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Old 26th July 2005, 10:21 AM   #21
edl is offline edl  Hungary
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Marshall lies.
They say:
Quote:
"As the science of amplification moves forward, players and manufacturers have had to adjust their approaches to creating great tone. For instance, we now understand that while all-tube amps have their advantages, they are bound by limitations. In response, Marshall has created the Mode Four, a hybrid amplifier that combines a tube-driven front end with a massive 350-watt solid-state power section and digital reverb. The results are nothing short of outstanding. In particular, the Mode Four has the widest tone range of any Marshall product past or present, making this one of the most versatile amps in the company’s long and venerable history."
But one of the hungarian guitar-amp diyers discovered that the Mode Four works with TDA chips. It uses 4 TDA chips in bridged mode.
http://stratofan.rentahost.net/elect...poweramp.shtml

I don't know why don't Marshall uses real discrete mosfet amp for the huge price of their amps...
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Old 26th July 2005, 10:23 AM   #22
tlf9999 is offline tlf9999  United States
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Default Re: Marshall and the TDA7294

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Originally posted by Dusk
The LM3886 is it a non-mosfet IC and don't u
have to worry about thermal-meltdown with this IC chip? LM3886. I go for the rugged mosfet at the output....but that just me.

the LM chip has internal thermal protection.

when I mentioned it earlier, I was thinking of using it strictly as a high voltage opamp, driving a mostfet output section as you had requested. The advantage of using the LM is that it can be powered by higher rail voltages so you don't have to bootstrap the supply anymore to achieve high output.
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Old 26th July 2005, 11:18 AM   #23
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And mosfet is not as rugged as you think.

If the amp you make don't have good protection circuit in it, it will probably burn anyway, despite MOSFET output stage.

I still strongly advise you to get LM3886 or something like it.
Bridge it if you want. This is the simplest and have internal protections that most of discrete amps dont have.
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Old 26th July 2005, 01:14 PM   #24
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Train of thought comes to a screaching halt. Hold on........ Why is a guitarist doing this at all??

Surely one of the significant cornerstones of guitar sound is the nature of distortion. By contructing an amplifier in this way this is completely bypassed.

Now, in fact just last weekend I built just the rig you are looking for. I got an old cab from my old hi (lo)fi. ( this is wrong), cut a 30░ corner off it (this is wrong), and filled the corner with MDF to make a wedge monitor shape ( this is wrong). Next, I mounted a 100W MOSFET P.A. power section from BK electrics (UK) (you shouln't do this). It has its own PSU ( which is handy, but can't be right). The Preamp was a Vellaman kit with a 741 ( ok , changed it for a NE5534AN but its still wrong.), and I used a seperate 12.5V switchmode PSU which was scrap stock at work, so I epoxied it in to the case ( this is bad). Between the two I set a 47K pot ( this or course, is wrong).

And guess what? It sounds great!

However, this is an active stage monitor that doubles as a bass amp so I don't want overt distortion. I would recomend that you build a MOSFET rig WITHOUT a preamp and buy a good modeling guitar preamp that is good with whatever amp you put it through.

................. but I could be wrong.
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Old 26th July 2005, 09:17 PM   #25
Dusk is offline Dusk  United States
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Smile Marshall and the TDA7294

Hi again
The Marshall has it's output in a bridge-paralle set-up ........by the way what is wrong with the TDA7294 ic i dont' know this chip?It is the one that they use in the Mode Four.
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Old 26th July 2005, 09:19 PM   #26
tlf9999 is offline tlf9999  United States
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Default Re: Marshall and the TDA7294

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Originally posted by Dusk
by the way what is wrong with the TDA7294 ic.

They aren't complicated enough to show our maniness?
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Old 26th July 2005, 10:21 PM   #27
Dusk is offline Dusk  United States
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Smile Maplin power amplifier circuit

Hi Craig405
Your circuit looks like a Hitachi appl. note circuit that was the first power amplifier i built. I used the newer flat-pak Hitachi made 2sk1058/2sj62 i used 1pair at first that gave me about 80watts. I wanted more so i paralleled another pair for 100watt/8ohm. I don't know if i could parallel more pair of mosfets and increase the power supply for more power....iam no amplifier Guru..just a guitar player..thanks to MR. Hendrix and Albert King .......anyway i added aclip circuit so i could see if i am getting to close to running out of headroom...(one of the good things about all tube amplifier.....soft-clipping)....also this is another reason for wanting a250watt amplifier...more headroom...and no power tubes to replace. A simple circuit few componts...op amp front..mosfets output fewer parts less headach.......i am not anti- tube amplifier......i use ahomemadetube pre amp in front of the power amplifier for overdrive and tone.....also i have a homemadeall tube Bassman based on the 1959 fender /Western Electric circuit.....i just don't like replacing power tubes. ........Fact the great Albert King used solid state amplifer and imo he had GREAT...tone

PEACE
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Old 26th July 2005, 10:32 PM   #28
Dusk is offline Dusk  United States
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Smile Back to the LM3886 & Mode Four

let try this ......what make the LM3886 Good....will this thing shut down when it get in the thermal zone.......and stop a jam section??


so the Mode Four has a ic for a brain is that so bad......sound ok to me massive power.
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Old 26th July 2005, 10:52 PM   #29
Dusk is offline Dusk  United States
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Smile LM3886 as front-end

tlf9999
sorry i just read your post ......are u saying i could use a LM3886 to drive the dicret mosfets in a power amplifier or am i not reading this right...........do u have a circuit/schematic. Never heard of this ..........but iam no amplifier Guru
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Old 27th July 2005, 01:19 AM   #30
tlf9999 is offline tlf9999  United States
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yes, Dusk. the problem with traditional opamps is that they run 12v - 18v rails top. so if you don't bootstrap them, your output is limited - a bigger issue with MOSFET output stages because of their higher Vgs.

The LM chips run at considerably higher voltage, without bootstrap. so You just treat the LM chips as high-voltage opamp and you are set to go.
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