Simple Killer Amp Constructor Thread

[float]

Hi,
if the design is right it should not respond to burn in.
In my opinion it should sound right within minutes of power up.

Fair enough, I don't believe it should happen, but (I believe) I've experienced it. Burn-in from new that is.
Regarding warm-up from cold, the SKA sounds great from the first note.

 

[AndrewT]

Hi,
let's suppose burn in does affect BG150.

I have had it soak testing with the fuses out to monitor the Iq and heatsink temps and take a few other quiescent measurements.

Has burn in started the moment I turned on the Variac?
or after GB150 first experienced full mains voltage?
or after I inserted the fuses?

Have I missed the boat? Since about 12hours of power on have elapsed between first turn on and feeding in some music some 30hours later.

 

[HiFiddle]

Stripped down my GB150 to do the zener PSRR mod. I also repositioned the little to92 temp sensing transistors by drilling a 4.8mm blind hole and inserting the body. I also fitted low ESR feedback capacitors.

Have soak tested it up and down in heatsink temp and the thermal tracking is excellent at < 10mA variation, much better than before.

Now to listen.

 

[AndrewT]

Hi,
Greg has just recommended the drilled hole solution.
I see you are confirming tighter feedback.
Did you apply heatsink compound to fill the gaps around the To92 cases?

I find mine, flat on the surface, hunts a bit more than yours. Sounds like my next iteration is looming, but my 5mm drill will be too big.

 

[HiFiddle]

Hello Andrew T,

I could have used 5mm but I had a 4.8mm drill for a really snug fit. It's funny but mine had Fairchild TO92's and theyre slightly larger than the Philips which fit in a 4.5mm hole. As it was I had to lightly file the mold seams at the sides for it to fit.

I didn't use any thermal grease. I might have smeared some on if I had some.

 

[AndrewT]

Hi,
I hope you polished out the file marks.
It really improves the sound!!

 

[Spartacus]

A quick and easy way of improving thermal coupling .... get some thermal adhesive tape, the sort often used for attaching heatsinks in computers, and apply it to the flat face of the transistor.

You can get the stuff dead cheap on eBay

 

[KLe]

let's suppose burn in does affect BG150.

Have I missed the boat? Since about 12hours of power on have elapsed between first turn on and feeding in some music some 30hours later.

Hi AndrewT
My 300D needed 25/30 hrs to burn-in

enjoy

 

[tinitus]

A couple of months without turning off

Shouldnt be long till I order GB300 from Greg, I hope

 

[doggy]

zener psrr mod.Have to

Hello all!

Have to agree totally with HiFiddle; this zener psrr mod. elevates the gb150;listening to some older vynil is a happy event.This is my main amp now.

My bias does hunt as well but have not noticed any sonic difference.

Here is a pic. of the zener mod.,since then I have gone to a more modern polypro .47uf bypass cap.

cheers
Thor

 

[ppcblaster]

What is the GB130 and 300

Is there a website?

Thank you

 

[yggdrasil]

http://members.dodo.com.au/~gregball/guru_001.htm

 

[HiFiddle]

Greg has a new web address for his site -

http://www.diyhifi.org/amplifierguru/guru_002.htm

 

[AndrewT]

Hi Doggy,
have you tried the drilled hole for the transistor diodes?
HiFiddle confirms good performance.

 

[coolbiz]

Greg has a new website at
http://www.diyhifi.org/amplifierguru/guru_001.htm

 

[doggy]

Hello Andrew T.

Not yet, no holes drilled. Letting the amp play and mod.s settle in Have you done the HiFiddle mod.? Eventually it will be done.

Now I am looking for a diy phono stage pre., I have a Graham Slee GramAmp2 which is opamp based, which is good but wanting to improve. I did look at Carlos's discreet stage and have no doubt that it would sound excellent.,I don't know that I could duplicate it, sourcing the parts etc. Another option is the Pass Pearl phono which in parts is about $450. TNT have this diy phono called "InDiscreet"but is not well known.-any advice?

Listening to some old classical last night, the sound stage is thicker, more palpable.


Cheers
Thor

 

[AndrewT]

Hi,
drilled holes completed but boards not re-tested yet.
Waiting till I get some more PSUs assembled. The Leach clones are playing at the moment on the first PSUs.

 

[wendell c]

what's needed for the zener mods?

 

[AndrewT]

GB150 Zener PSRR mod

Hi,
full schematic and construction details on DiyHiFi.org-sponsored threads.

 

[coolbiz]

on/off switch

Hi,

Anybody still reading this thread?

I am building a couple of SKA amps, each with 4xGB150D, 2XGB300S and 2x300VA toroids , and am trying to find a suitable on/off power switch.

Is a switch rated 5A/250V sufficient for this purpose? (I live in a 230V area)

If not, what kind of power switch are you guys using? I'd prefer something that can be mounted in a circular hole in the cabinet front.

Or should I seriously consider using a soft start for this amp? Or maybe a seperate power switch for each P/S ?

Thanks,