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Old 23rd February 2014, 06:17 PM   #121
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Quote:
Originally Posted by BobEllis View Post
Your PA application changes everything, I had assumed home use. Full protection is the way to go.

Mouser US and France show the MJE15034/5 in stock. The G sugffix just means RoHS compliant parts. ON Semiconductor MJE15035 Transistors Bipolar - BJT | Mouser
Actually most of the time it's for private use, but once in a while for PA. So I do want to make it rugged and ready for possible abuse.

Where can I get decent models for those 15034/35??? They would suffice for the needs and likely be much better than the 30/31 and 32/33.
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Old 23rd February 2014, 06:24 PM   #122
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Simulating? Bah! You know they will be better than the model you have, just build with them.
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Old 23rd February 2014, 10:11 PM   #123
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Originally Posted by BobEllis View Post
Simulating? Bah! You know they will be better than the model you have, just build with them.
Really?? You think the real thing would perform better than the sims? That would be great.

What I don't understand is why the leach amp sim doesn't perform as well as others that I've done, and that includes the 3055 amp, that does perform rather well with some mods.
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Old 23rd February 2014, 10:21 PM   #124
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Hi Guys

Has anyone mentioned that the XLRs are wired incorrectly?

pin-1 is ground
Pin-2 should be "hot", in-phase, non-inverting
pin-3 should be "cold", out-of-phase, inverting

Have fun
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Old 23rd February 2014, 10:30 PM   #125
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Originally Posted by Struth View Post
Has anyone mentioned that the XLRs are wired incorrectly?

pin-1 is ground
Pin-2 should be "hot", in-phase, non-inverting
pin-3 should be "cold", out-of-phase, inverting
Which project/pcb/schematic are you referring to?

If this is on my current design, I need to re-check. But I just looked at my schematic (eagle) and it's correct. So you must be referring to something else then.
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Old 23rd February 2014, 10:32 PM   #126
Struth is offline Struth  Canada
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Hi Guys

That is according to the schemo on the first page (posy-3). Haven't read the whole thread, hence my question.

You might also want to add RF filtering right at the inputs instead of after the INA.

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Old 23rd February 2014, 10:41 PM   #127
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Originally Posted by spookydd View Post
Which project/pcb/schematic are you referring to?

If this is on my current design, I need to re-check. But I just looked at my schematic (eagle) and it's correct. So you must be referring to something else then.
Hey , spooky .

If you could give me the .asc - a good bet someone in my "camp"
would build the IPS - I would keep it VERY close to your design ...
(just change to 4.5-5.5ma VAS I) We already have the OPS (EF3).
"spookyamp leach ips ?? "
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Old 23rd February 2014, 10:53 PM   #128
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Quote:
Originally Posted by Struth View Post
That is according to the schemo on the first page (posy-3). Haven't read the whole thread, hence my question.
Ha! Yes. Good catch. It was wrong back then, but I corrected that since.

Quote:
Originally Posted by Struth View Post
You might also want to add RF filtering right at the inputs instead of after the INA.
You mean you would drive the amp's input right off the opamp and move the input filter before it?

I wouldn't know how to do this right, since this is a diff input and both plugs need to be in parallel so a signal can go right through unchanged if need be.

All this is highly likely to change anyway. For one thing, I will do away with the output relays and replace them by mosfet based SSRs, and I will also use SSRs instead of fuses on the rails.

I want to have an input mute as well, and I am looking into having a clipping prevention circuit there as well, which would be switchable, so I think that INA may be changed to something else or it may be moved much farther ahead of the amp's input, if the clipping prevention sits there in between and can be used as a mute at the same time could be nice.

This amps must be able to withstand abuse from PA use, so I want to build in all the features that are needed (basic ones) and usually found in commercial amps.

I am quite likely to re-think the leach amp itself, at least the choice of parts, but this initial design will stay with mj15003/4. I have planned for using other devices later.

I've seen commercial amps with little transformers on those xlr inputs, although often switchable (bypass). I wonder what they are for.

Perhaps the hf filtering could be put on the feedback on the INA???
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Old 23rd February 2014, 11:15 PM   #129
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If you're designing your own board, I'm not sure why you want to use the INA at all. Just lift the feedback cap from ground and use that as your negative input. Tie the input to ground with 100K or so just so the input isn't completely floating. For single ended operation just ground the negative input.
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Old 23rd February 2014, 11:24 PM   #130
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Quote:
Originally Posted by ostripper View Post
If you could give me the .asc - a good bet someone in my "camp"
would build the IPS - I would keep it VERY close to your design ...
(just change to 4.5-5.5ma VAS I) We already have the OPS (EF3).
"spookyamp leach ips ?? "
Cool!

I'll attach the sim and model files.

I am not totally set on its exact current design, except that for this first edition I do want to keep using the MJ15003/4. I know they aren't the best, but they'll do fine and leach himself used them as well.

They do contribute to some good amount of thd, as I found out when swapping them for MJL4281/4302, but they'll have to do for now, I'll make others later with other devices.

But as far as the other parts are concerned, those can easily change, although I do have the MJE15030/31 needed on hand, it would be worth getting better ones if that makes a serious difference.

The MJE15034/5 seem like much better parts, although lower powered, they should do find driving 3 pairs of MJ15003/4.

I have been trying to decide which small signal types to use. My latest schematic in eagle is using the mpsa42/92, but having simulated with bc546b and then trying bc550c instead later, I think I should try making use of those high gain types, and they are also low noise at the same time.

The bc546 has been used in leach amps (Jens uses them) with much higher rails than the original leach amp v4.5 (at 58V), so I suppose the cascoding on the diff amps helps limiting the exposure. But how far can that go?

Using the bc550 instead of 546 lowers the vce0 at 45 instead of 65, so is this doable? I wish I was more advanced in spice to help figure this out properly.

My current schematic also calls for MJE340/50 for the vas and pre-drivers, but unless my models are not so good, I found them rather inferior. The KSA1381/KSC3503 seem better by far (because of their speed???)

I am flexible on most parts and will consider improvements in the schematic.

I definitely don't want to keep the diodes as sensors for the heatsink/bias. I want to use a TO126 at least, or perhaps a TO220, but that doesn't seem warranted. I want a part bolted on the heatsink and not some wires going to some parts in through holes in the heatsink or a pcb with wires. I know the heat sensing may have a bit of a lag, but since the sensing transistor is right on the heatsink near the TO3s, this may be limited.

What really surprised me when doing the leach amp sim, is how much worse it performed thd wise compared to other inferior amps that I've tried. I've tried quite a few, from cordell's examples from his book, some other low tim by a french engineer who published it in a magazine, the elektor 3055 amp that we'll do as a grounded bridge.... Even took a peek at the honey badger and the symasym... (wink wink)

I was able to reach below 100ppm thd on that elektor amp, using 3055s, and the leach comes up around .76% with MJ15003/4 and the other parts as in that sim attached. How come???
Attached Files
File Type: asc LEACH AMP v4.5_1.asc (20.2 KB, 25 views)
File Type: zip leach_v4.5_orig.bjt.zip (1.8 KB, 24 views)
File Type: txt models.txt (607 Bytes, 16 views)
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