My First DIY Amplifier (JLH 1969)

[saikatbiswas82]

Mine is a 10W version kit, as i couldn't able to get the PSU kit/PCB, so using the SMPS.
If you (or any one) could help me out in procuring the PSU kit/PCB, it would be great and thanks in advance.

0-24VDC per channel with 1.25A Quotient current is the requirement.

You might take a look at this

http://m.ebay.com/itm/220820887579

I think a 0-18v 4 or 5amp toroidal might be sufficient. You can check with torotrans for the same.

 

[IndianEars]

Just a regular transformer with a Bridge Rectifier + 10,000mfd or 20,000 mfd Capacitor will do

 

[keith_correa]

A cap multiplier or regulated PS is recommended.

The definitive website for JLH is: The Class-A Amplifier Site

 

[IndianEars]

Yes, I agree with you, Keith.

A well regulated PSU would be ideal.

However given the constructor's very limited knowledge of the subject, I thought it would be best to recommend to him the simplest Linear PSU.

 

[jls001]

Regarding the cabinet, I would suggest something of metal. Metal cabinet must be connected to earth lead of the power supply for safety. This earth connection to cabinet will prevent electric shocks in case of accidental shorts or leakages. Proper equipment grounding is a regulatory requirement anywhere in the world. Secondly, metal is a natural shield against external electromagnetic fields interfering with the electronics of the amp.

 

[saikatbiswas82]

Regarding the cabinet, I would suggest something of metal. Metal cabinet must be connected to earth lead of the power supply for safety. This earth connection to cabinet will prevent electric shocks in case of accidental shorts or leakages. Proper equipment grounding is a regulatory requirement anywhere in the world. Secondly, metal is a natural shield against external electromagnetic fields interfering with the electronics of the amp.

I'm kindda leaned towards metal cabs only. Now it's very hard to get (or get built). There are so many options on eBay. But none of them are cheap.

 

[omishra]

If you can buy 3mm aluminum sheet then its easy to cut at aluminum window maker. Drilling is DIY. Anodizing can be queried at same window maker or uNits.

 

[raj_krish]

Now its time to post the second part

After searching locally and by all possibles means, could not able to get the cabinet.
So ordered online....





Dismantled the heat sinks and took them to lathe machine guy, asked him for drilling and tapping. (Intentionally went around 8:30 so that they will be free)
He quoted 40rs per hole and finally accepted for 35rs , it took for more than a hour for completing the work.
Mounting the PCB's on the heat sinks done...



After verifying all the connections, switched on the amplified....
Only one channel was singing , immediately switched of the amp.
Removed the PCB and checked the soldering and re-soldered some of the parts.
but still no luck, as it played for 5 seconds and then stopped (asked friend for the help and figured out that one of the transistor is having a crak at back side, which can be observed in earlier posted pics )
Luckyily those transistors are available with friend and collected a pair as they are of different make (got sanyo transistor with kit, replaced with hitachi make 2SD669)
Now on one channel it is of hitachi make and on other it is of Sanyo (will replace once after finding the differences )









Cables used for internal wiring:
Finolex 18 gauge for power
Speaker cable for speaker out
Silver coated solid core for input (RCA)

DIY experts please let me know:

When i checked for DC offset without load (with out connecting to speakers) it is displaying as 12V, is it expected?
On switching the amplifier thumb is observed..

Thanks

 

[saikatbiswas82]

If you can buy 3mm aluminum sheet then its easy to cut at aluminum window maker. Drilling is DIY. Anodizing can be queried at same window maker or uNits.

Thanks a lot for your valuable suggestions. I will check with the local window maker.

Wow! The cabinet looks stunning. It's becoming an excellent diy pro build.

 

[jls001]

12V is too much!

 

[IndianEars]

Raj_krish said

When i checked for DC offset without load (with out connecting to speakers) it is displaying as 12V, is it expected?
On switching the amplifier thumb is observed..

You have not posted the Circuit of the kit that you are building. However if it IS the original circuit, the Output is Capacitor coupled, and it Runs of a Unipolar ( single Voltage Power Supply) ... NOT a + & - power supply.

If there is a Large ( approx 2000 mfd) capacitor just before the speaker, then its a Unipolar supply, and the side of the capacitor NOT connected to the speakers should be at HALF the supply voltage.

With a Capacitor coupled amp, a switch on Thump is Normal.

If the amp is running off a + & - Power Supply ( eg +15 Volts - 0 Volts - Minus 15 Volts, then a 12 Volt offset is VERY Wrong.....

 

[raj_krish]

Raj_krish said







You have not posted the Circuit of the kit that you are building. However if it IS the original circuit, the Output is Capacitor coupled, and it Runs of a Unipolar ( single Voltage Power Supply) ... NOT a + & - power supply.



