Now that my Radioplayer is back in full voice, I'm looking for the best way to connect standard line-level source to the old pickup terminals. First connection will be a FM tuner, and I'd like to leave it permanently connected.

I remember this radio being permanently connected to the passive magnetic pickup of the family gramophone, with no additional components and with quite a long shielded lead. It also drove a 10" external speaker quite nicely.

When I directly connect the RCA-plug line to the pickup, with the device turned off, I get an immediate drop in radio volume of around 5db. That's not acceptable for a permanent setup, even though the external signal amplifies quite reasonably when I tune the radio off signal.

The pickup positive terminal carries the negative bias voltage of -2.7v relative to ground, and I think the bias is being affected by connection to the external source device, and maybe pushing up the AGC.

I'm looking for a practical way to overcome that. I'd like to avoid having to use an external switch, but will do so if I have to.

Maven

I have not looked at the circuit but, I would consider that if there is bias required on the valve via the pickup, it would have likely been a magnetic cartridge as it will pass DC. Others and capacitors will not.

You may need an audio transformer?

Marc

I'm a bit puzzled because I would have thought that the coil of a magnetic cartridge, with one end connected to ground, would be shorting out the bias voltage - unless it had a high resistance/impedance.

I tried putting a potentiometer in series between the positive pick-up terminal and the external source. At highest resistance the internal radio signal came through the amp at normal volume and the external source was at zero. At lowest resistance, vice versa. My aim would be to have both signals connected in parallel, the way it worked with the old magnetic phono input. You "mixed" the phono signal higher by tuning the radio off-station. So both signals were always present on the amp circuit.

Maybe the lower-impedance circuits of modern devices rule out that balance, and a switch is the only practical way to do it?

Maven

You'll need to add a capacitor in series with the line level input to isolate the DC bias you have. Something in the order of 0.1μF (100nF) may work well but you may need to try either half or double this value if you find the tonal range is a bit off balance (ie, loss of treble or bass response).

I tried the capacitor-in-series over a wide range of values and it didn't seem to work. With higher cap values, the radio tuner signal is completely suppressed. With lower values, more signal is maintained. At pf values, the tuner signal is not affected, but the external signal is suppressed.

Since this is a negative bias situation, I tried the cap in series with the negative (chassis) as well as with the positive. No apparent difference.

I'm wondering whether a filter cap or circuit across the external source might be sinking the internal tuner signal, as if it were interference. The old magnetic pickups didn't have any filtering on them, just grounded shields. The RCA audio line standard is unbalanced connection.

For the time being, I've put a single-pole switch in series with the positive pickup terminal, so something can remain plugged in without affecting the radio tuner signal. Because I want this switch out the front, but not on the cabinet, I put the toggle switch on the end of a reasonable length of two-core shielded audio flex cable, so leading the pickup signal out one core and back the other, when switched on.

I'd still prefer a proper electronic solution, if possible.

Maven

What model was that again?

Do not like the terminology of the positive terminal, with negative on it?

I note that I will need to do something eventually with the AORSM's on CD as Win8 and the XP patch will not run it.

Old computers will and Linux .... needs a new batch of reader files.

Marc

I too am starting to get a bit concerned about what's going on and I went back and checked the circuit for the Philips Model 123.

This radio does not have an external signal input provision so I'm wondering how the phono pickup was previously wired into the radio.

Can you tell us how the external input is connected to the radio (i.e. to what component and which end). Due to the complex feedback arrangements used in this radio an external input is not very straight forward as you are starting to find out.

Sorry if my terminology is confusing.

Model is Philips Radioplayer 123.

One Pickup terminal (black) is grounded directly to chassis, the other (red) joins the audio circuit between IFT2 and the volume pot R10, from memory after R9.

I was calling the red terminal "positive" because it is the signal input. However the bias voltage holds that terminal negative with regard to ground.

It is strange that the AORSM and the Philips official documentation do not show the Pickup terminals at all. I understand they were standard on all Radioplayer models.

I'll double-check the circuit in the morning, mark the pickup connection on the relevant part of the schematic, and update this post.

Maven

If you have AORSM's see if any other models have that arrangement. I have a 132L.

There is house lot of radios here (not mine) and there a few Philips chasses in the pile. Cabinets & other bits different pile.

You don't need details other than I am not happy with the situation with these "piles"

Marc

OK, rechecked the circuit on my radio and the Pickup connects right at the input end of the volume pot. Amended schematic shows the pickup connections.

I also re-measured the resistance across the pickup input, and the resistance across the external source. This is the closest proxy I know for impedance, which I have read about but remains somewhat mysterious.

Pickup terminals - active to ground 50kohms
Source device jacks - active to ground 260kohms

Interesting, the connection is done correctly but the radio should also have a radio-gram switch otherwise how do you get the radio to stop while you play records? This is how it is done on the majority of radios.

I'll do a bit of digging around in the Philips circuits and see what is typically done.

My recollection is that the radio doesn't stop - you just tune it off station and hear only the pickup signal, when that is what you want.

My problem is that connecting a modern device to the pick-up terminals partially or completely squelches the radio signal

Maven

Looking at the circuit, could someone explain the connection from the speaker voice coil, via R23 to the screen of V3?

The AC audio signal level would be relatively low and decoupled by the capacitor (cannot read the number) connected to the screen.

The other effect would be to put a DC bias on the speaker, but given the low resistance of both the transformer and speaker, it would be quite low.

I don't think I have ever seen this before, is it just a quirky Philips thing?

Harold

My recollection is that the radio doesn't stop - you just tune it off station and hear only the pickup signal, when that is what you want.

My experience is about half and half with this. Whilst a lot of radios, usually the larger table and console models have a Gram/AM switch, the smaller mantels require tuning to a vacant spot. This creates enough silence to let the gramophone feed a good signal to the amplifier.

The output transformer has wires back, as that is part of the AF negative feedback. reverse it & the set will oscillate.

The PU is high impedance for a ceramic cartridge not a magnetic. Many of the more upmarket sets nobble the RF screens to shut the radio part down.

You will need to feed into what you have marked as positive via a capacitor to block the DC. Do remember it is Mono you will need to recombine stereo. Lest you only get one channel. Too much signal distorts.

Marc