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Author Topic: fender amp schematic  (Read 3106 times)

Hackinblack

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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|
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J M Fahey

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Re: fender amp schematic
« Reply #1 on: December 25, 2012, 12:20:25 PM »

I *used* to have that schematic somewhere, but some 3 or 4 hard disk crash / replacement behind, so ....
If I find it I'll post it.
It's not such a bad little amp, only you'll have to use it at quite a higher volume, power amp clipping smooths the nasty spikes.
At bedroom volume, yes, it can sound like broken glass.
The main problem is that they wanted to make a push-button amp, with not much brain input from the user.
And of course, those pre-set sounds and volumes never match.
From what I remember, not much you can tweak.
Meaning, you "better" something, you worsen all other sounds.
I'd use the very good clean sound with some external distortion pedal, your choice.
Quite loud for a small entry level amp, and, as I said before, pushing it smooths and evens the sound.
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Roly

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Re: fender amp schematic
« Reply #2 on: December 25, 2012, 07:13:27 PM »

"crafted" and "china" are not two words I would normally put together these days.

It's actually almost universal for rating plates to show the amp input power, and almost universal for it to be misunderstood, particularly by sellers on e-Bay.
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If you say theory and practice don't agree you haven't applied enough theory.

Enzo

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Re: fender amp schematic
« Reply #3 on: December 29, 2012, 05:21:32 PM »

An amp may put out 20 watts, and thus labelled 20 watts audio by the speaker connection, but will not be 100% efficient.  The law requires them to state on the amp the amount of power the amp USES from the wall outlet to MAKE that 20 watts.  THAT is what the 75w is all about, they are not trying to fool anyone.  It is only those people who do not know what they are looking at that are fooled.  Yes, many people do not know that, so they sell their "300 watt Marshall DSL100" on ebay.

Here is the service docs on this little amp.  There was also the JAM that came out with the HOT.
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Hackinblack

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Re: fender amp schematic
« Reply #4 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
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Enzo

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Re: fender amp schematic
« Reply #5 on: January 05, 2013, 02:27:43 PM »

The "few" not listed?  Oh the list of downloads on the Fender web site is just a small fraction of schematics they have.   They put up the ones commonly requested.  Even the entire content of their service discs does not cover all Fender models.  All available means is they have it and can send it to you.  Trust me, they are not hiding any of them, they just are not all readily available.   I have a whole shelf full of Fender schematics in binders.  Not all of the models, but a pretty good collection if I do say so.  There are a lot that do not seem to be scanned in anywhere.  I have scanned and posted quite a few over the years.  Not to say Fender doesn't have them in files somewhere, but honestly, they won;t spend an hour riffling through old files just to find an obscure one for someone.
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Hackinblack

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Re: fender amp schematic
« Reply #6 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!
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