juke
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Post by juke on Sept 1, 2013 22:12:16 GMT
If you want more travel on the volpot what may be best is to make a voltage divider. I assume it is playing MORE than loud enough with the adapter as it is now. If you make R1 and R2 33 Ohm the whole volume will come down 5dB (max SPL will be 108dB) When you want even less power make R1 = 47 Ohm and R2 = 22 Ohm (as if you are driving 500mW headphones) this will lower the volume by 10dB (that is half as loud). Max output power will be shrunk to 0.4W though. You will still get a very respectable 103dB SPL with that though. The HE6 It is very loud after maybe 1/6 of the dial's rotation. I'll order up some 33ohm resistors tomorrow. What watts do they need to be? The last line, beginning "The HE6" is missing, anything important? Thanks Frans, I'm really looking forward to sorting this.
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solderdude
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Post by solderdude on Sept 2, 2013 4:58:12 GMT
I guess I didn't remove that while editing that post earlier....
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juke
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Post by juke on Sept 8, 2013 10:27:14 GMT
Hi Frans The resistors arrived yesterday and I tried both ways. Turned out the 47/22 combination is best. The volco position 'dot' starts at 6 o'clock on this amp and with these resistors the usable range is 6 to around 10 o'clock, can stretch to 12 but you wouldn't listen for long. So much easier to make a small adjustment to volume, and a remote too. It's proved a really worthwhile exercise and put the lovely Sugden into use for the first time since I bought it about three years ago. I just need to get some thin replacement cable to make a longer lead from the Sugden to my listening chair, assuming I work out how to wire the spare screw-on connectors where it joins the HE6. Thanks for your advice, again! Syd
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Post by ajdelaghetto on Apr 20, 2014 7:51:24 GMT
I need help on my project, I brought 1 of these "5V Power Audio Amplifier Board" ( Link) and I'm planning to make a small headphone amp with it. I also brought this "Resistor Assortment" ( Link) and these "3.5mm Socket Panel Mounts" ( Link). I have a project box ready and will be using a 5V 2A power supply. I already know one of the "3.5mm socket" will be hook up to L, G, R on the "Amplifier Board" for audio input. I also know "Rout -" and "Lout -" will be ground connected to the second "3.5mm socket" for audio out ; "Lout +" is left audio (tip) and "Rout +" is right audio (ring). I using this guide, ( Guide Link). So what should be my "R1" and "R2" resistors for my project? I want to use it for many type of headphones I have, sometimes ear buds. Power Amplifier Specs: Operating voltage: 2.5V-5.5V Maximum output power: 3W*2(5V 4Ω) PCB size is about: length 30mm width 22mm overall height after installed is about 16mm Built with switch Potentiometer,can adjust the volume & control power switch freely! Flexible assembly usage.
Headphone A Specs: Frequency range: 20 to 20.000Hz Sensitivity: 113±3dB at 1kHz Distortion: Ω5% THD Magnet size: Ω15.5 x 2.0mm Impedance: 32 Ohms ± 15% Input power: 30mW (maximum)
Headphone B Specs: Frequency Response: 20 – 20,000 Hz Impedance: 32 Ω at 1kHz Sensitivity (@1khz, 1V/Pa): 110 ± 4dB at 1 kHz Max Input Power: 50 mW
P.S. If the set of resistor I brought won't work I can buy different ones.
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solderdude
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Post by solderdude on Apr 20, 2014 9:52:21 GMT
The problem here is that this specific board is designed to be used with (not high quality) speakers. Running of 5V means they used a 'bridged' output config. It is a class-D amplifier with a rather high typical distortion (class-T does better in this department). The warning in the bottom of the tutorial is applicable here. You will not be needing voltage division resistors at the output of this amp unless you are planning to use some really sensitive low powered earphones in balanced mode. For this reason you cannot use this board for driving headphones with a 3-pin plug directly as there is no 'common' that has half the supply voltage on it which is needed in this case. Of course there are some ways around this and can choose 1 of the solutions below: 1: you will need 2 boards to get it working and use one channel of the second board to act as a '3rd channel' 2: need to modify your headphones for balanced operation (4 pin plug and 4 wires in the cord). 3: need to use 2 output coupling caps (2200uF/10V), but will hear a 'thumb' in the headphone when switching it on/off. The output power will be quite limited as max output voltage will be 1.6V = 0.08W when dual boards or output caps are used but seems enough for your headphones When the headphones are modified (4 wire cable and different plugs) it will be able to provide 0.3W. Let me know how you would like to proceed with the build (options 1,2 or 3 above).
