MM / MC phone preamp needed

[kct]

Hi,

I am looking for a new project, I have two cartridges Denon DL110 and a Lyra Kleos. Can someone recommend a stepup transformer and/or pre amp for these ?
I would not mind building something.

 

[Osvaldo de Banfield]

Amp: which kind: tube, transistor, opamp. Net: passive, active???

Need to be more explicit, please.

 

[kct]

preferably active using BJT

 

[nattawa]

If you're comfortable handling 0805 size (reads easy😀) SMD soldering, I recently finished building a compact MM phono stage that I call Ofono that you may be interested in.

The circuit is based on TI AN-346 two-stage design. Op-amp used in prototype is OPA1641. The board takes power from a cellphone charge cord or a 5V power bank when you don't feel like plugging in a wall outlet, then a DC-DC module steps it up to +/-24V split rail, followed by a pair of 317/337 as post regulators that clean up and step down to +/-17V for the op-amps. All circuit is on a single PCB of dimension 100 x 49 mm^2. Prototype is excellent sounding and is dead quiet with no hint of hum. The assembly fits nicely in a Hammond 1590BB enclosure.

 

[rayma]

Hi,

I am looking for a new project, I have two cartridges Denon DL110 and a Lyra Kleos. Can someone recommend a stepup transformer and/or pre amp for these ? I would not mind building something.

You only need a standard 36dB-40dB gain MM phono stage (with suitable input impedance) for the Denon, which has 1.6mV output. In fact, you might get overload with more than 40dB gain.

The Lycra has 0.5mV output, so some extra gain should be needed.

 

[kct]

Thanks for the suggestions, rayma. I am considering the James Chadwick MC for the Lycra Kleos.

nattawa, what are the specs on this design ?

 

[nattawa]

nattawa, what are the specs on this design ?

I didn't bother the specs 😀 since I have no means of measuring. Was a rescue project as a friend of mine had a phono stage went dead in a receiver...

Anyways according to the app-note design objective (attached), it appears to have decent s/n. I expect better from OPA1641 as its voltage noise being on par with LM833 but absence in current noise due to the JFET input construction. The gain of the app note original design is 35dB @ 1KHz, my prototype build has it at 40dB.




P.S. frequency response against RIAA

 

[zgtc]

The board takes power from a cellphone charge cord or a 5V power bank when you don't feel like plugging in a wall outlet, then a DC-DC module steps it up to +/-24V split rail, followed by a pair of 317/337 as post regulators that clean up and step down to +/-17V for the op-amps.

Sorry for the off topic, but really interested to know more details about this, I’d like to use smth similar in my preamp. Did you use a dc-dc similar to this one or did you create your own circuit? Thank you

 

[nattawa]

...Did you use a dc-dc similar to this one or did you create your own circuit? Thank you

I used the off-the-shelf module

A0524S-2WR2 | MORNSUN | NAC Semi

It is a low power module capable of only up to about 40 mA per rail at +/-24V.

 

[zgtc]

I see, thank you!

 

[kct]

Thanks nattawa, looks very interesting.

 

[kct]

nattawa, on the RIAA correction amplifier, what is the expected nominal input signal amplitude ?

 

[rayma]

nattawa, on the RIAA correction amplifier, what is the expected nominal input signal amplitude ?

The midband gain is 35dB, so use any nominal 1mV level cartridge. The Denon would be happy with this.

 

[Hearinspace]

You might also want to take a quick look at Rod Coleman's "Shunt Cascode". I believe he is currently working on a new board though not sure whether he plans to sell it as is or with full kit. One Post here.

 

[kct]

Thanks guys, I realized I have a lot of reading to do.

 

[nattawa]

nattawa, on the RIAA correction amplifier, what is the expected nominal input signal amplitude ?

rayma was right. 35dB works with most MM carts. Besides, the 2nd stage of a two-stage design works as a flat gain-block/buffer, and can be easily altered for desired gain.

 

[rayma]

rayma was right. 35dB works with most MM carts. Besides, the 2nd stage of a two-stage
design works as a flat gain-block/buffer, and can be easily altered for desired gain.

If the second stage gain is set at around 16dB instead of 10dB, it should work ok for the Lyra.
For this, change R4 = 750R. Of course, the noise will go up by about 6dB also.

 

[PRR]

The input for a 100r MC is usually very different from the input for a 47k MM. And the total gain for MC is quite high.

We usually build a MM preamp, then put a MC head-amp (or SUT) in front for the MC needle.

McIntosh MA5100 MC phono stage?

 

[kct]

I didn't bother the specs 😀 since I have no means of measuring. Was a rescue project as a friend of mine had a phono stage went dead in a receiver...

Anyways according to the app-note design objective (attached), it appears to have decent s/n. I expect better from OPA1641 as its voltage noise being on par with LM833 but absence in current noise due to the JFET input construction. The gain of the app note original design is 35dB @ 1KHz, my prototype build has it at 40dB.
View attachment 786773

View attachment 786774

P.S. frequency response against RIAA

View attachment 786780

Hi nattawa,

what capacitor did you use for C0 ?

 

[nattawa]

Hi nattawa,

what capacitor did you use for C0 ?

Did you mean C1 in the LTspice diagram? It's 220uF 16V BP lytic by Matsushita, but any bipolar lytic will do, paralleled with a 10uF ceramic SMD cap in the actual build.