EC8010:
The Nature of Noise (ehm...) and the right choice of op-amp was a topic in the asylum thread as well. There wasn't a consent conclusion, so I'm looking foward to build a hack next weekend (hopefully...) and see how things perform, trying out the opa2604 I have around.
Maybe a discrete topology of this approach might work well, but that is way beyond my capabilities.
Rüdiger
The Nature of Noise (ehm...) and the right choice of op-amp was a topic in the asylum thread as well. There wasn't a consent conclusion, so I'm looking foward to build a hack next weekend (hopefully...) and see how things perform, trying out the opa2604 I have around.
Maybe a discrete topology of this approach might work well, but that is way beyond my capabilities.
Rüdiger
It certainly is an interesting topic. I think Kinergistics had a loony variation using a whole lot of junk in the NFB loop. An MC cart, a tape head, lots of poor solder joints and god knows also what. From the reviews it sounded amazing on some recordings (probably on bad ones) and dreadful on others.
JR's concept makes a lot more sense. I'll be very interested in your findings. Maybe we'll all start buying cartridges in pairs
peranders said:
Just exactly as I stated for the first case.
Its a voltage source driving the coil resistance and inductance
into a short circuit, output is current.
The F3 is stated for current output, not voltage for the first case.
For the second case output is effectively voltage, though there's
no reason you can't add a series resistor to the cartridge to drive
the virtual earth point, in this case F3 is also for current output.
sreten.I'll also add a cartridge body in the feedback loop will be next to
useless to balance the cartridge inductance by a factor of the gain.
Plain commonsense engineering should prevail here.
Using the cartridge DCR as one resistor in a shunt feedback
arrangement, effectively the cartridge driving the shunt feedback
virtual earth point, so gain depends on cartridge DCR will roll
off the treble, particularly for highish output MC's.
Its not for nothing MC's have recommended minimum loading.
sreten.
useless to balance the cartridge inductance by a factor of the gain.
Plain commonsense engineering should prevail here.
Using the cartridge DCR as one resistor in a shunt feedback
arrangement, effectively the cartridge driving the shunt feedback
virtual earth point, so gain depends on cartridge DCR will roll
off the treble, particularly for highish output MC's.
Its not for nothing MC's have recommended minimum loading.
sreten.
Balanced MC amp
Hi, the Moving Coil catridge is a natural for balanced operation. You will need some kind of instrumentation amplifier.
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=50205&highlight=elso+mat04&r=&session=
Replace the noisy zener by 5 LEDS in series. Now we are talking about REAL HIFI!! etc.,etc.
Hi, the Moving Coil catridge is a natural for balanced operation. You will need some kind of instrumentation amplifier.
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=50205&highlight=elso+mat04&r=&session=
Replace the noisy zener by 5 LEDS in series. Now we are talking about REAL HIFI!! etc.,etc.
Hi,
I'm listening to this amp at the moment. I use a LT1115 for input opamp and OPA 637 for the second one (my cartridge is Dynavector DV17 with DC resistance of 38 Ohms).
I have another pair of AD797 which I want to try as well, but the LT1115 does quite well. In fact, I'm listening to it right now (Pink Floyd, Delicate Sound of Thunder playing)
About a second cartridge in the feedback loop ... can anybody help me explain to my wife why I would buy a "dummy" cartridge somewhere in the box?
Maarten
I'm listening to this amp at the moment. I use a LT1115 for input opamp and OPA 637 for the second one (my cartridge is Dynavector DV17 with DC resistance of 38 Ohms).
I have another pair of AD797 which I want to try as well, but the LT1115 does quite well. In fact, I'm listening to it right now (Pink Floyd, Delicate Sound of Thunder playing)
About a second cartridge in the feedback loop ... can anybody help me explain to my wife why I would buy a "dummy" cartridge somewhere in the box?
Maarten
Attachments
Scott,
Yes a current-feedback amp would be interesting. I was thinking
of that on the way to work this AM. The only problem I know
is that the brand I tend to have access to has pretty high
1/f noise corner which may not be the best for this application.
After all the parts are intended for high-speed applications
Maybe a MA-centric semiconductor company would have
something more suitable.
Now the only problem with trying this is I don't have a MC
cartridge. In fact, no working turntable at the moment.
Thinking about this some, I believe that J Peter Moncrief of
International Audio Review advocated a transimpedance
stage for MC preamps years ago. And didn't Richard Marsh
publish a design in TAA? So this is not an unheard-of concept.
(both were single-ended, not "balanced")
Yes a current-feedback amp would be interesting. I was thinking
of that on the way to work this AM. The only problem I know
is that the brand I tend to have access to has pretty high
1/f noise corner which may not be the best for this application.
After all the parts are intended for high-speed applications
Maybe a MA-centric semiconductor company would have
something more suitable.
Now the only problem with trying this is I don't have a MC
cartridge. In fact, no working turntable at the moment.
Thinking about this some, I believe that J Peter Moncrief of
International Audio Review advocated a transimpedance
stage for MC preamps years ago. And didn't Richard Marsh
publish a design in TAA? So this is not an unheard-of concept.
