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chops

Crown D-75A amplifier OWNERS, please reply...

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I am trying to get a straight answer about this amplifier on the Crown forum, but I guess they feel it isn't an important enough question for them to bother answering, so I figured I'd try here. I have received one rather vague answer from a member here which didn't help me any either.

I did a search for this amp several days ago on here and know there are quite a few members here that own either the D-75A, D-75 or D-45, so I'm hoping someone will chime in here and help me out on this.

All I am wanting to know is if the speaker outputs on this amp go through relays first, as to not pass any kind of thump or power surge to the speakers when powered on or off. That's it.

The reason I need to know is because I have one on its way here and I plan on using it to power my Altec 902-8B drivers directly via a Rane AC 22B. IOW, I will NOT be using any kind of passive filter between the amp and driver. However, if this amp sends out a thump or power surge durring turn-on/off, I'll end up damaging (blowing) the Altec drivers the first time I power the amp up, which is something I do not want to do, AND cannot afford to do.

Anyway, if you guys/gals could please give me a helping hand on this little matter, I'd greatly appreciate it!

Many thanks in advance,

Charles

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If you have one on its way, just have a look once it gets there.

edit: Just looking through the manual, it looks like the answer is no relays.

Bruce

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"it does squeal on power off, tho"

Caps are dried out.

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My old Crown used to make somewhat distasteful sounds on power off - from day one, right out of the box. Like a gas bag gently deflating and then a final "fart" sound at the end.

Sort of a trademark sound as it discharges the PS caps when powered off.

DM

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very descriptive and quite correct from my experiences. I love that 'final fart' bit!

ROFTLMAO

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Ok, in regards to this Crown D-75A I'm getting, I have been told by

David Glass at Crown that this amp does indeed put out a thump durring

turn-on/off.

My question is this...

Other

than using relays, I have been told that I can use a capacitor in

series with the 902-8B for about a 400Hz rolloff @ -6dB per/oct which

should keep the driver from being damaged.

If so, what size cap should I use, a 50uF or 62uF?

Also, should I run a fuse inline with the 902 as well, and if so what size?

The drivers VCs read 6.1 and 6.7 ohms.

Thanks again for everything,

Charles

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It shouldn't be too hard to put a relay across the outputs...and it'd only cost you about $10.

Not extremely sure about the cap in series, but probably something around 70uF would be closer:

http://colomar.com/Shavano/crossover6db.html

Do you have a wiring diagram and part numbers for installing a relay. It seems that some sort of time delay is needed in addition to a relay. How do you do this?

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Charles, I ran my Crown DC150 for years on Klones with a stock T-35 tweeter and no fuses, etc., thumps and all - with ZERO problems ever. I wouldn't hesitate to use it on my current speakers, either, because if the old ones could take it in stride, the new ones certainly can as well. Just a note to say that in my experience, it really did not cause any problems at all.

Dana

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" I ran my Crown DC150 for years on Klones with a stock T-35 tweeter and no fuses, etc., thumps and all - with ZERO problems ever. I wouldn't hesitate to use it on my current speakers, either, because if the old ones could take it in stride, the new ones certainly can as well. "

You had a passive crossover in your Klones right?

Guess what happens to a turn of thump with passive crossovers? It gets directed to the woofer alone... woofers can handle that.

Hook a T-35 up directly to the thumping amp and see how long it will last.

Shawn

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" I ran my Crown DC150 for years on Klones with a stock T-35 tweeter and no fuses, etc., thumps and all - with ZERO problems ever. I wouldn't hesitate to use it on my current speakers, either, because if the old ones could take it in stride, the new ones certainly can as well. " You had a passive crossover in your Klones right? Guess what happens to a turn of thump with passive crossovers? It gets directed to the woofer alone... woofers can handle that. Hook a T-35 up directly to the thumping amp and see how long it will last. Shawn

Exactly. That's why you have to use a capacitor. I have the equation at home. I think that I used a 20Uf cap for the tweeter. You should be at lease 2 octaves below the crossover point (remember that octaves are measured on a log scale).

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Chops, you are on the right track - and correct in being cautious about your Altec aluminum drivers. There have been a couple of times when swapping out amps I almost thought I blew my 806s during shutdown. Now I'm much more careful about which amps I run with my Altecs.

Good to take precautions given the horror stories out there. The aluminum drivers sound great, but certain pops can take them out - especially with an active.

Carl.

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We have a lot of D-75s around the station. They do thump. Not loudly, but they do thump.

I had a friend in college who used a D-60 to power his Heil Air Motion Transformers. When he turned it off, it sounded like a BB dropped on glass. Kind of a dit............dit.........dit.......dit.....dit...dit...dit.ditditditdit.

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Well according to Altec, I should be running a 50uF cap to the 902s for a -6dB slope at 400Hz. The only thing is that they recommend a mylar cap, but say that a non-polar electrolytic can also be used.

Is there a difference between going with either type of cap? (sound quality)

http://alteclansingunofficial.nlenet.net/publications/techletters/TL_205.pdf">http://alteclansingunofficial.nlenet.net/publications/techletters/TL_205.pdf

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