150watt power amp build problem

[blindboybenton]

Hi

Ive had a old 1980 ss amp with one of those all in one power amp modules that just have input and voltage supply and output
unserviceable as you can't get at the components HY364P

anyway this module is not working well at all
I have Built a 150watt power amp from a circuit i found on the net. I built it to spec and using all new and correct components
Worked the first time i turned on.
checking the signal on the scope the sine wave looks perfect,

but when i play guitar or bass though it. it has a low level of distortion. Ive checked it with my own speakers and used the pre amp though another power amp and the new built with another pre amp.
The sound is almost like a knacked speaker. Im not sure what to do now,

Can anyone offer any idea's on the design and wherever its got any floors

Bassman

[J M Fahey]

Yes, I know that amp well, itīs very popular because itīs very simple, designer took a regular design and chopped off as much as he could.
Only problem is that he chopped a little too much, but Iīll tell you a couple parts you need to add.
If you made one of the PCBs which are floating around, please post it here, also a picture showing PCB and transistors mounted on heatsink.
The annoying low level distortion you hear and which sounds like a scratching or dirty speaker voice coil is called crossover distortion, which is caused because the amplifier is not biased properly, and what Iīll ask you to add *must* be in contact with the heatsink, hence the need for actual build pictures.

Whatīs the actual rail voltages you have?
Whatīs the speaker impedance?

No 150W available by ny means, but decent clean 80W or so ... if you correct the small errors

In any case, if you use the HY364 original supply, you will get the same power as before into 8 ohms.

That amp, as is, can NOT drive 4 ohms.

Also beware it does not have any short circuit protection.
No big deal in a combo, but if you use it as head and cabinet, better replace connectors with speakons (which do not short) instead of jack/plug which do.

[blindboybenton]

Hi

The speaker is 4 ohms in the cabinet But im not using it , workshop speakers are 8 ohm and that's what im running it in to. The Tip142/147/41 are all mounted on the back cover, they are not getting hot or even warm
Voltage rails are +/- 47v un loaded. loaded at 42-44v

would be better off starting a new one of a different design ?

Many thanks Bassman

[J M Fahey]

Oh, now that you built it, use it
tweaks are minimal and inexpensive, but please post a picture, because you will need to add 1 or 2 1N4002 compensation diodes which must be touching or epoxied to the heatsink or the panel which works as such.
It was not important in the published version because itīs way underbiased (you already noticed that ) but when properly biased diodes must be at the same temperature as the heatsink.
If you want to drive 4 ohms, you need to add an extra pair of TIP142/147 and the coresponding 0.33 ohms wire resistors.
Just curious, which page did you get it from?

[blindboybenton]

I got it from
150 Watt amplifier circuit ? Electronic Circuits and Diagram-Electronics Projects and Design it states in there that i will work on 4 ohms
I have made the out of vero board. Very little space left. The only way i can fit 2 more 0.33r 5 watt it will look a bit crappy
I like neat. I knew it didnt have protection or a way of Biasing. i think the protection thing has got a thing going in my head
If it fails and blows up the speakers i won't look good on me. so ive decided to start again with biasing and protection.
would like to see any circuits you recm'd

[J M Fahey]

This one looks good: ready made, reasonable price, if you donīt trust EBay you can buy straight from Factory, speaker protection.
Most important: has built in speaker protection (very few do) , can be mounted against a single flat heatsink or back panel and is *designed* to work with +/-45V supplies.
Forget the inflated power spec, it will put out the same as your dead power module, since supply and speaker are already there.
L28 Mono Audio Power Amplifier Kit Amp 350W 4ohm Board with Speaker Protect | eBay
https://www.yuan-jing.com/l28-mono-p...plifier-350w-a


Or you can bias your existing amplifier , adding extra transistors or not is your option , they are mounted straight to the heatsink and emitter resistors can be silicone glued to heat sink or mounted on terminal strips, if using only 2 transistors you can still use it, just donīt load it with 4 ohms.

You can build this Universal DC protector on perfboard.
Itīs so universal that it does not even need to be attached to amplifier or inside chassis, it can even be mounted inside the speaker cabinet, because action is simple: if it detects more than 12V DC for more than a couple seconds across speaker terminals, it shorts across them.
Yes, it nukes the power transistors, but in any case, they are already dead and worst case, are much cheaper than any speaker and way easier to replace.

[blindboybenton]

I looked all over the place never even thought about ebay. I wasn't really happy with the last amp it look ok done on vero board
as it didnt work properly from the outset made me loose confidence in it and the design
the one you linked in will just about fit
just done some reading up on the amp made in 1980s alligator ac150 its a 120 watt

[J M Fahey]

Is this the one?




unusual cabinet design

[blindboybenton]

thats the one its a bit shitty really. and the guy uses it for blues harmonica oh well