Philo said:
The 549 is current limited at 10A when you short I_lim.
The 541 in not limited at all when you do this. You won't have a problem with this approach until the you overdrive the amp or short the outputs. If the output of the 541 is shorted, you will have your rail voltage over you speakers
If you draw more current than adviced, the chip may go up in smoke, and your speakers might be 
Peter Daniel said:
Whilst we wait for Philo's response, I thought I'd share my experiences.
I connected ref and lim to each other, then to ground, left the status pin floating, and used the minimised inverted config with the addition of adding back the 1uf cap across the + & - pins.
I used (for testing only) a 75VA 18-0-18 AC traffo, as my bigger 300VA that I use for my LM3875 and OPA548 at 24-0-24 AC seemed to cause the inbuilt protection to cut in, even though it gave only 28.5V regulated
(edit) I meant to say 22-0-22, not 24-0-24
Now that I've finished my LM3875 based GainClone, I'll go back on my TDA7294 based amp so expect news from me soon.
Just to make a short story, I had some problems with TDA7294 concerning oscillation and mysterious explosions (I finally found out that it was due to overvoltage hmmm hmmm).
The TDA7294 has very impressive dynamics and detailed sound (not to mention high output power. If more power is needed, there's the TDA7293 which accepts higher voltage rails and can be bridged using several 7293 ICs)
Philo said:
i dont want to limit the current, i want to have the maximum current limit. shorted the pin to what?
Mad_K said:
The 549 is current limited at 10A when you short I_lim.
The 541 in not limited at all when you do this. You won't have a problem with this approach until the you overdrive the amp or short the outputs. If the output of the 541 is shorted, you will have your rail voltage over you speakers
how can i protect my speakers? (with the chip)
Whoa, I leave for one quick trip to the electronics surplus store and the flood gates open. 
Anyway, my philo-sophy 
, some from what I have been reading in these threads, is when you use any of the attenuation/limiting functions of the chips it can have an affect on the sound and not for the better. I live(love?) KISS. I know about the 541s unlimiting problems, but since this is only a prototype at this point and being used with cheap speakers I am not that concerned. If I decide to build a finished amp with it I might try the limit. I my I am using the same setup as PM with both chips. Shorting the Ilim and the Ref together then to ground. I haven't run the 549 through it paces yet as I am still comparing the 541 to my LM3875 GC and mucking around with it. I have to share the PSU between the 2 prototypes as Apexjr ran out of the toroids I am using and I only have three of them left.
Peter, I just built it the same as your LM configuration except I put a zobel(.1uF and 220k)on the pos leg to ground. Probably a little to high on the resistor but I had them together already so in they went. I wanted to make sure it was stable before I did anything else. I plan on pulling it or shorting it out with a lead here soon. My toroids say they supposed to be 18-0-18 but after rectification the rails are around 27VDC so I think I am ok with the power. I haven't heard the 549 clip yet but I haven't run it hard either. I am being sent out tomorrow to the Persian Gulf for ten days to evaluate security procedures so I might be out of touch for 10 days or so. Hopefully, I can get internet access occasionally and keep up to date. Things change fast here..
Anyway, my philo-sophy , some from what I have been reading in these threads, is when you use any of the attenuation/limiting functions of the chips it can have an affect on the sound and not for the better. I live(love?) KISS. I know about the 541s unlimiting problems, but since this is only a prototype at this point and being used with cheap speakers I am not that concerned. If I decide to build a finished amp with it I might try the limit. I my I am using the same setup as PM with both chips. Shorting the Ilim and the Ref together then to ground. I haven't run the 549 through it paces yet as I am still comparing the 541 to my LM3875 GC and mucking around with it. I have to share the PSU between the 2 prototypes as Apexjr ran out of the toroids I am using and I only have three of them left. Peter, I just built it the same as your LM configuration except I put a zobel(.1uF and 220k)on the pos leg to ground. Probably a little to high on the resistor but I had them together already so in they went. I wanted to make sure it was stable before I did anything else. I plan on pulling it or shorting it out with a lead here soon. My toroids say they supposed to be 18-0-18 but after rectification the rails are around 27VDC so I think I am ok with the power. I haven't heard the 549 clip yet but I haven't run it hard either. I am being sent out tomorrow to the Persian Gulf for ten days to evaluate security procedures so I might be out of touch for 10 days or so. Hopefully, I can get internet access occasionally and keep up to date. Things change fast here.
