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my_ref revC group buy (Mauro Penasa LM3886 design)

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troystg

troystg

Member
Joined 2004
pinkfloyd4ever said:

That's +/-36 volts DC that the chip can handle (datasheet says 84v so the absolute max is +/- 42Vdc, but you don't wanna run it too close to that) Unless you have DC mains power (you don't), your transformer puts out AC. When AC is rectified to DC, you need to multiply the AC voltage by 1.4 to get the rectified DC voltage

So 25VAC*1.4=35VDC
35VAC*1.4= 49VDC you get +/- when you use a transformer with dual secondaries and a separate bridge rectifier for each secondary

please correct me if I'm wrong on this anyone (or confirm if I'm right)
Click to expand...


"you get +/- when you use a transformer with dual secondaries and a separate bridge rectifier for each secondary"

You can also get +/- with a single BR too... Does not have to be dual rectifiers.

But everything else is right on.


MartinQ-

What are the specs of the transformer?

Input voltages
Output voltages
Number of input primaries
Output primaries.

If the x-former is 36VAC dual secondary with 2 pairs of primary inputs you can use the x-former as a 16VAC unit.

That would work for testing and general use, but not to bring out the full potential.
 
schro20

schro20

Member
Joined 2008
multires.caltech.edu/
raw PCBs

There was a question regarding availability of the plain PCBs. We intend to run additional PCBs, so do let us know. I can't tell you the price yet since it will strongly depend on the total. Basically, its a constant + linear term in the price with a large constant. But in the end the number of kits really needs to get to a certain point for this to be economically feasible. We are getting pretty close. So with another push this weekend (tell your friends!) we should be there.

Uriah has been working with a couple of vendors to make sure we get the quality we want while staying as tight as possible in the pricing. He is at this moment waiting on 2 prototypes to check that everything is in good order.

Peter
 
schro20

schro20

Member
Joined 2008
multires.caltech.edu/
current total

madisonears said:
Time for another "running total". I notice that neither of you, udailey and schro20, is on the list. Don't forget to count yourselves!
Click to expand...
Hi Tom,

happy to oblige:

bacood_2000 x2
warp_foo x2
Coreyk78 x2
SRMcGee x2
troystg x4
samsagaz x2
widman x2
billyk x2
korben69 x2
tube-arama x2
bandol83 x2
erikdebier x2
Joshua Adams x6
helfred x2
vglaso x2
Dxvideo x2
nvrgdenuf x4
Mindcrime x2
ben_lesmana x2
Daveze x2
Fredlock x2
argofanatic x2
GiovanniM x2
bhm x2
jERiCOh x2
TonyX x2
madisonears x2
mikesnowdon x2
vonfilm x2
pinkfloyd4ever x2
farl x2
Carl_Huff x2
schro20 x2
udailey x2
noodle x2

Total: 78

Almost there!
 
grimberg

grimberg

Member
Joined 2002
Re: current total

bacood_2000 x2
warp_foo x2
Coreyk78 x2
SRMcGee x2
troystg x4
samsagaz x2
widman x2
billyk x2
korben69 x2
tube-arama x2
bandol83 x2
erikdebier x2
Joshua Adams x6
helfred x2
vglaso x2
Dxvideo x2
nvrgdenuf x4
Mindcrime x2
ben_lesmana x2
Daveze x2
Fredlock x2
argofanatic x2
GiovanniM x2
bhm x2
jERiCOh x2
TonyX x2
madisonears x2
mikesnowdon x2
vonfilm x2
pinkfloyd4ever x2
farl x2
Carl_Huff x2
schro20 x2
udailey x2
noodle x2
grimberg x2

Total: 80
 
M

MartinQ

Member
Joined 2004
The transformer (and the rest of it) is from an SAE 2400 amplifier. Just pulled it out and checked voltage:

Input: 118 - 119 VAC
Rectified output on caps: +/- 39.0 VDC

That seems to be cutting it a bit close, but I think it'll do the trick. Not sure what the rating on the transformer is, but I'm guessing around 1000VA. That should do about 8 channels of LM3886?
 
troystg

troystg

Member
Joined 2004
MartinQ said:
The transformer (and the rest of it) is from an SAE 2400 amplifier. Just pulled it out and checked voltage:

Input: 118 - 119 VAC
Rectified output on caps: +/- 39.0 VDC

That seems to be cutting it a bit close, but I think it'll do the trick. Not sure what the rating on the transformer is, but I'm guessing around 1000VA. That should do about 8 channels of LM3886?
Click to expand...


