Hope you're using an MM or high output MC, that's what your phono pre schematic is best suited for despite the MM/MC switch.
2nd stage could be inverting to eliminate common-mode issues there, but you'd need to increase 2nd stage gain, R11 would double and 2nd stage input resistance would equal new R11 value.
As soon as the MM cartridge's stylus meets the moving groove, choice of bipolar vs FET input op amps or passive vs active EQ based on noise at 1kHz becomes an academic discussion. I'd be more concerned about 1/f noise noted by jcx.
I have an MM phono pre similar to your schematic using OPA637 or AD8610 for first stage, LM6171 for second stage, cascoded FET current sinks on both outputs. It sits on the shelf, replaced by a tube phono pre with 2 triodes, first stage FET CCS-loaded, second stage FET/bipolar "mu follower" loaded, active EQ with 2-pole compensation.
The op-amp pre is compact, noise is low enough, and sounds clean and detailed, certainly better than a Dyna PAS, but the tube/CCS pre seems better at revealing low-level detail and ambience.
You can't go too wrong with your design for MM, give it a try.
2nd stage could be inverting to eliminate common-mode issues there, but you'd need to increase 2nd stage gain, R11 would double and 2nd stage input resistance would equal new R11 value.
As soon as the MM cartridge's stylus meets the moving groove, choice of bipolar vs FET input op amps or passive vs active EQ based on noise at 1kHz becomes an academic discussion. I'd be more concerned about 1/f noise noted by jcx.
I have an MM phono pre similar to your schematic using OPA637 or AD8610 for first stage, LM6171 for second stage, cascoded FET current sinks on both outputs. It sits on the shelf, replaced by a tube phono pre with 2 triodes, first stage FET CCS-loaded, second stage FET/bipolar "mu follower" loaded, active EQ with 2-pole compensation.
The op-amp pre is compact, noise is low enough, and sounds clean and detailed, certainly better than a Dyna PAS, but the tube/CCS pre seems better at revealing low-level detail and ambience.
You can't go too wrong with your design for MM, give it a try.
Yes, current sinks connected to op amp outputs bias the output stage to class A. Op amp outputs are already biased class A to a certain current output, the current sinks increase the output current for class A operation and can reduce distortion with low impedance loads. A good source of information on this subject is here. Your preamp will measure well without them. Some like them and some don't, they're simple to add so try one and listen for any difference.
The design you have settled on should be fine - although, by providing full gain wideband from the first stage, it suffers from a 20dB reduced signal handling capability in the HF. It will clip on a 10 times lower HF signal, whereas, had you chosen the full 'around one stage' RIAA 10x more HF signal could be accomodated.
For lowest noise a discrete FET front end could be used with 1 op amp AND provide >40dB extra OL gain into the bargain.
Topology shown below for Nch pair. ( for your 2SK146's mlloyd!)Flip cct for Pch FETs. RIAA as per standard (see Andy C's WWW).
jcx, It's arguable which is a better chip while surface noise is some 20dB+ higher as soon as the needle drops.
Cheers,
Greg
For lowest noise a discrete FET front end could be used with 1 op amp AND provide >40dB extra OL gain into the bargain.
Topology shown below for Nch pair. ( for your 2SK146's mlloyd!)Flip cct for Pch FETs. RIAA as per standard (see Andy C's WWW).
jcx, It's arguable which is a better chip while surface noise is some 20dB+ higher as soon as the needle drops.
Cheers,
Greg
Attachments
phono preamp
Hi Peter,
I have an interesting discrete phono preamp design, namely AEM6010. It is 20 years old and was designed by Dave Tilbrook. I have never built this preamp but I listened to it and in those times it was probably one of the quietest and detailed preamps available.
I have a copy of the article with PCBs etc and associated PS and control unit schematics as well. A zip file with its schematics is attached. Of course it could be redesigned to accept different components including low noise fets. It may not be what you are looking for but some food for thought.
Cheers,
Hi Peter,
I have an interesting discrete phono preamp design, namely AEM6010. It is 20 years old and was designed by Dave Tilbrook. I have never built this preamp but I listened to it and in those times it was probably one of the quietest and detailed preamps available.
I have a copy of the article with PCBs etc and associated PS and control unit schematics as well. A zip file with its schematics is attached. Of course it could be redesigned to accept different components including low noise fets. It may not be what you are looking for but some food for thought.
Cheers,
Janusz, wow that circuit is complex!
I like to follow Einsteins advice:
"keep everything as simple as possible, but no simpler"
In my research I have found a huge number of Phono/RIAA circuits out there on the 'net, and they appear to fall into a few distinct categories (IMHO!)
