gainclone speaker questions

[keidori]

I am looking to build a gainclone and Ive been researching the matter for a few days now. I can't find any solid information on compatible speakers or specs. Bottom line is I have 2 speaker cabs that are rated for 4-6ohms at 150w RMS and I was wondering how I would go about building a gainclone that would be compatible with these cabs. Below is the manufactures specs. Any help in the right direction would be greatly appreciated.

# Dual 8" woofers and silk dome tweeter
# Power Handling - 150W RMS
# Freq response - 42-23,000 Hz +/-3dB
# IMP - 6 ohms
# Fused circuitry
# SENS. - 89 dB/2.83V/m
# X-over point 3500Hz
# THD < 0.5% about 75Hz at 1W resonance 55Hz +/- 5Hz

[ianpengelly]

Have a look at the specifications of the various chip options, some will drive loads of 4-6 ohms and there are a variety of power outputs. Just about an LM3875, 3886 or 4780 will do the job, either as a single chip or parallelled.

[keidori]

Ill take a look thanks for your recommendation.

[digits]

ran 86db jobbies off lm3875 and ref c for ages.... works just fine.

[AndrewT]

Use a 3886 single as the amp.
Do not parallel yet. Learn first.
Use a lower transformer voltage, following National's guidelines for 4ohm loading. The 4ohm bass/mid will dominate the loading seen by the amplifier and the amp PSU must be designed to not overheat the chipamp with that 4 to 8 ohm speaker.

BTW,
you are in the chipamp section. Don't build a GainClone. It will give all beginners a headache.

[wintermute]

Originally Posted by AndrewT

BTW,
you are in the chipamp section. Don't build a GainClone. It will give all beginners a headache.

This is a trap I still fall into (ie calling a chipamp a gainclone... I think that a lot of people don't realise that a gainclone is actually a clone of the original 47 labs gaincard, which from memory had a very minimal parts count (ie none of the stuff that helps to make the amp stable under all conditions).

I think that there is a wide adoption of the word gainclone to mean any amp based on a chip such as the LM3886, LM3875 etc. Perhaps there should be something in the forum heading to set this straight

Tony.

[digits]

I like the 75 for beginners, as you can snip off N/C pins and end up with a 5 pin case similar to LM1875, much easier to cope with 5 pins at the start than a bazillion.

[AndrewT]

But the 3875 has a guaranteed maximum cold output current of only 4Apk.
Great for 8ohm speaker, not so good for a 2.7ohm speaker.

[digits]

True that....

[6L6]

AndrewT -

What exactly do you mean by "GainClone" (As opposed to "Chipamp")? A point-to-point wired LM1875? A point wired LMXXXX? One of the same without all the stability components? Just curious in your observations on the subject and your terminology.