Advice on a DIY A/B class power amp.


2006-05-03 8:06 pm
Hey!, I have a pair of DIY JBL 4530 scoops and would like to DIY myself a power amp to drive them properly :D .
I always wanted to find myself a SAE 2400 or 2600 vintage power amp but they are rare :( .

What i would like is a 200 to 400 WPC A/B class DIY power amp and preferably with dual honking VU meters :rolleyes: .
I do not want a chip (cheap) amp, or anything but A/B class.

I did put together a AmpsLab Synergy and a DIY Nelson Pass F-5 that gave me no trouble at all. I am no electronic tech tho :no: , so i need a proven design.
It does not need to be Audiophile grade, but i'd like the vintage SAE style sound!.
I plan on making the chassis myself (i have the equipment to do this).

Thanks in advance guys!
The honey badger kit is sold by diyaudio store, link up in the band at the top at the page.
The LM49810 kit is sold by panson who started this thread
His store is Panson Audio Laboratories
Having circuit boards to build on saves a lot of time. Circuit boards may be the only way to do a LM498xx amp without oscillaing.
Both the above are split supply amps that will cook your speaker voice coils if the 1/4 phone plug to your speaker gets pulled part way out then re-inserted. Output transistors short then put DC on the speaker. One bad solder joint can also set off DC to your speaker.
The protection kit from diyaudio involve a relay to disconnect the speaker. The contacts on these relays are not ideal and can oxidize and stop sound in a few years. State of the art is rail power supply disconnect on DC or overheat event using nFET's. I found the panasonic photovoltaic drivers that will push the gate above the top supply rail without a separate power supply winding at Digikey- APV1122 in 6 pin dip. The project boards for dip package is I'm using Fairchild fdp52n20 fets. The most famous fet speaker protection thread is bonsai's who uses surface mount parts, which take about $1000 in tools to work, so I don't recommend his thread. RGKeen first (I think) proposed the fet rail disconect. You can also disonnect the speaker line with fets, which lets all the other output transistors go up in smoke after the first one goes.
Power supply transformers come from , He also has whole amp kits. There is a place in new jersey that imports toroid transformers with 65 v twin windings and also a 15 v winding for op amps (handle balenced input or volume variations) but I forgot the name. Look under power supply thread. Regular distributors like farnell, digikey, allied, are very expensive on transformers. The switcher power supply place connex in hong kong that used to be in vendor forums has disappeared.
Speaker capacitor amps that are inherently protected from toasting the speaker, are build it yourself. Famous ones are the 6 transistor apex AX6, the 7 transistor TGM8, and for higher wattage the Panasonic SU380 with dual output transistors. The first two have board pictures online, the latter you have to lay it out yourself.
Have fun.
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2012-09-13 12:25 am
I'm plus-one-ing the OP question :D

What are, acording to you the best amps designed here able of that ?

Mia's FMC-100 with 30V feeding instead 37 V for instance ?

Or amps with less 200/400 W but with huge instant current capacity >= 50A (for vet low impedance 1.5/2 ohms in the bass aera) ?


2012-09-13 12:25 am
Andrew & Indiana were very courageous with their advice as here there is few place at Diya between the 400 W of an Hypex class D and the 20 W or less of a Pass amp... (both being good by reputation but not for all the diyers whishes about their hifi system...)... look at the number of answer ;) !

One A/B seems to deserve very good critic : the Mihai's Fc-100 amp : I would go for this myself if matching of the transistors was not a problem... like the pcb avibility today, although gerber files can be asked !
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