Jump to content
Sign in to follow this  
6v6

DIY Mosfet Hybrid amp, Donor amp suggestions?

Recommended Posts

Hi All,

I'm considering making a DIY hybrid amp (tube preamp, mosfet power amp), "inspired by" a mesa walkabout/m-pulse, probably with the addition of a tube compressor, and maybe with two different switchable preamp circuits/channels.

I've been looking at parts for the poweramp, and it looks like the mosfets, heatsinks and transformer are going to be a lot more expensive than I'd anticipated (the mosfets alone are £11 each and I'll need at least 8!)

So it occurred to me that there must be some suitable donor amps (old PA amps, other hybrid heads with a similar power stage etc) out there, which I can pick up cheap and modify...

I'm looking for something with a decent sized power section (say 300-600w), ideally with BUZ901/906 Mosfets or similar in the power amp - any suggestions?

Share this post


Link to post
Share on other sites

The original series Ashdown ABMs used those trannies I believe... Might be able to find one of those cheap enough.

Or you could try and find a B&O icepower module if class d was of any interest to you.

Edited by Bigwan

Share this post


Link to post
Share on other sites

[quote name='Bigwan' timestamp='1381137602' post='2234671']
The original series Ashdown ABMs used those trannies I believe... Might be able to find one of those cheap enough.

Or you could try and find a B&O icepower module if class d was of any interest to you.
[/quote]

Thanks, the Ashdown is a good suggestion, particularly if I can pick up a cheap faulty spares/repair one somewhere.

I did consider class D (in particular these [url="http://www.hypex.nl/product/ucd-amplifier-modules/ucd700hg.html"]Hypex[/url] modules), but I'm going for a more classic/vintage vibe, which based on many reviews seems to be more readily achievable with more traditional mosfet (or tube, obviously) power amps.

Share this post


Link to post
Share on other sites

[quote name='Bigwan' timestamp='1381137602' post='2234671']
The original series Ashdown ABMs used those trannies I believe... Might be able to find one of those cheap enough.

Or you could try and find a B&O icepower module if class d was of any interest to you.
[/quote]

Yes, and the Trace Elliots too. An alternative to the BUZ901 is the Exicon ECF10N20 and it's complementary device, but is probably not much cheaper. I recently fitted some BUZzes in my TE AH200 and are great, though.

How about the suggestion of a class D module?

EDIT: 8 Devices? That's a chunk of current :)

Cheers

Geoff

Edited by RandomBass

Share this post


Link to post
Share on other sites

Try out these guys: http://www.bkelec.com/Modules/Amplifiers.htm - I had one of their 450W modules years ago - it was bullet proof. My first 'big' amp was something I put together myself using one of these!

Share this post


Link to post
Share on other sites

[quote name='RandomBass' timestamp='1381140462' post='2234752']
Yes, and the Trace Elliots too. An alternative to the BUZ901 is the Exicon ECF10N20 and it's complementary device, but is probably not much cheaper. I recently fitted some BUZzes in my TE AH200 and are great, though.
[/quote]

Thanks for the suggestions, will look into TE, and the Exicon device!

[quote name='RandomBass' timestamp='1381140462' post='2234752']
How about the suggestion of a class D module?
[/quote]

Yeah as mentioned in my reply above, I have considered using a Hypex class D module, but tbh I'm drawn towards a more traditional mosfet design, because I can understand how they work, and fix it if it breaks, whereas I don't really understand how class-D amps work, and the component density and surface-mount stuff on the Hypex modules pretty much means if it fails I'll have to replace it.

[quote name='RandomBass' timestamp='1381140462' post='2234752']
EDIT: 8 Devices? That's a chunk of current :)
[/quote]

Yeah, well based on the schematic's I've looked at so far, the walkabout uses 6 mosfets and the m-pulse 600 uses 12, so I think I'd want 8 at a minimum, since the walkabout only delivers 165w RMS into 8ohms. Obviously I'll start with one pair if I build from scratch to avoid a huge fire if I wire them up wrong :D

Share this post


Link to post
Share on other sites

Those modules mentioned by dood look interesting too. And easily fixed if something goes pop. Not that it will, of course.

Another Edit: the ABM and TE designs are very straightforward to understand and utilise.

