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Preamp and impedance question

I am asking a custom builder to build an amp using Luxman mq-300 schematic.  I have two questions:

1) the Mq-300 is a power amp.  I don’t have a preamp.  Can I just add a volume pot to a power amp schematic?  I did some research about passive preamp, but it seems even a passive preamp has a circuit and a transformer.  Is it better to buy a separate passive preamp?

2) the transformer is designed for 8 ohm.  If I want it to support 4 ohm, I need to upgrade the transformer.  I know that the speaker impedance curve can dip to 5 ohm at 30Hz.  Is it important to have 4 ohm support?

thanks.
gte357s
georgehifi's avatar
georgehifi
10,312 posts
 
Taken on board Ralph, with a yawn.
But for anyone to say EPDR (combination of impedance and -phase angle) "does not matter", is dreaming.

Your M60 mono blocks "could not drive the bass" of the JBL 1400 Array’s a 90db speaker without obvious stress playing the bass notes, even at "medium levels" and they were 100% fully functional.
And nowhere! near!! the EPDR load that a Wilson Alexia would present.

https://img.usaudiomart.com/uploads/large/1922864-fcdeac94-atmasphere-m60-mk-33-monoblock-otl-tube-a...

https://www.stereophile.com/floorloudspeakers/jbl_synthesis_1400_array_bg_loudspeaker/index.html

roberttdid
534 posts
 
I think for someone to make this statement, they have to understand how EPDR impacts an amplifier. By all indications from what you have posted, you do not.


Taken on board Ralph, with a yawn.
But for anyone to say EPDR (combination of impedance and -phase angle) "does not matter", is dreaming.

georgehifi's avatar
georgehifi
10,312 posts
 
Like I said anyone to say EPDR (combination of impedance and -phase angle) "does not matter", is dreaming.

The odds are very against you sunshine. Over and out👎

roberttdid
534 posts
 
George,

Everyone reading this thread can see that I and atmasphere talk in very specific terms and in detail when we talk about EPDR. You are not fooling anyone but perhaps yourself.

Since you are such an expert on EPDR, tell everyone, specifically, what was inaccurate about atmasphere's post about tube amplifiers and EPDR. Here, I am reposting the relevant section:
Tubes are a bit different from transistors in a number of ways as we all know :) One of the ways they are different is the Safe Operating Area (SOA). With tubes you can exceed the SOA without damage to the tube if the tube is allowed to cool off afterwards. A tube dramatically overtaxed, such as in a loss of bias, can turn cherry red from heat, but if allowed to cool off, and the problem corrected, can continue to give normal service.

atmasphere's avatar
atmasphere
11,807 posts
 
@roberttdid  I think its pretty obvious this isn't about EPDR...
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