First Gainclone (Hell, first amp...)

[ronc]

Sorry , should have included this note, if the arm is too long for the pot, a dremel and a cut off disk solves that . Just dont cut the arm too short.
ron

 

[jcactaur]

llamas you did not comment on the music quality, I'm interested because i have ordered similar parts. Is there still much hum?

 

[ronc]

I get absolutly NO hum what ever.My config is battery P/S (+/-12v) no input cap,250k feedback resistor,500k multi turn pot from pin 7 to ground (just dial in 0 offset) 10k/50k shunted pot(to ground, however i want to try some larger values) for volume control.6,8uf on the power rails to ground and 1uf between the P/S pins.
Speakers are fostex fe-103e horns (my own design) and the room has been fully treated with bass traps, mid traps and HF traps.Speaker wires and innerconnects are 24 gage solid core copper.
ron

 

[ronc]

Sorry , should have included this in the last post.
As far as quality, its hard to beat.Very tight strong bass with a clarity and dynamics that is almost scary.
I had a friend who has the krell/B&W combo come over and his jaw hit the floor.He admitted that the dynamics and clarity far surpassed his combo but also stated that his LF extension was greater (hay its a 4" driver with the horn tuned to 57Hz LOL).
I believe that for the LM3875 GC that efficent (=> 88db/watt/meter) with 8ohms loading works best as i have tried many speaker /amp combos and this looks to work well.I also believe that the GC works best with TL or horn loaded full range speakers.
Please , please dont let the naysayers (see post above) keep yall from trying this amp.Even my 80 yr old dad prefers the GC to either my hotrodded restored marantz 2230 or my homebrew 6bq5 PP amps.
ron

 

[Llamas]

I'll need to finish things off, and hook up to non-test speakers before giving my opinion (as inexperienced as that opinion is...).

As soon as I finish cleaning the garage, I'll be assembling the cabinets. I'll have pics and opinions after that.

But, I can clarify the hum/quiet thing. When I say that I turned on the amp, and there was silence, I mean there was no noise. I wasn't sure things were working until I turned up the volume.

--Mike

 

[Carsound]

realy a biginners question...

Hi, you have done a realy good job, keep on posting pic, I love those.

Now fore my question, I plan on building pretty much the same thing, a basic dual mono gainclone. I have already ordered the parts.

I'm planning on building the amp inside an aluminium box surounded by wood for the front, sides and mayby back.

Heres my question, For the speaker binding post. I guess I have to isolate those from the aluminium chassis. How to I do that?

Told you it was a realy basic question.

Thanks in advance

PS: sorry for my not so good english, I am french and sometimes I get mixed up when I'm writing.

 

[ronc]

Speaker binding posts(some of them) come with a plastic isolation sleave that is effective. I would think hard about a rear wood panel as its difficult to mount posts and other objects to wood,I have done it in the past by using a drill press and marking the depth desired on the shank of the drill and countersunked the hole to allow a thin enough wall thickness to mount attchments.Its even more difficult mounting attachments on the front(ie: pots,selectors ect ect) , but the wood does give a better look than alum.
ron

 

[JOE DIRT®]

a simple plate can look nice with a wood panel for binding posts or inputs and if you flush mount the plate it it looks like it belongs there

DIRT®

 

[Carsound]

I have an idea about the wood surounding the aluminum box, but it'S hard to tell in words.... I waiting for my power transformer and bridge rectifiers.

As soon as I get them, I'll start building and I'll post pictures to let you see how it comes out.

Would polishing my aluminim case be a good idea, look wise?

Marc