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MyRef_C with Ultimate BOM

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A

AndrewT

R.I.P.
Joined 2004
R1 pulls 12.5mA through the regulator.
R3 pulls 10mA through the regulator.
Is 22.5mA OK as the minimum load current for the 338?
317 needs >=5mA for proper operation. 337 needs >=10mA for proper operation.
Change the 500r to 510r and add a LED as an indicator.

Most do not like tantalum caps due to the reputed "fail to short" when they let go.
Use PES (MKT or MKS) for the regulator decoupling.
I prefer to see C2 (10uF) of much higher value, maybe 100uF or 150uF.
R2 (300r) can be replaced with a forward biased LED or a Zener for better regulation. 2LEDs totaling 3.75V will give ~5V output.
 
Last edited:
regiregi22

regiregi22

Member
Joined 2009
haciendodelpunkunaamenaza.blogspot.com
I take into accound what the datasheet says about the LM338. Maybe tantalums are worse, they say they are the recommended ones. They say too that, if you prefer to use electrolytic rather than tant, you need to use higher values.
Datasheet chip specifications are measured at a Iout of 10mA and 5v of difference between Vin and Vout.

Thanks for your answers, Andrew.
I am right now looking at the LM 338 datasheet. I will quote the most important topics about their bypassing:

Input capacitor:
An input bypass capacitor is recommended. A 0.1 uF disc
or 1 uF solid tantalum on the input is suitable input bypass-
ing for almost all applications. The device is more sensitive
to the absence of input bypassiing when adjustment or out-
put capacitors are used but the above values will eliminate
the possiblity of problems.
Click to expand...

Adjustment pin capacitor:
The adjustment terminal can be bypassed to ground on the
LM338 to improve ripple rejection. This bypass capacitor
prevents ripple from being amplified as the output voltage is
increased. With a 10 uF bypass capacitor 75 dB ripple re-
jection is obtainable at any output level. Increases over
20 uF do not appreciably improve the ripple rejection at
frequencies above 120 Hz. If the bypass capacitor is used, it
is sometimes necessary to include protection diodes to pre-
vent the capacitor from discharging through internal low cur-
rent paths and damaging the device.
In general, the best type of capacitors to use are solid tanta-
lum. Solid tantalum capacitors have low impedance even at
high frequencies. Depending upon capacitor construction, it
takes about 25 uF in aluminum electrolytic to equal 1 uF
solid tantalum at high frequencies. Ceramic capacitors are
also good at high frequencies
Click to expand...

Output capacitor:
Although the LM138 is stable with no output capacitors, a 1 uF solid tantalum (or 25 uF aluminum electrolytic) on the output swamps ringing and insures stability.
Click to expand...
 
regiregi22

regiregi22

Member
Joined 2009
haciendodelpunkunaamenaza.blogspot.com
Continuing with the topic, I will quote from the wikipedia:
Farad - Wikipedia, the free encyclopedia
A farad is the charge in coulombs a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second. Example: A 47 mA current causes the voltage across a capacitor to increase 1 volt per second. It therefore has a capacitance of 47 mF
Click to expand...
So if the Lightspeed consumes a maximum of 40mA, can we say that we need a 40.000uF cap to have a decrease in voltage of 1v/s? What is the voltage threshold at which the Lightspeed starts to misbehaviour?
 
regiregi22

regiregi22

Member
Joined 2009
haciendodelpunkunaamenaza.blogspot.com
MyRef_C Documentation Compilation v1.0

Well guys, I have spent some really hard days reading all the GB thread and the original MyRef C threads to make an attempt to compile all the information regarding this design, specifically oriented to the components used in this Group buy.

In the attached file I have included all the schematics, all board layouts (silk, composite...), the BOM that Udailey is going to provide us, Lightspeed info about its implementation, performance measurements from Mauro and Peter, the simulations I made for the input capacitor, user pictures from the amp and some text files with all the relevant information from the forum to build the amp.

Really folks, this is a very complete documentation file with all the information you will need to know to build this amp. Including the amp specifications and all the important things users have apported to the thread.

Can anybody see something lacking? I will really appreciate any comment or suggestion.

