2000 Ohms headphones? Vintage components?

Hi,
what about making a simple amplifier for common low impedance headphones?
An idea is here http://ok1sip.czweb.org/amp.gif

VBR from Ivan

Hi Noli,
yes, an input buffer may increase the input impedance significantly. There is no need to deal with FETs. A follower made of nearly any opamp (a non-inverting amplifier, where the inverting input is coupled directly to the output) has its input impedance in the megaohm range. I tested it successfully years ago (yes, we are in the Memory Lane ) with an old uA709 clone.
A single transistor emitter follower is not much worse. I wonder why you think your AF amplifier has its input impedance smaller than 1 kiloohm. If it has say a 600 ohm line input, it is probable that the impedance can be increased quite much by an appropriate modification of the input circuitry.

VBR from Ivan

Wow, that is some workbench. A friend of mine has all sorts of these test equipment as well. Like your workbench, and the one pictured below, his is the same. No wonder he has a healthy mind.

One of this day Ill pay him a visit and snap a picture then post here .

Back to the high impedance input, should I just make a buffer with high impedance input for my existing AF amplifier?

Best Regards,

Noli - 4G1ZYS

n0th1n6 wrote:... my already messy table haha.

I found this on the web. To me this is organised
This looks something like my my bench.

("A clean desk is a sign of a sick mind" - Albert Einsein)

BR Harry

Ivan wrote:I see no purpose to add a preamp.

Hi Ivan,

The pre-amp is for an existing amp that has lower impedance input. I just don't want to add more clutter in my already messy table haha.

Best Regards,

Noli - 4G1ZYS

Hi Noli,
if the active analog loudspeaker has input impedance somewhere around 1000 - 10000 ohm and suitable sensitivity (usually regulated by a poti), yes, it should do without modifications. The drawback is that it requires a power supply. A bluetooth loudspeaker will never do. I see no purpose to add a preamp.
The similarity between a high impedance headphones and active loudspeaker? Both can change weak electric AF signals into hearable sound.

VBR from Ivan

Hi Ivan,

You mean the active loudspeaker without any modification? What is the similarity with a high impedance earphone? Should a preamp using fet opamp works the same?

Best Regards,

Noli - 4G1ZYS

Hi Noli,
It is hard to test e.g. a crystal receiver without high impedance headphones. The army surplus from the 60es probably came to an end here in Czechia. Fortunately, it should be possible to use certain active loudspeakers instead. Yes, those loudspeakers widely available for use with PC soundcards.

VBR from Ivan

Runem wrote:

Oh I see. Well, if someone are interested, they're still here. I think i can send to almost anywhere in the world, so if/when shipping is payed for, they are yours.

Hi Runem,

Very interesting. Never had one of those since I'm not able to experience the glory days of home brewing.

Would you mind if I ask where you from? Maybe I can afford the shipping fee

BR,

Noli - 4G1ZYS

[quote="Admin"]That was very kind of you and I appreciateit. But since the original post Ivan has already sent me a pair, which I received last week.[/quote]

Oh I see. Well, if someone are interested, they're still here. I think i can send to almost anywhere in the world, so if/when shipping is payed for, they are yours.

Hi Harry,
you were lucky you could have an external LW antenna. When I was a kid, I lived in blocks of flats, built in 1896. There was no chance to erect an external antenna for AM broadcasting or HF ham radio there. The springs as an antenna and a water tap as a ground were probably the best I could have there.

I had a normal weekend. I hope you have much joy with the headphones.

VBR from Ivan

Hi Ivan,
I don't know how sensitive they were in the beginning but they are still very sensitive now.

It was really interesting to hear that age-old and familiar "tinny-click" when you apply a small battery, then to hear the AM broadcast stations with no selectivity. Brought back loads of memories. Thank you once again.

The antenna I was using was a 40-metre long dipole but it is resonant at 3.7MHz, 7.1MHz and 14.175MHz. 39m band was so strong.

When I was a kid I had a 30m long wire antenna up the garden to the clothes post. It was perfect for HF. I long remember having a set of thóse phones and an antique commercial regen receiver that I borrowed. The receiver was loaned to my by a SWL in Rotherham - a good deed for a schoolboy. He pointed out that it was missing one valve (an old HL2) but it took me about a month to source it in those days. But I got the tube with 2-weeks pockey money and the guy came round two days later and took back the wireless

Sorry but I have a lot of memories and they seem to be quite strong with very small sparks. I think it is perhaps normal that with age you have a better recall for early years than more recent memories.

