• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

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

Status
Not open for further replies.
Jump to Latest
#145
JCoffey said:
Brian,
Since I have the Chips already, is it possible to order the kits without the 3875s? No biggie if not, just curious.
Click to expand...

I am sorry, but I am not going to modify the contents of the kits in anyway, as don't want to make this order impossible for me to manage. Putting together a large batch of kits with the same components list will make the order managable for me.

Another reason for this, is that I do not promote the abuse of National's sample program for use with this project. $8 is a minimal price to pay for these chips.

Link to Wiki:
http://www.diyaudio.com/wiki/index.php?page=NI+GC+PCB+Group+Order

EDIT: I didn't see your latest post until after I posted this.

--
Brian
 
#147
A little off subject... but anwering a question...

widman said:


I'm a long time lurker, drawn out of hiding for this group buy. When I first started tracking down parts for a GC, I looked at the following tranformer from Parts Express:

Avel

Is this an acceptable alternative?

widman
Click to expand...

The only thing to consider here is the ability to drive lower impedance loads. With the transformer that you have selected, you are going to net ~+/- 34 V on your voltage rails. If you look at the data sheet for the LM3875, you will see that at these higher rail voltages, the LM3875 does not like to drive lower impedance loads. If your speakers are a nominal 8 ohms, this should not be a problem however, if your speakers have any significant impedance dips in their response, you could have issues with the LM3875.

That being said, many a GC has been built with the transformer rating that you specify, and they have worked well. Just keep the impedance issue in mind.

Later,
 

Attachments

  • nom.png
    nom.png
    5.8 KB · Views: 234
#149
Re: A little off subject... but anwering a question...

stadams said:
The only thing to consider here is the ability to drive lower impedance loads. With the transformer that you have selected, you are going to net ~+/- 34 V on your voltage rails. If you look at the data sheet for the LM3875, you will see that at these higher rail voltages, the LM3875 does not like to drive lower impedance loads. If your speakers are a nominal 8 ohms, this should not be a problem however, if your speakers have any significant impedance dips in their response, you could have issues with the LM3875.

That being said, many a GC has been built with the transformer rating that you specify, and they have worked well. Just keep the impedance issue in mind.

Later,
Click to expand...

I am using the a transformer with the same exact specifications in my gainclone, and it works perfectly with my Seas Thor TL speakers, which are a 4-ohm load. The above mentioned transformer should work just fine. I contacted Parts Express and they currently have 5 in stock, but the lead time is only 2 weeks.

Here is a picture of my setup in lab last night. I hauled my 100+ lb speakers into lab to do some good testing with my cdpro2 and gainclone. The circuit is identical to the the one implemented in the pcbs. I love it! I compared it with a leach amp, and it the gainclone is much better sounding.

Link to Wiki:
http://www.diyaudio.com/wiki/index.php?page=NI+GC+PCB+Group+Order

--
Brian
 

Attachments

  • setup.jpg
    setup.jpg
    90.3 KB · Views: 926
#150
closeup of gainclone and cdpro2.

Last night, with this setup, was the best sound that I have ever heard from my Seas Thor TL speakers in the last 1.5 years, since i have built them.

I did add some 4.7uF BG N caps on my power supply boards.

--
Brian
 

Attachments

  • lab-002.jpg
    lab-002.jpg
    95.6 KB · Views: 946
#151
The circuit is identical to the the one implemented in the pcbs. I love it! I compared it with a leach amp, and it the gainclone is much better sounding.
Click to expand...

Very interesting. I’ve been curious for some time if you've met or taken classes from THE professor himself. (having in my ute built a couple of Low TIM-3) It would be interesting to hear his impressions on the GC.
 
#152
Vdrop with dual bridges?

Brian,

What voltages are you seeing on the rails with your configuration? I am assuming that you are using the dual bridges. It is good to know that the sound of the amplifier is not adveresly effected by the impedance drop, but it would be interesting if you had the time to experimentally verify the nomograph in the LM 3875 data sheet that I posted.

Thanks,
 
#156
Da5id4Vz said:
Very interesting. I’ve been curious for some time if you've met or taken classes from THE professor himself. (having in my ute built a couple of Low TIM-3) It would be interesting to hear his impressions on the GC.
Click to expand...

I actually started off the evening in his audio lab, a large room filled full of speakers, and tested my Seas Thor TL speakers, showed him the response, and played lots of music with his LowTim amp, and the gainclone. He was grading papers in his office most of the time, but my 4 friends in the room clearly liked the sound of the gainclone better. Dr. Leach is skeptical with the gainclone, and didn't give it a listen, since he was busy grading papers. After 8:30pm (got there around 6), I moved the stuff into the project lab and started playing the gainclone with my cdpro2 project. We were there listening to music until 2:30am (while working on other projects). It was addicting. At full gain into my 4 ohm Seas Thor TL speakers, the gainclone was loud enough to be too loud for the 24' x 32' room that were were listening to it in. I did add 4.7uF Blackgate N capacitors ($4 each) into my power supply, over the dc lines of each bridge, and it made the gainclone sound excellent.

Dr. Leach is a very nice person, and when he isn't busy working on stuff, we end up talking for hours. I only had a chance to take his analog class, and not his audio engineering class. I did buy the textbook, though.

--
Brian
 
#157
Re: Vdrop with dual bridges?

stadams said:
Brian,

What voltages are you seeing on the rails with your configuration? I am assuming that you are using the dual bridges. It is good to know that the sound of the amplifier is not adveresly effected by the impedance drop, but it would be interesting if you had the time to experimentally verify the nomograph in the LM 3875 data sheet that I posted.

Thanks,
Click to expand...

I actually didn't measure the rails under load, but they were at +/- 34v before I applied the load.

--
Brian
 
#159
I'm in too......

I just added myself to the Wiki as well.

I'm in for 2 kits, and 4 additional LM3875TF chips as well..

Was I supposed to updates the total at the bottom of the table??? -- I didn't....

Steve

PS Brian,... any chance you could guestimate the shipping cost to New Zealand?...:xeye:
 
#160
Re: I'm in too......

BlackDog said:
I just added myself to the Wiki as well.

I'm in for 2 kits, and 4 additional LM3875TF chips as well..

Was I supposed to updates the total at the bottom of the table??? -- I didn't....

Steve

PS Brian,... any chance you could guestimate the shipping cost to New Zealand?...:xeye:
Click to expand...

As for the totals, you should update them, but I run sanity checks on the totals once and a while and update them if the numbers do not work out correctly. I just updated it for you, so don't worry about it.

I will have no idea of shipping until later. I will take a sample package to the post office, and get estimates for the shipping, then go from there.

--
Brian
 
Status
Not open for further replies.
Top Bottom