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PostPosted: 31 Jan 2017, 10:01 
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Joined: 31 Jan 2017, 09:36
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Hello, all
I've made this amplifier 3 days ago
I really liked the character, which is natural (this may subjective)

Thanks for sharing :D
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PostPosted: 02 Jul 2017, 07:01 
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For the 100k variable resistor, what is the power rating ?


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PostPosted: 20 Jul 2017, 12:52 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
buzztiger wrote:
For the 100k variable resistor, what is the power rating ?

Sorry for the late reply. I've been using the small blue square Bourns multi-turn trim pots and they have worked excellent. I believe they are rated at 0.5W.

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PostPosted: 07 Jan 2018, 19:33 
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Hi guys, I made it too, in a Blaupunkt bqa107 amplifier case. I used the only Mosfet I had for the moment, IRF530.The highs sound harsh, is it because I used the 530? Anyway, it sounds strong with a punchy bass and louder even if it has <1 gain. The headphones are in-ear Sennheiser. The supply is a Sony Vaio charger, 19.5V.
Regards.

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PostPosted: 09 Jan 2018, 21:57 
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Welcome to the forum. I really like your build. Unfortunately the IRF 530/540 will not work. Here is my experience with the various mosfets

Quote:
An IRF610 MOSFET is used in this example, but a wide variety of FET devices can be used in its place. I've had success with IRF510, IRF610, IRF611, IRF612 and IRF710, all of which worked well. You will want to stay away from IRF530 or IRF540 types (commonly found in power supplies) as there will be terrible roll-off of the highs.


The amp is a mosfet follower and a gain is about 0.8.

Are you using a 12v regulator with the power supply? Otherwise those SMPS tend to be noisy with class-A circuits.

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PostPosted: 11 Jan 2018, 19:28 
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I'll change the IRF530 soon. The supply is 19.5V and has a low, soft noise. Do you think it will go away if I use a LM317 to down it at 17 or 16V?
Another question, is this amplifier short circuit proof? I never plugged or unplugged the earphones while is powered.


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PostPosted: 12 Jan 2018, 22:24 
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Yes, using a regulator is an effective way to clean up the power supply noise for this amp. How are you dropping the voltage for the heaters down to 12?

The circuit is minimalist and has only DC blocking capacitors on the input and the output is capacitor coupled. It will depend on the headphone jack if a short is made when the plug is pulled out.

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PostPosted: 12 Jan 2018, 22:48 
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Gio wrote:
How are you dropping the voltage for the heaters down to 12?

It will depend on the headphone jack if a short is made when the plug is pulled out.


What do you mean by "heaters"? It works on 19.5V at the moment.

So if the plug makes a short while music is on it will burn the MOSFET? I was thinking to move the CCS above the MOSFET, this way the short will not draw more current than what the CCS gives. Will that change the sound?

Regards.


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PostPosted: 12 Jan 2018, 23:17 
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Nevermind about the heaters. My mistake I thought I was in the 12AU7/IRF510 headamp thread. No more wine for me tonight!

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PostPosted: 25 Jan 2018, 18:36 
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I want to point out that with any siwtched mode power supply or switching step up or down regulators. Any circuit that dosen't have high frequency compensation built in will have parasitic osscliations.

I had built a zero negative feedback amp with gret scope results, zero compensation required.
However I built a newer model involving a switching ste up module, with the same topnology my amp started oscilatting under a proper scope that has bandwith of 50mhz.

The class a head amp irf610 dosen't have any high frequency/parasitic compensation built in, it will osscilate when a smps is used. A computer scope cannot detect osscilations becuase its sampled and has a filter cutting off 20+khz. Parasitic Osscilations are typically in 1+mhz range.

Typicalkly because parasitic oscillations are well above 20khz range in theory the oscillations cannot be heard. However in my real world testing, getting rid of oscillations will improve sound quality.

A lm317 typically has poor ripple rejection in mhz range, therefore I reckon smps+317 regulator will not solve parasitic osscilations, however realworld testing is required to prove this.

acomeau wrote:
thinkbrown wrote:
I have an old PSU from a computer somewhere. I believe it supplies 85ish watts at 12volt. Would that do it?


A power supply is not a power supply..........that is just because the rating is the same does NOT mean its performance is the same.

SPSU [switching power supplies] are notorious for noise and IMHO should be avoided entirely for audio circuits. Would be experts claim SPSUs are more efficient - and that is usually but Not always true - but they fail to understand that SPSUs are noisy and can be less stable [in some conditions] and have other problems.

I Never use a SPSU in development work, nor in audio circuits.

In addition, SPSUs can fail with terrible results - destroying what the circuit they supply. I had that happen twice.

In summary then never use an old SPSU for a circuit you care about, and never use for audio circuits.


I've used a duall 24v switch mode supply for my class a amp no plorbems


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