.Ccomparisons please
Ok it's an apples vs bananas comparison, unfair on $ terms,
but could some of you worthy gaincloners say how you think that a gainclone might compare to:
(a) planet10's recent suggestion to me of a good value amp, a 4 watt class A push-pull fully differential valve amp:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=12477&perpage=15&pagenumber=4
in Post #60
(b) or an Aleph 2?
particularly (for an active system) in the ranges 150 Hz - 1.5 kHz; and >1.5 kHz?
(please don't say build it, I may well when time and space resources allow)
TIA
Ok it's an apples vs bananas comparison, unfair on $ terms,
but could some of you worthy gaincloners say how you think that a gainclone might compare to:
(a) planet10's recent suggestion to me of a good value amp, a 4 watt class A push-pull fully differential valve amp:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=12477&perpage=15&pagenumber=4
in Post #60
(b) or an Aleph 2?
particularly (for an active system) in the ranges 150 Hz - 1.5 kHz; and >1.5 kHz?
(please don't say build it, I may well when time and space resources allow)
TIA
Hi,
While I am waiting for the OP549's I am looking for a transformer. I have read the OPA549 datasheet and got some doubts confusing me. It says that this chip can handle 8A continuous or 10A intermitent. If I consider a 25V supply, from the datasheet the output of the OPA549 can go to +/-21V. So for 8A we have the maximum power of 336W?! I think I made some error here . But which is the maximum power this chip can handle? I don´t want to limit it on the PSU so I do have to figure this out.
Miguel
While I am waiting for the OP549's I am looking for a transformer. I have read the OPA549 datasheet and got some doubts confusing me. It says that this chip can handle 8A continuous or 10A intermitent. If I consider a 25V supply, from the datasheet the output of the OPA549 can go to +/-21V. So for 8A we have the maximum power of 336W?! I think I made some error here
. But which is the maximum power this chip can handle? I don´t want to limit it on the PSU so I do have to figure this out. Miguel
Hi!
First of all, the current limiting pin must be connected to V- for no limiting (simply a drop of lead on the pins does the trick)
I do not use the current limiting, have broken off the monitoring pin, and otherwise use the "normale" inverting GC setup, but with a 25-0-25 toroid (which is a little bit out of the specification, but so far no negative result).
The sound begins to clip on my 8 ohm speakers (being fed from DSP from 64 Hz upwards) at a very high volume level only, actually too high to use it in my surroundings (not disturbing my neighbours and my landlord are the keywords... ).
Since I implemented it, I did not go back to the LM3876, and since lately National (or their German distributor Spoerle) refuses to ship any more samples - they did that twice before, without complains), I just ordered OPA449 from TI (I have the impression that they ship anything they can...), to try it out.
But I think I will switch over to my yet to finish P3A (no case right now), since it sounds more analytical and powerful to me (which I like).
Oh, and for me a 2 W resistor from star ground to case was enough... bypassed it with 0.47 uF MKP, though
Bye,
Arndt
First of all, the current limiting pin must be connected to V- for no limiting (simply a drop of lead on the pins does the trick)
I do not use the current limiting, have broken off the monitoring pin, and otherwise use the "normale" inverting GC setup, but with a 25-0-25 toroid (which is a little bit out of the specification, but so far no negative result).
The sound begins to clip on my 8 ohm speakers (being fed from DSP from 64 Hz upwards) at a very high volume level only, actually too high to use it in my surroundings (not disturbing my neighbours and my landlord are the keywords...
).Since I implemented it, I did not go back to the LM3876, and since lately National (or their German distributor Spoerle) refuses to ship any more samples - they did that twice before, without complains), I just ordered OPA449 from TI (I have the impression that they ship anything they can...), to try it out.
But I think I will switch over to my yet to finish P3A (no case right now), since it sounds more analytical and powerful to me (which I like).
Oh, and for me a 2 W resistor from star ground to case was enough... bypassed it with 0.47 uF MKP, though
Bye,
Arndt
National nastiness
"National (or their German distributor Spoerle) refuses to ship any more samples."
Imagine that! I can't understand why. Another thing that is a puzzelment, is that some semiconductor companies require a real company Email adress instead of a free one like hotmail for example. It just doesn't seem to make any sense.
Wake up and smell the coffee you deadbeats*. I wonder how many of you go to the super market to checkout the free samples tray at dinner time. Damn I just gave the freeloaders another idea............
