You can buy ic opamps for a few bucks that'll do that, opa1611 on the mc side fits the bill. The maxim version of the op27 for the mm side is a significant uplift.
Yeah, I know, at the moment I gave 4x OPA27GP for MM cart and it works really great. However, I'm considering changing to much much better MC cart (around $1500) so I'm looking for possibilities to upgrade my Emerald
Discrete op amps will not work in the Emerald for two reasons. First, the S-reg current shunt circuit only supports low currents up to about 30 mA or so, and two discrete op amp modules will usually exceed that by a lot
Second, and most critical, is the input offset currents and/or voltages of these modules are orders of magnitude higher than ICs, where input transistors can be thermally matched and precisely trimmed. The Emerald doesn't have DC blocking caps on the interstage or the inverting inputs, so the DC gain remains high (up until the output coupling cap). If ICs aren't used, the signal will lock up at either the positive or negative rails due to the excessive DC offsets.
I assumed ICs were going to be used from the onset of the design process. Discrete modules are NOT a drop-in replacement.
An issue with the OPA27 is that it has input bias current cancellation circuitry, meaning the current noise will be much worse than the datasheet figure in an asymmetrical circuit (such as any preamp basically!). For MM this is crucial for low noise at higher freqencies as the MM source impedance rises to high levels at higher frequencies (inductance of cartridge), so low current noise is important. NE5534A is still about the best bipolar opamp for an MM preamp, or go to JFET input opamps (negligable current noise) like OPA1656.
I have plots comparing noise spectra for NE5534A and OPA1612 (the dual 1611), using 500mH to simulate a cartridge, in a RIAA preamp:
OPA1612:
And NE5534A:
See how the large hump is very much reduced at higher frequencies, the OPA1612 is noiser from 1kHz upwards, manifesting as higher levels of hiss.
Hi All, just a quick post to share my build, I bought my PCB's August 23..
And only got round to building them up a few weeks ago! Everything went together very well with no problems, the build instructions are very clear and this discussion group a brilliant source of information.
Like everyone else I'm really please with the circuits and blown away with the result. And a complete improvement from the Pro-ject Box S I was previously using.
I've attached a few photos
And only got round to building them up a few weeks ago! Everything went together very well with no problems, the build instructions are very clear and this discussion group a brilliant source of information.
Like everyone else I'm really please with the circuits and blown away with the result. And a complete improvement from the Pro-ject Box S I was previously using.
I've attached a few photos
Attachments
@gt6hudson Thanks for sharing. Interesting, 1-up-1-down mounting configuration for the boards. I haven't seen that one before!
Just finished my implementation of Emerald, in 2 boxes(phono stage + power supply/TF) and did a first test on my system.
Sound is just amazing, and I haven't yet tried my best cartridge - I'm currently running with a Sumiko Pearl MM.
However, there're a few things I need your feedback on
1. Q6 on right channel gets burning hot once I turn power on. V+/V- are at 12.5V/-12.5V so I was wondering what could be wrong here.
I haven't let it run for more than a minute for fear of burning Q6. Same transistor on the other channel is fine.
2. With my amp at 12.00 and no input I can hear a bit of hum on my speakers and something that sounds like FM reception(!)...It's impossible
to hear when I'm playing a record but I can't imagine why this circuit would have such a problem - Any ideas?
Here are a few pictures of my implementation
Sound is just amazing, and I haven't yet tried my best cartridge - I'm currently running with a Sumiko Pearl MM.
However, there're a few things I need your feedback on
1. Q6 on right channel gets burning hot once I turn power on. V+/V- are at 12.5V/-12.5V so I was wondering what could be wrong here.
I haven't let it run for more than a minute for fear of burning Q6. Same transistor on the other channel is fine.
2. With my amp at 12.00 and no input I can hear a bit of hum on my speakers and something that sounds like FM reception(!)...It's impossible
to hear when I'm playing a record but I can't imagine why this circuit would have such a problem - Any ideas?
Here are a few pictures of my implementation
@busoni
Q6 shouldn't have any significant heat dissipation, and it's hard for me to imagine a scenario where the circuit can be wrong and still produce the correct voltages. I suspect Q6 or, in particular, Q7 is damaged or installed incorrectly.
Remove IC1 and IC2 just in case.
With power off, center the trim pot R22 so it's 500 ohms per side, approximately.
Double-check the values of R17 and R19
Double-check the orientation of R6 and Q7
Still the same?
Finally, I would replace Q6 and Q7
Q6 shouldn't have any significant heat dissipation, and it's hard for me to imagine a scenario where the circuit can be wrong and still produce the correct voltages. I suspect Q6 or, in particular, Q7 is damaged or installed incorrectly.
Remove IC1 and IC2 just in case.
With power off, center the trim pot R22 so it's 500 ohms per side, approximately.
Double-check the values of R17 and R19
Double-check the orientation of R6 and Q7
Still the same?
Finally, I would replace Q6 and Q7
Thanks @rjm ! That's what I also thought, it couldn't be a circuit problem. I have triple checked that all transistors are installed
correctly. Running the Emerald again yesterday, I didn't observe any overheating in Q6.
I will replace Q6 and Q7 just in case once I get new parts and update the thread.
correctly. Running the Emerald again yesterday, I didn't observe any overheating in Q6.
I will replace Q6 and Q7 just in case once I get new parts and update the thread.
Well, it only took near enough to 5 years, since I purchased the boards (Oct. '19) - and populated them in May' 21. Since then, I've really only needed to finish up internal wiring and fitting the RCA sockets. I've had a few short periods of work on this, over the last couple weeks, and last night I finally got the in-/outputs wired up, and the last power wires done. Voltage is 12.7 on left channel and 12.8 on the right channel.
External wiring and setup is very rudimentary at the moment, as my turntable also have been packed up for the last 4 years - but good enough to that I can enjoy some music now.
Initial impressions are good, but mid-level seem a little muddled. Is anyone else running an Ortofon 2M Red?
External wiring and setup is very rudimentary at the moment, as my turntable also have been packed up for the last 4 years - but good enough to that I can enjoy some music now.
Initial impressions are good, but mid-level seem a little muddled. Is anyone else running an Ortofon 2M Red?
I drag an Ortofon 2M Bronze across my records. I didn't notice anything particularly lacking in the mids when I was using this phono stage. My friend now uses my Emerald stage and she has one of the MC Ortofons. Ain't nothing wrong with her mids either. Granted, we both run Rega P3 turntables with upgraded P6 platters and putting that on made a huge difference to the mids compared to the stock P3 platter.
Thanks, good input to have. I'll finish up, and get everything mounted as intended, before any upgrades. I have a Pro-Ject RPM 5.1, all stock though. I do plan to upgrade both platter and cartridge at some point.
Let it play for 100 hours or so, that "chestiness" should gradually clear up.
Hi , very good job.
where did you find those RCA Sockets ? have you an code / link?
BR Nikos.
Hi
I am just in the process of completing my second Emerald build but have hit a snag. On one of the boards, I am getting 0V between Ref and V+, I have power going into the board and I have checked the solder joints.
What should I be checking next?
Thanks
Jerry
I am just in the process of completing my second Emerald build but have hit a snag. On one of the boards, I am getting 0V between Ref and V+, I have power going into the board and I have checked the solder joints.
What should I be checking next?
Thanks
Jerry