive, but that empty cab always seemed to invite me to fill the void where the chassis was with a handmade amp. the only trouble is that the chassis would need to be 22" wide, 5" high and 3" deep. that is not a lot of room to build an ac30 type of amp in. i decided on building a 15w version of the ac30 to save some
room and to save my ears from ringing.

after following a few posts about the ac30hw limited edition i ran across one plexi palace board member who posted photos!! i also received a schematic from another member. with pics of the board layout and the schematic, i made up my own detailed layout and started staking the turret board.

here is a picture of the empty turret board:



then the components for the turret board were ordered and installed into the turret board: (seen here by its eventual home)



for a chassis, i had a local metal shop fold and weld a chassis for me from a piece of 16 gauge mild steel. it wasn't the prettiest thing, but it fit in the cabinet just fine. the shop took a few weeks to complete the chassis, they ended up just doing
the work for free, so the chassis cost me a cool $10!!

i created the faceplate using photoshop. i took the image to a local sign shop and had them print me one up and attach it to a thin piece of aluminum that I found laying around at work. I carefully laid out the chassis area where the faceplate would be, clamped the faceplate to the chassis and drilled out the holes as needed.



now for the hard part...
....after some more chassis preparation and a lot of soldering and wiring the
amp was nearly completed.



now its time to talk a little about the details...

you will notice the power transformer is mounted in a strange way. i didn't have the resources to cut a huge hole in the chassis, so i punched a 1" hole for the wires to pass through, mounted some threaded standoffs to the transformer and then mounted the threaded standoffs to the chassis. it seemed a good a sturdy mounting to me.

you will notice on the front panel an "eq" switch like on the AC30CC series. this switch has the same function, but i used a switched potentiometer to do the switching. there is only an on-off setting, the pot itself is not in the circuit.

you may also notice the mercury magnetics output transformer and choke. i wanted this amp to have an authentic tone, so i splurged on these components (in comparison to the $30 power transformer!!)

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here you can see the crude back panel. one feature of note is the pentode /
triode switch. this will get the amp down to 6 watts, if need be. this, along
with the master volume, is very useful in an apartment. note again the
strange mounting of the power transformer.




this view shows just how cramped the chassis is!! all of the components
barely fit in the amp!! not room for much else in there... you may also noticed that i did something potentially harmful to the sound of the amp by placing the phase inverter tube away from the power tubes. this makes long wires which in turn can cause problems with humm and parasitic oscillations. i did have some of these problems initially. replacing these leads with shielding wiring helped a lot there.

after successful testing, the next step was to mount the chassis in the cabinet.
i bought some taps and threaded it for the proper sized bolts and soon it was looking good!!





not too shabby!! and its just the right size for an amp.

How does it sound? Well Hear it for yourself....

MP3 Clip (currently not hosted)

2 comments:

Orycay said...

I am building a Vox AC10 and I am having trouble with the face plate. I have been using photoshop but my skills are not up to the highest order. How do you do the curved lines at the corners and then also how do you write the text with the gaps in the lines? All the help you can give would help.

Mike said...

Cool blog, and nice work on the Vox. I'm building kits currently but hope to build from scratch one day.
@ Orycay: In Photoshop you can get the rounded corners by doing a rectangular selection and then go to the Select menu. Choose Modify and then Smooth. Try a value of about 10. This should get you your round corners.