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Post by dicky on Dec 30, 2012 13:52:49 GMT
Hi Folks, I've been rummaging around in my loft and found my old Naim NAC 22/NAP 120 (40W into 4 ohms). I've opened the cases up and they look very good inside (hopefully some pics attached). As I remember, it was a lovely little amp and I was wondering if I could use it to drive my AKG K340? If so, would I need to protect the headphones in any way - or just connect them straight to the speaker terminals and go easy on the volume levels? Regards, Dicky
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Post by Deleted on Dec 30, 2012 14:06:30 GMT
You can connect direct but it probably won't sound to good. I tried that once and there was a lot of noise. You also have to be very careful about the volume.
On some amps, the headphone out is merely taken from the speaker output with a resistance in the way, which isn't really the best for headphone sound.
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Post by Deleted on Dec 30, 2012 14:52:34 GMT
Wow, they look in great condition and are approx. 35yrs old? Nearly completely original, AFAICS just the 'speaker terminals have been changed. Might be worth a few bob to a collector or Naim devotee. I've been thinking of getting a bit nostalgia for the restaurant, either an old receiver like the Marantz/Rotel/Sansui or an old Exposure/Naim pre/power. Need a bargain though! Miguel runs a Marantz receiver for 'phones and a couple of gents run Sansui integrateds the same way, hopefully they'll be along soon.... Found this;
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Post by dicky on Dec 30, 2012 15:18:16 GMT
Hi cj,
I've owned them since 1982. In 1984 I re-capped the NAP, changed the LEDs for green (I hate red LEDs) and swapped the banana speaker connectors for Michell posts. I seem to remember reading somewhere that people were connecting 'difficult to drive HPs' to power amp speaker terminals.
Not that I'd sell them - but what do you think they're worth?
It'd be a shame to put them back in the loft, but other than driving HPs, I have not use for them.
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Post by Deleted on Dec 30, 2012 15:58:34 GMT
The Nac22 is the less valuable of the pair (although you'd want to sell them together, if at all).
Most Naimees like to buy there stuff totally original or "approved" maintained.
The nac22 should get anything from £150 to £200 and the nap120 amp, which is up there with all the other favourites, should pull £250 to £300.
As a pair that could go up or down dependant on market mood.
Of course in Spain they're only worth €50 each ;D
Float them over on PFM where the Naimees live for the best chance of a good price.
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Post by dicky on Dec 30, 2012 16:30:39 GMT
They're not for sale. It's either HP use or back in the loft. I suppose I need to check for any DC on the output before I make the adapter cables up.
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Post by pandapops on Dec 30, 2012 20:08:26 GMT
There are a couple of other things you can do but only if you really know what you're doing, in other words if you have to be told, it might not be a good idea. That said:
1. reduce the gain and improve the gap between the signal and noise floor, only do this if the amp is stable enough. I wouldn't do that as I wouldn't trust the amps to be that stable and don't have knowledge or equipment to do the testing. In general a lot of people are running headphone amps with way more gain than they need, if you're volume control never gets to 12 o'clock then you're one of them.
2. reduce the bias current to the output transistors, not sure that this would improve the sound quality at all but its an approach that people have taken in the past.
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Post by pcourtney1 on Dec 31, 2012 18:41:32 GMT
you really need to recable your K340 with four wire cable, you can then safely connect them to your speaker terminals (no need to bother with grounds that way) I have had my K-340's running off speakers terminals on various amps up to RMS 60wpc, so your Naim will be fine The pins on the 340 are numbered like so : pin1 = left signal. pin2 = left ground pin3 = right signal. pin4 = right ground The 340's are 360ohms nominal (I measured mine and they were 320ohms) They will happily cope with 30Vp-p or 10Vrms when I saw this from Jason about a tube amp design for the 340's users.livejournal.com/_philodox_I had my 340's cabled back to 3 wire and plug to go into the front of my X-Cans V2, I must admit though that the 340's sound really nice when connected to a nice amp, and I think your Naim amp could be perfect, please let us know what you do I have another K-340 and I am thinking about recabling to 4 wire again and mating to a nice old amp, having said that I know quite a few people who really rate Tripath amps with the 340's, so I may look at that as an option as well
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Post by dicky on Dec 31, 2012 19:45:36 GMT
Thanks, the cable is already 4-wire so I'll terminate with an XLR connector and make a couple of adapters - one for speaker terminals and one for 1/4" jack.
