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Ashdown MAG300H bass head (no EVO)
Posted: 26 Apr 2013, 15:24
by lolbou
Hi,
Does anyone have this schematic on hand for this unit please? It's a no EVO model, but a chinese-made one (production moved from theu UK to Asia).
PCBs read:
- APC041 issue 3 (03/12/04) (power amp section)
- APC044 (sub board)
- APC021 issue 1 Electric Blue/Mag (main board)
Any input is welcome!
ps: there used to be files on music-electronics-forum, but these have dissappear due to a deleted directory from their database. Ashdown didn't reply my request, though they did last year for a FA-60 head.
Re: Ashdown MAG300H bass head (no EVO) schematic?
Posted: 26 Apr 2013, 16:59
by karul
lolbou, someone has already posted the schematics:
http://music-electronics-forum.com/t28046/
Re: Ashdown MAG300H bass head (no EVO) schematic?
Posted: 26 Apr 2013, 19:16
by lolbou
Yes, i've seen it.
PCBs don't match though. My request at MEF was to re-post the missing file named APC041-1.pdf, therefore I did not mention my PCB details... I'll answer at MEF, but please keep popping!
Re: Ashdown MAG300H bass head (no EVO) schematic? [schematic]
Posted: 30 Apr 2013, 01:49
by mozwell
are these what you are after ?
Re: Ashdown MAG300H bass head (no EVO) schematic?
Posted: 30 Apr 2013, 05:39
by lolbou
mozwell wrote:are these what you are after ?
Looks right for the power amp, really close (first sight) for the preamp, ut still different for the SUB board (APC044 in my unit).
I'll have a closer look at it tonight...
Thanks a lot for your input and help on this!
Re: Ashdown MAG300H bass head (no EVO) schematic?
Posted: 01 May 2013, 10:33
by lolbou
Finally start the debugging process. Easy, even without a schem : shorted primary winding in the power transformer. Not that lucky.
Looks like a known issue on these transformers. Will try and contact Ashdown or the french Service dealer.
Other option is to find two transformers : 230V/48V-0-48V and 230V/15V-0-15V. Don't know power ratings though, but there may be some way to find out...
Re: Ashdown MAG300H bass head (no EVO)
Posted: 02 May 2013, 02:39
by rcustoms
i dont know, if this info, help you. anyway ,here we go
parts values
and the cherry on top
regards
Re: Ashdown MAG300H bass head (no EVO)
Posted: 02 May 2013, 02:43
by rcustoms
oops sorry there are the real parts photoshot
Re: Ashdown MAG300H bass head (no EVO)
Posted: 02 May 2013, 05:55
by lolbou
Thanks! That's the very power amp board indeed!
The schem you provide is really close, although it stops at issue 2. But that's enough for debugging I guess.
I did unwind the transformer for visual check (and curiosity), and here's what I found when I've reached the primary winding:
Same problem
here apparently. Here's what the author says about the different windings:
The first winding was the low current 15-0-15V secondary. This was wound
with doubled up .45mm wire in one go so reducing the number of shuttle
passes to wind on. The 2 wires brought together to form the "0". Thought to
myself, perhaps that is ok for low voltage winding as only 50V peak or so
maximum for 2 thicknesses of lacquer to sustain.
Then the 3 amp 48-0-48 wound as 2 separate layers of 1.06mm wire, not run as
paired winding, fair enough. Anyone know why 3 runs of loosely packed turns
per layer when one run of tighter turns per layer could have been done, so
avoiding overlaps?
Get down to the unruptured thermal fuse, tails of the primary and the .7mm
wire primary and nothing obviously wrong in the way of hot spots. But
blow-me-down a return to the paired up winding and ends joined to give
120-0-120V for 240 UK use. But of course now 2 thicknesses of lacquer having
to sustain a normal maximum differential of about 350 volts. Not wound off
yet but somewhere in the bulk of windings must be bridge/s.
Too bad!
