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Messages - Hackinblack

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Schematics and Layouts / Blackstar HT-1 schematic
« on: November 10, 2015, 11:40:42 AM »
for the good people of the forum;at long last i found a proper schematic for the little blackstar HT-1
on the same day i snapped up one used 'locally' only 150Km round trip! :duh it's christmas already <3)
 courtesy of the wierd wired interweb,via Korea.. 8) (an official factory PDF no less!) :tu:

you say you sorted the dirty pots;did you replace them or just clean them?
the reason i ask is i had a hughes and kettner tubeman hybrid pre-amp (which is their take on the valvestate) which made some horrible noises i suspected of being the tube;only when i turned the gain pot several times it cleared up;cleaning it cured it completely.
 a similar problem happened on my valvestate VS-65R;but this time it was a combination of 2 faults!;the pot's had been cleaned by an idiot using spray anti rust oil,this created a conductive mess across the PCB,especially when the amp stood around getting made the amp produce a speaker-killer buzz.problem 2 the tube had gone faulty;bizzarely,although the tube is used in clean and overdrive circuits, it only showed a fault when in overdrive (presumeably because of higher gain through it)
the VS amps are old enough now to have dried up smoothing caps (maybe a cause of the supply rail borne noise hinted at) another possibilty is a dying op-amp;the switching ones used in the VS can and do fail;there is an updated version which marshall recommend;as the ones used are now obsolete.

Amplifier Discussion / Re: Marshall mg30dfx Repair - Gain Not Working
« on: October 23, 2015, 05:08:40 PM »
with these amps the clipping LED's light up when the overdrive is past 12 o'clock;in fact if you,look closely at the front panel,where the gap around the 'drive' switch is, you can see the red one slowly glowing inside as the gain or (input signal) rises.
nice amps these;both channels sound good...well worth repairing.
if it turns out the op-amp is poached cut it's legs off and pull the legs out from the TOPSIDE of the PCB,one at a time,while heating the solder joint with your iron;these PCB's on these Indian-made amps are not as tough as the fibreglass ones in more up-range marshalls,it's easy to pull traces off the board.

Tubes and Hybrids / Kustom tube 12A
« on: October 23, 2015, 04:09:37 PM »
picked up one of these used,based on the 'tube amplifier' label...very misleading! 1 x RC4558P and 1 x 12AX7 feel the power :lmao:
i read this forum's post
and noted the errors on the 1 schematic wafting about the web (the one on the forum is corrupt too)
but the photos of the errors posted seem to be corrupted;anyone have copies of these?
this little amp has the makings of a nice one, 'Champ-meets-Valvestate' the thing a has a remarkable bass response,considering the 8" speaker and an open-backed cab
but boy is it StRanGe:-no gain adjustment on the clean channel,but with the gain switch on HORRIBLE RAT-type raspy distortion;like a cross between a small PA amp and the worst distortion pedal ever made :duh
i can't wait to scope,prod,and tweak mercilessly...

Amplifier Discussion / Re: Marshall MG30DFX op-amps
« on: March 09, 2014, 04:13:07 PM »
Thanks for the replies...Sooo it looks like a factory mod :tu:
i did notice that the early MG series where criticised for excessive noise;maybe marshall get very good price break on 4558's ;)

i'll be interested to play this amp and see how much difference the change of op-amp makes;my little MG15DFX is a pretty noisy amp as stock,a good mod was adding an metal screen between the mains transformer and the PCB;this alone halved the hum;then on to improving the filtering and smoothing on the supply rails

i noticed one poor bit of design on the '30 Watter;the O/P IC shares a heatsink with the main voltage regulator supplying the DFX card,any failure of the LM7805 would fry the DFX card.
i may run it into a dummy load and see if the PSU is adversely affacted by the power amp's heat..if it does i will seperate the siamese twins surgically :duh

Amplifier Discussion / Marshall MG30DFX op-amps
« on: March 08, 2014, 06:07:42 PM »
a new addition to the Obidia Trumpworthy home for badly behaved amplifiers >:(

a slightly ill MG30DFX which wouldn't switch from clean to grubby
fixed that, but i am slightly puzzled,as the amp is full of TL072 op-amps;whereas the schematic i have (dated 2002) is full of 4558 DD's
(the high gain version of the 4558)

is this a factory revision, or has someone 'upgraded' it? anyone have a more up-to-date schematic to compare?

