[da_burl]

Sorry, I hope crossposting to the "Big Two" (wize and fi) is not frowned upon. Here goes:

As some of you may recall, I decided to build a multiloop buffered output amp using the HA-5002 instead of the more popular EL-200x's or BUF634's. I just thought it would be beneficial to go ahead and try them, because of the limited availability of the EL200x's and morsel's dislike of the BUF634
So anyway, I ordered four the first time. Due to improper PS connections, I took two out pretty quickly
Now it appears I am down to one, I rebuilt the whole circuit using pad per hole, and tried to come up with the best layout I could, after a lot of experimenting with powerpoint! I am finally at the point that I can put my one good one in either side, and I get music, YAY!!! I am now awaiting 6 more from Allied, Newark owes me four also, but they are showing out of stock, and it had said 39 days lead time for about 2 weeks now!
So, I just want to ask a few questions to avoid blowing the last one as well.

I have resolved the PS issues obviously (don't ask, I swear I measured three times before plugging them into the board and applying power, but my eyes or my brain must have deceived me, and they do have four connections each, must have just gotten confused!!).

So here comes the questions:


It is ok to tie the two V+ and V- pins together? (If you don't want to limit the current?)

On the current limiting, the formula is Rlim = Vout+/I-out-max = Vout-/I-out-max. If you express the I-out-max in Milliamps, you come up with a pretty small resistor, so I am assuming it is in amps

For 12v supply, I come up with 60 ohms and 15v comes out to 75 ohms, assuming 200mA max out, is this right, or did I miss something?

The resistor goes between the respective Vx source and V2x lead, am I safe calculating for 200mA per side?

My normal procedure when first powering up is to leave the output open, measure for any nasty DC on the outputs, then plug in my cheapie walkman phones, and listen. Only after listening to this horrid sound for a few minutes, and re-measuring DC a few more times do I plug in my Grado's!!

Is this cool for this chip? I read it has no output protection, but with no load, will it just not output any current, or just blow right away? Would I be better off putting in a 30-50 ohm dummy resistor before applying power? (Guess I could have just tried it

One last question, the output resistor, R8 and R9 in the meta42 schematic, I haven't got one for now, the way I understood it was you could add it if you have hiss or noise. Would this be a good idea, does it help to limit current also?

Sorry, I'm not an engineer, just a guy who can usually wire something from a schematic!!

Thanks again, and if anyone else is actually using these, please post your results and ideas, either here or in the parallel thread under Buffer Distortion Measurements!! I think a couple of people mentioned they are using them, but didn't go into a lot of detail about how.

 

[aos]

You can connect two v+ and two v- pins together - that's what I did and chips worked great. They suck 10mA each though at +-5V which is much more than about 1.5mA each I get from EL2001. Compare 20mA to 3mA...

 

[KurtW]

My measurements were with the power pins for each supply tied together.

You can leave the output unconnected, but when you do plug in your headphones, make sure the volume is all the way down or better yet your cd player on pause. Measuring the DC voltage on the output first is always a good idea when checking out a new board.

The current limiting calculation is basically ohm's law, where I is always in amps. I haven't used the current limiting resistors but your calculations and assumptions look correct.

Using an output resistor will provide some protection but it may impact the sound in a negative way. I haven't tried it but you can try it and see it you like it. I have not had any issue with blowing the 5002, but I have a locking phone jack which helps to remind me to pause the input before pulling the plug.

 

[da_burl]

Ok, cool. I probably blew the other one during the PS debacle. As much as I try, I still get a little impatient some times. I think I will put in a resistor just to be sure. I've got 100 and 220 ohms, which would give me 120 ma or 55 ma, which would be good until testing is complete!! And yes, now that you mention it, it does appear to be Ohm's law, with some impressive looking suffixes added

Thanks again

da_burl

 

[tangent]

The previous posters are right, you can safely connect the two + pins together, and the two - pins. And, you don't absolutely have to have some sort of output protection. Your safety procedure (no headphones at first, test, then try cheapies, then try good ones) is exactly correct. That's what I do myself, when building a new-to-me design. When building an amp whose design I'm confident in, I skip the cheapie headphone step, since the DC meter test is usually enough to ensure that plugging the good cans in is safe.

