MM / MC phone preamp needed

If you're comfortable handling 0805 size (reads easy:D) 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.
 

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rayma

Member
2011-04-29 8:37 pm
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.
 
nattawa, what are the specs on this design ?

I didn't bother the specs :D 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.
fig-3.png

noise.png

P.S. frequency response against RIAA

RIAA.png
 
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zgtc

Member
2016-11-03 1:50 pm
Barcelona
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
 

rayma

Member
2011-04-29 8:37 pm
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.
 
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kct

Member
Paid Member
2006-12-24 2:45 am
KW, Ontario
I didn't bother the specs :D 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 ?