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Post by dicky on Jan 1, 2013 11:54:43 GMT
OK, so I've popped a 4-pin XLR on the 340's and made up a speaker fly-lead. However, I measured the DC on the speaker terminals which was in the region of 23mV. This is quite high compared to my Panda which is around 2mV. Will this level of DC damage the 340s?
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Post by pcourtney1 on Jan 1, 2013 17:38:48 GMT
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Post by dicky on Jan 1, 2013 18:40:02 GMT
Thankyou. It looks like I'm borderline then. I might just pop a 470uF cap in series - just to be safe. I assume non-polar refers to a BP electrolytic? I'm not sure how the resistance power equation helps here?
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Post by pcourtney1 on Jan 1, 2013 22:28:47 GMT
the service docs can still be downloaded from AKG www.akg.com/site/products/powerslave,id,668,pid,668,nodeid,2,_language,EN.html Impedance @ 1kHz: 361 Ohms Power Needed for 94 dB (SPL) 2.5 mW Volts RMS required to reach 94 dB SPL: 1 Vrms this thread also makes a point that testing for channel imbalance around the 3kHz area might be in order ( luckily my pair don't seem to have that problem, but I should really find a way to test for it to be sure) www.head-fi.org/t/635290/akg-k340
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Post by pcourtney1 on Jan 1, 2013 23:26:16 GMT
I'm not sure how the resistance power equation helps here? the wish for low dc offset isn't so much a quest to keep the coils from overheating, it's more about maintaining as much dynamic range as possible with the 340's after all, the dc offset will push (or pull) the coil away from its resting position, reducing the total excursion in one direction while uselessly increasing it in the opposite. if you want to calculate this yourself, it's simply Ohm's law: P=(V^2)/R NB If V is in mV, then P will be in uW
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Post by Deleted on Jan 2, 2013 0:21:33 GMT
Personally, I would do something similar to the drawing that Chris provided. As Ian noted, unless you attenuate the output as Chris has shown, you wll hear quite a bit of noise, and risk damaging both the headphones AND your hearing ! You could always put it all in a little Jiffy box with a 6.3mm headphone socket, and and 4 banana sockets for the short incoming output leads. You would need 4 banana plugs too, but cheap plastic ones don't cost much more than $1 each.
Alex
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Post by Deleted on Jan 2, 2013 10:26:20 GMT
I found that headphones don't sound right as well. It's probably something to do with the output impedance. I don't know.
In my case, when I tried it, the sound was noise ridden and very hefty in the bass.
The only reason I tried it was that I wanted to have lots of power available for the headphones in order to drive them better, but for me, it wasn't worth the trouble.
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Post by dicky on Jan 2, 2013 11:58:50 GMT
Thanks everyone for your replies. I'm keen to give this a try - at worst it'll cost me a few resistors and some wire; at best it'll give my little Naim something to do. And, if I use Chris' diagram I'll be less likely to damage the HPs and shouldn't have increased noise problems that Ian has mentioned. However, I'd like to clarify the diagram. For each channel at the amp end the screen and 2 of the 4 conductors are connected to the -ve of the channel. Then there is a voltage divider which taps off some of the output which would connect to the 1/4" jack Tip. So, in wiring the 1/4" jack there would be 2 pairs of ground connectors AND both screens connected to the Sleeve. Could someone confirm this is correct? Also, what is the reason for having so much (5 - 10 feet) of cable -is this necessary? Could I build the resistors into a box with short leads to the amp and an XLR chassis plug to connect the HPs to the box? Thanks again for your help and suggestions. Dicky
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Post by dicky on Jan 2, 2013 12:51:32 GMT
If the Naim produces 40W into 4 Ohms (RMS) then that equates to a supply voltage of 12V.
