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Class D Switching Power Amplifiers and Power D/A conversion

Converting an old Peavey Bass Amp into a D class amplifier
Converting an old Peavey Bass Amp into a D class amplifier
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Old 21st October 2017, 04:35 AM   #1
JulianRojas is offline JulianRojas  Colombia
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Exclamation Converting an old Peavey Bass Amp into a D class amplifier

Hi everyone... I'm just a newbie that has a bass amplifier but wants more power to drive bigger speakers.

Currently I own and old Peavey Mark IV 400BH bass amplifier that was built in the earlies 80's, this amp works well but has a little problem for me... It lacks power to drive bigger speaker cabinets and it gets too hot when driven hard so i was thinking in a way to replace the 400BH power amplifier of this baby and put a D class amp board and integrate all in the bass head chassis. (Sounds like crazy) This amp can give a total of 300 watts at 2 ohms but I need it to handle 600 watts rms at 8 ohms. Sorry for my english, this is not my native language, but I try . My knowledge in electronics are low medium but i am going to use a friend's help that is a technician. I Will attach the original schematic:
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File Type: jpg MK IV Bass Amp schematic_Página_3.jpg (790.6 KB, 137 views)
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Old 21st October 2017, 06:45 AM   #2
JMFahey is offline JMFahey  Argentina
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Short answer:
1) leave amplifier as is.
use it as a preamp only, don´t touch the power supply and power amp; IF someday you need a mid sized head, use it as original.

If you do not connect speakers to it, power amp will stay cold.
2) get a cheap but powerful Rack type power amp.
If necessary, you can use both channels bridged to get high power into 8 ohms.
You stack: speaker, rack amp, and your Peavey on top.

3) just curious, what "8 ohm 600W" Bass speaker will you use?
Unless it{s a *beast* you´ll destroy it (unless it´s actually a 4 x 10" Bass cabinet or similar).
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Old 21st October 2017, 07:06 AM   #3
JulianRojas is offline JulianRojas  Colombia
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Thanks for replying...

Well I rig that bass head everywhere I go and currently to drive most 8x10" bass cabinets like Hartke HyDrive 810 / Ampeg SVT 810 (similar 8x10" cabinets you need from 800 watts to more than 1200 at 4 ohms) or using a single 4x10" ampeg at 8 ohms that needs 500 watts rms, or a 1x15" + 4x10" in parallel.

I haved used that configuration of using the head as a preamp and run a rack power amp but it's bulky and heavy, I would love to integrate all in the head... What I understand about this particular head is that is built in modules, one module for preamplification (front) a power current module (transformer and rectifier) and the power amp board. (I think that in the schematic is all that specified, there is a cable that transmit the signal from the preamp to the amp and that's it) integrating a class d amplifier board with it's power supply is way smaller than the actual amplification stage that this head has.
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Old 21st October 2017, 08:45 PM   #4
JulianRojas is offline JulianRojas  Colombia
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Here is the head in question so you can see how the modules are setup... YouTube

Or is a craziness to convert it
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Old 22nd October 2017, 04:32 PM   #5
dzwer is offline dzwer  Bulgaria
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On this picture it is listed 800W max power from mains: https://www.talkbass.com/attachments...-4-jpg.937116/
Is the transformer inside 800W?
The supply voltage is +/-52 on the schematics, so you'll need two class D modules, which to work in bridge mode and will have about 400-450W at 8 ohm speaker. With 4 ohm speaker configuration you will blow the power transformer at full power and continuous usage.
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Old 22nd October 2017, 04:40 PM   #6
Khron is offline Khron  Finland
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Just a small question - the gigs / venues where you use this rig, don't have any sort of PA?
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Old 22nd October 2017, 05:28 PM   #7
dzwer is offline dzwer  Bulgaria
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The big personal stage setup is for bassist's own pleasure, while playing.
Almost every music club has at least basic PA.
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Old 22nd October 2017, 06:04 PM   #8
Khron is offline Khron  Finland
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That's what i figured too

That being said, turning up to a gig with a humongous bass rig AND running it full-blast is a sure way to 1) pi*s off the sound-guy, 2) potentially pi*s off your bandmates, and 3) making your whole band sound like a*s...

Sounds silly perhaps, but i'd rather invest in some in-ear monitoring. Less "stage bleed" (bass guitar bleeding into all the other mics), and you (would) get to save your hearing too
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Last edited by Khron; 22nd October 2017 at 06:30 PM.
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Old 22nd October 2017, 06:12 PM   #9
Andrew Eckhardt is offline Andrew Eckhardt  United States
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On top of all the other discouragement in this thread, even if you were to change the power stage to class D, you'll still be lugging around the old line transformer and rectifier supply, which means your marginally more powerful cool running amplifier will be just as heavy.

If this head bothers you, sell it and buy a switcher/ class D amp.

Of course you can do anything else for the raw educational benefit..
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Old 22nd October 2017, 06:29 PM   #10
Khron is offline Khron  Finland
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Lugging the head around pales in comparison to the bulk of an 8x10, so... the weight-saving benefit's arguable
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