*dead·beat1 ( P ) Pronunciation Key (ddbt) Slang
n.
One who does not pay one's debts.
A lazy person; a loafer.
adj.
Not fulfilling one's obligations or paying one's debts: a deadbeat dad.
Synonyms: asker, bag lady, bankrupt, borrower, bum, bummer, cadger, chiseler, deadbeat, dependent, destitute, freeloader, hobo, indigent, lazar, lazzarone, mendicant, moocher, muzzler, panhandler, pauper, promoter, ragbag, rustler, scrounger, sponge, sponger, stiff, street person, stumblebum, suitor, supplicant, supplicator, touch artist, tramp, vagabond, vagrant, ward
"National (or their German distributor Spoerle) refuses to ship any more samples."
Imagine that! I can't understand why. Another thing that is a puzzelment, is that some semiconductor companies require a real company Email adress instead of a free one like hotmail for example. It just doesn't seem to make any sense.
Wake up and smell the coffee you deadbeats*. I wonder how many of you go to the super market to checkout the free samples tray at dinner time. Damn I just gave the freeloaders another idea............
*dead·beat1 ( P ) Pronunciation Key (ddbt) Slang
n.
One who does not pay one's debts.
A lazy person; a loafer.
adj.
Not fulfilling one's obligations or paying one's debts: a deadbeat dad.
Synonyms: asker, bag lady, bankrupt, borrower, bum, bummer, cadger, chiseler, deadbeat, dependent, destitute, freeloader, hobo, indigent, lazar, lazzarone, mendicant, moocher, muzzler, panhandler, pauper, promoter, ragbag, rustler, scrounger, sponge, sponger, stiff, street person, stumblebum, suitor, supplicant, supplicator, touch artist, tramp, vagabond, vagrant, ward
Re: National nastiness
Hi Fred,
I agree with your sentiment.
I'll admit it can be tempting, I get calls every month from just about all the chip suppliers and I know I can get whatever I want from them even if I told them it's for my hobby activities. But just because something would benefit me or be easy to do doesn't make it morally right.
In my opinion, using a vendors samples policy is only appropriate in the following cases:
- You are actually considering using the part in a commercial product.
- As part of an educational program (and you indicate this is what the request is for).
- The part is not available from any of the available low quantity sales channels (DigiKey, Mouse, Avnet, etc) and you are honest about why you want it (don't claim you are going to use 100K annual quantities if it's for your hobby).
Any other use of sample parts is in my opinion deception and theft. Remember that every time you request sample parts it costs that company at least $100 above the cost of the parts to handle your request. Somebody has to evaluate the request and process the order. Then someone in the sales department is assigned to follow up on the sample request. This cost money and distracts them from real customers who pay them the money they need to stay in business and keep developing the cool new stuff we want to use.
When times where good, chip makers could ignore this, but I have noticed that just about everyone is tightening up their sample policies. Times are pretty hard for the chip makers now and I think the days of "free samples, no questions asked" have come to an end. Most of them are laying off people and struggling to stay in business and freeloaders and parasites just make this harder.
Phil
Fred Dieckmann said:
Hi Fred,
I agree with your sentiment.
I'll admit it can be tempting, I get calls every month from just about all the chip suppliers and I know I can get whatever I want from them even if I told them it's for my hobby activities. But just because something would benefit me or be easy to do doesn't make it morally right.In my opinion, using a vendors samples policy is only appropriate in the following cases:
- You are actually considering using the part in a commercial product.
- As part of an educational program (and you indicate this is what the request is for).
- The part is not available from any of the available low quantity sales channels (DigiKey, Mouse, Avnet, etc) and you are honest about why you want it (don't claim you are going to use 100K annual quantities if it's for your hobby).
Any other use of sample parts is in my opinion deception and theft. Remember that every time you request sample parts it costs that company at least $100 above the cost of the parts to handle your request. Somebody has to evaluate the request and process the order. Then someone in the sales department is assigned to follow up on the sample request. This cost money and distracts them from real customers who pay them the money they need to stay in business and keep developing the cool new stuff we want to use.
When times where good, chip makers could ignore this, but I have noticed that just about everyone is tightening up their sample policies. Times are pretty hard for the chip makers now and I think the days of "free samples, no questions asked" have come to an end. Most of them are laying off people and struggling to stay in business and freeloaders and parasites just make this harder.
Phil
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