100W HIFI Amp

[Aniket]

Yes this is most used (as I've seen) but my request was purely to keep the protection circuit close to outputs as the trace is not long,if we have a separate PCB then the wires from output to that and from there to terminal,to me this is bit lengthy process (too much wires degrading the sound)

But if you think that is the logical way then please do that itself and share it.

Alright Soundcraft,
I would design a PCB with the protection circuit on it for you.

"too much wire degrade the sound"

Don't worry about the wires. imagine the length of the wire of the wire you would need for a separate protection board. 20cm ???? or max 50cm. then, consider the length of your speaker wire. 5~10m. it would have enough inductance and capacitance to "degrade the sound". Then again, consider the resistance of the terminals and relay contacts. we can't do much about these things. just ignore these trade offs. Moreover, we can't hear the difference.

Regards,
Aniket

 

[Aniket]

Here's a proposed power supply design with a single bridge rectifier and a common capacitor bank for both channels. The max capacitor diameter is 40mm that could fit. Either 3 or 4 caps per rail could be installed.

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Another design with dedicated bridge and filter caps per channel is also on the way.

 

[linuxguru]

I would advise changing the bridge rectifier outline to the 4-pin inline type, widely available in 15, 25 and 35A ratings at reasonable pricing. These have a o--o-o-o pin spacing.

 

[linuxguru]

Added speed switch off cap, C20 across R16 and a little more changes. What I was missing till now, was to analyze the clipping behaviour. Before the above modifications there was rail sticking on the -ve rail during clipping and a little oscillation, because of the saturation of the VAS transistor, Q7.

To improve the rail-sticking clipping behaviour in the Blameless-type topologies, an anti-saturation diode in parallel with C3 will help. This should typically be a fast, low Cj type device with a reverse blocking voltage of around 200V - something like a BAV21 or similar in standard DO35 through-hole package will be fine.

The non-linear reverse-biased capacitance of the diode contributes to distortion in normal (non-clipping) operation, but it's still worth the tradeoff because of improved behaviour during hard clipping.

 

[SoundCraft]

Alright Soundcraft,
I would design a PCB with the protection circuit on it for you.

Thanks a lot for the same Aniket,but I meant it for all the DIYers not specifically for me !!

So please feel free to make the PCB as majority would deem it fit,Like you mentioned earlier a softstart with protection or any such combination that you and others feel is good.

I will go with the majority and not burden you with any personal preference of mine.

 

[kanwar]

To improve the rail-sticking clipping behaviour in the Blameless-type topologies, an anti-saturation diode in parallel with C3 will help. This should typically be a fast, low Cj type device with a reverse blocking voltage of around 200V - something like a BAV21 or similar in standard DO35 through-hole package will be fine.

The non-linear reverse-biased capacitance of the diode contributes to distortion in normal (non-clipping) operation, but it's still worth the tradeoff because of improved behaviour during hard clipping.

Linuxguru & Aniket,

Yes, Blameless & similar topologies are notorious for rail sticking....

To get a proper working Baker clamp we need another diode also[the other diode in the collector leg will ensure we have enough voltage drop across B-C terminal of VAS transistor+ EF combined in case of full rail swing], in order to restrict the VAS transistor entering saturation and shooting its reverse transfer capacitance high enough to cause a glitch. This will ensure much fast recovery along with anti-saturation of VAS. Though in this arrangement the non-linear capacitance effect will decrease somewhat but still better to have low capacitance diodes.

Cheers,
Kanwar

 

[Aniket]

Updated PCB without power supply module integrated.

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Also added the option of baker clamp across C18, 100pF.

 

[Aniket]

PCB with on board protection circuit is attached. The protection circuit is based on this: Speaker Turn On Delay and DC Protector Board Set (V3) - diyAudio

It has turn on delay of 3~5 seconds, and a LED indicator for fault and operation. The LED will lit continuously in normal operation and would blink in fault condition.

Here's the PCB:

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Regards,
Aniket

 

[SoundCraft]

Aniket thank you for the same,Have checked all the things ?? are you planning to make PCB's ??

If you are making the PCB's then I'll be interested in the same,else once all the things are checked if you can send me the gerber files can have it made here locally !

Once again thanks.

 

[Aniket]

Aniket thank you for the same,Have checked all the things ?? are you planning to make PCB's ??

If you are making the PCB's then I'll be interested in the same,else once all the things are checked if you can send me the gerber files can have it made here locally !

Once again thanks.

Hello SoundCraft,

I will be making PCB's but without the protection circuit on it. Let me know ur mail ID I would send you the Gerber files.

Regards,
Aniket

 

[linuxguru]

Updated PCB without power supply module integrated.

Also added the option of baker clamp across C18, 100pF.

Thanks, looks good though I haven't checked all the nets. Only one trace needs improvement - the ground trace between the two 470uF/63V caps through the GND connectors needs to be wider. It should be as wide as the power traces. Luckily there's enough space to widen this trace by slightly moving a few devices by about a mm or so.

 

[Tanoj]

Here's a proposed power supply design with a single bridge rectifier and a common capacitor bank for both channels.

@ Gurus : Does it make difference in SQ to separate the power supply circuit for both left n right channel ?

@ Aniket , was curious to know, did you make the change ( adding Diode ) as suggested by Kanwar ?

Tanoj

 

[Aniket]

was curious to know, did you make the change ( adding Diode ) as suggested by Kanwar ?

Hello Tanoj,

After the schematic was updated with improved CCS for VAS and LTP and reducing the VAS current (3~6mA is good for TEF output stage), there was no rail sticking and oscillation and amplifier was clipping neatly with no side effects in simulation. So, I left those diodes as they are not absolutely necessary. however i have given the provision of baker clamp on the PCB. which also is not mandatory.

Linuxguru,
thanks for reminding me, while laying components I left that trace to be modified later.

next post would be the final PCB, and would order in this week.

Regards,
Aniket

 

[Aniket]

Possibly the Final PCB. widened the ground tracks and some more minor changes.

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Would order the Amplifier PCBs and the Power supply PCBs as well by this weekend.

 

[Aniket]

Collected almost all of the components of the amp.
Some pics:

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Only PCB's are left

Cheers!!!!

 

[SoundCraft]

looking forward to the build Aniket !! You are going to make PCB yourself or having it made professionally ?? How many are you making ??

Hope to see the complete pics of the build as and when it happens !

 

[keith_correa]

Are you building more than 1 amp? From the amount of diodes/resistors/caps, it sure looks like it.

 

[Aniket]

Are you building more than 1 amp? From the amount of diodes/resistors/caps, it sure looks like it.

Actually these components are available only in multiples of 50/100 in Lajpat Rai market, Delhi. and are cheaper in bulk. for example, a single 1/4W resistor costs 1 Re. elsewhere, but here you could buy 100 for 50 INR.
From these quantities, I could actually build 5 stereo amps excluding the transistors and heatsinks.

Regards,
Aniket

 

[Aniket]

looking forward to the build Aniket !! You are going to make PCB yourself or having it made professionally ?? How many are you making ??

Hope to see the complete pics of the build as and when it happens !

Hi,

I would have the PCB's made professionally, the minimum order here is 20. So, I would get 20 PCB's each for the amp and the power supply.
I could send you the Gerber files for the PCB with on board protection if you want.

Regards,
Aniket

 

[hydrovac]

Hi Aniket,

There are PCB makers here, undertake minimum 6 qty. I can get a quote if you can send me the Gerber files of amp and PSU.

Rgrds