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Group order of non-inverted LM3875 pc boards? Anyone interested?

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#823
Stupid Questions

Hi Brian,

I've been reading up on your NI Gainclone and have a few questions. I want to order some of your kits but not sure how many I need.

I have CC (MTM 2way) and two mains (WtmW 3ways).
CC MTM
tweeter- 8 ohms, two midwoofers parallel- 4 ohms load
Two Mains WtmW
tweeter- 8 ohms, midwoofer- 8 ohms
two woofers parallel for 4 ohm load

I know it is 8 channels minimum but would the drivers that are wired parallel be better having separate crossovers and channels.

I know your rectifier boards are designed for two channel duty. Can I add another channel to that board (for my 3ways)?

What size toroidal transformers will I need if I build my amps into the rear of the speaker enclosures? What size if I build them in one chassis?

Where can I get mounting plates and fins for rear of speakers?

Other than ebay, where can I get cheaper toroidal transformers?

Thanks
 
#824
Re: Stupid Questions

mrlots2do said:
questions
Click to expand...

I sent you an e-mail a little while ago answering these questions. Let me know if you have any more.

For everyone: I am placing parts orders on wednesday night, so please try to get your order in by then, so that I can get an accurate estimate of what is needed. I will continue to accept orders for quite a while, so don't consider wednesday a deadline.

Order page:
http://www.BrianGT.com/order

--
Brian
 
#826
Re: Stupid Questions

chipco3434 said:
I wouldn't mind seeing these answers...I am sure many others would like to share in this knowledge.
Click to expand...

I will include a response to his message below. I expanded on it a bit more.

mrlots2do said:
...
I have CC (MTM 2way) and two mains (WtmW 3ways).
CC MTM tweeter- 8 ohms, two midwoofers parallel- 4 ohms load
Two Mains WtmW tweeter- 8 ohms, midwoofer- 8 ohms two woofers parallel for 4 ohm load
...
I know your rectifier boards are designed for two channel duty. Can I add another channel to that board (for my 3ways)?
...
What size toroidal transformers will I need if I build my amps into the rear of the speaker enclosures? What size if I build them in one chassis?
...
Where can I get mounting plates and fins for rear of speakers?
Click to expand...

For your speakers, if you are using a passive crossover, you shouldn't need to use more than a single channel per speaker. Bi-amping and Tri-amping is nice, but I couldn't justify the extra cost.

Assuming you still want to do bi/tri-amping:

The rectifier boards could support 3 channels, if you spliced the wires or used terminal blocks.

For the transformers, I would recommend Avel Lindberg from Parts Express:
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=3
Most people seem to be using 100-150VA per channel. At a low volume level, the current draw of the LM3875 is quite low. 2x25vac seems to be fine for the gainclone. I am using 2x24vac for my 4ohm speakers, and it works perfectly.

As for the plates for the back of your speaker, I am not exactly sure what you should use. You should be able to use any reasonably sized heatsink, maybe 3"x4"x0.5" or so for one channel. For 3 channels inside one speaker, I would get a fairly big heatsink, since there will be poor ventilation inside the speaker.
An externally hosted image should be here but it was not working when we last tested it.

might be interesting (using 1 per channel):
HEATSINK
Aluminum, no holes ~4" x 4" x ¾"
23Z102 $3.49
from Alltronics.com

or this:
http://www.allelectronics.com/cgi-bin/category.cgi?category=270&item=HS-966&type=store
even more of a bargain 🙂
or this:
http://www.allelectronics.com/cgi-bin/category.cgi?category=270&item=CF-75&type=store
if you want to try something active...
or some of these from apexjr:
http://www.apexjr.com/images/APEXJRTUNNELHEATSINK1.jpg

(these are just random links I pulled up thru a quick search through surplus companies on my bookmarks. You can probably find something more suited to your application, but these are some ideas)

You will probably have to do some testing with heatsinks to see how much of a heatsink you actually need for your application, as it can vary quite a bit. I would make a reasonable estimate, and see if it gets too hot first. I have heard some say that during the burn-in period on the gainclone, it runs hotter than afterwards. I have not verified this myself, as I didn't look at the temperature when my amplifier was burning in.

Let me know if you have any more questions.

--
Brian


Still taking kit orders:
http://www.briangt.com/order
 
#827
Re: Kit received

rentiap said:
Hi Brian:


Is there any reason to use the 2w rikens as apposed to the 1w and was wondering if anyone has tried AN tantalum resistors for GC? I know they are verry expensive but they made quite a difference as up grades in my AN M2 pre line stage.

Regards.
Craig
Click to expand...
I understand that Brian is very buisy with trying to get orders out and trying to get the lm470 group buy situated and doesn't have time to answer everybodys little questions.
And maybe I wasn't specific enough. I was refering to the bypass resistor connected to the amp chip.

Could somebody that has some time answer my questions from post#800

Much appreciated.
Craig.
 
#828
Re: Kit received

rentiap said:

Is there any reason to use the 2w rikens as apposed to the 1w and was wondering if anyone has tried AN tantalum resistors for GC? I know they are verry expensive but they made quite a difference as up grades in my AN M2 pre line stage.
Click to expand...

I'm using 1/2W Rikens and they are fine. Higher wattage resistors might sound slightly better, but the difference is not that big. In my layout, there is simply no space for bigger size.

