original la sound amps.. crappy? decent?

[ppia600]

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??

 

[ppia600]

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?

 

[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.

 

[ppia600]

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.

 

[shagone]

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?

 

[EnvisionAudio]

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.

 

[EnvisionAudio]

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.

 

[shagone]

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!

 

[ppia600]

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.

 

[EnvisionAudio]

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.

 

[shagone]

Interresting. can anyone explain the self oscillating design further? i have heard of it but don't know much about it.

 

[EnvisionAudio]

Interresting. can anyone explain the self oscillating design further? i have heard of it but don't know much about it.

A self oscillating power supply is simply a resonant tank circuit with feedback. Adding a tertiary winding to the transformer and passing it through an auxillary core coupled to a feedback circuit sets the oscillation frequency of the power supply. This functions as a current-mode control, but variable frequency rather than pulse width. Pulse width actually is a function of frequency in these designs as higher frequencies move the BL curve further away from optimal and the operation becomes discontinuous. Current limiting in these designs is handled in such a manner.

Design of self-oscillating power supplies can be difficult to get right. I've never tried since there are dozens of adequate control IC's on the market for all manner of designs. I only maintain vague knowledge for situations where I need to repair one.

 

[damage]

LA Sound - AKA Metrosound vintage 1992. Not ALL oldskool amplifiers are worth owning.

Actually, I have a Hermosa amp I just got off eBay to practice repairs upon to find out it works fine. It too runs TIP35s and TIP36s. It uses ST parts for the outputs and 2 pairs of Int. Rect. IRFZ44s for the PS. It also has provisions for 2 more pairs.

The surprising part is that it uses 1% metal film resistors and propylene caps.

Not sure how it sounds yet other than quick testing.

 

[ppia600]

I sold mine to a guy at work and it sounded great. It sounded like a lot more than 75 by two but thats probably because we were running it 2ohm stereo into two sets of eclipse speakers.