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Post by ajdelaghetto on Apr 20, 2014 17:11:29 GMT
Thanks for the reply. Option 3 please
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solderdude
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Post by solderdude on Apr 20, 2014 17:51:25 GMT
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Post by ajdelaghetto on Apr 20, 2014 19:42:29 GMT
Thank You so much!!! Would these capacitors ( Link) work? Also I have this exact 1/4W resistor set ( Link) but it doesn't have 100 ohm, can I use the 82 ohm one. If not, what wattage of 100 ohm resistor should I buy? Will these 2W 100 ohm resistors work ( Link 1) or ( Link 2)? If yes, should I buy Carbon Film or Metal Film?
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solderdude
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Post by solderdude on Apr 20, 2014 21:47:30 GMT
Those caps will work fine. Any voltage rating between 10V and 35V is O.K. The higher the better but higher voltage ratings are also bigger in size.
The resistor can be 82 Ohm, values up to 270 Ohm could also be used. They are only there to bleed the caps when no headphone is connected and supply a minimal load. 1/4W is more than sufficient. Material doesn't matter at all in this application. The ones from the resistor kit will do fine, strange it doesn't have 100 Ohm, it is such a 'standard' value.
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Post by ajdelaghetto on Apr 20, 2014 22:03:58 GMT
I just order the caps and the power amplifier board should arrive in a week since its coming from China. I let you know how the project goes and if I need any help. I very appreciate the help. Thanks!!
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solderdude
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Post by solderdude on Apr 21, 2014 6:50:04 GMT
You can reduce RFI somewhat as well (if you feel the need to comply to rules) The Chinese board is kind of 'basic' and lacks any form of RFI measures. Your headphone cord will form a 260kHz/780kHz/1.3MHz RFI transmitter antenna. The board is intended for direct connection to speakers in a small enclosure with short wiring.
1: Mount another 2200uF (I thought you were buying 4 of those) directly across the 5V power supply pins (+ and -). 2: Use small ferrites on the wires going TO the headphone socket. 3: Use a metal enclosure and connect that enclosure also to the - pin of the power supply. 4: Mount small 56pF caps (must use the ferrites in this case) directly on the output socket between the tip and ground, and one from ring to ground.
If you are going to feed the board with an external power supply I highly recommend to mount a (x Amp) Schottky diode in REVERSE over the 5V input (so cathode connected to the + terminal and anode connected to the - terminal). Where the x (in X Amp) needs to be higher than what the power supply can deliver so if the PS is 2A the diode must be 3A (or higher). It MUST be a LOW voltage drop SCHOTTKY diode.
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Post by ajdelaghetto on Apr 21, 2014 17:55:47 GMT
I brought 10 of the caps ( Link) Will these Schottky Diode ( Link) work? Will these 56pF Capacitors ( Link) work? Here's my template so far: I'm having trouble understanding step 1-4, please feel free to add on to the image.
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Post by ajdelaghetto on Apr 21, 2014 18:38:16 GMT
Is this what step 1 & 4 looks like?
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solderdude
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Post by solderdude on Apr 21, 2014 19:04:11 GMT
the caps and diodes will do but you don't need a 100 caps. You could try to sell the remaining 98 caps in smaller batches though. Perhaps the same with the diodes. Some 5V/2A wall wart power supplies may not like 2200uF as a load. When the power supply doesn't start, hick-ups or produces weird sounds (in the headphone) try it without the added capacitor. Of course many power supplies do not struggle with 2420uF capacitive loads though.
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Post by ajdelaghetto on Apr 22, 2014 0:34:27 GMT
I brought the items, when everything arrives I let know how the project goes. By the way, since I have 2 of the power amplifier coming in and have more than enough supplies for 2 builds. I was wondering if I can make it in to a single build in one project box. With 2 Amplifier Boards, 2 3.5mm Socket Input, 1 Power Supply, but 1 3.5mm Socket Output. I already measure the dimension of the project box I have and its more than enough space for 2 boards. Will it work? What are the problems?
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