one of the things i like about headphones is the 3D soundstage in your head and i like to hear things placed in that soundstage within my head, what i dont like as you put it is "blobs-in-the-ears" effect where you just get left/right at your ears. having the soundstage out of my head would be weird but intresting. i always close my eyes while listening to headphones as it send me away to a distant place.
Two of the first things that come to my mind when talking about increasing the bias current are: 1) you are less dependent on your PSU high-frequency response since you go more class-A and 2) perhaps this lowers the effect of Hfe's non-linearity.
Have anyone tried transistor rolling like BD137/BD138 instead?
Have anyone tried transistor rolling like BD137/BD138 instead?
BD135,137 and 139 are exactly the same, but for the different voltage rating. BD136, 138 and 140 ditto. I have not tried any other family. Contrained to the same package and pinout there are not too many viable options.
"more class A" does not change the magnitude of signal current, only the ratio of the signal to static currents. I don't think you can say it would be "less dependent" on the power supply. But yes, the output stage does become more linear. In theory anyway.
"more class A" does not change the magnitude of signal current, only the ratio of the signal to static currents. I don't think you can say it would be "less dependent" on the power supply. But yes, the output stage does become more linear. In theory anyway.
Hello, rjm.
I don't say "less dependent on power supply", I say "less dependent on power supply high-frequency response capability" meaning with a more stable current draw, more power will be already there for sharp changes in the signal. In the opposite case, your power supply will have to be able to provide quickly more current, i.e. low impedance on high frequency. This is more hearable on class-B amps, creating more muddy/smeared picture.
You say BD135 = BD137 = BD139 are same but with different voltage rating. Hance, despite the datasheet may state the same current figures, capacitance and transition frequency figures are missing and this is what makes difference, not some voodoo magic. And as these are omitted, they might be actually different. I am curious about the 137/138 combo.
I don't say "less dependent on power supply", I say "less dependent on power supply high-frequency response capability" meaning with a more stable current draw, more power will be already there for sharp changes in the signal. In the opposite case, your power supply will have to be able to provide quickly more current, i.e. low impedance on high frequency. This is more hearable on class-B amps, creating more muddy/smeared picture.
You say BD135 = BD137 = BD139 are same but with different voltage rating. Hance, despite the datasheet may state the same current figures, capacitance and transition frequency figures are missing and this is what makes difference, not some voodoo magic. And as these are omitted, they might be actually different. I am curious about the 137/138 combo.
Hi RJm, thanks in advance for making such a great built log.
As an Electrical engineering student and audio enthusiast, I decided to build this amp to power my hd650, which is currently being run from my pc output!
I`ve bought all the components and I`m on the protoboard stage..but I have a doubt: Could you please explain what are the C15b1 and C15b2 on the schematics and what are those X that these caps are connected on?
Also my V+/gnd is 16.50V and V-/gnd is 16.51V, are these acceptable values?
Thanks!
As an Electrical engineering student and audio enthusiast, I decided to build this amp to power my hd650, which is currently being run from my pc output!
I`ve bought all the components and I`m on the protoboard stage..but I have a doubt: Could you please explain what are the C15b1 and C15b2 on the schematics and what are those X that these caps are connected on?
Also my V+/gnd is 16.50V and V-/gnd is 16.51V, are these acceptable values?
Thanks!
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Thanks! Now before you get too far into this, please note that the schematic (reproduced below) is just a guide thats produced in the process of making the board layout. For the actual parts values please download and follow the BOM list.
EagleCAD doesn't always have the exact parts, and sometimes I neglect to keep the values current.
The schematic below is correct as of this post however.
C15b1 and C15b2 are just the alternate pads for connecting the capacitor C1.
D1 and D2 are 12V Zeners. The input voltage V++ and V-- need to be at least +/-14V. +/-18V is the nominal design value. At around 14 V R15 R16 should be lowered to 500 ohms or so to keep enough current flowing through the Zener. Or use a 9 or 10 V Zener instead of 12 V. The circuit can be adapted to run at even lower voltages, just reduce R7, R8 to match.
EagleCAD doesn't always have the exact parts, and sometimes I neglect to keep the values current.
The schematic below is correct as of this post however.
C15b1 and C15b2 are just the alternate pads for connecting the capacitor C1.
D1 and D2 are 12V Zeners. The input voltage V++ and V-- need to be at least +/-14V. +/-18V is the nominal design value. At around 14 V R15 R16 should be lowered to 500 ohms or so to keep enough current flowing through the Zener. Or use a 9 or 10 V Zener instead of 12 V. The circuit can be adapted to run at even lower voltages, just reduce R7, R8 to match.
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One more for the collection!
An externally hosted image should be here but it was not working when we last tested it.
after much messing i finally got my Sapphire working. the problem was i had 3 of the transistors the wrong way round. i only worked it out after looking at the PDF of the devices and noticed that the emitter pins were the opposite way round. the confusion was me and my dyslexia not understanding Richard's instructions properly. all the transistors decals should be facing outwards e.g. the 3 dimples = front and the emitter is the left hand pin.
my giddy aunt this thing is fantastic. i have a dodgy headphone socket but apart from that i'm delighted. thanks Richard for such a nice headphone amp.
my giddy aunt this thing is fantastic. i have a dodgy headphone socket but apart from that i'm delighted. thanks Richard for such a nice headphone amp.