1/ Too simple, and not technically great.
(eg: single Opamp)
2/ Simple, and potentially great, with careful component selection.
(eg: FET frontend + Opamp, Dual Opamp etc)
3/ Complicated because they date from an era when good sound dictated complex electronics. Probably still sound good, but modern components can do the same with less.
(eg: John Linsley-Hood, AEM6010)
4/ Complicated and very good
(eg: some commercial designs)
5/ Complicated because they are snake-oil
I am looking for Option 2, and I think I'm close to settling on a dual-opamp design, although "amplifierguru's" topolgy using a front-end built from 2SK146's is making me thing again.....
This is fun...
I like to follow Einsteins advice:
"keep everything as simple as possible, but no simpler"
In my research I have found a huge number of Phono/RIAA circuits out there on the 'net, and they appear to fall into a few distinct categories (IMHO!)
1/ Too simple, and not technically great.
(eg: single Opamp)
2/ Simple, and potentially great, with careful component selection.
(eg: FET frontend + Opamp, Dual Opamp etc)
3/ Complicated because they date from an era when good sound dictated complex electronics. Probably still sound good, but modern components can do the same with less.
(eg: John Linsley-Hood, AEM6010)
4/ Complicated and very good
(eg: some commercial designs)
5/ Complicated because they are snake-oil
I am looking for Option 2, and I think I'm close to settling on a dual-opamp design, although "amplifierguru's" topolgy using a front-end built from 2SK146's is making me thing again.....
This is fun...
PeterMoreton said:
As well it should. One thing I'd like to mention regarding some of the info on my WWW as it relates to ampllifierguru's design. The analysis on my site assumes a single-pole compensation of the op-amp. In this configuration, it's necessary to have an op-amp with a very large DC open-loop gain for accurate low-frequency equalization. For accurate high-frequency equalization, an op-amp with a large gain-bandwidth product is needed. There are very few op-amps that satisfy both requirements at once. Amplifierguru's circuit uses two-pole compensation, which elegantly sidesteps this problem. The additional FET stage at the input provides a higher DC open-loop gain, allowing much more flexibility in the choice of op-amp for the second stage.
PeterMoreton said:
This is going to be expensive. Erno Borbely stocks them at www.borbelyaudio.com. But they are 25 euros each.
MCM shows they can be ordered. I have found they can always deliver items like this. Do not know their sources, but all kinds of rare old transistors are available at reasonable prices. Look at www.mcminone.com to get an idea of cost and lead time.
Usually the wait for the parts like this that are not stocked at MCM is 3 - 4 weeks. They must have access to a transistor graveyrd somewhere.
They came through with all the transistors to build an original Le Monstre a year ago or so. Some of those were hard to find ten years ago. Same with the original transistors to build the Krell KSA-50 clones.
George
A thread about an MC phono pre with discrete input and op amp output, passive/active EQ is here, could be modified for MM. Input is single-ended so expect tweaking for DC operating point.
If you have NE5534s and matched discrete transistor pairs you can disable the on-chip bipolar input pair and connect a discrete differential pair as I described here, OL gain will be lower and stability compensation is probably easier than amplifierguru's example. I highly recommend cascoding the input pair to reduce common-mode effects.
If you're going to the trouble of adding discretes to an op amp you might also consider adding an output buffer using BUF634 or discretes, this uses discretes, you could class A bias the op amp output stage by removing Q1 and placing D1 in series with D2, and smaller output transistors like 2N4401/4403 would be OK.
If you have NE5534s and matched discrete transistor pairs you can disable the on-chip bipolar input pair and connect a discrete differential pair as I described here, OL gain will be lower and stability compensation is probably easier than amplifierguru's example. I highly recommend cascoding the input pair to reduce common-mode effects.
If you're going to the trouble of adding discretes to an op amp you might also consider adding an output buffer using BUF634 or discretes, this uses discretes, you could class A bias the op amp output stage by removing Q1 and placing D1 in series with D2, and smaller output transistors like 2N4401/4403 would be OK.
Although not a simple circuit, Robert Grodinsky patented a passive/active RIAA circuit back in 1982. It is Patent No. 4,312,060. Here is the abstract:
The preamplifier has a first stage or section of low or unity gain, such as an emitter-follower circuit, which also isolates the preamplifier from impedance variations of the cartridge, and with a bandwidth for greater than the audio range to reproduce signals with a very high amplitude, rapidly changing wavefront without slew or amplitude overload distortion. A RIAA high frequency de-emphasis network is coupled between this first stage or section and a second amplifier section. A RIAA low frequency emphasis network is preferably placed in a negative feedback circuit of the latter amplifier section where the feedback circuit does not contain the high frequency components filtered out by the high frequency de-emphasis network. The second amplifier section need not have the bandwidth of the first amplifier stage or section.