(both were single-ended, not "balanced")
Briant, you are correct. This is an early idea, that we ultimately 'scrapped' over the years. I contacted EMT and Ortofon about optimized cartridge loading about 30 years ago. Their responses were vague. Also, AJ Vandenhul recommended low Z loading on EMT cartridges that he retipped.
As the years went by, optimum loading has tended to go to higher values, rather than lower values. Why, I don't know for sure.
As the years went by, optimum loading has tended to go to higher values, rather than lower values. Why, I don't know for sure.
FETs Versus Bipolars
Hi,
Funny thing thing is I started with bipolars (MAT02) but ended with FETs (2SK389). Now you wouldn't believe it. The circuit did NOT get more noisy! Yes I know it is against all textbook explanations. Horowitz has several pages about this noise problem. I simply cannot corrobate it.
EC8010 said:
Hi,
Funny thing thing is I started with bipolars (MAT02) but ended with FETs (2SK389). Now you wouldn't believe it. The circuit did NOT get more noisy! Yes I know it is against all textbook explanations. Horowitz has several pages about this noise problem. I simply cannot corrobate it.
Re: FETs Versus Bipolars
I'm amazed! It took a lot of searching, but I finally found some data on the device, and see it has a transconductance of only 20mA/V, even when you thrash it. That sort of number certainly doesn't sound promising. Did you measure the noise when you compared against MAT-02, or was it by listening? Details, details?
Elso Kwak said:
I'm amazed! It took a lot of searching, but I finally found some data on the device, and see it has a transconductance of only 20mA/V, even when you thrash it. That sort of number certainly doesn't sound promising. Did you measure the noise when you compared against MAT-02, or was it by listening? Details, details?
Re: Re: FETs Versus Bipolars
Hi,
Picture simply taken from the datasheet. The MC-cartridge is connected between +IN and -IN with 100 Ohm resistors to ground from the inputs. So the dartridge leads are totally floating with respect to ground. I replaced the opamp by an AD817. Later went totally discrete. I did not suspect the cross-quad would work with the FETs but it did!
I judged the noise form the same high volume setting, no measurements available.
The sound was much better than the circuit I built with the SSM2017 which again was better than the Mark Levinson JC1-AC, to my ears.
EC8010 said:
Hi,
Picture simply taken from the datasheet. The MC-cartridge is connected between +IN and -IN with 100 Ohm resistors to ground from the inputs. So the dartridge leads are totally floating with respect to ground. I replaced the opamp by an AD817. Later went totally discrete. I did not suspect the cross-quad would work with the FETs but it did!
I judged the noise form the same high volume setting, no measurements available.
The sound was much better than the circuit I built with the SSM2017 which again was better than the Mark Levinson JC1-AC, to my ears.
Attachments
Folks, this is the situation:
Noise has several sources. One is base resistivity or Rbb'. This can be 2-400 ohms. The very best NPN transistors have about 4 ohms.
Then the Voltage noise generator. For transistors, it is .5/Gm = 13 ohms at 1ma, 1.3 ohms at 10ma. For fets, it is .7/Gm or.7/.035 = 20 ohms at 10ma.
There is also a current noise generator, which will be neglected here.
Elso has a 33 ohm resistor in series with his input, so it pads any differences between the 2SK389 and and pair of transistors. This difference will be small in this case. Now what if you ran the transistors at 10 ma? Then the transistor would be best, BUT it would be made more noisy than necessary by 1/f noise and added current noise.
Also, Elso's circuit 'might' add some noise from the current sources that are not completely degenerated for noise gain. I hope that this helps.
Noise has several sources. One is base resistivity or Rbb'. This can be 2-400 ohms. The very best NPN transistors have about 4 ohms.
Then the Voltage noise generator. For transistors, it is .5/Gm = 13 ohms at 1ma, 1.3 ohms at 10ma. For fets, it is .7/Gm or.7/.035 = 20 ohms at 10ma.
There is also a current noise generator, which will be neglected here.
Elso has a 33 ohm resistor in series with his input, so it pads any differences between the 2SK389 and and pair of transistors. This difference will be small in this case. Now what if you ran the transistors at 10 ma? Then the transistor would be best, BUT it would be made more noisy than necessary by 1/f noise and added current noise.
Also, Elso's circuit 'might' add some noise from the current sources that are not completely degenerated for noise gain. I hope that this helps.
Noise
John,
You mean by 33 Ohm the Rg resistor? Is this one in series with the signal?
I do not remember the current I am using through the FETs or the transistors MAT02. I cranked it up a bit above the value of fig.6 by having more LEDs in series as a replacement for the 3.9V zener diode. I started with two or three LEDs ended with five.
All in one the noise is low enough for me as the record surface is FAR more noisy than the electronics. I hear the stylus ploughing through the groove!
John,
You mean by 33 Ohm the Rg resistor? Is this one in series with the signal?
I do not remember the current I am using through the FETs or the transistors MAT02. I cranked it up a bit above the value of fig.6 by having more LEDs in series as a replacement for the 3.9V zener diode. I started with two or three LEDs ended with five.
All in one the noise is low enough for me as the record surface is FAR more noisy than the electronics. I hear the stylus ploughing through the groove!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.