500 series LA-3A

[strangeandbouncy]

Hi Peter,



  round meter looks the mutts nuts in there! HubbaHubbaHubba . . .



      Kindest regards,


      ANdyP

 

[peter purpose]

Isn't that the Pye eq?

It is.

 

[peter purpose]

Homing in on a job finished... but it's a greedy little bastard... 400mA at full limiting, so it'll be out of spec.
I'm loathe to make it a 2 space job, but I'm open to persuasion.

How would you guys feel about pulling everything from the positive rail?
We could dispense with the pricey dc-dc converter.

Also.... any ntc thermistor gurus out there?.... at turn on the MC34063 is pulling 900mA which needs to be tamed.
Any suggestions other than a 10W resistor?

toodle pip
peter

 

[Crusty2]

Do you really need a dc convertor? If you have transformer isolation, why not make the -15V the 0V point and the +15V becomes a 30V rail? (Couldn't do a sidechain insert easily though...)

 

[peter purpose]

Do you really need a dc convertor? If you have transformer isolation, why not make the -15V the 0V point and the +15V becomes a 30V rail? (Couldn't do a sidechain insert easily though...)

It want's 40V and I'm using an MC34063 to boost the dc.

 

[ruckus328]

Do you really need a dc convertor? If you have transformer isolation, why not make the -15V the 0V point and the +15V becomes a 30V rail? (Couldn't do a sidechain insert easily though...)

It want's 40V and I'm using an MC34063 to boost the dc.

Just a little input since I'm dealing with the same beast:

400mA doesn't seem right.  I don't know what changes you've made so I can't say for sure how yours compares to mine, but my dual unit isn't even pulling anywhere near that, and I've got illuminated meters, relays, etc.. 

Audio (28V) rail is pulling around 30mA per channel.  Even worst case, call it 50mA.
Sidechain (35V-36V) is pulling about 5mA (I measured 30mA with no signal present with peak reduction maxed)
My relays/power LED/meter LED's are pulling about 80mA for a dual unit.

Add that all up (worst case) it's about 240mA for a dual unit, 120mA for a single.

Keep in mind too if you try to power the sidechain any lower than the original 36V you'll be reducing the maximum possible compression, since you'll be limiting the maximum sidechain gain possible to the step up xfmr.  If you try to run it directly off the 500/51X 24V supply (I think that's what you meant when you said run it off of the positive rails), I suspect it will have very adverse effects.

 

[peter purpose]

Wow... I must have set the 34063 up incorrectly. I'll experiment further.

 

[haima]

does it still pull a lot of current if you run it from a 40v bench supply instead of the DC-DC converter?

 

[peter purpose]

Mine only goes to 30V.

 

[peter purpose]

Mike,
Running it off the bench supply at 30V gives me figures like yours..... must have seriously screwed up the boost circuit.
I'll fiddle and report back.

 

[peter purpose]

Keep in mind too if you try to power the sidechain any lower than the original 36V you'll be reducing the maximum possible compression, since you'll be limiting the maximum sidechain gain possible to the step up xfmr.  If you try to run it directly off the 500/51X 24V supply (I think that's what you meant when you said run it off of the positive rails), I suspect it will have very adverse effects.

Mike,
I'm getting 20dB of gain reduction with a  30V sidechain.... enough for any fugger I reckon.

 

[Crusty2]

Do you really need a dc convertor? If you have transformer isolation, why not make the -15V the 0V point and the +15V becomes a 30V rail? (Couldn't do a sidechain insert easily though...)

It want's 40V and I'm using an MC34063 to boost the dc.

If you have the 51X rails available, then how about using the -24V as 0V and you get 48V across the pair...

 

[peter purpose]

Has to be 500 compatible.

 

[haima]

if you need 30v and all i/o is TX isolated, it seems like using the +/-15v as floating 30v makes sense (as Crusty2 suggested)... what's the downside?

 

[peter purpose]

if you need 30v and all i/o is TX isolated, it seems like using the +/-15v as floating 30v makes sense (as Crusty2 suggested)... what's the downside?

I've heard stories if things not playing nicely together and lunchbox power start problems.
I'll stick with what I know works.

 

[peter purpose]

Sorted.... getting 30dB gain reduction with a +10dB input.... nice.
Pulling the right amount of juice too.... marvellous.

 

[ruckus328]

Peter, have you started doing any RMAA tests yet?  I'm wondering if you can check some things so we can compare notes.  First off, I'm guessing you're hardwired into "mod" mode, correct?  What frequency tone are you hitting it with to run your tests?  Hit with a 1K tone and check the voltage on the step up xfmr from output to gnd.  Now spit out a 400hz tone and check it.  Getting alot more voltage?

Do you hear any clipping hitting it with your +10dbu?  Original specs list 0dbu as max input with no pad.  Don't hear anything audible on my end with that loud a signal, but I do when I start getting around the 15dbu area.

Also, have you ordered / gotten the replacement transformers from cinemag for production?  I don't want to jump to conclusions quite yet, but I have one of the replacements in my left channel, and original B11178 from studio electronics in the right.  Things are very strange.  I'm getting massive amounts of more gain with the replacement.  The frequency response is also shit.  Like really really bad.  It might be a grounding issue because I'm getting some noise on my left channel whereas my right is dead quiet, but I'm pretty sure I know why, but still doesn't explain the results I'm getting.  My outputs are terminated with 600 ohm.  I'm going to replace the original in my right channel with the 2nd production version I have tonight and see if it goes to shit as well.  I'll let you know how it goes as this is something that majorly affects us both.

 

[peter purpose]

Mike,
I'm too stupid to learn rmaa..!!

+4dB @ 1kHz max reduction step up out to ground... 46V ac
+4dB @ 400Hz max reduction step up out to ground... 49V ac

Not sure of which mod you talk, but....
R28 wound all the way.
R14 13k.
No pad
Terminated 604R.
All iron from Studio Electronics.

Not done any listening tests yet, but I'll try some after lunch.

Peter

 

[haima]

Sorted.... getting 30dB gain reduction with a +10dB input.... nice.
Pulling the right amount of juice too.... marvellous.

good to hear!

 

[peter purpose]

Guys,
This thing is working like a champ on 30V, so do I go for the conversion to the readily available rails, or do I upset the cheap bastards among us who want to save the price of a dc-dc converter?
If you want the the cheaper option.... I'll charge you more... cough.