Another MoFo

What people are working on at the moment
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#76 Re: Another MoFo

Post by Ray P »

Mr. DPD had to work hard today, delivering a nice haul of ebay purchases - both unused and a total outlay of less than £100..

Image

The one on the right is the work of Terry at Canterbury Windings. Audio specific with interwinding screen. Two secondary windings, each 15V, 150VA . It will be used for my MoFo build feeding a couple of Cap Multiplier power supplies.

On the left is an Airlink audio specific transformer. One secondary of 30-0-30V 500VA and a second 18-0-18V 4VA. A bit of an overkill but this one will be used in the chipamp for the bass section of my SLOB project with the 18V secondary powering a Muses volume control module.

Bargain!
Sorry, I couldn't resist!
User avatar
Nick
Site Admin
Posts: 15708
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#77 Re: Another MoFo

Post by Nick »

Always useful to have on hand. I must admit that my last delivery of transformers arrived on a pallet. Noting exciting just lots of 30,60,120 and 160 va ones.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#78 Re: Another MoFo

Post by Ray P »

You have your sights set rather higher than my own Nick!
Sorry, I couldn't resist!
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#79 Re: Another MoFo

Post by Ray P »

Test MoFo up and running.

Image

This is just running with my 'naked' test (sacrificial) speaker - sounds OK if rather tinny. I now need to cut a baffle for the proper full-ranger and do some measurement of the FR.

I'm surprised at the lack of heat, the MoFo thread on DIY Audio makes a lot of the need for big heatsinks but I'm only measuring a very small rise in the heatsink temperature (biased at 1.7A).
Sorry, I couldn't resist!
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#80 Re: Another MoFo

Post by pre65 »

Ray P wrote: Fri Jan 22, 2021 3:11 pm
I'm surprised at the lack of heat, the MoFo thread on DIY Audio makes a lot of the need for big heatsinks but I'm only measuring a very small rise in the heatsink temperature (biased at 1.7A).
That'll be the "soft" aluminium. :lol: :lol: :lol: :lol:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#81 Re: Another MoFo

Post by Ray P »

Yes Phil. :roll:

I tried one of the full-range units, still naked, but a much better sound.
Sorry, I couldn't resist!
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#82 Re: Another MoFo

Post by Ray P »

pre65 wrote: Fri Jan 22, 2021 3:20 pm
Ray P wrote: Fri Jan 22, 2021 3:11 pm
I'm surprised at the lack of heat, the MoFo thread on DIY Audio makes a lot of the need for big heatsinks but I'm only measuring a very small rise in the heatsink temperature (biased at 1.7A).
That'll be the "soft" aluminium. :lol: :lol: :lol: :lol:
Doh! not the soft aluminium, just me being a bit of a dunce.

I've set the bias current using a 0.1ohm resistor: 1.7A * 0.1 = 0.17V = 170mV, not 17mV! :oops: :banghead:
Sorry, I couldn't resist!
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#83 Re: Another MoFo

Post by Ray P »

Moving on!

I quickly hooked up the full-ranger again this morning with the correct bias current; I heard enough to know this path has some good potential. The missing heat put in an appearance too.

So, today I soldered up two more MoFo boards, sans input cap until I've done some FR measurements, and started working on the 'preamp' stage by soldering up two of Andrew's DHT filament supply boards, two Bartola 'Gyrator' PCBs for the 2P29Ls and a CRC supply to supply the Gyrators.
Sorry, I couldn't resist!
User avatar
nic
User
Posts: 69
Joined: Wed Apr 23, 2008 9:45 pm

#84 Re: Another MoFo

Post by nic »

Those 35mH chokes work well as loads
hf amp.jpg
. Been running my follower amp , using four (2 in PSU , 2 as loads) , for a while . Getting nice sounds out of the thing . I left the top cover off until I can get round to playing with bias circuitry , it's running rather lean at 1A bias at present . Good for 3 watts and plenty enough for >150Hz duty into 98dB efficient speakers . You should really look into the device I used , RD16HHF1 , as the highs you get with these are crystal-clear . Much better sounding than vertical MOSFETs and even better than the audio laterals I've tried in the same application . It also makes the driver stage design much easier . Currently running triode connected 2P29L with 10k resistive loads , found I needed a bit of 2nd order , too sterile otherwise
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#85 Re: Another MoFo

Post by Ray P »

Thanks nic and that's a nice looking project. I'll give the deivices you recommend a try when I get further down the line.

I'm working on the preamp /driver at the moment, also using 2P29Ls (with Ale's 'gyrator').
Sorry, I couldn't resist!
User avatar
nic
User
Posts: 69
Joined: Wed Apr 23, 2008 9:45 pm

#86 Re: Another MoFo

Post by nic »

Fakes a plenty on Ebay . Just make sure if you intend using those devices , buy from a reputable source or you'll just get reprinted IRF510 :)
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#87 Re: Another MoFo

Post by Ray P »

Hmm, I was surprised to find they're TO220 devices when I start checking them out - not that I have a downer on TO220, just different to my preconceptions.

Possibly a pricey experiment- £20 a throw at LittleDiode - but will give them a try once I get the thing up and running with some decent gain upfront.

Incidentally, I'll be powering my MoFo boards with Cap Multiplier power supplies, I have a pair of single-rail SLB boards (from DIY Audio) to populate.
Sorry, I couldn't resist!
User avatar
nic
User
Posts: 69
Joined: Wed Apr 23, 2008 9:45 pm

#88 Re: Another MoFo

Post by nic »

Those devices are about £5 a piece for genuine parts , stockists that hold parts for amateur radio usually hold them such as RFparts.com . With a generous enough heatsink running at 20 watts dissipation should be ok . I have tried IRF verticals , laterals (BUZ900P) , Semisouth R085's and R100's and RD16HHF1 are much nicer sounding devices in follower duty . A much cleaner top-end
Post Reply