Borbebly adopted a similar split feedback topology in the late 80s. He just published a recent article on it, but I haven't read it yet. His new article claims a low cost version, but his idea of low cost and mine differ. I doubt it deals with the time constant mentioned above in the thread. Anyhow, his web site has the published articles:
Borbely articles
The preamplifier has a first stage or section of low or unity gain, such as an emitter-follower circuit, which also isolates the preamplifier from impedance variations of the cartridge, and with a bandwidth for greater than the audio range to reproduce signals with a very high amplitude, rapidly changing wavefront without slew or amplitude overload distortion. A RIAA high frequency de-emphasis network is coupled between this first stage or section and a second amplifier section. A RIAA low frequency emphasis network is preferably placed in a negative feedback circuit of the latter amplifier section where the feedback circuit does not contain the high frequency components filtered out by the high frequency de-emphasis network. The second amplifier section need not have the bandwidth of the first amplifier stage or section.
Borbebly adopted a similar split feedback topology in the late 80s. He just published a recent article on it, but I haven't read it yet. His new article claims a low cost version, but his idea of low cost and mine differ. I doubt it deals with the time constant mentioned above in the thread. Anyhow, his web site has the published articles:
Borbely articles
Hi Peter,
The 2SK146 (dual N fet I suggested because mlloyd has some) can be substituted with 2SK389 or a pair of 2SK170. The design I gave does not need selected GR,BL, or V grading just a pair the same - the duals are generally within 10%. For the 2SK170's, if they're not a perfect match then 22ohm or smaller emitter resistors should balance them up. If you want offset adjustment the op amp has this facility.
Hi Nuvistor,
I note your comments re the 5534 and your link and suggestion to cascode - but I like to use all that I've paid for rather than disable one stage. The discrete diff'lly loaded stage feeding , say, a 5534 front end should be fine despite it's unknown CMRR - it will cope to the error tolerance of the 3K9 source resistors.
If you're wanting Class A output at 3mA see pic. Probably not so good as will limit negative swing unless made much higher Iq. especially when it comes to driving the hf low Z RIAA network - the 5534 would do better with just the pull down R to -Vs.
If you wanted all discrete the op amp could be replaced by a second diff'l stage with current mirror load then the Class A output.
lot's of fun without the noise.
Cheers,
Greg
The 2SK146 (dual N fet I suggested because mlloyd has some) can be substituted with 2SK389 or a pair of 2SK170. The design I gave does not need selected GR,BL, or V grading just a pair the same - the duals are generally within 10%. For the 2SK170's, if they're not a perfect match then 22ohm or smaller emitter resistors should balance them up. If you want offset adjustment the op amp has this facility.
Hi Nuvistor,
I note your comments re the 5534 and your link and suggestion to cascode - but I like to use all that I've paid for rather than disable one stage. The discrete diff'lly loaded stage feeding , say, a 5534 front end should be fine despite it's unknown CMRR - it will cope to the error tolerance of the 3K9 source resistors.
If you're wanting Class A output at 3mA see pic. Probably not so good as will limit negative swing unless made much higher Iq. especially when it comes to driving the hf low Z RIAA network - the 5534 would do better with just the pull down R to -Vs.
If you wanted all discrete the op amp could be replaced by a second diff'l stage with current mirror load then the Class A output.
lot's of fun without the noise.
Cheers,
Greg
Attachments
2SK146? forgetaboutit ...
sorry,
these devices are pretty much unobtanium these days. Stick with 2SK389/2SK369. I just happen to have a few purchased a long time ago when i was single and could buy expensive semiconductors without somebody looking over my shoulder.
oops, oh hi honey ...
and thanks ampguru. i'll give it a shot.
mlloyd1
sorry,
these devices are pretty much unobtanium these days. Stick with 2SK389/2SK369. I just happen to have a few purchased a long time ago when i was single and could buy expensive semiconductors without somebody looking over my shoulder.
oops, oh hi honey ...
and thanks ampguru. i'll give it a shot.
mlloyd1
amplifierguru said:
Even with the added burden of the extra lag and the (perhaps incidental and unneeded) opportunity for increased slew rate when the 5534 1st stage is off? With a discrete 1st stage followed by 5534 at low closed-loop gain I'd rather bypass the 5534 1st stage and not have to work so hard at stability compensation, after all single-stage active EQ RIAA forces a low closed loop gain above 20kHz, about 5 from 200 - 500 kHz to open loop gain intercept even with the 50kHz zero in the modified RIAA EQ.
