How to interface to the GRAM socket?

[Geaney]

Hi Everyone, where I live I can pick up very few english language stations. I'd like to play some of the oldies through my radios via the GRAM input but don't know how to interface something like a modern mp3 player to it. I've got three PYE sets (2 x P53 and an unknown) but the headphone output of the mp3 player doesn't work on any of them. I know the ideal approach is to build and AM transmitter and I may try that at some stage. In the meantime any suggestions/pointers on how to get the correct impedance/level match would be most appreciated.

Thanks, John

[tiv48]

hi john do you get any output at all ,most gram inputs are for high output ceramic or crystal cartridges ,so as you surmise there is an impedence mis match, in practice it will still work well. what happens if you touch the input with your finger? do you get a hum.
try conecting a 100k resistor in both the left and right hot wires from the mp3 player and conect the grownd wires together to create 1 mono feed, hope this some help
rob t

[Geaney]

Thanks Rob, I'll give that a try and post the results. At the moment I get very faint output with lots of noise so not useable. Interestingly on the fist P53 it seemed to work quite well when the RF section wasn't working. I replaced a valve and got the receiver working but then the gram input didn't work - strange.

John

[Mark Hennessy]

Hi John,

Is your Gram input on a phono socket? If so, it's possible you're not using the right sort of phono plug; the older ones had a much longer centre pin, and the modern ones don't reach the right part of the socket...

Don't worry about level or impedance at this stage; you should easily get enough signal from the headphone socket of an MP3 player to get a reasonable signal. The faint noise you get might indicate that you're only getting capacitive coupling from a plug that isn't quite reaching the socket...

Mark

[tiv48]

i dont think a pye p53 woul have phono sockets far too old
rob t

[tiv48]

correct jamie two holes that take wander plugs
rob t

[tiv48]

i have just tried my iphone 4 with my pye p45 using a jack plug to 2 phonos ,using one channel only to a phono socket and two wires with wander plugs works fine ,(distorted at high output from i phone)
rob t

[Geaney]

Major thanks Rob, the couple of 100K resistors got me 90% of the way - plenty of level but still not much treble. Since I had the P53 chassis on the bench I removed the .01uF shunt capacitor from the Gram input and bingo, works a treat. I'll do the mod to the other radios when I get a minute.
Cheers, John

[Geaney]

Thanks Guys, The suggestion from Rob got me 90% of the way - plenty of level but not much in the way of treble. Since I had the P53 chassis on the bench I removed the .01uF shunt capacitor from the gram input and bingo, works a treat. I also discovered that part of the noise problem was radiation from the small fluorescent light on my bench. I think I'll remove that shunt cap from the other radios as well.
Cheers, John

[Joe]

Hey, Jamie, that DIN connections chart would be handy in the Service section along with any similar things you've got - I notice it's number 3.

I've always had to resort to trial end error with those and am pleased they seemed to have a fairly brief main-stream life. The most modern things I can recall them being on were the 5-pin version on PC keyboards until the mid-90s.

- Joe