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Old 6th January 2014, 01:22 AM   #141
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You MUST adjust the pots so that the output is near 0V before connecting the speakers!!! adjust VT3 first, then VT2 and VT1.
Quote:
Originally Posted by speedless View Post
Hi
A friend and i just build a set .
His a faster builder than i am and he send me a sms;"DO NOT CONNECT TO POWER YET
SOMETHING IS WRONG,BURNED ALL MY BD139 AND 4 MJ15003!!!"
We checked his boards against mine and the diagram,all just as the doctor ordered.
Components;right values,right placed and orientated,No shorts,no Discontinuity.
Newer the less,my boards acted exatly the same as his.ARRRGG!!!
The bd139 blows after a few seconds,taking the mj15003 with it !???
Whats wrong?
What should i check ?
Is there a startup position of the potmeters,BEFORE power is applied?

Getting tired and annoyed.

Jan
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Old 6th January 2014, 01:24 AM   #142
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Quote:
Originally Posted by schultzsch View Post
can I run this amplifier on +/- 9 volt power supplies ?
how much output power it will give with 4 amp bias on 3.5 ohm speakers?
You won't get enough power with 9V. +-15V at least for this design.
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Old 6th January 2014, 01:25 AM   #143
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Yes the free JLH boards are created from this schematic
Quote:
Originally Posted by e_fortier View Post
Hi,

I just ordered a stereo kit, for your answers please see Fig. 2 from my link below, it's the schematic Ray used to create his PCB ;-)

I hope the small transistors are matched.

The Class-A Amplifier Site - JLH Class-A Update

BR,
Eric
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Old 6th January 2014, 01:30 AM   #144
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Quote:
Originally Posted by samratsarkar View Post
Hi Siliconray,
I am interested to use this amp. I will be using this amp for powering the High frequencies and mid range drivers respectively in my stereo active amplifier system. Let me know if this amp is worth having for my type of set up.

let me know these queries as mentioned below-
1. Do you provide assemble kit?
2. Which transistors you suggest for High frequencies
3. Which transistors you advise for Mid range frequencies?
4. What other kits are required for making a complete stereo system? i mean PSU if any..
5. Give me Heat sink dimension for this class A amp.
6. Do you ship to India?

Regards,
Samrat
Yes we provide assembly kit. MJ15003 works excellent for both high and mid range frequency. this PSU is highly recommended:
Hi-End Power supply board with speaker protecting - Boards | Kits | Components | Modules | Tools
there's a newer version for this PSU recently, looks different.
200x150x50mm heatsink is suggested for each MJ15003
Yes we ship to India.
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Old 6th January 2014, 09:39 AM   #145
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Quote:
Originally Posted by siliconray View Post
You won't get enough power with 9V. +-15V at least for this design.
thank you siliconray
just ordered 2 boards, maybe in the future I will manage to do an A/B comparison with my Aleph Js
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Old 6th January 2014, 11:43 AM   #146
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Quote:
Originally Posted by siliconray View Post
You MUST adjust the pots so that the output is near 0V before connecting the speakers!!! adjust VT3 first, then VT2 and VT1.
Hi
As stated in my last post,speakers not connected,input shorted.
No chance to measure or regulate anything,the bd130 blows instantly when power is applied ?
Faulty bd139 ? all 4 ?,I dont think so ! but then there is another post here #63,same problem ? Shorted bd139 !
It seems his worked with just a replacement.

Jan
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Old 3rd February 2014, 11:30 PM   #147
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Thank you sooooooo much Siliconray for this PCB and your excellent site !!


A quick question, is this transformer OK for this project?

ebay.com/itm/220V-200W-R-Core-Transformer-Output-20V-20V-/121189176316


Last edited by K Lacer; 3rd February 2014 at 11:56 PM.
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Old 5th February 2014, 11:22 PM   #148
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Hi everyone,

Can someone please explain the difference to me if I use a 60W transformer or a 200W transformer?

With the 60W, will I get lower volume on my speakers?

My speakers are quite small and specified at "nominal impedance 8 ohm" and "max power handling 50W".
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Old 6th February 2014, 09:20 AM   #149
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by K Lacer View Post
..........With the 60W, will I get lower volume on my speakers?...............
The operator and how far he/she adjusts the volume control determines the sound output coming from the speakers.

A sensible operator does not overload the speaker, nor do they overload the amplifier.

The Maximum volume before these two overload conditions is determined by the speakers' abilities and the amplifier's abilities.

The amplifier transformer Vac rating determines the the voltage supplied to the amplifier and that determines the maximum output from the amplifier.

VA of itself does not determine maximum output voltage/power.
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Old 6th February 2014, 10:50 AM   #150
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Thanks.

I'm still lost though. The PCB says "+-18V to +-25V" at the top, then at the right side of the PCB it says "+22" and "-22".

http://www.siliconray.com/media/cata...2005-pcb_1.jpg

So should I get a transformer that is from 9V+9V to 12.5V+12.5V, or should I get a transformer that is 22V+22V?

I noticed "speedless" posting above me was using 25V+25V, is that twice the maximum voltage specified? Is that why he fried four transistors?

I've ordered everything except for the transformer because it's so confusing and there's so many different kinds, they also have different Ampere output.

Everything in this article tells me I should select the R-Core type Products - Custom Magnetics, Inc.

I'm happy to get an R-Core 200W 24+24V from here if it doesn't make the transistors hot like hell so I need a cooling fan?
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