Hardy 990s run a little warm ?

In my recent Eisen / A.P.I. post [ can someone tell me if the MP3
sound files work for them ? the drum files are only a few meg to host ]

anyway the 990 seems to get alittle warm , while the 25*20 stay cool
, i know it it's subjective to say how warm , just wondering if this is
normal for them in this circuit , before i really start using it next week

tia Regards Greg

Greg,
The 2503 has a 75 ohm primary. The 990 is not designed for that kind of load.

peter

Thanks peter , makes sense i guess that is the danger having sockets
thinkng it is all plug & play .
Although i thought for the toms anyway the difference was not as Dramatic as i expected .

I'll check out the cinemag site to see what the grp order outputs are ,
i know the forssels are specific in load needs as well .

thanks again regards Greg

the 990 seems to get alittle warm

Click to expand...

That is normal.

John Hardy
The John Hardy Co.
www.johnhardyco.com

The 2503 has a 75 ohm primary. The 990 is not designed for that kind of load.

Click to expand...

How did you derive the 75 ohm primary figure? And what is the impedance that the 990 (or any op-amp) would see at 20-20 kHz?

Thank you.

John Hardy
The John Hardy Co.
www.johnhardyco.com

Jayzus John... don't go all technical on me..!!

The primary impedance of an api 2503 output transformer is 75ohms. That, as I'm sure you know is what an api 312 circuit is designed to drive.

I've heard that your 990 is far more comfortable driving 600ohms.
Or am I talking out of my bottom?

Impedance is a forgen mystery to me..!!
peter

Was it the 990 or another that was said to [ i don't know who ? ]
to be able to drive a short for hours ? , maybe a misquote
but thanks for the customer support John , that is it's fine to drive
the A.P.I. output .
And take it easy on peter , please
reagrds Greg

What the amp sees at that "75 ohm" primary has a lot to do with the construction of the transformer, and what's connected to the secondary!

I'd go into more detail but I've one foot out the door at the moment.

I shall now be quiet.

[quote author="peter purpose"]I shall now be quiet.[/quote]
Oh now Peter, don't go getting "quiet" on us! :wink:

You were probably thinking about the Forssell 992. IIRC, Fred said he didn't recommend loads less than 600 ohm.

We're all cool! :grin: :sam:

The 990 would only see 75 ohm if you load the output with 600 ohm which you'll hardly do. And even then, it will not hurt this opamp. It will increase distortion, but don't think that a 2520 doesn't distort--in fact it will likely have higher distortion.

The 2520 runs much cooler because it draws less current--at the cost of lower slew rate and higher voltage noise.

Samuel

[quote author="okgb"]...anyway the 990 seems to get a little warm , while the 25*20 stay cool...[/quote]
Are you using a real 2520 or a DIY version? (Just curious)

Greg, that 2503 has 4 identical windings.
One for input-75 ohms
Two for Output- Series Conn For 600 Ohms
And one extra.
Some people think the extra winding is a real bonus, but anything you do to one winding will translate to the other windings, so there is really no difference between hanging a couple of dropping resistors into an op amp to drive a VU Meter off of any of the output windings.

So, this means you can use the extra winding in series with the primary winding coming off the Hardy, to get your 600 Ohms.

See that you will have 1/2 the voltage output for a given input.
So you will need to drive the input twice as hard.
Will this put you right back where you started?

Good question. Your output ratio now 1:1 instead of 2:1.
This means the load will have less leverage on the 990, which might make a difference, if the load is down near 600.
If you are going into a 10 K modern input, then the leverage difference will make little difference.

Dropping the ratio is like dropping down to the small chain ring on a bike. The pedaling gets easier, but you don't go as fast. You do the same amount of work to get to the top of the hill, but it took longer. So if you drop down to the small ring, AND pedal faster, (increase your input), you get to the top of the hill in the same amount of time, and you did the same amount of work, but you did it in a way that matches up with your body, or in the electronics case, the amplifier.

Oh, BTW, how hot?
They are supposed to get a little warm.
Thermal stability is a welcome perk.
The 990, does not care if it is on the North Pole, or sitting out on the Gobi Desert, the operating point will stay the same, due to constant internal temp.

