Help needed with Dynatron RG11 Berkeley

[HoverJohn]

Atleast it fits nicely - so light it doesn’t actually lower the tone arm any more (it just stays where it’s put) so I either need to add 4g or relax the cantilever spring on the butt end of the tone arm.

[Edward Huggins]

That's a good fit. There should be a -15 degree negative rake on the stylus when viewed from the side. You will need to bridge the 2 channels and then connect to the original 2 wires in the head shell. Don't worry about the matching issues until the preamp/amp are up and running.

[HoverJohn]

Thanks again for all the help so far- I’m about to begin replacing duff bits - the soldering iron is warming up….slowly

[Jan Zodiac]

Hi,

When it comes to matching a crystal/ceramic cartridge (constant amplitude) to an MM cartridge input (constant velocity), it is necessary to use a simple network. If not, the RIAA curve (or any other given curve) will be far off, as well as the output of the ceramic unit probably will overload the MM input and create distortion. Even if the output is lowered through a voltage divider or potentiometer, the playback characteristics will still be far off. A solution would be to connect the cartridge AFTER the RIAA stage (line input), which would match the ceramic cartridge relatively well to the RIAA curve (and signal level) because of its constant amplitude characteristics. However, even better matching is possible as shown in the article below.

On this page, you can see how the matching is easily done. Scroll down to page 11 + 12, which is about ceramic cartridges, and matching them to normal MM inputs.

www.filmaker.com/papers/UPDATES_RMiller-Better Sound of the Phonograph.pdf

Over the years I experimented a lot with crystal cartridges, because I find them interesting. I can confirm that with the simple network shown (and calculated according to the resistive load inside the preamp/RIAA), it works flawlessly, and a quality ceramic/crystal cartridge will sound just as nice as most magnetic cartridges from that era.
I only experimented with mono carts though, so you would probably need a pair of matching networks, or adapters as they are called in the article, to match a stereo ceramic cart to a mono input.

There is plenty of space inside the headshell though, so that would be the obvious choice of placing the parts. Another benefit is that it lowers the impedance, making the cable capacity between the turntable and amplifier input less significant, which otherwise would be a factor to consider with a high impedance ceramic cartridge. Probably not much of a problem in a radiogram though, where the signal cable is relatively short.

Kind regards,

Jan

[Herald1360]

http://www.filmaker.com/papers/UPDAT...Phonograph.pdf



Should work......

[HoverJohn]

Thanks for this - a great article I now understand what the RIAA equalisation is which was probably my main knowledge gap!! It also gives me food for thought - is there any preference to doing this on each channel then combining? Or combine the stereo then modify?
Note to others the link needs to be modified as the last bit isn’t copied right.

[HoverJohn]

Ok this is what I’m thinking of trying (unless it’s nuts?) my reasoning is that I don’t like the idea of joining the 2 stereo outputs directly as if physics be anything and every action being reacted I’m concerned that the asymmetrical part of the output on one channel affecting the other channel making the ceramic move making resonances etc. (I seem to remember the little Crystal speakers as a kid in everything I took apart)
So here I’ve tried to adjust the Crystal output for each channel then combine them placing at least something between the 2 stereo outputs.

Pic attached.

Is that feasible or hade I still got the wrong end of the stick??

JB

[Jan Zodiac]

Originally Posted by HoverJohn

Thanks for this - a great article I now understand what the RIAA equalisation is which was probably my main knowledge gap!! It also gives me food for thought - is there any preference to doing this on each channel then combining? Or combine the stereo then modify?
Note to others the link needs to be modified as the last bit isn’t copied right.

You are welcome Sorry about the link, I don't really know how it changed as I attached it to the post.
Since I didn't experiment with stereo crystals/ceramics (yet), I am not really sure what the best solution would be. Maybe others here have inputs on that. A ceramic cartridge acts more or less like a small capacitor (around 2nF or so), which makes it a little difficult to work with (high impedance), but I guess when two channels are combined, one could assume that the capacity is now doubled, as a starting point. I would simply try to double the 560pF cap, reduce the 68k resistor to around half, and then calculate the load as being half, since now two generators are in parallel.
Since there are only 3 components that needs to be matched together, I think it would be relatively easy to fiddle with values to get the best results. There are no calculations shown in the article on how he reaches the given values, so the easiest way would be to experiment.
If you are lucky to have a test record with a frequency sweep in your collection, it would actually be easy to match the values perfectly to the cartridge/input. I have done that several times myself, and it is indeed possible to achieve a pretty flat frequency response from a crystal/ceramic cartridge. One that impressed me was the Ronette TX-88 (mono though).

Kind regards,

Jan

[Jan Zodiac]

Originally Posted by HoverJohn

Ok this is what I’m thinking of trying (unless it’s nuts?) my reasoning is that I don’t like the idea of joining the 2 stereo outputs directly as if physics be anything and every action being reacted I’m concerned that the asymmetrical part of the output on one channel affecting the other channel making the ceramic move making resonances etc. (I seem to remember the little Crystal speakers as a kid in everything I took apart)
So here I’ve tried to adjust the Crystal output for each channel then combine them placing at least something between the 2 stereo outputs.

Pic attached.

Is that feasible or hade I still got the wrong end of the stick??

JB

I think it is worth a try. I would probably lean toward that solution myself. Again, it is an easy, low cost experiment. As for the two ceramic elements reacting on each other when put in parallel, I don't think it would have any significant impact on the sound or mechanical movement of them. They are extremely high impedance, so I doubt the output of one element would affect the other.

Jan

[HoverJohn]

Bits ordered - postage was more than the bits!!

[HoverJohn]

Thought I better give the cabinet some love so I have stripped off 60 years of tobacco and given it a polish. - it was quite gross. But removed that dull haze the smoke leaves.

JB

[Herald1360]

That veneer figuring is just..... WOW!

[HoverJohn]

Hang on it’s better than that it matches the top…… we had not noticed until I got the nicotine off.

JB

[Jan Zodiac]

It really looks amazing! What a beautiful piece of furniture.

Jan

[HoverJohn]

Ok so I’ve had a go at unwinding resoldering and rewinding the variluctance coils and think it’s a goer so I have ordered some fresh wire and going to have a go - however I’ve also realised that the variluctance coil is not like MM or MC and has a flat freq response like a ceramic so all the above chat I’m making ceramic match the RIAA curves is potentially not needed (and I now understand more of the previous posts!!) I also now know what the different gram settings do in the tone control unit… adjust the equalisation for the different response curves used…

Imagine a penny dropping in very slow motion……

[HoverJohn]

Ok so I’ve finally managed to sort one pickup coil and now to match the other one…

Next question- do people leave the old can capacitors in place and put the new ones inside the chassis so it looks old ?? Or bin the old ones off and mount the unimpressive modern ones on the chassis outside?

[Station X]

That's a choice for you to make. Either way the old caps must be disconnected.

[Edward Huggins]

You could leave the old caps in-situ and fit the new, smaller ones under the chassis leaving room for some reasonable air-gap ventilation. To go to the extreme, you could remove all the foil content of the old cans and stuff the new components insde....

[Nickthedentist]

Definitely don't discard the originals. This is a high quality machine and deserves the best, most conservative restoration which you can manage. Don't do anything irreversible if possible.

[HoverJohn]

Ok I’ve ordered some p clips so I can mount the new caps underneath and leave it looking stock from outside. I’ve also got a 2nd head shell so I can keep the original rewound cartridge and also make up a modern head shell for modern vinyl the blu tooth will just be fitted in the main cabinet and wired into the spare AF channel so all fully reversible.