If there is a Large ( approx 2000 mfd) capacitor just before the speaker, then its a Unipolar supply, and the side of the capacitor NOT connected to the speakers should be at HALF the supply voltage.



With a Capacitor coupled amp, a switch on Thump is Normal.



If the amp is running off a + & - Power Supply ( eg +15 Volts - 0 Volts - Minus 15 Volts, then a 12 Volt offset is VERY Wrong.....

This is the circuit



I placed the capacitor of 4700uf with 35v

Thanks
Raj

 

[IndianEars]

What you have posted above is a PCB, not a circuit diagram.

However, from the PCB it is apparent that:

1. The amp runs from 0 & +24 Volts DC.

2. The Amp has a Output capacitor.

Hence :

1. The 12 Volt "Ofset" is Perfect, and Good.

2. The 4700 mfd Output Capacitor is a good value ( above 200 mfd is good)

3. The Switch on thump is Normal.

Enjoy !

P.S: Great Chasis. How much did it cost you ? ( with Duty ? )

 

[hifiramr]

DC offset 12V man its a killer don't connect your speaker to it there is something wrong in there.Never ever connect speaker it will blow first of all the tweeter and the second one is midbass.

Just recheck the dc offset will be in mv even 1v will damage your tweeter I think your amp will be oscillating as well.Please check everything normal.Use a single speaker specially for testing dont connect your main speaker .Also use speaker protection circuit also soft start to avoid inrush current and speaker output sound.

1. The 12 Volt "Ofset" is Perfect, and Good. ???????????

What you saying 12v dc offset fine well you may be mistaken by 12mv

A well diy power amp should be having less than 10mv dc offset.Even matched pair of transistor will give much more result maybe less than 1mv is achievable according to the design and other factors.

 

[raj_krish]

DC offset 12V man its a killer don't connect your speaker to it there is something wrong in there.Never ever connect speaker it will blow first of all the tweeter and the second one is midbass.

Just recheck the dc offset will be in mv even 1v will damage your tweeter I think your amp will be oscillating as well.Please check everything normal.Use a single speaker specially for testing dont connect your main speaker .Also use speaker protection circuit also soft start to avoid inrush current and speaker output sound.

1. The 12 Volt "Ofset" is Perfect, and Good. ???????????

What you saying 12v dc offset fine well you may be mistaken by 12mv

I too worried about the DC offset, but later my friend suggested to place a 10ohm resistor and check. So did the same and it is very minimal like 0.03.
Have connected my speakers and they are working fine with out issue

 

[Sumanta]

Regarding the cabinet, I would suggest something of metal. Metal cabinet must be connected to earth lead of the power supply for safety. This earth connection to cabinet will prevent electric shocks in case of accidental shorts or leakages. Proper equipment grounding is a regulatory requirement anywhere in the world. Secondly, metal is a natural shield against external electromagnetic fields interfering with the electronics of the amp.

Joshua,
Questions from me a noob -
1) Accidental shorts or leakages through a mdf sheet is less possible than a metal sheet, MDF being a bad conductor. If it is a direct contact, then both cabinet has equal danger. Because earthing is anyway, at least there throughout the circuitry. Right am I, or I am understanding it wrong?
2) Not all metal restricts electromagnetic field, say Aluminum (if my memory is right). If we have shield plates inside an mdf cabinet, and my understanding of item 1 is correct or there is no chance of leakage by certain means, then mdf cabinet works. True?

Thanks for raising such points. I am learning.

 

[IndianEars]

hifiramr

What raj_krish is describing as an "offset" is NOT the Offset.. that is why I have referred to it as "Offset"

The 12 Volts measured is the Mid Point Bias of the Output Transistor pair at Exactly 50% of the Supply voltage. Hence this IS PERFECT

This is a Capacitor Coupled Amp, NOT direct Coupled. ....

 

[jls001]

Sumanta,
If a live wire accidentally touches the cabinet, then it gets passed to earth through the metallic cabinet if the cabinet is earthed. If non-conducting sheet is used as cabinet material and one accidentally touches a live wire, it gets passed to earth through the human body.

Yes, some metals are better than others at RFI/EMI rejection. It is possible to line the inside of non conducting cabinet with metal sheet.

 

[saikatbiswas82]

Just one updated -

I am very much inspired by Raj's feedback on this amplifier. Started procuring the parts/kit. I think this is going to be my 2nd DIY amp project. [emoji4]

Sent from my Nexus 5 using Tapatalk

 

[raj_krish]

From where you are going to get the kit/parts, let me know as me too require the psu for the amp

You require a really big heat sinks to handle the heat


Sent from my iPhone using Tapatalk