Gainclone Ideas

[reaper996]

I am new to the forum and looking to the more experienced members to help me decide on a gainclone amp kit to purchase for my first build. I have a basic understanding of electronics and recently picked up the Evil Genius - Electronic Circuits as a primer.

The last few days I have been perusing the forum reading up on amp design/projects and have also been reading some of Nelson Pass's literature.

A couple of questions that I would like to get clarification on are the following:

Pros/Cons of inverting and non-inverting amps?
Pros/Cons of mono versus stereo amps?

I would like to build an amp that provide between 25 - 40 watts of power using a toroidal transformer and the LM3886 similar to the kit available at chipamp.com.

Also, any links to articles about diy audio components and such would be greatly appreciated.

Thanks.

[Francec]

reaper996,
From what I've gleaned from my relatively short period here (and learning daily), the inverting phase was early on and then fell from favour because of the impedance problems and non-inverting is now 'de rigeur'.
I can't comment about mono and stereo amps, except to say that I think you mean the power supply.
Also, from what I've read and seen, an amp is far less influential on the quality of the sound than the speakers, that is, a good amp is not heard but bad speakers are.
I have used Rod Elliott LM388s amp module happily and successfully, others have done the same with Peter Daniels' units. Others are also said to be good. I don't think you can go to far wrong with either.
That said, I am designing a PCB for a LM4780 that is 2 by 3 inches (50 by 75 mm) that includes parallel and bridged format, with the shortest side parallel to to the chip. Why? So that many can be put side by side along a heat sink to get as much grunt into the least width as possible.

Frank

[pacificblue]

Originally posted by Francec
with the shortest side parallel to to the chip. Why? So that many can be put side by side along a heat sink to get as much grunt into the least width as possible.

That is not a promising setup. A single LM4780 is already difficult to heatsink. Several of them would need some active cooling technique with fans, water cooling, Peltier elements or so. And they will certainly need space between each other.

Be aware that you cannot just increase the heatsink size. There is also a limited amount of heat that can be dissipated across the small superfice those ICs offer. If you calculate it, you will find out quickly, why National chose the LM3886TA for BPA-200 and not the LM4780. The LM4780 is only good for its rated 2x60W for short periods of time due to its thermal limitations.

[AndrewT]

Hi,
make sure the schematic and the PCB include DC blocking caps on both the input and the Negative FeedBack leg. This is AC coupled.

Include all the optional components that National mention in the datasheet. In general they are not optional but compulsory if you want to lessen the risk of problems.

Once you know and understand what each component does, then you can makes decisions on which components could be removed or improved or adjusted. By then you may want to design your own schematic and PCB and do the whole thing.

[AndrewT]

Originally posted by Francec
That said, I am designing a PCB for a LM4780 that is 2 by 3 inches (50 by 75 mm) that includes parallel and bridged format, with the shortest side parallel to to the chip. Why? So that many can be put side by side along a heat sink to get as much grunt into the least width as

that sounds like ill informed decisions that may result in either no sound or intermittent sound or severely protected output that just plain sounds bad.

[reaper996]

I believe that the discussion is a bit off topic to the original post. I am looking for some feedback as to what kit(s) would be a great one for my first build and I am looking for some additional information/links to gain a better understanding about building amps.

Though the comments are insightful, they at this point in time have no relevance to my initial questions.

[pacificblue]

Originally posted by reaper996
Pros/Cons of inverting and non-inverting amps?

From http://www.mhennessy2.f9.co.uk/artic...lone_intro.htm
The differences between the two are reasonably subtle and the arguments for either are fairly nebulous in all honesty.

The biggest practical issue is caused by the low input impedance of the inverting version, which some preamps and source components object to. Perhaps ironically, this loading effect probably causes more difference in the percieved sound quality than the configuration.

Originally posted by reaper996
Pros/Cons of mono versus stereo amps?

Pro mono:
- Better channel separation.
- Less issues with ground loops.
- Set-up next to speakers possible.
Con mono:
- Higher component count.
- More space required.
- Higher price.

[Peter Daniel]

Originally posted by reaper996
I am looking for some feedback as to what kit(s) would be a great one for my first build and I am looking for some additional information/links to gain a better understanding about building amps.

This thread will provide all the info you may need: Commercial Gainclone kit- building instructions

[reaper996]

Peter, thanks your thread is one of the threads I have been reading about building an amp. Very informative.

[Francec]

Thanks for the feedback, guys.
The "grunt" I referred to means being able to parallel a board and then bridge it. The higher current capacity from the parallelled pairs should avoid the SPIKE kicking in and also should not cause any heating issues.
Yes, I am including all of the 'extras' from the datasheet, even though they will be used for an active speaker and will be physically positioned in the speaker box.

Frank