I've Never Seen One of These Before...

scubalab

Found this simple little amp and couldn't resist picking it up. I believe it's made by a local audio company that does a lot of custom work for Penn State. I believe it's a 45 WPC amp but not sure if that's 8 ohms or 4... very nicely made and sounds surprisingly good. Very warm sounding, similar to my old Parasound HCA-750A. Here's some pics:

heiney9

It's a chip amp (Gain clone amp). Rossman was an amateur audio guy that built and sold some of these "kits". They come in all shapes and sizes (no standard cases)

Google LM3875, that's the chipset part number.

A chip amp has all the resistors, diodes and transistors in one I/C "chip".

Mixed reviews, but there are a few ways to implement them.

http://audiosector.com/lm3875.shtml

These were all the rage about 10 years ago

H9

heiney9

http://diyaudioprojects.com/Chip/Synergy-LM3875-Gainclone/index.htm

Brian Bell and Peter Daniels are other popular DIYer's that sold kits for the gaingclone chip amps.

H9

heiney9

47Labs made the very 1st gain clone amp and the rest are more or less copies. There are lot's of variations of parts and power supply sections used. But the chipset is the same LM3875

I had one for awhile that had all Caddock resistors and Black Gate caps. It was way to sterile and lifeless sounding to me. Robotic bass and very dry, flat presentation. I didn't keep it long.

H9

scubalab

I got my learn on - Thanks Brock!

msg

Pretty cool, Al!
Jeez, good info Brock - between you and Doc H, who needs Wikipedia and hifiengine.

Which speakers are you using with it, Al?

And tidy up your desk. Looks like an engineer works there.

heiney9

They are neat and everyone should experience one in their journey. They just didn't do it for me with the 1C's. I had been wanting to build one for awhile before I found an excellently built unit for a decent price.

Mine was a power amp, not an integrated amp. The weakness I see in the integrateds is there is no "pre-amp" stage so you are relying on the semi-poor quality of the volume control usually. Although I think because it's a chipamp there may be enough gain to not need a pre-amp section, but a quality volume pot costs as much as the entire chip amp parts so many builders use a very modest volume pot.

Enjoy

H9

scubalab

Scott - Shut up man... that WAS the tidy portion of my desk!

I just 'found' this yesterday and don't really have any plans for it, but it was about the price of a lunch or two, so I figured I'd 'try' it out. The speakers you saw in the pic were very cheap/low end speakers that came bundled with the HCT HMS-100 that I have in my office. I also tried it with the Polk RT25i's that I have in my office. I just plugged my iPhone in with a cheap 1/8"-RCA cord to try it out, so it certainly wasn't ideal.

Brock - What is the difference between a power amp and integrated in these things? Is it just the inclusion of a single volume pot? Thanks also for all the cool info.

heiney9

Pretty much (as I understand it). I have yet to see one with another stage added being the pre-amp section. The 47 Labs unit (IIRC) used a very nice stepped carbon resistor volume control. Pricey but ultimately better than a $10 unit that most DIYers implement.

I believe the original T-amp was also a chip amp using the same chip set. It used a walwart for power whereas most of the DIY versions added a simple to complex power supply depending on the DIYer's choice.

I thought those were speakers from that HMS package. I have the same HMS tube integrated, but I sold the speakers long ago. The RT25i's would be the ticket. I have a pair of those in the closet as well.

Nice score for that price

H9

heiney9

From the pics it looks like yours has the typical power supply section with a torodial tranny

scubalab

The volume pot (and the speaker terminals) on this do seem cheaped out.

So, using similar logic, could any amp with volume level pots (like older B&Ks, Parasounds, etc.) be considered 'integrated'? Or would the fact that they typically have separate pots for each channel change that logic?

Would using this amp (with it's volume pot set to max) with a separate pre-amp or receiver with pre-outs be the same as using any 'non-integrated'?

Also, I bought that HCT on your recommendation! It's a nice little tube setup for not a lot of money. It pairs nicely with the RT25i's. Thanks for steering me in that direction!

heiney9

scubalab wrote: »

The volume pot (and the speaker terminals) on this do seem cheaped out.

So, using similar logic, could any amp with volume level pots (like older B&Ks, Parasounds, etc.) be considered 'integrated'? Or would the fact that they typically have separate pots for each channel change that logic?

Would using this amp (with it's volume pot set to max) with a separate pre-amp or receiver with pre-outs be the same as using any 'non-integrated'?

Also, I bought that HCT on your recommendation! It's a nice little tube setup for not a lot of money. It pairs nicely with the RT25i's. Thanks for steering me in that direction!

No, line level controls on the amps in question are different and serve a different purpose.

You can't use it as straight amplifier w/o rewiring it. Probably not a difficult task, but you'd need to hit up one of those DIY sites to delete the volume control from the equation or perhaps someone here like FredV could tell you how to do it.

scubalab

Oh... glad I asked. I was going to try it as a straight amp. I would not have known otherwise. Thanks for the info. I'll have to do a little more research!

heiney9

You might be able to, I'm not sure and I'd err on the side of caution until you know more.

Usually a line level output for a source component is different than pre-amp output signal. But in the case of the chip amp, I don't know.

The idea is to get the cheap volume pot out of the signal chain. Even if you can run it like you are asking, the signal is still being degraded by the volume pot.

H9

mhardy6647

Yeah, the Gaincard clones ("Gainclones") were a thing some years back.
I have a feeling it was more than 10 years ago, though

As mentioned above the sine qua non of the genre was the "Gaincard" amp by Japan's 47Labs:
http://www.stereophile.com/solidpoweramps/120147/#d0Q8zOqleVZsUvhe.97



Based on the date of that review, maybe the Era of the Gainclones was about a decade ago!
It might be entertaining & instructive to read the Stereophile reviewspeak & compare and contrast it to Brock's pithy assessments above

There was a dedicated Gainclone Forum in the Old Days -- but I cannot remember any thing else about it (e.g., who ran it!). There is a subform @ DIYaudio on chip amps, though:
http://www.diyaudio.com/forums/chip-amps/

msg

scubalab wrote: »

Scott - Shut up man... that WAS the tidy portion of my desk!

lolol

scubalab wrote: »

The speakers you saw in the pic were very cheap/low end speakers that came bundled with the HCT HMS-100 that I have in my office. I also tried it with the Polk RT25i's that I have in my office. I just plugged my iPhone in with a cheap 1/8"-RCA cord to try it out, so it certainly wasn't ideal.

heiney9 wrote: »

The RT25i's would be the ticket. I have a pair of those in the closet as well.

ooh, yeah, RT25i's definitely - in fact, when I was looking to build a small desk system for the home office, Brock recommended them to me as well. That's turned out to be one of my favorite little systems to date, and that setup images nicely and sounds just beautiful. I currently have them oriented upside down so the tweeters are not obscured by the bottom edges of monitors. Does need a sub, but for an office environment, might need to reserve the headphones for heavier rocking sessions?