Kev's weird ass Mark Lucitt amp thingamabob

jbeckva

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Heheh... catchy title, eh? Anyway, so Kev is having me take a look at this subwoofer amp from Mark (whereabouts unknown but hey no probs). Kev I got it apart and will say at minimum all outputs are fried.. Going to need a run to mousers for parts, then we'll see what we have. Nice heavy construction on this guy... the crossover network seems pretty "interesting" too...

IMG_2909.jpg IMG_2910.JPG IMG_2911.jpg
 
R1200S

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The more detail you can provide on how those outputs are attached to the heat sinks the better. I have 5 NHT sub amps I need to tear apart and I'll need to pull the outputs off the heat sinks. I have no experience with how those things are thermally joined.
 
orange

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A PCB! My kingdom for a PCB!

(okay, so I don't have a kingdom and my loan applications for a fiefdom and peasant village for feudal control were laughed at by the bank)...
 
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jbeckva

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Ok, so I have it all back together. Needed to replace the switch as it would seem the one Mark had installed was not quite up to handling in inrush current (basically it welded itself shut)...

Now.. hmmmm.... First a foremost, it would appear that the overall gain as "set" is pretty low. I have to drive it pretty hard (with at least a couple of volts), for any meaningful output. Here's where I may need some "Joe" help.... Take a look at the schematic for the driver board. This is basically "the" schematic from what I can tell, but also with a major set of chokes and caps and whatnot that Mark had added to the output.

I'll map those out and show them, but for now.. hey Joe.. where should I start looking at adjusting the input or gain?

p68-f1.gif
 
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jbeckva said:
Ok, so I have it all back together. Needed to replace the switch as it would seem the one Mark had installed was not quite up to handling in inrush current (basically it welded itself shut)...

Now.. hmmmm.... First a foremost, it would appear that the overall gain as "set" is pretty low. I have to drive it pretty hard (with at least a couple of volts), for any meaningful output. Here's where I may need some "Joe" help.... Take a look at the schematic for the driver board. This is basically "the" schematic from what I can tell, but also with a major set of chokes and caps and whatnot that Mark had added to the output.

I'll map those out and show them, but for now.. hey Joe.. where should I start looking at adjusting the input or gain?

View attachment 23983
Click to expand...
Change R2 and R12 to 43K
 
jbeckva

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Going to put in a 1K probably, but also noticing another deviation from the original circuit. Joe - R16 and R17 are actually 1 ohms versus 3.3, with the main emitter resistors (R18-R21) being .1 ohms instead of .33. For this type of application being a sub amp, does that make more or less sense to you? What would be the goal to lower the resistances - less heat with more current or ??

not3ohms.jpg
 
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jbeckva said:
Going to put in a 1K probably, but also noticing another deviation from the original circuit. Joe - R16 and R17 are actually 1 ohms versus 3.3, with the main emitter resistors (R18-R21) being .1 ohms instead of .33. For this type of application being a sub amp, does that make more or less sense to you? What would be the goal to lower the resistances - less heat with more current or ??

View attachment 24274
Click to expand...
Looks like you cannot trust anything on that schematic Jer. The 22K in the front end is an immediate attenuator, moving from nearly no attenuation to 50% attenuation. There goes half your gain right away, plus the rolloff is lower in frequency than with 1K. With a sub, that probably matters not at all.

The 1 ohm in the bias circuit for R16/17 increases the bias current and heat generation in the static condition of the amp just sitting there. The 0.1 ohm emitter resistors will just not promote as even current sharing as the 0.33 ohm resistors. One of the 2 paralleled devices can be more of a current hog.

Hope this helps.
 
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Gepetto said:
Looks like you cannot trust anything on that schematic Jer. The 22K in the front end is an immediate attenuator, moving from nearly no attenuation to 50% attenuation. There goes half your gain right away, plus the rolloff is lower in frequency than with 1K. With a sub, that probably matters not at all.

The 1 ohm in the bias circuit for R16/17 increases the bias current and heat generation in the static condition of the amp just sitting there. The 0.1 ohm emitter resistors will just not promote as even current sharing as the 0.33 ohm resistors. One of the 2 paralleled devices can be more of a current hog.

Hope this helps.
Click to expand...
I figured as much, but dayum if it didn't go kerplooey again. Like I was telling Kev, there's too many differences from the original posted schematic, plus the damn thing blew both of the fuses (violently I may add). I can pull it back out and show yas, but basically you can see where the outputs were replaced MANY times before I took a crack at it. They're shorted out again.

Lots of good heavy parts to play with tho.. So maybe I can do something with this guy and a WO PL14.. heheheh... crazy talk?
 
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jbeckva said:
I figured as much, but dayum if it didn't go kerplooey again. Like I was telling Kev, there's too many differences from the original posted schematic, plus the damn thing blew both of the fuses (violently I may add). I can pull it back out and show yas, but basically you can see where the outputs were replaced MANY times before I took a crack at it. They're shorted out again.

Lots of good heavy parts to play with tho.. So maybe I can do something with this guy and a WO PL14.. heheheh... crazy talk?
Click to expand...
Looks like Ohmite WW resistors for the emitter and bias resistors too Jer. A big no-no in circuits of this type. One for the dumpster...
 
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Yes !!! Dumpster is a better place for it !!! Thank you jerry and you Joe for looking at it !!! Only reason I bought the thing was Mark built it ...... He was trying to sell a bunch of stuff...... and the rest is history !!! You two made a great effort to a save it !!!
 
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