★★Free JLH Hifi Headphone Amp PCB, 0.008% THD★★

[Kram]

Trying again, lol.

Q1 collector 10v
Q2 Emitter 10v and Base 5v
Q3 collector 5v
Q8 collector 5v
Q6 collector 0.5vp-p

Q4 base 102mV, emitter 0.5 v p-p

Thanks for trying to help out kenpeter, what you said did seem strange to me too so I went back and measured again, results above.

 

[epicyclic]

Try a 15pF ceramic capacitor across the base and collector of Q3 .

 

[Kram]

Thanks for the tip, it seems to have worked so far.

 

[epicyclic]

Thanks for the feedback

 

[OV54ZXH]

JLH Hedphone Amp as Preamp

Could I use this as a preamp for the JLH Class A Amp?

 

[cHoc]

Oppps..Both should be 500 Ohm.

Both 10 and 20 works for R15. For low impedance headphone 10Ohm is better. Just keep them the same value.

Sorry for the inconveniences.

Do the 10 and 20 Ohm resistors then work better for the higher impendance headphones, 300ohm and up?

 

[K Lacer]

This will be my first DIY power amplifier and I have ordered almost all the necessary parts today. I really like to make this high-end.

I will be using the free JLH 2005 circuit board, and the Darlington design power supply discussed earlier in this thread Free Power Supply PCB For JLH Amplifier - Boards | Kits | Components | Modules | Tools

Transformer not yet... I remember when the company TeraDak changed all their transformers to R-Core type, they said it took away the hum.

I saw some comments about a 200W transformer earlier in this thread, is 200W recommended?

My power sockets are around 230V. How are these specs 220V, 200W, 20V+20V output?

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

Is it better to use one with two output values? For example there is one with 40V+40V and 15V+15V.

When I type "R-Core 200W" into Ebay I get 10 results, which one should I pick? I hope someone can help me find the ultimate transformer !!

K Lacer

 

[K Lacer]

What would actually happen to the amplifier if I used a 50W transformer? Like this one? 50W 220V R Core Transformer 18V 18V | eBay

I don't really get the difference. Thanks for any help!

 

[K Lacer]

- deleted, these questions were meant for the power amp thread -

 

[nautibuoy]

What sort of current load do these headphone amps impose on the power supply - I believe they run at 100mA quiescent current? I have some +/- 12V supplies based on LM317/337 devices that I would like to use, one per channel; only problem is they already have PCB mounted transformers that only deliver around 330mA, though they could be replaced with off-board transformers if necessary.

Thanks

 

[nautibuoy]

I received my free headphone amp boards thank you. Nice boards too.

Ray

 

[e_fortier]

Hi Siliconray,

I have recently built the JLH 2005 power amp version and it sounds great. The only issue I had was that the spacing on the small transistors TO-92 style are VERY close to each other, also the size of the pads are too small unless you are used to doing surface mount soldering, if you do a re-spin of the PCB please think about this request.

Is it the same for this headphone amp ? I would buy a kit if these spacing and pad were bigger.

Thanks for offering these PCB and kits.

BR,
Eric

 

[nautibuoy]

Hi SiliconRay

It's time for me to assemble my boards but some questions if I may;

1. I've not tracked down any heatsinks like those you've used. Can you advise where I can get some or tell me what spec (deg C/Watt) I need to obtain? I plan to use 15V supplies with 150-200mA quiescent current.

2. Where can I find the instructions for setting up the boards for quiescent current and dc offset once I've assembled them?

Thanks

Ray

 

[nautibuoy]

I’ve had a good look around and I can find little information to support the build process, so I’m piecing things together for myself. Grateful to anyone who can check the following.
Regarding setting up the boards, VR2 sets Quiescent Current and VR1 adjusts DC offset.
I should adjust the quiescent current, then the DC offset, then iterate a couple of times through the process to reach optimal settings.
Input should be shorted and connections made after set up.
Dummy load resistor should be connected across outputs during set up.
To set Quiescent Current (Iq):
Voltage across R10 = Iq * R10
Therefore, assuming R10 = 0.51R and required Iq = 200mA
Voltage across R10 = 0.2 * 0.51 = 0.102V DC
Connect multimeter probes across R10 and adjust VR2 until the voltage measured = 0.1V.
To adjust DC Offset:
Connect multimeter probes across the output and adjust VR1 to lowest level of DC.
Other Considerations:
There seem to be some examples of alternative output transistors causing oscillation. I propose using BD937 transistors for Q1 & Q2 as these seem to be a safe option with respect to stability and sound quality and have the same pinout as the MJE3055 devices?
I will be using regulated supplies at +/-15V, which is within the range shown on the PCB.
Suitable heatsinks?
Sorry if this is basic stuff by I am no electronics expert and would rather be safe than sorry.
Thanks
Ray