Edited by RandomBass

Share this post


Link to post
Share on other sites

[quote name='dood' timestamp='1381140501' post='2234753']
Try out these guys: [url="http://www.bkelec.com/Modules/Amplifiers.htm"]http://www.bkelec.co.../Amplifiers.htm[/url] - I had one of their 450W modules years ago - it was bullet proof. My first 'big' amp was something I put together myself using one of these!
[/quote]

Interesting, that's the sort of module I've been looking for, but only found lower power or class D modules so far, thanks!

I may shoot them a mail or give them a call, as there's not much detail on their website but it definitely does look promising!

Share this post


Link to post
Share on other sites

Trace Elliot AH/GP 200/300 heads look promising. People are asking silly money for them on Ebay tho.

Share this post


Link to post
Share on other sites

Why not just buy a cheap used Ashdown head and use the whole power amp section and transformer?

Share this post


Link to post
Share on other sites

[quote name='JapanAxe' timestamp='1381146226' post='2234874']
Why not just buy a cheap used Ashdown head and use the whole power amp section and transformer?
[/quote]

because the power transformers are pants and ticking timb bombs

Share this post


Link to post
Share on other sites

[quote name='JapanAxe' timestamp='1381146226' post='2234874']
Why not just buy a cheap used Ashdown head and use the whole power amp section and transformer?
[/quote]

Well that's basically what has already been suggested above, and I am considering it. The main thing putting me off atm is the ebay definition of "cheap" in this case appears to be around £300, which doesn't make sense to me as a donor amp, particularly when you can get something like a Hartke LH500 for less than than new.

Share this post


Link to post
Share on other sites

[quote name='JapanAxe' timestamp='1381146226' post='2234874']
Why not just buy a cheap used Ashdown head and use the whole power amp section and transformer?
[/quote]

Fire!!

Share this post


Link to post
Share on other sites

I've got some of those BK modules sitting around doing nothing, they were used with our PA for awhile. Really nice amps. PM me if you're interested.

Share this post


Link to post
Share on other sites

[quote name='bertbass' timestamp='1381163394' post='2235209']
I've got some of those BK modules sitting around doing nothing, they were used with our PA for awhile. Really nice amps. PM me if you're interested.
[/quote]

Ooh, PM incoming! :)

Share this post


Link to post
Share on other sites

[quote name='umph' timestamp='1381148157' post='2234909']


because the power transformers are pants and ticking timb bombs
[/quote]
Really? Look like pretty standard toroidals to me. Never had an issue with them myself.

Share this post


Link to post
Share on other sites

[quote name='LukeFRC' timestamp='1381179072' post='2235573']
what schematic/type are you building the preamp from?
[/quote]

Not decided yet, but I've got boxes of tube amp bits sitting around, as well as several guitar amps in various states of modification, so initially I'll probably raid the spare parts and build a fairly simple 12AX7 based preamp, then add features when I've got a solid basic tone.

I started out looking at the mesa walkabout schematic, and it's essentially just a Fender style preamp, into a solid-state active EQ, then a solid-state compressor, a tube driver, and a mosfet power stage. So I might emulate that, or just go more all-tube and copy something like an SVT preamp with an LA2-a compressor.

Share this post


Link to post
Share on other sites

Just a thought, had you considered a Baxandall type eq, rather than the FMV stack? I built one a couple of years back, and found it more versatile. I had to apply a little voltage gain before and after the EQ to accomodate the inherent (but small) losses. Mine wasn't a valve pre though.

Cheers

Geoff

Share this post


Link to post
Share on other sites

Thanks to all for the suggestions - this is now sorted, I've got some BK modules (thanks bertbass!), and have made a start on the preamp.

Link to build thread:

[url="http://basschat.co.uk/topic/220279-diy-tubemosfet-hybrid-amp/"]http://basschat.co.uk/topic/220279-diy-tubemosfet-hybrid-amp/[/url]

I'm still mulling options for the preamp design, but I will definitely consider the [color=#282828][font=helvetica, arial, sans-serif]Baxandall eq idea - I'll post schematics to the build thread, so feel free to post suggestions over there :)[/font][/color]

Share this post


Link to post
Share on other sites

Excellent! I like the sound of this! I'll be checking back for sure!

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.



×
×
  • Create New...