MyRef_C_Ultimate_Documentation.rar

Regards,
Regi
 
U

udailey

Member
Joined 2008
picasaweb.google.com/udailey/MyRef#
I will put alligator clips on a few different cap sizes and test them on my old Lightspeed. Sorry I have been late answering. The idea hit me yesterday, duh! Been fixing 5 messed up sink drains in the new house, built a crib and am now building two tomato plant planters. They are massive. 4'x2'x2'. I want to line them with plastic on the inside then fill a few inches with water. Then another planter sits down inside the main planter. This 'insert' has the dirt and plants with holes drilled in the sides and bottom. The main 'container' planter, with the water, evaporates up into holes in the 'insert' and keeps the dirt moist all the time. Has a hole in the main to fill with water. We overengineer everything dont we!?
So anyway, I will test the caps by clipping a big cap onto the +/0V of the Lightspeed, powering up the Lightspeed, clipping DMM on one of the LDRs, unplugging and watching the resistance. When it starts to dive I will take the time and see how many seconds it lasted.
Thanks Regi for the hard work. You will be an expert at this circuit and a great resource if you choose to help answer questions. Either way, a great resource with your compilation.
Uriah
Uriah
 
regiregi22

regiregi22

Member
Joined 2009
haciendodelpunkunaamenaza.blogspot.com
OK mates, I will read your apports and see if I can include them in one way or another. I will release them ASAP.

Uriah, you are an awesome tomato hacker :p Please, post some pictures if you have them in the lounge subforum.
Do you have around any regulator circuit in which you can dial voltage? Or can you take one with a fixed voltage resistor and add a pot? That way, you could start dialing less voltage and see at what point the Lightspeed starts to misbehaviour.
Having in mind that voltage, we could make calculations for the size of the cap, and the time it would take to reach the dangerous voltage limit.

Regi
 
U

udailey

Member
Joined 2008
picasaweb.google.com/udailey/MyRef#
Any voltage less than the voltage you set it at to begin with will be to little because the LDRs will begin instantly to increase in resistance. As the shunt increases it catches up easily to the series and we have very fast volume increase. It has always been suggested to either leave the Lightspeed on 24/7 or to turn it off after you turn off amp for this reason. Will get to the caps before bed tonight. I think a big cap is the solution. Think of how long your amp stays playing after you turn it off and this is just a few LEDs.
Uriah
 
ClaveFremen

ClaveFremen

Member
Joined 2005
inserra.it
Paid Member
4

40 watt

Member
Joined 2009
regiregi22 said:
I take into accound what the datasheet says about the LM338. Maybe tantalums are worse, they say they are the recommended ones. They say too that, if you prefer to use electrolytic rather than tant, you need to use higher values.
Datasheet chip specifications are measured at a Iout of 10mA and 5v of difference between Vin and Vout.

Thanks for your answers, Andrew.
I am right now looking at the LM 338 datasheet. I will quote the most important topics about their bypassing:

Input capacitor:


Adjustment pin capacitor:


Output capacitor:
Click to expand...

Impedance of electrolytic capacitors at high frequencies...?

From a measurement by Bill P:

http://www.diyaudio.com/forums/atta...trolytic-capacitors-nichicon-es-impedance.pdf
 
regiregi22

regiregi22

Member
Joined 2009
haciendodelpunkunaamenaza.blogspot.com
ppcblaster said:
Not sure what I need to order for two channel amp,

two kits

one or two LDR with board

Two transformers.

Please advise
Click to expand...

For an stereo amp you will need to buy 2 amp kits, 2 trafos (optional) and 1 LDR kit (optional). Keep in mind what it is said in the LDR description, you will need to add a +5v PSU and a 100k dual log pot.

Regards,
Regi
 
P

ppcblaster

Member
Joined 2006
regiregi22 said:
For an stereo amp you will need to buy 2 amp kits, 2 trafos (optional) and 1 LDR kit (optional). Keep in mind what it is said in the LDR description, you will need to add a +5v PSU and a 100k dual log pot.

Regards,
Regi
Click to expand...

Thank you,

I am hoping other builders will come up with the +5v PSU and select a 100k dual log pot.

I don't have the skills to design a PSU board.
 
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