Stereo Phono Cartridge to both Stereo and Mono Amps

Shabaz explains the principle in his message. (Although I think 1k resistors may be too low for some pre-amps)

The problem is that a good mono mix is not made by adding the two channels of a stereo mix. The two resistors do as good a job as anything else but it may well not sound quite right.

If you mean to feed two different amps you will need the preamp with RIAA equalization (if its a magnetic cartridge) or a high input impedance preamp (if its a ceramic cartridge).

Can you describe your simple methods and the cartridge ?

Are you willing to make the pre-amp yourself  ?

MK

The turn table is of a 1953, Rock-Ola 1446, AKA Fireball Comet 120.  The cartridge is a TN4 and the tone arm wire is a three conductor 30AWG Shielded wire. The internal mono amp assembly is a Rock-Ola 18640-A Tube Amp with an internal 12" speaker and horn. The external Stereo amp is a Sony STRDH190 2-ch Home Stereo Receiver with Stereo Phono Input that I am using. 

One of the simple methods I referred to was similar to what Shabaz described (1K Ohm) accept no preamp is used where shown. The mono sounded fine but stereo signal lost all its depth and dimension.

The second method used I replaced the two resistors with two Iso Transformers (EI14/EI-14 Audio Coupling Isolation Transformer Audio Transformer 600:600 1:1) . When connected he Stereo signal strength dropped so low I had to turn the volume to 10 on the Sony and it was very tinny sounding. Due to the poor signal strength I was unable to determine any loss in stereo dimension. This might require a preamp before the Iso transformers. 

Thanks MK, 

The quick answer is 2, I'm OK with perf board and through hole soldering (I have done surface mount repairs on game systems using a microscope for this work but I have not created any PCB's since school in the 80's). Through hole will be great.

Tom

Below: This is a diagram of the Tube Amp. I have replaced the caps, resistors and poorly performing tubes. Sounds great!

The amplifier has a reasonable input impedance (1.5M). There doesn't seem to be a volume control anywhere, otherwise the ceramic cartridge could drive it directly (although there might not be enough gain). Is there a volume control off to the left somewhere ?

MK

MK,

Yes, here it is.

I should also mention there is a mute circuit for when the mechanicals are picking up and returning the record disk. In the tube amp circuit this is accomplished by grounding the B terminal. I am hopeful there is a way this can be incorporated into the stereo amplifier solution.

Thank you kindly for your time and consideration. I am much appreciative, thank you. - Tom

Hi Michael,

I found a reference to ceramic pickups on http://www.douglas-self.com/ampins/library/ampartew.htm which directed to a Wireless World article.

In the August 1971 PDF issue of Wireless World page the author of the article has a 'economy version' circuit (reproducing here since the PDF version is freely available):

and also a "luxury version" which is claimed to be compatible with many ceramic cartridges:

I know nothing about any pickup tech ceramic or otherwise! : ) so I have no idea if these circuits, or front end of these circuits, are any good or not.

Nice that they use only easy-to-find BC109 though! The author must have had a whole bag of them to use : ) 

The volume control impedance is so low that you really will need a pre-amp. Shabaz has suggested a Doug Self circuit (below) which I think could be simplified to suit your purposes.

It can use readily avaialbe NPN transistors so should be easy to build.

If you think that would be a good way to go I'll re-draw just the bits you need and run a simulation of it.

MK

MK,

I reviewed the PDF article (located on the PDF's page 59). The writer is very thorough. Based on what I know and read here it seems like a tailored and viable model.

Tom

Sorry, I was a bit hasty there. The input is buffered by the first stage amplifier before the volume control so you can connect the ceramic cartridge directly to the amplfier.

MK

MK

I went ahead and ordered the BC109's so I have them on hand this week.

Tom

It looks as if you are going to try building a pre-amp based on the WW design.

Meanwhile I have a little charge amplifier from Jan Cumps to test. He designed the board based on some suggestions from me and kindly sent a pcb and parts. I'm going to re-tune it to work as a ceramic cartridge pre-amplifier. I've bought a really cheap cartidge from Amazon to test.

I'll do a proper blog about it when I have some data.

MK

michaelkellett said:

I'll re-draw just the bits you need and run a simulation of it.

MK,

Will you be doing this? I purchased the BC109's in anticipation of it.

Tom

michaelkellett said:

I'll re-draw just the bits you need and run a simulation of it.

MK,

Will you be doing this? I purchased the BC109's in anticipation of it.

Tom

Hi TC,

Want to try a parallel suggestion?

Michael's op amp method will likely be a lot better since the WW article is old.

I had some time and simulated the luxury version WW circuit, but I'm limited because (a) I don't know how to simulate a ceramic cartridge, and (b) I was hitting a component license limit with the software.

Also, (c) I don't have audio experience whereas Michael does, so it's best to go with any recommendation from Michael.

Anyway, you could try both circuits if you like, if you have the parts.

From the simulation, it seems pretty reasonable (I subjected what I thought was a large signal, 200mVp-p, and the output was around 2.6Vp-p, and the distortion was 0.1% at 100Hz, 1kHz, and 10 kHz. At 100mVp-p, the distortion dropped to 0.06% at these frequencies. I subjected the input to C1 in the simulated circuit below. The response was good across the entire audio range, and the tone controls functioned. However none of this matters if the input isn't the same, and I can't add much to the simulation since I'm at exactly 50 components (the limit) unless I split up and test portions.

Anyway, if you think it's worth a gamble, I'm happy to put this into a CAD package and generate a simple circuit board CAD files (it's only a few tens of $ including postage, if you give the files to any PCB manufacturer to get the board printed).

If you do get it printed and you have spares (usually they give 5-10 boards) then if I could make a request, I wouldn't mind one to experiment with (and perhaps Michael would like one too).