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Old 8th January 2008, 02:12 AM   #1
ppia600 is offline ppia600  United States
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Default original la sound amps.. crappy? decent?

I'm asking because I just picked one up for cheap and its all original with no problems. Its the hermosa 150s, I believe its 75w rms by two into 4 ohms and about 150w by two into 2 ohms. The outputs appear to be tip 35 and 36c's and there are four per channel which seems sufficient for 150w per channel and each side of the power rail is almost 50vdc. I can't tell if the power supply uses fets or regular transistors though. Back in 91 I had a malibu 100 back when I lived in cali. and it was ok, but don't remember being too impressed with it although it never had a problem even when I ran it at 2 ohm mono a few times (just seeing what it could do ) The circuit design is very simple on the power supply and audio stages as well, except for a couple of very tiny ic's in the stage between the input and output drivers. They appear to have six legs and look like something out of a fosgate or newer sony amp. Anyone have opinions on these amps? I know they are a cheap brand but they seem to be built reliably. Remember back when they were selling component sets and those clean looking and nice sounding bandpass boxes??
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Old 9th January 2008, 04:16 PM   #2
ppia600 is offline ppia600  United States
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And amazingly, this one has no turn on noise I can hear. The malibu 100 I had in 91' had a little turn on thump. Does anyone know if the hermosa 150s uses fets in the power supply?
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Old 9th January 2008, 05:42 PM   #3
shagone is offline shagone  United States
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i can't remember the last amp that i saw that did't have fets in the power supply unless it was very old as in pre-80's or it was a chip-amp. so, yes i think they have fets. i threw one out after opening it a few years back before i was into repairing amps much because it had bad caps or something.
i remember having a Malibu 100 in my old nissan pickup pushing 2 8" truck boxes behind the seats. not the ideal set-up but it worked. yes it did have a turn on thump. i'm sure that the Hermosa is a half way decent amp but not for sound quality. open it up and take some pics for us and ampguts so we can get a better idea of whats going on inside of it.
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Old 9th January 2008, 06:31 PM   #4
ppia600 is offline ppia600  United States
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Quote:
Originally posted by shagone
i can't remember the last amp that i saw that did't have fets in the power supply unless it was very old as in pre-80's or it was a chip-amp. so, yes i think they have fets. i threw one out after opening it a few years back before i was into repairing amps much because it had bad caps or something.
i remember having a Malibu 100 in my old nissan pickup pushing 2 8" truck boxes behind the seats. not the ideal set-up but it worked. yes it did have a turn on thump. i'm sure that the Hermosa is a half way decent amp but not for sound quality. open it up and take some pics for us and ampguts so we can get a better idea of whats going on inside of it.
The reason I'm thinking it may not have fets is because some of the amps I owned back then (japanese JVC's, Black pyramid pb amp, Blaupunkt bma) didn't have fets. (the ones I owned, for anyone who has to prove me wrong ) Some may have but the ones I had didn't. These were late 80's models. I would take some pics, but ampguts has no La sound yet and the photos I sent of my sony 2252hx never got posted. They never even responded to my emails. I also notice they only have a couple of the later 90's models jvc amps shown, none of the 80's japanese made models that were actually reliable and sounded nice.
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Old 9th January 2008, 08:21 PM   #5
shagone is offline shagone  United States
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Can you read the part numbers in the heatsink mounted devices in the power supply section? do you se a tl495 or 594 chip or simmilar anywhere on the board?
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Old 10th January 2008, 12:30 AM   #6
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Quote:
Originally posted by shagone
[B]i can't remember the last amp that i saw that did't have fets in the power supply unless it was very old as in pre-80's or it was a chip-amp. so, yes i think they have fets.
Well, you haven't seen too many amps, then. Most pre-1994 amps used BiPolar transistors in their SMPS rather than FETs. I have several Alpines, Orions, A/D/S, USAmps (yes, a 1990 US Amps KA250) and many off-brand style that use them. I believe Rockford was the first to use VFETs then most manufacturers followed suit with the BUZ71, MTP50N06 and then the venerable IRFZXX series.
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Old 10th January 2008, 12:39 AM   #7
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Quote:
Originally posted by ppia600