With a 100MHz GBW op amp like LM6171 or AD817 in place of 5534 the lag below 10MHz is much less and you don't have access to the 1st stage collector nodes so disabling 1st stage is not an option, higher open-loop gain should be possible, for compensation I would consider NFB around the op amp for Miller-integrator compensation with some source degeneration if noise requirements permit.
5534 uses NPNs for output source/sink with feedback around the lower NPN, I've driven discrete output stages from 5534 comp pin 5, 5mA into this pin from V+ biases 5534's lower NPN on and also can bias a Vbe multiplier or diode string for class AB, with 2N4401/4403 you have a pretty good headphone driver, or just use pin 5 as output if no short circuit protection is OK. 5534 pin 5 is at lower NPN collector, sinks to negative rail, output pin 6 adds a diode and resistor. Sure it's a small step to a completely discrete op amp, but with IC op amps there's less to build and 5534 smoke is cheap. If 500uA 1st stage tail current is enough, 1st stage load resistors can be the 5534's internal 13k to V+. For inverting gain common-mode is not an issue and a simple resistive tail is OK, for non-inverting I would use an active current sink.
Hi Nuvistor,
You know your 5534's - I thought using these was a good idea as they are cheap as chips, universal and good output drive.
The RC comp is simple - starts at 10KHz and back to unity by 1.5 MHz but gives an extra 40 odd dB at audio frequencies - in partic at LF where , with high gain MC gain at 80dB, it's needed for NFB. At the other end the MM gain of say 40dB means 12 dB or (x4) from 50KHz up - so the decomp 5534 (no 22pF) will be stable to 7 MHz.
cheers,
Greg
You know your 5534's - I thought using these was a good idea as they are cheap as chips, universal and good output drive.
The RC comp is simple - starts at 10KHz and back to unity by 1.5 MHz but gives an extra 40 odd dB at audio frequencies - in partic at LF where , with high gain MC gain at 80dB, it's needed for NFB. At the other end the MM gain of say 40dB means 12 dB or (x4) from 50KHz up - so the decomp 5534 (no 22pF) will be stable to 7 MHz.
cheers,
Greg
Take a look:
http://www.users.nac.net/markowitzgd/phonopre.html
There are some threads about this phono pre here, eg this:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=9628&highlight=
When you need MC pre, do not use 2SK170 instead of the 2SK147 (out of production, look at the prices from Borbely...
) on that schematic, but use 2SK369 (which has same specs as 2SK147 except power handling). It has lower noise at low source resistance (=MC) than 2SK170. See attached graphs. And it is cheap.
Btw, same goes for 2SK146 vs 2SK389, they are not really the same. It's only that both are out of production now....
Tino
http://www.users.nac.net/markowitzgd/phonopre.html
There are some threads about this phono pre here, eg this:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=9628&highlight=
When you need MC pre, do not use 2SK170 instead of the 2SK147 (out of production, look at the prices from Borbely...
) on that schematic, but use 2SK369 (which has same specs as 2SK147 except power handling). It has lower noise at low source resistance (=MC) than 2SK170. See attached graphs. And it is cheap. Btw, same goes for 2SK146 vs 2SK389, they are not really the same. It's only that both are out of production now....
Tino
sometimes you CAN find unobtanium ...
Well, maybe I exaggerated a bit. I don't want to unnecessarily scare off anybody that may be determined to try some of the ideas here.
While it is true that Toshiba no longer makes the 2SK146, 2SK147 devices and others have pointed out some (expensive) sources for NOS....
There is a thread on this board somewhere that mentions new product of similar (or better) specs from either InterFET or Linear Systems, I can't remember which one. You can get duals or singles. They're probably not cheap either, but at least they are new production devices.
However, no P channel complements, unfortunately.
mlloyd1
================
[edit] ok, I found them:
http://www.interfet.com/pdf/DS_IFN146.pdf
http://www.interfet.com/pdf/DS_IFN147.pdf
group buy anyone?
================
Well, maybe I exaggerated a bit. I don't want to unnecessarily scare off anybody that may be determined to try some of the ideas here.
While it is true that Toshiba no longer makes the 2SK146, 2SK147 devices and others have pointed out some (expensive) sources for NOS....
There is a thread on this board somewhere that mentions new product of similar (or better) specs from either InterFET or Linear Systems, I can't remember which one. You can get duals or singles. They're probably not cheap either, but at least they are new production devices.
However, no P channel complements, unfortunately.
mlloyd1
================
[edit] ok, I found them:
http://www.interfet.com/pdf/DS_IFN146.pdf
http://www.interfet.com/pdf/DS_IFN147.pdf
group buy anyone?
================
zinsula said:
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