Mi big gainglone

[uvodee]

i am not a terrorist

but you can easily ?~🙂 anodize aluminum at home
like this ...

http://www.focuser.com/atm/anodize/
anodize99.html

Jean-Pierre

 

[peranders]

nice case but your rectifier without cooling

 

[Bricolo]

nice case but your rectifier without cooling

It's only a gainclone 😉

 

[Bricolo]

I made some measurements today, with a cheap frequency generator and my scope.

It measures flat (flat, not -3dB) from 10Hz to 450kHz (approx.) This is a wide bandwidth for an amp, is this normal?

Sine waves looks good. Squares ones start to have some small transiants at 10kHz

 

[GregGC]

I made some measurements today, with a cheap frequency generator and my scope.

It measures flat (flat, not -3dB) from 10Hz to 450kHz (approx.) This is a wide bandwidth for an amp, is this normal?

Sine waves looks good. Squares ones start to have some small transiants at 10kHz

Yes, absolutely normal. If you look at the speck sheet it should give you 0dB at 300kHz. It's a mean nasty amp. Have to be handled with care if you want to be free of nasty HF trash.

And even 100kHz LF filter at the front may be a good idea.

 

[Bricolo]

There's a problem

With a 10R load (a resistor), everything's OK
But with a loudspeaker, the signal is distorted. The sine wave has another signal on it, like clearly visible harmonics

 

[Netlist]

The sine wave has another signal on it, like clearly visible harmonics

Picture of the scope pattern?

/Hugo

 

[Bricolo]

Sorry, my syster has the digital camera for all the week end


After further testing, this could be a noise problem (by noise I mean HF garbage), because:
when the volume pot is at 0%, there's not any output signal, no amplified signal, no noise
when I slowly turn the pot, there's the sine wave send by the frequency generator, and this other signal (that looks like 5% harmonics)

But when I continue to turn the volume pot up, and that the output signal is higher than 0.5V (1Vpp), the noise isn't visible anymore.


And I still haven't eadthed the chassis (it's not connected to earth, and not to the amp's ground), maybe it's tome to do it.

But I'm sceptic about this, I'm not sure it will help. Since the scope's probe connected to the -out is earthing the amp (but not the chassis)

 

[Bricolo]

but if it's noise, why isn't it also present with the resistor load?

 

[Netlist]

Hi Bricolo,
It seams to me that you'll have a huge ground loop.

Could this be your problem?

What if you connect amps ground to signal ground (trough a resistor perhaps). I always measure if there's no voltage between amps ground and signal ground before doing so.

Hf garbage? It's not oscillation or mains hum?

/Hugo

 

[Bricolo]

Could this be your problem?

What if you connect amps ground to signal ground (trough a resistor perhaps). I always measure if there's no voltage between amps ground and signal ground before doing so.

Hf garbage? It's not oscillation or mains hum?

/Hugo

what do you call amps ground and signal ground? do you mean power ground and signal ground? Or are you talking about earth?
For the momment, the amp isn't cinnected to earth at all.

It may be HF garbage, so, closing the chassis, and earthing it will help
oscillation? I don't think so. It doens't happen witout input signal, and only at very low volume
Mains hum? No, I haven't measured the frequency, but it's much higher than 50Hz

 

[Netlist]

what do you call amps ground and signal ground? do you mean power ground and signal ground? Or are you talking about earth?

Sorry, had to post quickly, dinner was ready and delicious. 🙂
I meant: What happens when you connect the signal ground to the amps case?

It may be HF garbage, so, closing the chassis, and earthing it will help

Well yes, what happens when you close the amp? Are there neon lights, a computer, other RF generators in the neighbourhood?
Can you HEAR the garbage? I think you said it doesn’t go up with the signal, but has constant amplitude. 0.5Vpp? Are you sure your generator is ok? Is the connection between generator and amp sufficiently shielded?

/Hugo

 

[Bricolo]

I haven't tried to connect the case and ground, I'll try today.

With it's current configuration (case conected to nothing (neither ground nor earth) and amps ground also not earthed), the amp is dead quiet from 0%vol to 50%vol. At 100% I canhear a slight hum, but when I'm more than 10cm away I can't hear anything.

But when I touch the case, thus hum is a little louder. I looked with the scope, it's 50Hz. Earthing the case (not the amps ground) totally solves the problem.


I haven't closed the amp yet, I'll also try this. Theres' no neon, but a computer 3m away, a scope and a signal generator just aside. A coaxial TV cable is 2m from it, and the frisge is 7m away (but this one is too usefull, I won't move it 😀)

I can't hear this noise. It's only visible when the output signal is itsefl very low.
But 0.5Vp isn't the noise's amplitude! It's the signal amplitude when the noise becomes invisible. The noise is 5-10mV pp
The generator is OK, the input signal is clean. The generator is connected to the amp with a coaxial cable, and at the amp there's a coax-->RCA adapter.


But now I'm clearly thinking it's noise, some pickup noise. Because even with the amp switched off, with the mains plug unplugged, I can see noise on the output terminals with my scope.

I must earth/ground everything correctly before doing further testing

 

[Bricolo]

OMG!

I made some crosstalk tests, there's a small signal on the left channel (with no input signal (nothing connected to the input)) when the right channel has a signal and that the volume is 100%

So I let the volume full up for a few minutes, havine a loudspeaker on the left output (with no input signal) and a 10W 10R resistor on the right output (with the frequency generator at the input)

When I looked at the resistor, it was red! Red like a very hot puece of metal

 

[Bricolo]

Crosstalk is -78dB, is this good? (when the right channel is at 48Vpp, the left one is at 6mVpp)

 

[Netlist]

When I looked at the resistor, it was red! Red like a very hot puece of metal

Euhh, seems ok to me. That means your right output has given you about 10W or more for a couple of minutes. 😎
Crosstalk? Some will say it can be improved; perhaps you'll have to redesign the whole concept for that... like building two separate gainclones. I'm not sure that at normal listening sessions you will be able to hear that -78db.

/Hugo 🙂

 

[Bricolo]

Euhh, seems ok to me. That means your right output has given you about 10W or more for a couple of minutes. 😎
Crosstalk? Some will say it can be improved; perhaps you'll have to redesign the whole concept for that... like building two separate gainclones. I'm not sure that at normal listening sessions you will be able to hear that -78db.

/Hugo 🙂

In fact, the "little" 10W resistor got 30W 😀


And no, I won't change the case! Absolutely no way. It's 4 months of work.
I was just asking if it's good, considering it's a stereo amp

You're right, I won't certainly hear it.
I got a small sound from the left speaker, when the volume was 100%.
The right channel's output was 48Vpp, on the left it was 6mVpp. Imagine the difference

 

[carlosfm]

And no, I won't change the case! Absolutely no way. It's 4 months of work.

😱
That thing will turn out more expensive than a Rolls-Royce.😀

 

[Bricolo]

😱
That thing will turn out more expensive than a Rolls-Royce.😀

In fact, I spend more hours of work on it, than euros 😀

 

[carlosfm]

In fact, I spend more hours of work on it, than euros 😀

😀
Like an old Philips CD650 I have (not in my main system).
I wouldn't have the money to charge myself the hours I spent tweaking it.
And I'm still waiting to receive an XO clock I bought to Guido Tent to install on the CD650.😉