The reason I'm thinking it may not have fets is because some of the amps I owned back then (japanese JVC's, Black pyramid pb amp, Blaupunkt bma) didn't have fets. (the ones I owned, for anyone who has to prove me wrong ) Some may have but the ones I had didn't. These were late 80's models. I would take some pics, but ampguts has no La sound yet and the photos I sent of my sony 2252hx never got posted. They never even responded to my emails. I also notice they only have a couple of the later 90's models jvc amps shown, none of the 80's japanese made models that were actually reliable and sounded nice.
LA Sound - AKA Metrosound vintage 1992. Not ALL oldskool amplifiers are worth owning.
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Old 10th January 2008, 01:19 AM   #8
shagone is offline shagone  United States
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Quote:
Originally posted by EnvisionAudio


Well, you haven't seen too many amps, then. Most pre-1994 amps used BiPolar transistors in their SMPS rather than FETs. I have several Alpines, Orions, A/D/S, USAmps (yes, a 1990 US Amps KA250) and many off-brand style that use them. I believe Rockford was the first to use VFETs then most manufacturers followed suit with the BUZ71, MTP50N06 and then the venerable IRFZXX series.
So is that why the older amps ran way hotter than modern amps of any class??
i have installed plenty but back then i never opened them up. i just remember the big deal about Mosfet being printed accross many amps in the early 90's so i guess your right and i do remember now some that had BiPolar's (Orion)but i thought the LA sound was Mosfet. anyone else remeber? Most of the veterans to this forum know alot more than i do about the guts of amps. i'm learning more everyday!
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Old 10th January 2008, 04:18 AM   #9
ppia600 is offline ppia600  United States
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Quote:
Originally posted by shagone


So is that why the older amps ran way hotter than modern amps of any class??
i have installed plenty but back then i never opened them up. i just remember the big deal about Mosfet being printed accross many amps in the early 90's so i guess your right and i do remember now some that had BiPolar's (Orion)but i thought the LA sound was Mosfet. anyone else remeber? Most of the veterans to this forum know alot more than i do about the guts of amps. i'm learning more everyday!
Yeah, the older ones did run hotter and yeah several used bipolars back in the early to mid 80's. I also worked on a us amps for a friend about a year ago and remember thinking "wow, this thing is pitiful.. look at the bipolars in the power supply and the wimpy transformer" (obviously it wasn't total junk but I expected mosfets and better build quality)
I remember noticing several of the older amps using bipolars, even back in middle and high school I was tearing them apart for fun. I remember punch bragging about the fets. I was just trying to avoid pulling one of the metal rails but I'll do it and check the part numbers soon.
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Old 11th January 2008, 06:57 PM   #10
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Quote:
Originally posted by ppia600


Yeah, the older ones did run hotter and yeah several used bipolars back in the early to mid 80's. I also worked on a us amps for a friend about a year ago and remember thinking "wow, this thing is pitiful.. look at the bipolars in the power supply and the wimpy transformer" (obviously it wasn't total junk but I expected mosfets and better build quality)
I remember noticing several of the older amps using bipolars, even back in middle and high school I was tearing them apart for fun. I remember punch bragging about the fets. I was just trying to avoid pulling one of the metal rails but I'll do it and check the part numbers soon.
They ran hotter because they were biased higher. MosFets are a little more efficient than BiPolar at switching supply speeds - but FETs can switch at higher speeds, making transformers, filter caps and CM inductors smaller. Plus, FETs don't suffer from secondary breakdown the way BiP's do.
US Amps used self-oscillating power supplies during their Bi-Polar years. The transformers had few windings, but they were solid designs - far better than what was available at the time. Their switching frequency was low ~25kHz, so Litz-type wire was less necessary. I think their assembly style left a lot to be desired, but their heatsink mass was high for such a compact design.
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