Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on August 21, 2017, 03:07:18 pm
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Finally drew up my schematic for the bass amp. I will have to tweak the values in the tone stack since it was cut from an Engl guitar preamp. I am trying to implement a cathode follower so it can drive the solid state power amp even though the spec sheet of the SS amp does not even list a recommended impedance. This is just a very generic CF. I will mess with it on my breadboard before I build it into a rack space. I will also have to work on a power supply. Any suggestions on a PT would be much appreciated. I would like to install it inside the rack space rather than on top of a chassis.
This is the SS power amp I am using
https://www.parts-express.com/sure-electronics-aa-ab31282-1x200w-class-d-audio-amplifier-board-t-amp--320-3360 (https://www.parts-express.com/sure-electronics-aa-ab31282-1x200w-class-d-audio-amplifier-board-t-amp--320-3360)
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Take a look at the Antek transformers....You might want to take a read through this thread...http://www.ax84.com/bbs/index.php?area=23 (http://www.ax84.com/bbs/index.php?area=23)
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The link I had posted above didn't work. I fixed it. I found this transformer that would work fine for the solid state amp.
http://www.mouser.com/Search/m_ProductDetail.aspx?Hammond-Manufacturing%2F182Q9%2F&qs=savM97goi5i9GBJGkpYUzg%3D%3D (http://www.mouser.com/Search/m_ProductDetail.aspx?Hammond-Manufacturing%2F182Q9%2F&qs=savM97goi5i9GBJGkpYUzg%3D%3D)
I'm guessing i won't find a PT that's all in one. I'm going to need a separate PT for my plate voltage and filaments. But could use a very small one for only two 12ax7's.
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I found this transformer that would work fine for the solid state amp.
http://www.mouser.com/Search/m_ProductDetail.aspx?Hammond-Manufacturing%2F182Q9%2F&qs=savM97goi5i9GBJGkpYUzg%3D%3D (http://www.mouser.com/Search/m_ProductDetail.aspx?Hammond-Manufacturing%2F182Q9%2F&qs=savM97goi5i9GBJGkpYUzg%3D%3D)
not if you want 200W output. you're going to need at LEAST a 200VA PT if your class D truly is 100% efficient. not likely. plus datasheet states REGULATED.
you need a 36V 250-300W regulated switching PS for full 200W output into 3? ohms. see note number 8 on datasheet. (https://www.parts-express.com/pedocs/manuals/320-3360--aa-ab31282-1x200w-audio-amplifier-board-manual.pdf)
bah! 3 ohm load - they publish bigger numbers with that. never heard of a 3ohm speaker. probably makes less than 60W into 8 ohms. you can do much better than that module.
if you must, then this one (https://www.amazon.com/GENSSI-Regulated-Switching-Power-Supply/dp/B005CLCJA6) should work... 35bux + ship
--pete
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Three 8 ohm speakers in parallel is slightly less than 3 ohm. will handle 4 speakers in parallel.
regarding input impedance, spec sheet states typical 10k with a max of 11k ohm.
Post some sounds when finished.
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There's a few things I missed on the spec sheet. I don't know how I didn't see the input impedance is at 10k.
I'll most likely be using a 4 ohm cabinet with this one. I might try a higher power module later but I already have this one.
Would it make sense to just buy a power supply like suggested and mount it inside chassis rather than building one?
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You sure do not need 3 stages of gain!!
You sure don't want to build a cathode follower and then add 220K of added resistance.
The attached is closer to what you want.
> never heard of a 3ohm speaker.
For a constant voltage (low resistance) source, lower Z is higher power, obviously. In TV-sound and some car audio we are seeing "3 Ohm" speakers to cheat the ratings on 4-Ohm chips, and now chips rated for 3 Ohms. Obviously if he does not want to cheat some more with three 8r (2.66r) then he will apply 4 Ohms and take the 4 Ohm rating.
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From what I saw on the website, you might want to include a master volume, also a plugin.
I would purchase a power supply and mount in the the cabinet. Now how are you going to power the pre-amp?
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PRR that seems exactly like what I should be doing. Thanks for that edit. I will go that rout.
I think I am going to find a more suiting class D module for this build.