As Simon said, R22 trims the positive and negative voltage rails to make them equal. It's for peace of mind really, as the circuit works fine even when they are not.
Looks to be a two op amp per channel amplifier design, with an unusual choice of (custom wound?) inductors in the RIAA filter. The power supply is a traditional linear regulated type as far as I can see, with the option of using batteries. I cant tell you anything further I'm afraid.
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Hi all. Almost complete with the build then I'll report back.
To start with I've built as per BOM. Once it settles in I would like to find the best sounding load resistance point for my Koetsu Rosewood (one of the early ones). To do this I am thinking of...
- remove R1 (I don't intend to use MM) and the jumper
- connect R2 jumper to a 2-way pot
- trim to the sound I like best - need to be able to go down to 30R so thinking 200R
- replace with Charcroft of the same value
Any comments as to the wisdom of this?
To start with I've built as per BOM. Once it settles in I would like to find the best sounding load resistance point for my Koetsu Rosewood (one of the early ones). To do this I am thinking of...
- remove R1 (I don't intend to use MM) and the jumper
- connect R2 jumper to a 2-way pot
- trim to the sound I like best - need to be able to go down to 30R so thinking 200R
- replace with Charcroft of the same value
Any comments as to the wisdom of this?
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I've been diggin' my Emerald but just the other day am noticing more hiss than I was used to. Actually, the amount hasn't changed but my different set-up is requiring a higher gain setting on my pre-amp than I was using and some hiss is intruding. Muting the stage silences the noise as does using shorting plugs on the inputs. It sounds like tube rush - sort of a soft hissing like leaves blowing in the wind. I have shielded Litz wire from headshell to RCAs but the noise is there when I replace those with a set of well-shielded Blue-Jeans cables interconnects. Thoughts on where to begin looking would be appreciated.
@RhythMick
Closing JP1-1 inserts R2 in parallel with R1. Since R1 is 47kohms, it has no effect left in when put against a couple of hundred ohms. It's best to leave it in.
If you connect a x ohm trim pot in place of the shorting jumper, it will add 0-x to the value of R2. This allows you to add loading resistance, but you can't subtract... you wont be able to test values lower the R2. As long as you are OK with that, the plan seems sound to me.
@WntrMute2
Hiss (as opposed to hum or buzz) can be a lot of things. It shorting the input stop is, though, then we can right away assign it to the front end, and not the op amp baseline noise. What are your gain and load settings?
I do recommend the "post a short .wav file of the output" diagnostic tool.
The build is generally impeccable, though you could do better with the cable dressing. I'd prefer to see the power wired as twisted pairs, and the signal wiring likewise. Not that that is likely to be the source of the hiss, but it won't hurt to fix.
(your pictures are a wee bit large, fyi)
Closing JP1-1 inserts R2 in parallel with R1. Since R1 is 47kohms, it has no effect left in when put against a couple of hundred ohms. It's best to leave it in.
If you connect a x ohm trim pot in place of the shorting jumper, it will add 0-x to the value of R2. This allows you to add loading resistance, but you can't subtract... you wont be able to test values lower the R2. As long as you are OK with that, the plan seems sound to me.
@WntrMute2
Hiss (as opposed to hum or buzz) can be a lot of things. It shorting the input stop is, though, then we can right away assign it to the front end, and not the op amp baseline noise. What are your gain and load settings?
I do recommend the "post a short .wav file of the output" diagnostic tool.
The build is generally impeccable, though you could do better with the cable dressing. I'd prefer to see the power wired as twisted pairs, and the signal wiring likewise. Not that that is likely to be the source of the hiss, but it won't hurt to fix.
(your pictures are a wee bit large, fyi)
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No, not with a microphone. Plug the line out of the Emerald into a recording device line input.
If there is no hiss with the inputs shorted, the noise is generated by a high impedance on the input. If there is no cartridge attached, for example, there will be a lot of noise because all the op amp sees is 47 kohms. With the cartridge, it's the impedance of the cartridge, a few hundred ohms for MM, but anything the phono cable and stylus armature picks up will come through as well.
BOM should give you +39 dB midband for the MM settings. There would not be any noise, and there isn't, as proved by your shorting experiment. How about with no cartridge attached, does the noise get much worse?
If there is no hiss with the inputs shorted, the noise is generated by a high impedance on the input. If there is no cartridge attached, for example, there will be a lot of noise because all the op amp sees is 47 kohms. With the cartridge, it's the impedance of the cartridge, a few hundred ohms for MM, but anything the phono cable and stylus armature picks up will come through as well.
BOM should give you +39 dB midband for the MM settings. There would not be any noise, and there isn't, as proved by your shorting experiment. How about with no cartridge attached, does the noise get much worse?
The Per Windfeld is a Low Output MC cartridge with an internal DC resistance of 4 ohms. The noise gets slightly louder with the cartridge disconnected but not much.
What could I use as a recording device? Smartphone or laptop?
thanks for the help!
What could I use as a recording device? Smartphone or laptop?
thanks for the help!
Sorry, I missed the post of the cartridge specs earlier. 0.3 mV, 4 ohms, >10 ohm load. Got it.
The photos show the JP1-1 and JP1-2 both open and the Switchboard DIP switches all open. In this config, the Emerald would operate as a MM phono stage. So normally, what setting do you use?
The photos show the JP1-1 and JP1-2 both open and the Switchboard DIP switches all open. In this config, the Emerald would operate as a MM phono stage. So normally, what setting do you use?
In that case there shouldn't be any undue noise even with the phono cable unplugged since R2 is shorting the op amp effectively. However, if you turn the volume way up you will here some hiss. That's normal. The higher the signal gain the quicker it becomes audible. Normally, it isn't.
Got an aha moment with rjm emerald for mm
This combo works for most of the mm I use .
R1 100k
R2 82k bypass 100pf
R3 100
R4 330
100k loading works great for older stuff which requires more openness ..like grace , epc 205, basically ..some old Japanese carts love this loading ...
47k/100pf works very well for rest .mid is more highlighted
Higher gain works well for gain below 4.5mv or carts that lacks bass or dynamism . This really opens it up! Eg ..grace 3.5mv , ortofon om .
Lower gain for dj and Stanton 500.
It brought my beloved emerald to a new level.
Share your settings and thoughts
This combo works for most of the mm I use .
R1 100k
R2 82k bypass 100pf
R3 100
R4 330
100k loading works great for older stuff which requires more openness ..like grace , epc 205, basically ..some old Japanese carts love this loading ...
47k/100pf works very well for rest .mid is more highlighted
Higher gain works well for gain below 4.5mv or carts that lacks bass or dynamism . This really opens it up! Eg ..grace 3.5mv , ortofon om .
Lower gain for dj and Stanton 500.
It brought my beloved emerald to a new level.
Share your settings and thoughts
Still 1.5k
I find that with slightly lower gain carts . The high gain setting changes the character and openess of the preamp ..which is desirable
Which sometimes can sound dull and lack of bass
6.5mv works very well for lower gain .
I find that with slightly lower gain carts . The high gain setting changes the character and openess of the preamp ..which is desirable
Which sometimes can sound dull and lack of bass
6.5mv works very well for lower gain .
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