We use this at work, had some GFI sensors that got burried in a Chicago railway installation. They were watching some rail heater shorts. (It gets so damn cold in Chi Town, that the railway switches freeze u. Not good! Sitting in a box, that was sitting in ice. The trip point kept drifting, shutting down the whole system. We fixed all 200, and the engineer went back to France, and the trains started running again.
.
.

Nice info...........................that is what or the CJ is

They get a little warm , but not hot , since i hadn't ran them for a long time , i wasn't sure if they would stop there or not and thought i'd check before i blew my investment [ a measuring standard ]

there is REAL 25*20 , please have a listen to the soundfile , tell me
what you think .

I hung the recommened 3k6 resister off of the extra output winding , and the soundfle was recorded this way although i installed switches to break
the meter path so i wouldn't have to hear the poor needles slam in some cases but i could always consider this the record mode after level set .

happy weekend everyone

very cold here -34 C this morning past -40 with the windchill and thats where our two temperature systems meet , we call it " car breaking weather "

The primary impedance of an api 2503 output transformer is 75ohms.

Click to expand...

I believe that the 75-ohm figure is the DC resistance of the primary winding, not the AC impedance. Those are two very different things. If your audio consists of DC, then 75 ohms is a concern. Otherwise, it is not.

I've heard that your 990 is far more comfortable driving 600ohms.

Click to expand...

The 990 is specified as able to drive a 75 ohm load at an output level of +24 dBu at 20 kHz with less than .06% THD. That is using power supplies of +/-24 VDC. This is asking a lot from any op-amp. It would be a very unusual situation for a 990 to encounter a 75 ohm load impedance (not to be confused with the 75 ohm DC resistance of a transformer primary winding), but it will perform very well into a 75 ohm load. The 990 would exhibit less distortion into a 600 ohm load, so I suppose it might be "more comfortable", but it will kick ass either way and not complain. A 2520 would be considerably worse off.

Impedance is a forgen mystery to me..!!

Click to expand...

I have my good days and my bad days. The main point here: Please do not confuse the DC resistance of a transformer primary winding with AC impedance of the overall circuit that the transformer is in. They are very different. Basically, the AC impedance that the 990 sees is determined by the load that the secondary of the transformer sees. If the load on the transformer secondary (the next piece of equipment in the signal path) is a high impedance load, the 990 will see a high impedance load, not 75 ohms.

Thank you.

John Hardy
The John Hardy Co.

Hi John!
I'm the weirdo who takes digi pics of all your cool stuff, VP Modules, etc. at AES SF.

Anyway, the 2503 is indeed 75 ohms.
DCR is about 6 or 7.
Most API type circuits feature a big lytic coupling cap between the op amp and the primary.




cj

Most API type circuits feature a big lytic coupling cap between the op amp and the primary.

Click to expand...

No, the 312 micpre doesn´t. It alows some mV of offset a heathy 2520 would put out directly on the primary of the 2503 output transformer.

which in this [ my ] case was a Digidrsign 002 ch 7/8

Glad that's sorted out then..!!

Gentlemen,
I was under the impression that these old circuits performed best when terminated with 600 ohms. i.e. if the 2503 output transformer is connected to a 10k input, then the transformer should ideally have 600R strapped across it's secondary. If outputing into a 600 ohm input, then the termination is taken care of.

Is I wrong, or is I right?

peter

[quote author="CJ"]We use this at work, had some GFI sensors that got burried in a Chicago railway installation. They were watching some rail heater shorts. (It gets so damn cold in Chi Town, that the railway switches freeze u. Not good! Sitting in a box, that was sitting in ice. The trip point kept drifting, shutting down the whole system. We fixed all 200, and the engineer went back to France, and the trains started running again.[/quote]

Gotta love my city. It is -1 Farenheit right now, and windchill factor makes it feel like -19. I'm a bit worried about my mics over at my rehearsal space, it is not well heated enough for me to rest easy.

The bad railway engineering decision was clearly because our brains get frostbitten at these temperatures. Now where did I leave my snorkel? :green: