gainclone speaker questions

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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
 
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.
 
Just another Moderator
Joined 2003
Paid Member
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.
 

6L6

Moderator
Joined 2010
Paid Member
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.
 
Last edited:

6L6

Moderator
Joined 2010
Paid Member
AndrewT said:
BTW, you are in the chipamp section. Don't build a GainClone. It will give all beginners a headache.

He (wintermute) may have answered some of the questions, but I was trying to ask you (in a round-about way) what you mean by the above quote. Looking at this analysis of the actual 47Labs GainCard here - Mick Feuerbacher Audio Projects - you can see that the original does have the stability items, specifically the DC blocking input cap and the output Zobel...

And those items should solve most of the headaches, right?
 
Just another Moderator
Joined 2003
Paid Member
Looking at this analysis of the actual 47Labs GainCard here - Mick Feuerbacher Audio Projects - you can see that the original does have the stability items, specifically the DC blocking input cap and the output Zobel...

And those items should solve most of the headaches, right?

Hmmm I should have googled rather than relying on memory ;) by the looks of that, the only component missing that would normally be advised for a newbie is the feedback cap, certainly a dc blocking cap on the input and zobel on the output are standard inclusions for a problem free amp.

It could be that the original gaincard minimalism brought about a new wave of diyers trying to be more minimal still,and it is circuits based on these that have brought a reputation for troublesome builds for newbies.

Tony.
 
Hi Keidori,

I've recently made a pair of Frugel Horn Mk3's with 4 Ohm, 85 db, 18 watt, Mark Audio CHP-70's. I use an inverted LM3875 chipamp powered by a pair of 25-0-25 160 VA toroids with just 2 1000 uf caps at the chip [Thorstens circuit]

The setup has been running quietly for 2 weeks at low volume using a tuner and now I can turn up the volume. I am still gobsmacked by the dynamic range with about 1/4 turn of the volume pot, enormous!!

Your system will be fine :)

Warmest wishes - Jim
 
Hi Winter,
I would not be so kind to the Gain Clone.
It has omitted RF attenuation. It has omitted half the Thiele Network. It has omitted the DC block in the NFB. It has omitted the HF section of the decoupling.

Feuerbacher claims it has electrolytic decoupling and DC block on the input.
That is just 2 out 6 = potential headaches.

I can only recommend including 6 out 6 for beginners and even beyond beginners.
 
Just another Moderator
Joined 2003
Paid Member
Point taken Andrew :) I'm not sure about the RF attenuation though, are you talking about a small cap (in the pf range) across the NFB resistor? Not something I've seen in any of the chipamp schematics I've come across but after the measurements I did recently it is something that could be of use for me... I've got an amplitude modulated radio carrier on the scope output in the low megahertz range, seems to be coming in over the power cable (as it is there even when the amp is turned off, but goes away if I unplug the power lead!) I realised after I posted that the GC schematic didn't have any small caps for PS decoupling. Its also interesting looking at the datasheet for the LM3886, I hadn't studied it as carefully as I would these days when I made my chipamp, I did to a degree, but pretty much went with the BrianGT schematic, It only shows both the cap and the RL on the output in the single supply example. In all the other example circuits there is either just the RL or nothing at all! The other thing I am missing on mine is the DC blocking cap. Its something I've wondered about every now and then.... If you have the DC block in the NFB then how important is the input cap? (not suggesting it is good practice to omit it!) I guess if your source is faulty and puts out 15V or so DC then it could be important ;) but for normal amounts of DC on an output of a source, with unity gain at DC even a volt or two (though undesirable) is not likely to do any harm to the speakers would it? Maybe I've just been lucky! Tony.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.