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Old 23rd September 2013, 01:48 PM   #21
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Quote:
Originally Posted by agdr View Post
That is the overall voltage gain on the O2 since the second stage is set up as a unity gain (voltage gain = 1) current buffer. Only the first stage provides voltage gain.

That makes perfect sense now that i look at the circuit diagram, so basically the 2068 chip does the amplification, then the two parrallelled 4556's add the oomph. Question though, whats the purpose of the tiny 1ohm resistor on the outputs?

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Originally Posted by sgrossklass View Post
As guidance on how much gain you need, this table here may be helpful. The ODAC basically delivers CD player output level, so you can apply the results as-is. Grados are listed with -7 dB, so unity gain is plenty.
Another interesting read, thanks. I only noticed last night the silk screen on the PCB says 464r not 464k, and sure enough when i dug out the parts bag a 264 ohm resistor was supplied with the kit. I swapped them in for a test and confirmed 1x gain is spot on, 12 o'clock on the volume is around my comfort limit.

Back to your original post, and playing with your website does 464r for Rf, 121k for Rg, and a 10k pot sound like a suitable combination? Using the calculator on your site those figures give me nice low noise and 1x gain. I am just unsure on the relationship of Rg vs other components, and i cant really see any gains from raising or lowering that value. Should it closely match the value of the pot or whats the theory behind it?

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Originally Posted by availlyrics View Post
You have got it all wrong. See attch. I hope you are not using HD650 for testing Use only elcheapos h/p
The switch supplied with my kit is a two pole, double throw, i.e. 6 pin. I assume the intention was to wire both the + and - rail through the switch. I totally agree, use crappy cans while testing as i have experienced the missing rail popping sound first hand, not pleasant to the ears or the cans. I've also noted on my scope the - rail takes longer to discharge on power down so you get that imbalance and noise when powering off. As i have read its always good practice to disconnect the headphones before powering on or off for that reason. Personally i will NEVER plug my HD650's into this amp, just no.

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Originally Posted by coffin View Post
Hi, Inside the wood chassis of Ra1, what is the paint applying on surface? It must be conductive, but what is it?
I would like to know too as i was thinking about a wood cigar box enclosure, as an alternative i was thinking of lining the box with some of this..

2m Adhesive Copper Foil EMI Shield Tape Conductive 50mm width | eBay
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Old 23rd September 2013, 04:00 PM   #22
agdr is offline agdr  United States
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Quote:
Originally Posted by prezden View Post
This is how I have it now but I don't think the switch connection is right.
I was guessing you may have wired it up that way, with one (or two) batteries into the PCB +/- terminals and no center ground connection.

availlyrics' diagram will fix up your circuit. Another is below. You don't use 2 of the 6 terminals on the switch. Their connection diagram on the website is also not clear that the center connection between those two batteries (ground) connects to that common connection of the B, C and "2" parts. There should be a hole on the PCB marked "ground" or with a ground symbol that connects to that point.
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Old 23rd September 2013, 04:10 PM   #23
agdr is offline agdr  United States
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Originally Posted by mcandmar View Post
That makes perfect sense now that i look at the circuit diagram, so basically the 2068 chip does the amplification, then the two parrallelled 4556's add the oomph. Question though, whats the purpose of the tiny 1ohm resistor on the outputs?
That is right about the 2068. To be more exact you can say that the NJM2068 stage does "voltage amplification" while the NJM4556A stage does "current buffering" (sources or sinks more current but provides no voltage gain).

The 1 ohm resistors act to balance up the two sections of the NJM4556A that are being paralleled. Without the 1R's the two sections can "fight" with one section trying to sink/source a lot more current than the other.
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Old 23rd September 2013, 05:30 PM   #24
prezden is offline prezden  Canada
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Thanks availlyrics- Now I see how it goes. I didn't have any build instructions or even a picture of the completed amp. And no I haven't used any good phones fortunately.
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Old 23rd September 2013, 11:06 PM   #25
prezden is offline prezden  Canada
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Thanks again for your help
I think I have it wired correctly but can't get the switch to work properly. With the 2 wires from the board on one side of the switch it will not turn on. If wired to the other side it will not turn off
Any suggestions?
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Old 24th September 2013, 12:40 AM   #26
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I just buzzed my switch out with a DMM for sanity sake and that should work, sounds to me like the switch is faulty and stuck in one position.
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Old 24th September 2013, 01:54 AM   #27
agdr is offline agdr  United States
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Yep, bad switch. That is wired correctly now.
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Old 24th September 2013, 02:44 AM   #28
prezden is offline prezden  Canada
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Thanks - that's what I was afraid of. I'll have to put it on the shelf until I make another order to DigiKey.
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Old 24th September 2013, 05:33 AM   #29
prezden is offline prezden  Canada
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I have been looking at switches and all I can find for the two pole double throw switches are on-on or on-off-on or on-on-on which means that either on side is on at a time or both at once without an off possition. What kind of switch allows you to turn on/off both sides at the same time or is it a different wiring that is required?

Here are some sample layouts that I found. Have to admit it's rather confusing
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File Type: jpg s2.jpg (29.0 KB, 113 views)
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Old 24th September 2013, 05:42 AM   #30
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The original switch is a two pole on-on type, power in the center pins, depending on the switch position the output is directed to the top or bottom row of pins, if you only connect one row of pins it functions as an on/off switch.

Its a toggle switch basically, then the on-off-on and on-on-on switches have a middle position where they dont direct power to either sets of pins.

Last edited by mcandmar; 24th September 2013 at 05:45 AM.
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