I did some current testing with this chip recently, and with no sound coming out, you basically can't short the chip out when plugging and unplugging the headphones. It's only when music is playing that you risk blowing the chip due to the jack shorting the output to ground momentarily. I've unplugged and plugged the headphones with music going before and I haven't killed my first set of chips yet. Also, I've put a 10 ohm load across the output with a 7V signal (i.e. chips attempts to put out 700 mA and goes crazy trying) for a few seconds at a time and still haven't killed the chips.

I'm not saying that you can't kill these chips by shorting their outputs, just that they're reasonably robust if you treat them with some respect.

I'd recommend that you use a 1/4" jack only, by the way. The contacts are larger, so you have to pull the plug out farther before you start shorting the contacts. This reduces the risk of pulling the plug out just a little and getting a short. Also, although the plug is bigger, I don't find that it takes me significantly longer to plug or unplug a 1/4" jack intentionally. I feel more confident just ramming the thing home with a 1/4" jack, so I put it in faster. With a 1/8" jack, I'm more restrained, because I don't want to break the poor little thing.

 

[ppl]

The Lack of any output current limiting allows the ability to drive large peak curents into low impedance or reactive loads but in both cases the available output curent will rise untill one of the following happen Exceeding the Bonding wire limit and instant open circuit not often harfull to the load. OR thermal meltdown of the Semiconductor itself and result typicaly in a short Generly not good for the load since about half the DC supply voltage can be on the output untill somthing open circuits. However for the Bref transients encountered in your typical audio program large peak curent's several times the rated continious Output can safley pass.

If used with caution and as tangent so wizely pointed out the Locking Phone Jack just seems manditory with devices like the HA-5002 lacking output protection.

If you want protection then the BUF-634 is hard to beet. i have applyed rev supply voltages and overtaxed the heat dissipation of the package it just turns off. However the current output is going to be at the continious limit since the output protection will automaticaly limit that to rated current.

 

[ppl]

It's back by popular demand the great sounding HA-5002 buffer. it is available at Newark electronics in both the Metal can (Real Cool) at this time about 200 available http://www.newark.com/NewarkWebComme...5002-5&x=7&y=7 The Plastic dip is also available at http://www.newark.com/NewarkWebComme...NTERSIL&KWord= Yes the Metal can costs more.

 

[da_burl]

PPL is the master of the understatement

The cans cost almost 4x as much. But they are cool!!


There are also 853 PDIPs in stock right now, which will diminish appreciably when the PPA starts up in earnest!!

Interesting how Newark kind of summarizes or paraphrases the data sheet. The datasheet states Maximum Voltage of 44V (+/- 22V), regardless of the package, but Newark says +/- 12 for the PDIP and +/- 15 for the Metal Can. Also Newark states 5mv offset, and as I found out firsthand, it can be from 0 - 20 mv. So don't put too much faith in their descriptions.

 

[aos]

Metal can opamps are usually military grade, and as such cost a fortune. It's also the reason they are often the first package to be discontinued.

 

[ppl]

aos the Metal can for the HA-5002 is an industrial grade. the Mil grade has a 30 day lead time. and cost twice as much as the industrail can type.

I like Metal can devices i grew up on Metal can devices. i look at these as Tube guys would look at a old glass bulb type of output tube vs. the straight newer glass types.

Moreover the can package is hermeticaly sealed and the Metal can dissipates heat better due to lower thermal resistence. Moreover some claim that Metal can's and Cer-Dips sound better. (I will leave this subject alone)


I have set aside a set of metal can OPA-627/OPA-637 and HA-5160 opamps and Metal can HA-5002's along with TO-18 type J-Fets for use in my personal PPA when that Amp gets done in the Future. now if only the TLE;s could be got in TO-18 cases.