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Emile

Pre-amp voltage out vs clipping, etc.

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Hi All,

 

Hope you can enlighten me :D  Just do NOT understand pre-amp output voltage vs amp input voltage :( 

 

OK; just got a pair of JBL 18" woofers (SR4718A, 4 ohms, 98dB, 30-3300Hz) and am trying these in my (secondary; small) stereo room.  Just cannot get enough volume ... yes, underpowering it with a Marantz 1060 :(  (Haha; more power will be ordered shortly.)

 

But ... do not understand pre-amp output. Running a JVC P3030 ( https://www.hifiengine.com/manual_library/jvc/p-3030.shtml ) pre-amp. Specs say 20V max out.  Thought most amps are looking for less than 2V and clipping results if a higher voltage is send to them.  So what about 20V out????

Making it more complicated ... I have a miniDSP 2x4 to set crossovers for the JBL's and K-510 horns.  Max input on the miniDSP is 2V ... and YES; clipping if I turn my pre-amp past 10 o'clock :(  

 

Any suggestions?

 

Many thanks, Emile

 

 

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That Pre amp has + and - 37 volt rails so it can put out the 20 Vrms that is spec'd. That is a LOT of output signal capability like +28 dBu. If you want to use more of the volume control you will have to attenuate that pre amp output signal. Yes it is true most power amps will drive rated output with only 1 or 2 volts input. That is with the gain controls fully clockwise. If there are no gain controls it is expected that the source/pre amp does all the volume adjusting. If you intend to drive a miniDSP with 2 volt max input with that Pre amp it is going to be tricky. I have no hands on experience with miniDSP units, but 2V max input?

Perhaps someone with experience with miniDSP will jump in.

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The miniDSP 2 X 4 input max is .9 volts or 2 volts, depending on a jumper setting.  The output voltage, however, is set at .9 volts.  If the input setting is 2 volts, the output has a 7 db insertion loss.

 

Mike

 

 

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Is the input impedance/resistance spec'd so we can build Emile an attenuator?

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Something is very wrong.  I don't see how a pre-amp can use all those semiconductors.  I think the spec for the M-3030 crept in.  A 20 volt output from a power amp is not unreasonable.

 

WMcD

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2 minutes ago, WMcD said:

Something is very wrong.  I don't see how a pre-amp can use all those semiconductors.  I think the spec for the M-3030 crept in.  A 20 volt output from a power amp is not unreasonable.

 

WMcD

I assume the 20 volt preamp output would be for a current amplifier instead of a voltage amplifier.

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Thanks @babadono , @mboxler and @WMcD  Sounds like that miniDSP is a piece of crap - but it is set at 2V.  Don't feel like spending $1000 on a Xilica (it's just for a seperate stereo "tinkering" room and only use it as a xover). So; should I look into passive xovers, active xovers, attenuators, or???

To show how little I know :)  found this ART CX310 active xover ... https://www.parts-express.com/art-cx310-2-way-3-way-crossover--245-880?utm_source=google&utm_medium=cpc&utm_campaign=pla&gclid=EAIaIQobChMIh_fgn8_64AIVjYnICh1uggDNEAQYAyABEgI5SPD_BwE

Cheers, Emile

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12 minutes ago, WMcD said:

Something is very wrong.  I don't see how a pre-amp can use all those semiconductors.  I think the spec for the M-3030 crept in.  A 20 volt output from a power amp is not unreasonable.

 

WMcD

Why not? The Japanese do (or did) things like this all the time. Not trying to pick a fight or challenge your expertise.

The original saying "parts is parts" came from Japan:)

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The Japanese have bean counters too. 

 

It seems impossible to use the more than 30 transistors and FETs (combined) for a channel of pre-amplification even if cost is no object and we include the phono section.

 

If a manual becomes available we'll know for sure.

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11 minutes ago, Emile said:

Sounds like that miniDSP is a piece of crap - but it is set at 2V. 

I'm not saying that. But they give no other input spec? Like headroom above 2 volts? How do you know you are clipping its input?

Is this it? https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4?lang=en&gclid=EAIaIQobChMI9-_n17mC4QIVZCCtBh0G6wX4EAQYAiABEgL79PD_BwE

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3 minutes ago, WMcD said:

If a manual becomes available we'll know for sure.

The manual is available at HiFi Engine from the link in Emile's first post. That's how I knew it has +/- 37 volt rails.

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1 minute ago, babadono said:

Is this it?

Yes :D  Had bad sound when I initially tried it ... was "clipping sound."  And ... the software has a page that shows power/clipping levels :(  

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2 minutes ago, babadono said:

The manual is available at HiFi Engine from the link in Emile's first post

Yes; tried to upload it here, but of course it's too big :( 

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Thanks!  Anyone's guess how many dB's I would need?

Also found these "fixed" ones from Harrison Labs ... they come in 3,6 or 12 dB's.

s-l1600.jpg

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OK; an attenuator would solve my volume knob sensitivity (if I find out what dB's I need).  

But ... if I may :) ... one more "shot in the dark" for my speakers.  The 18" JBL's seem to need some power ... haha, found a cheap Crown XLS 2502 (775W each into 4 ohms) which does have crossover settings.  How about just buying that PLUS using a fixed 600Hz 12db xover for my K-510 horns? Pretty sure the horns will do 500Hz, but with the slow 12dB slope I "guess" 600Hz would be better???

Many thanks, Emile

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OK so i think that would work but not optimally. Doesn't the 510 horn need some EQ?

And regarding the Harrison Attenuators I think as strong as your pre is you could easily go with 12dB.These things have been discussed before and never have I been able to determine what input impedance they are designed for. And yes that is important.

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2 minutes ago, babadono said:

OK so i think that would work but not optimally. Doesn't the 510 horn need some EQ?

Haha ... probably yes :)  Maybe I can still use the miniDSP on the horns :)  BTW, thanks for the 12dB recommendation :D 

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OK; ordered the Crown XLS 2502 :D  (actually awaiting approval of my offer ... was OK'd last week :) ).  If I do not like it, I've got @babadono's address and number :D

Add-on ... ordered and paid :)  

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So I 've got a free amp coming.....SWEET.

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