I tried those AN tantalums and I was not impressed. While midrange and bass is very good, they lack extention in high frequency and sound a bit dull for my taste.
 
#831
More: Stupid Questions

BrianGT said:


For your speakers, if you are using a passive crossover, you shouldn't need to use more than a single channel per speaker. Bi-amping and Tri-amping is nice, but I couldn't justify the extra cost.

Assuming you still want to do bi/tri-amping:



Brian,

My intent is to remove the WtmW passive 3way crossovers, recalculate active 3way crossovers, place them in pre-amp out signal path before tri-amps.

I was thinking of replacing the 22k resistor before the LM3875TF with a variable resistor (? ohms) on the tweeter and midwoofer circuits. Would this allow me to match the db of drivers?

I was also thinking of paralleling two amps for the parallel woofer circuit (4 ohm circuit). This would allow more power when base calls for it.

I was thinking again about placing supply transformer in remote enclosure, fuse primary and secondary sides. Don't know if this is a good idea so comment on it please, run separate 25-0-25 ac lines to each speaker and pre-amp out cable to each speaker. The active crossovers, bi/tri-amps and diode rectifiers will be inside each speaker.

Thanks again for your assistance, Phil

BTW.... how do you place quote in separate window and then post message.
Click to expand...
 
#832
Re: Re: Stupid Questions

BrianGT said:


As for the plates for the back of your speaker, I am not exactly sure what you should use. You should be able to use any reasonably sized heatsink, maybe 3"x4"x0.5" or so for one channel. For 3 channels inside one speaker, I would get a fairly big heatsink, since there will be poor ventilation inside the speaker.
An externally hosted image should be here but it was not working when we last tested it.

might be interesting (using 1 per channel):
HEATSINK
Aluminum, no holes ~4" x 4" x ¾"
23Z102 $3.49
from Alltronics.com

or this:
http://www.allelectronics.com/cgi-bin/category.cgi?category=270&item=HS-966&type=store
even more of a bargain 🙂
or this:
http://www.allelectronics.com/cgi-bin/category.cgi?category=270&item=CF-75&type=store
if you want to try something active...
or some of these from apexjr:
http://www.apexjr.com/images/APEXJRTUNNELHEATSINK1.jpg


Thanks for the links to heat sinks
Click to expand...
 
#833
Re: Re: Kit received

Peter Daniel said:


I'm using 1/2W Rikens and they are fine. Higher wattage resistors might sound slightly better, but the difference is not that big. In my layout, there is simply no space for bigger size.

I tried those AN tantalums and I was not impressed. While midrange and bass is very good, they lack extention in high frequency and sound a bit dull for my taste.
Click to expand...


Hi Peter.
Thanks for the quick reply I was actually hoping that you would be the one to reply. As your opinion means alot .
I will go ahead and use the 1/2w rikens no need for the extra expense.
Have you used the caddock TFo2o ultra precision resistors? sourced from Michael Percy's sight. I have used them in the signal path of tube output in my Jolida 603a cd player. they seemed to open up with more clarity and air actually.

maybe it was that I didn't hear them!?
Sorry I didn't mean to hijack this thread.
Thanks.
Craig.
 
#836
Re: Re: Re: Kit received

rentiap said:


Have you used the caddock TFo2o ultra precision resistors? sourced from Michael Percy's sight. I have used them in the signal path of tube output in my Jolida 603a cd player. they seemed to open up with more clarity and air actually.
Click to expand...

I didn't have the chance to use those. I believe they are bigger, so it's a bit harder to fit them in a feedback loop and make the path really short. They might be better, but who knows. I tried Vishays S102 there once, and MK132 Caddocks were preferred.
I have some nude Vishays waiting to be tested in GC, but again, I didn't have time to try those yet.
 
#839
Re: Re: Re: Re: Kit received

Peter Daniel said:
I didn't have the chance to use those. I believe they are bigger, so it's a bit harder to fit them in a feedback loop and make the path really short. They might be better, but who knows. I tried Vishays S102 there once, and MK132 Caddocks were preferred.
Click to expand...

Yes they are much wider.75 as aposed to .290 they sound so good to me that I have been to afraid to change them out (my friends tell me that I tweak to much):scratch: but someday I will.

A couple of more Questions if you will? Peter.
after I get this first trial pair of GC monoblocks finished, I plan on building a pair of four chanel GC monoblocks possibly a double stacked version of your Patak on your site.AS I need four chanels per speaker.(my next project a pair of Sigfried Linkwitz Orions) I will use Brazilian Epay(AKA iron wood)for the wood side panels alot like the rosewood but a little darker and much denser.

1.Will I need two trannies for each power supply or can I split one using a terminal block using a larger tranny IE 330va,450va,600va? or is a larger tranny needed?

Is it worth using seperate power supplies as apposed to intigrated?
Cleaner power. they will also be regulated supplies.

I've been trying to figure out how you were able to attach the amp chips to the other side of the PCB without flip flopping or rebending the legs.Maybe I'm trying to overthink and is probably very simple.

I have to many more questions but I should stop for now.

I've been lurking( I think that's the right term?) for quite a long time now trying to read and learn from other posts before asking questions.But haven't seen these asked.

Thanks for your time.
Craig
 
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