Hope you had a nice weekend. BR Harry

Hi Harry,
when I began with radio, I always heard the strong local Prague station (639 KHz/1,5 MW) only. My "crystal" set (with a germanium diode) did not have enough selectivity. BTW, my antenna were steel springs in my bed ...

I am glad the headphones did not lose their sensitivity during the long storage.

VBR from Ivan

Today I had call to connect a long-wire antenna to my new headphones with a diode and a very crude tuned circuit with the object of making a simple crystal set - a bit of nostalgia.

But when I unplug the tuned circuit I have the phones connected directly to the antenna with the diode and god did that bring back a few memories. I heard the cacophony of all the HF AM channels received at the same time, just the same as I remmebered them from 1961. I was able to pick out the od strong station with unbelievable clarity.

I think that today we have lost a lot of quality experimenting with these low-sensitivity 36-Ohms walkman-style phones. But thanks to Ivan I have got a nice pair.

I will have routine surgery in just over a week and then I will be at home for a couple of weeks. I have a few small battery valves with wire leads, used in hearing aids of the 40s and 50s. If I find the time and energy then you may see a couple of new projects on the homepages, if I feel up to it :-) No promisses, though.

BR Harry . SM0VPO

Runem wrote:If you are still interested, I have a pair here that I don't use anymore.

That was very kind of you and I appreciateit. But since the original post Ivan has already sent me a pair, which I received last week. Now I can get on with a couple of projects I have wanted to do for a few years.

Thank you very much Ivan and Runem.

BR Harry

If you are still interested, I have a pair here that I don't use anymore. Not because they are bad, but simply because they can't compare to my Telefunken EH333's, which is the next thing to "Sound Powered" phones. These were originally 32Ohms, but I rewound them (by hand) to 1.8k per element. Many thousands of turns with 0.05mm wire. The headbands had goat skin on them, but they were halfway rotten and extremely yucky, so I ripped them off. Maybe The Wife can fix something for you(?)
I strongly suspect the phones are of British origin and typical "government" issued.
Send me a PM if interested.
[img=http://s7.postimage.org/qqa23hwev/IMG_0094.jpg]

Ok Ivan, I understand completely. If I had a pair I would covet them as long as I could.

Thinking back I seem to remeber having a pair with chamois-leather covers when I was living in the UK. I also had an AR88 but they and many other items were disposed of by an ex-wife.



Best regards from Harry - SM0VPO

Hi Harry,
this type of headphones is still quite frequently sold in OK and OM. The are 4000 ohm, construction comes from the end of the 50s. They were widely used with military radio equipment for a long time. To be honest, they are not much comfortable. And yes, they were often completed with a straight Morse key of similar construction.
Sorry, I do not want to get rid of those I have.

VBR from Ivan

They're available on ebay, am pretty sure of it.

Also have a vague memory of Ivan mentioning something about these a while back, around the same time we were talking about a guy over there selling czech made morse keys.

http://www.ebay.co.uk/itm/GENERAL-RADIO-Crystal-Set-BBC-Headphones-WKG-2k-Radiophone-Headset-Wireless-/140895303230?pt=UK_Collectables_RadioTelevision_Telephony_SM&hash=item20ce03b63e

Bit pricey, and they usually have a better selection. Just a case of biding your time I think

Hi again,
Does anyone know of a source of those old Hi-Z headphones that you used with older equipment?

I have a pair that were "retro made" in that they are plastic and stainless steel band. Does anyone remember the ones that that you could actually wear on your head without getting pressure sores after 5 minutes?

The nearest I have found today was early in-flight headphones when the phones used a single plug with two mono-jacks moulded into one housing. I stole a pair from BA in about 1983 and was very surprised that they were all Hi-Z. Perhaps that's why the stewardesses went round and collected them after the flights! - They probably had radio hams as passengers before. The last pair I got were provided for a price and that was SAS and they are most definitely low impedance.

Alternately, if anyone has a pair they want to get rid of then I would be grateful.

BR Harry - SM0VPO