Amplifier Discussion / Re: fender amp schematic
« on: January 05, 2013, 04:08:34 PM »
yep,i suppose some models are of such low interest,and value;that putting their schematics online is not worth the bother for fender or other manufacturers.the service cost outweighed the value of the amp.
a good example was a reply i had from gibson,over one of their valve amps;they sent a scanned advert from a different model,a PDF for another TOTALLY different amp 'which should be the same' :loco and what must rate as the worlds worst quality PDF schematic;almost unreadable! this amp was about 4 years old! GibsonPRO Audio you must be kidding!

nice project;but a couple of things could be improved on
1. there are no filter caps around the heater smoothing circuit,i'd sprinkle small ceramics liberally here supply to ground,to kill any high freq noise before it gets to any audio sections
2. putting electrolytic caps right next to a valve/tube is not a good idea,they dry out when exposed to heat
nice PCBs though;are they available,or maybe a kit? i looked into doing something like this but the cost of post on the valves plus a hammond case was going to quadruple the cost :-\

Amplifier Discussion / Re: fender amp schematic
« on: January 05, 2013, 12:30:41 PM »
sorry for the delay,many thanks for the schematic 8)
saves me bugging fender to send it to me
it's one of the few not listed in their downloads list,though strangely, it is listed in the schematics 'available' elsewhere on their site ???

though its such a horrid design i'm not surprised they dont release the schematics into the wild :duh
wouldn't want the buggers breeding

i dont understand why the clipping is switched in for the 'full' channel not the 'crunch' it would have made more sense to be the other way round;
it looks like the switch between  'gain' resistors is responsible for the horrible transistor clipping on the 'lead' channel AND the lack of volume(or much else!) on the 'crunch' channel;what planet was the designer on?
now i know the switch routing i stand half a chance of making it behave properly :trouble

Amplifier Discussion / fender amp schematic
« on: December 25, 2012, 11:24:40 AM »
i've just got hold of a 'Fender H.O.T.'solid state amp made in the good ole' US of A ;along with a battered 10yr old squier strat 'crafted in china' yeah right...

i have never heard of this model before,and can't find any references on the web apart from people slagging them off,or selling them(encouraging,no?) anyone have a schematic for this or similar?

basic spec:- 2 input channels,high and low, 1 'contour' control (no other tone controls)volume and reverb,'CD input' RCA jacks(80's vintage?)headphone output, line out,and unusually, effects send and return jacks

it has 3 TL072 op-amps feeding a UPC1188H NEC power amp IC which is rated at 20W

as a supreme example of BS from fender the only thing on the chassis label says 'input power 75W' to fool people into thinking it's a 75W amp.

the clean channel sounds REALLY nice,but switching onto the 'crunch' or 'lead' channel and it all goes HORRIBLY wrong;the crunch channel is quieter than any of the other channels,and the 'lead' channel makes the  £15 fuzz pedal i bought as a kid sound like velvet...IT SUCKS
though bizzarely;if you turn the volume on the guitar right down it gets a 'just on the edge of overdrive' sound which is fantastic! it sounds like someone stuffed the wrong parts on the board :loco the gain on crunch is way too low and on lead WAAAY too high ???
i can see a couple of diodes on the board but without a schematic/prodding it with a meter i dont know whether they are input limiting or op-amp clipping.once i've found the gain setting resistors for the crunch and lead op-amps i can tame its unruliness :trouble ;and maybe Marshall-ize its crunch  8|

Amplifier Discussion / Re: Can anyone identify this Amp?
« on: December 25, 2012, 10:48:13 AM »
ahh HH, i have one;an L100 guitar combo
the Rolls Royce of SS amps!
as used by Marc Bolan,America and countless other groups in the late 70's early 80's
brought out a stupid keyboard amp in the 80's (for ORGANS? oops...) it was such a flop it sank the company;who eventually sold the factory to Laney for producing their speaker cabs.
reliable,tough,and the sound from the clean channel could clear the wax out of your ears at 300m :duh
coutesy of a celestion G12H100 inside the open backed cab
currently residing in the Hackinblack rest home for unloved old tranny amps :-[ donations gratefully received

Schematics and Layouts / Re: Digital JFET Test Rig
« on: December 25, 2012, 07:36:51 AM »
an interseting project;one that could be done using BASCOM AVR  (free BASIC compiler for the AVR microcontrollers) for the arduino-phobic :-\

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