 

[e_fortier]

I’ve had a good look around and I can find little information to support the build process, so I’m piecing things together for myself. Grateful to anyone who can check the following.
Regarding setting up the boards, VR2 sets Quiescent Current and VR1 adjusts DC offset.
I should adjust the quiescent current, then the DC offset, then iterate a couple of times through the process to reach optimal settings.
Input should be shorted and connections made after set up.
Dummy load resistor should be connected across outputs during set up.
To set Quiescent Current (Iq):
Voltage across R10 = Iq * R10
Therefore, assuming R10 = 0.51R and required Iq = 200mA
Voltage across R10 = 0.2 * 0.51 = 0.102V DC
Connect multimeter probes across R10 and adjust VR2 until the voltage measured = 0.1V.
To adjust DC Offset:
Connect multimeter probes across the output and adjust VR1 to lowest level of DC.
Other Considerations:
There seem to be some examples of alternative output transistors causing oscillation. I propose using BD937 transistors for Q1 & Q2 as these seem to be a safe option with respect to stability and sound quality and have the same pinout as the MJE3055 devices?
I will be using regulated supplies at +/-15V, which is within the range shown on the PCB.
Suitable heatsinks?
Sorry if this is basic stuff by I am no electronics expert and would rather be safe than sorry.
Thanks
Ray

Very good job at figuring this by yourself. A few details I would do differently ;

1. Adjust DC offset via VR1 while amp is cold. No loads connected to output.
2. Adjust Bias via VR2 while amp is cold. No loads connected to output.
3. Measure bias across R10 like you mentioned, perfect.
4. If your running the amp at +/- 15Vdc instead of +/- 12Vdc maybe the 200mA intended for +/- 12Vdc supply will be different for your +/- 15Vdc setting. Siliconray to confirm.
5. Once amp is warm (wait 1h) repeat step 1-3.

For the heatsink, running your amp at +/-15Vdc gives you 30Vdc at 0.2A therefore 6W of heat to dissipate / channel (3W for Q1 & 3W for Q2). If you need a heatsink maximum temp. rise of lets say 15C your heatsink requirement will be 15C/3W = 5 C/W for a final heatsink temp. of 15C + 25C ambient so roughly 40C.

An exemple : http://uk.farnell.com/multicomp/mc33267/heatsink-to220-218-3-1-c-w-notched/dp/1710610

I built the JLH 2005 power amp using +/- 14Vdc supply, I got 10W/ch. It's a great sounding amp

Keep us posted on your built.

Rgds,
Eric

 

[nautibuoy]

Thanks Eric, that is very helpful.

Upon further consideration, it's easy enough to adjust the voltage of my power supply modules so I will do that and run +/-12V rails. That'll mean I will need to dissipate 2.4W per output device; allowing a temp rise of 25C means a heatsink of circa 10C/W or better (to allow for the inevitable inefficiencies).

I'll update in due course.

Ray

 

[e_fortier]

You are welcome Ray.

Final temp of 50C is on the high side, aiming for a lower value would prolong the life of your output transistors and improve reliability. It's up to you.

Have fun building the headphone amp.

Rgds,
Eric

 

[nautibuoy]

I've got all the parts together now and started soldering up the board today; I have to say that it's a dog to solder though, the ground pads in particular. I don't know if it is just the extremely small pads or the a combination of that and the gold finish but it's really hard to get good solder flow and I keep getting dry joints.

I'm using good quality Stannol brand solder (4% silver, lead free) and a 60W temp=controlled solder station with a very small chisel tip. Never had a problem soldering up boards before.

Anyone else had a problem?

Ray

 

[e_fortier]

I don't know if it is just the extremely small pads or the a combination of that and the gold finish but it's really hard to get good solder flow and I keep getting dry joints.

I'm using good quality Stannol brand solder (4% silver, lead free) and a 60W temp=controlled solder station with a very small chisel tip. Never had a problem soldering up boards before.

Anyone else had a problem?

Ray

Have a look at my comments on post no.72 they are identical as yours...there is no reason for having such small pads soldering becomes a PITA.

If the pads were bigger I would buy one of these board right away.

Rgds,
Eric

 

[nautibuoy]

Yes Eric, PITA is about right. I have the joy of soldering the small transistors in the morning!

Ray