So, using Chris' diagram the output voltage supplied to the headphones would be 12*2/22 = 1.1v and the resistor would be dissipating about 0.6W and the 20R would disspate 6W. This seems a little low and would only produce 94dB - should I change the voltage divider to provide more voltage to drive up to 112dB @ 160mW (or 200mW max)?
Also, if I build this into a little metal box, I guess I won't need a great length of screened cable?
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Post by dicky on Jan 2, 2013 19:01:39 GMT
OK, bear with me, guys as I'm trying to get to grips with dBs, voltage and power etc. The spec sheet for the AKG K340s states the SPL is 94dB @ 1v. So to get the maximum specified SPL of 112dB that requires an increase of 18dB or ~8x voltage. So the amp needs to generate ~8v to drive the 340s at max SPL? The voltage divider values in Chris' diagram will only produce 1v across the output resistor. If I change the 2R resistor to 33R that would give ~8v (170mW). Is any of this correct, or am I barking up the completely wrong tree?
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Post by Deleted on Jan 2, 2013 20:45:58 GMT
OK, bear with me, guys as I'm trying to get to grips with dBs, voltage and power etc. The spec sheet for the AKG K340s states the SPL is 94dB @ 1v. So to get the maximum specified SPL of 112dB that requires an increase of 18dB or ~8x voltage. So the amp needs to generate ~8v to drive the 340s at max SPL? The voltage divider values in Chris' diagram will only produce 1v across the output resistor. If I change the 2R resistor to 33R that would give ~8v (170mW). Is any of this correct, or am I barking up the completely wrong tree? Dicky Just because the headphones will go to a maximum SPL of 112dB before self destructing, doesn't mean YOU should , especially if you value your hearing! Those values don't need to be set in concrete. You could get a little more level by simply changing the 2 ohms resistor (usually available as 2.2 ohms) to 3.3ohms. The leads from the amplifier to a plastic Jiffy box (or metal if you are paranoid) could be quite short, with banana plugs on both ends.You could use red and black plugs for example, and 2 each of red and black banana sockets on the box. The other side of the box could have a normal 6.3mm stereo socket.The resistors could be mounted using a couple of 5 pin tag strips to keep them suspended without heating the box. The larger value resistor shouldn't get overly hot with most source material. Of course, if you like listening to high level sine waves , or highly compressed MP3s at high SPLs....... Ask Miguel what levels he normally listens at, to avoid hearing damage. Regards Alex
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Post by dicky on Jan 3, 2013 7:53:01 GMT
Thanks Alex, I assume then that the *additional* 18dB is for headroom?
I'll buy some bits and see what happens.
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Post by Deleted on Jan 3, 2013 8:28:11 GMT
Thanks Alex, I assume then that the *additional* 18dB is for headroom? I'll buy some bits and see what happens. Don't forget too, that as headphones approach anywhere near maximum SPL, they are likely to have high distortion and vibrations/rattles etc. Remember also, where the SPL in the chart may be at a 1M distance from a speaker or whatever, headphones couple directly to the ear canals.
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XTRProf
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Pssst ! Got any spare capacitors ?
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Post by XTRProf on Jan 11, 2013 22:48:45 GMT
Just to take note. Your hp is at about 300 ohms. So you will get much lesser power than 40w from the Naim. Email Prof Frans as I think he has a program to simulate what power you will get at various hp resistances and amp powers.
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mrarroyo
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Our man in Miami!
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Post by mrarroyo on Jan 12, 2013 14:25:54 GMT
You guys/gals will be deaf at those high volumes! I listen at 62-68 dBs and it is a very comfortable listening level plus it helps to prevent hearing damage.
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Post by dicky on Jan 12, 2013 16:23:33 GMT
Sorry, say again .......
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