Retro - A fully symetrical phono stage with RIAA filter

[billshurv]

With a few tweaks the LowZ can be used with MM but I would not recommend it unless you are brave. I built one for just such a purpose but have yet to fire it up as life in general has got in the way!

 

[BrianDonegan]

Both versions of the Retro are back in stock.

 

[mmai]

I built one, but need help with gain calculation

With my main phono stage in repair, I quickly whipped up a Retro to tie me over in the meantime.

I took the Edison approach and settled on the following resistor values:
R18 & R19 = 100R
R2=249R
R13=121R

With my Denon Dl-103R (it's out-of-spec w/ unusually high output @0.4mV) I get ~3,000x gain (@69.8dB and ~1.3mV) and with my Audio Technica OC9ML/II, I get ~2,850x gain (@69db and ~1.0mV).

I must say the unit sounds very good with mostly stock parts and low noise level, although I miss my tubed unit.

As I mentioned above, I took the Edison approach. But there's gotta be a mathematical method to derive gain -- Brian, or anyone, please help!

 

[Wikkehel]

Retro H-riaa

Hi There.

I am going to build a H version of the Retro riaa, and want that the network
dont supress the treble as must as normal.
So the question is which components I have to change for getting there.

I have a anti Riaa filter, so I can measure the difference.

 

[UltimateX86]

Hi

Do you still sale the phono kit ?

Thanks

 

[free2dev]

Hello,

I built a Retro Hi Z version and would like to know how to increase the output gain. My cart is Ortofon 2M bronze which produces much lesser volume compared to when connected using the phono input of the pre-amplifier. Should I also change the 22pf capacitor to match 150 - 200pf load capacitance of the cart?

Thanks

 

[Theodosis O.]

Hi,

In order to have load impedance 400 Ohm, the R18, R19 must be 200 Ohm ?

Thanks

 

[Cyberkul]

Hi! Is one Low Current Bipolar Supply Kit ok for driving both Retro boards?

Thanks!

 

[BrianDonegan]

Hi! Is one Low Current Bipolar Supply Kit ok for driving both Retro boards?

Thanks!

Yes

 

[Cyberkul]

Is there any (noticeable..) benefit to use separate powerboards? Also, are the boards and 2x15V, 50VA transformer available?

 

[pixelpusher]

I used Jan Didden’s “Silent Switcher” power supply. It’s available here at the DIY Audio store

 

[Cyberkul]

Thanks! Will have a look👍

 

[thematikma]

Input Voltage?

I used Jan Didden’s “Silent Switcher” power supply. It’s available here at the DIY Audio store

I will also use the silent switcher for the Lo Z version. What input voltage did you use? I am concerned 150mA per rail (when using 5V input) could be a bit on the short side.

Thanks!

 

[pixelpusher]

I am using a 5 volt regulated wall wart. No problems.
IIRC, my Retro measured around 35 mA going into the BPBP. Current usage varies with the input impedance of your preamp. I don’t recall the exact input impedance of the BPBP but it is on the high side. I’m thinking around 100k.

 

[thematikma]

Thanks, that helped a lot. I do have 20kOhms input impedance, so current draw should be slightly higher in my case. I guess I'll just measure when everything is ready.

 

[thematikma]

I had ordered the Retro kit some time ago and finally finished my build yesterday. It really sounds amazing and the kit was so nice arranged, with every part marked and separated per channel. A huge thanks to Twisted Pear Audio for that!
I have a small issue, what is not related to the Retro, but my record player. It happens only to my diy phono pres. Hum! I have my rega Planar 10 modified with separately wired ground. It is located approximately 30cm away from mains equipment. If I move it further away, the hum (it sounds like ac transformer noise) gets attenuated. With the pres I did buy ( SPL Phonos, EAT eglo perit) there is no hum at all. What do manufacturers implement, to make their units immune to hum?
I do at least think, the tonearm wires or the arm itself is picking that up link an antenna. I also tried the cartridge floating and a wire from mains earth to ground, what did not help. Only if I unplug the player from the pre, the hum is gone.

Any clues are much appreciated. Moving everything further away from each other is not really an option, as my space is really limited. Maybe rewire the arm and use XLR plugs would also help?
Thanks!

 

[pixelpusher]

Pin 1 of the XLR should go directly to the chassis and not be connected to anything else.

 

[thematikma]

Thanks again for your input. Based on suggestion, I did a little research, reading AES48 and "Pin 1 prroblem" bits. So I decided to connect pin 1 direct to the chassis near the input/output and made a star ground, where I tied all circuitry gnd to another place further away to the casing.
But the outcome is the same. Dead silent without the record player connected, and hum when the leads are plugged. I suspect the rega plugs and cable acting as a antenna.
So I will either relocate my stuff connected to mains supply, or rewire my tonearm to xlr, hoping the common shield will get rid of the hum.

 

[pixelpusher]

Try lifting that ground. Hum is usually caused by ground currents.

 

[mbrennwa]

Can you make a drawing of your audio connections, ground connections, and earthing to the wall sockets?