You can throw a CL60 inline with the AC input and drop a little, and you can do a CRC filter and lose a little more.

Actually you can't do the CRC filter on these boards because of the on board rectification.

But you can do the CL60.

In your next post you mentioned bridging..

I would NOT bridge these boards. I would use a BPA200 if you needed more power, and if it were me I'd bi-amp with this amp on top and the BPA-200 on the bottom.

Remember these are NOT gainclones. These are REALLY well designed amps that just use the LM3886 chip for current.
 
M

madisonears

Member
Joined 2007
Having two threads going simultaneously is getting a little confusing; people are ordering on both threads.

Seems like we're getting very near, or possibly over 100, counting only boards. Since that is probably the long lead item, perhaps you would consider "pulling the trigger" on those when we reach or exceed 100, then order parts when we reach 100 kits. After all, if we don't reach 100 kits, I bet most interested parties would still buy just boards and buy parts on their own if provided with a BOM. I certainly would.

Are people buying extra boards to have them on hand in case they screw something up? Or are people buying them so they can build that many more amps? Or are people buying extra so they can experiment with different parts without having to tear apart a finished amp?

Because of all the accolades this design has received, I was eager to try it when I first read about it. It was extremely disappointing to learn that, by that time, kits were no longer available. Many thanks to you guys for resurrecting it. Please don't let this project die if we get to only 99 kits!

Peace,
Tom E
 
M

MartinQ

Member
Joined 2004
Troy, I'm a bit confused by CL60, can you explain?

You mention that these amps use the 3886 for current only. Either I need to read over the 3000 posts in the 'other' thread, or I need to study the schematic some more.

Is there a post / page / doc that outlines the specs on this design? How is it any different from a spec 3886 board?
 
troystg

troystg

Member
Joined 2004
Cl60 is a thermister. It acts as an inrush current limiter. As high current passes through it it heats up and the resistance goes up. But even cool it has a set resistance thus voltage drop across it.

Mr. Pass uses them in his amps.

As for the Lm3886 chip...

I do not profess to be an expert, and I would never want to offend the experts here on our forum. However I will try to sum it up briefly. If I am mistaken ANYONE is welcome to correct me.

To my knowledge the amp is actually built around the OP AMP where the gain is produced. The OP AMP amplifies the original signal x amount of times and hands off the voltage reference to the LM3886 to provide the current.

The reason Mauro's implementation works so well and is NOT a gainclone is that the OP AMP is nested IN the feedback loop of the LM3886. They act as one node in the circuit.
 
schro20

schro20

Member
Joined 2008
multires.caltech.edu/
new running total: 86

bacood_2000 x2
warp_foo x2
Coreyk78 x2
SRMcGee x2
troystg x4
samsagaz x2
widman x2
billyk x2
korben69 x2
tube-arama x2
bandol83 x2
erikdebier x2
Joshua Adams x6
helfred x2
vglaso x2
Dxvideo x2
nvrgdenuf x4
Mindcrime x2
ben_lesmana x2
Daveze x2
Fredlock x2
argofanatic x2
GiovanniM x2
bhm x2
jERiCOh x2
TonyX x2
madisonears x2
mikesnowdon x2
vonfilm x2
pinkfloyd4ever x2
farl x2
Carl_Huff x2
schro20 x2
udailey x2
noodle x2
grimberg x2
frog993 x2
cprof1 x2
kraljmatjaz x2

Total: 86
 
schro20

schro20

Member
Joined 2008
multires.caltech.edu/
madisonears said:
Having two threads going simultaneously is getting a little confusing; people are ordering on both threads.
Click to expand...
Agreed. I am keeping the updated list only on this thread.
Seems like we're getting very near, or possibly over 100, counting only boards. Since that is probably the long lead item, perhaps you would consider "pulling the trigger" on those when we reach or exceed 100, then order parts when we reach 100 kits.
Click to expand...
Not to worry. Uriah has been working on getting the boards. The first 2 prints were mailed to him yesterday. If they check out we should have quick turnaround on the boards. But before we shell out actual money (including big bags of parts...) we want to be reasonably sure we are not totally misjudging the demand. Things are looking good. I think it is safe to say that we will move ahead. I am rerunning bids this weekend to make sure we can hit the cost envelope even if we order only 80 or 90 parts kits.

One word of caution to all who are considering ordering from other countries. I have no idea what the additional cost for shipping will be. It may well render the economics unattractive to those. Basically we will choose whatever reasonable mailing method so long as it comes with tracking. (I don't expect weight to be a huge issue.)

Peter
 
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