USMC Spike
Well-Known Member
Derek do you have a link to the it?
AD797 Phono Stage Build and Help Desk Thread
- Thread starter HypnoToad
- Start date
Derek do you have a link to the it?
tabarddn51
Super Member
Hi Spike,
- no the AD797 phono amp cannot be used with MM cartridges.
- what did you want a link to?
Cheers
- no the AD797 phono amp cannot be used with MM cartridges.
- what did you want a link to?
Cheers
Well, the answer to the question is yes- after all the AD797MCPRE design is essentially a fixed gain stage (approximately 80 for a 250uv @1kHz cartridge- the AD797) plus an RIAA de-emphasis stage (The LME49710), but there are trade-offs- such as the cartridge termination RC will be different (i.e. the 47k vs, say, 200 ohms). The MM cartridge also has a large DC resistance (unspecified but useful to know) which makes the AD797 not the best choice for noise/offset.
To accommodate a MM cartridge like the one you are talking about you could just reduce the input stage gain to about 3.6 or bypass the AD797 completely and just use the 2nd opamp with a somewhat increased gain. In fact having the RIAA stage at the input gives the best overload characteristic of all.
Also- do you want to make the stage switchable between MM and MC?
All of these things can be done, but it might mean significant changes to the components/wiring of the board.
Is this what you want?
sachu888
Spare the tigers, kill me
Hi
As Wyn mentioned this phonotage won't suit MM carts. You can build a CNC phonostage for MM http://www.audiokarma.org/forums/in...igh-end-phono-stage-no-expense-spared.371889/
Regards
Sachin
USMC Spike
Well-Known Member
The Gram Slee Fanfare.
USMC Spike
Well-Known Member
Thanks for getting back Derek, Wyn Sachin.
I guess making the phono amp switchable between MC & MM kind
of defeats the purpose of the project with the ready made board,
unless a simple switch etc can be improvised somewhere.
Otherwise is designing and laying out a brand new board
configuration in which I have no experience doing.
I have a few very nice op amps in PDIP as I've said, including
the AD797. LME4990 (adapter) the tin can versions of LME49710,
LME49720. LT1468, a smattering of OPA134, OPA2134,
and some of the other LT devices. I'm just not experience
with them yet.
I was a tube guy then got into test and measurement and ran
into some problems trying to upgrade some HP test gear. So
I went back to school to learn electronics and should finished up
with a little Electrical Engineering Technology: Associates at my
local community college next semester or next fall depending on
the if I can handle the course load and find a two day afternoon
day care for my little girl. Everyone wants you to book 5 days a
week...but that is another story.
I've got preamps that can do some of this I assume, and the turntable
a Thorens TD-147. It's opamps are dated and include the following:
MC34001 Single Opamp
LM324 14 Pin opamp
BC547 Transistor
BPW34 OSRAM, Si PIN Photodiode, suitable from 400nm to 1100nm.
Still available? Yes, cannabas' bandwidth is about center in that range.
4x1n4150 = Bridge.
I've got the following pre amps with their Phono sections:
Audio Research SP3A1 & SP-10 along with a Marantz 3250.
However I'm not a design guy, I'm more of a nuts and bolts kinda guy.
Do we want to review schematics build something into these or keep it
external and interface to one of these?
I don't want to Hijack the thread, but I do need more information to move forward.
Its kind of not so fun to build the wrong something then find it won't work out.
As I look through various threads, sites, forums, many are out there for review
yet many are not supported by any measurement data so how do we sort it
all out.
It also seems that most of the designs, boards, kits are for MC cartridges.
So do I look at Walt Jungs stuff? Nelson Pass? Look at various Handbooks?
Find Samual Groners research?
I guess making the phono amp switchable between MC & MM kind
of defeats the purpose of the project with the ready made board,
unless a simple switch etc can be improvised somewhere.
Otherwise is designing and laying out a brand new board
configuration in which I have no experience doing.
I have a few very nice op amps in PDIP as I've said, including
the AD797. LME4990 (adapter) the tin can versions of LME49710,
LME49720. LT1468, a smattering of OPA134, OPA2134,
and some of the other LT devices. I'm just not experience
with them yet.
I was a tube guy then got into test and measurement and ran
into some problems trying to upgrade some HP test gear. So
I went back to school to learn electronics and should finished up
with a little Electrical Engineering Technology: Associates at my
local community college next semester or next fall depending on
the if I can handle the course load and find a two day afternoon
day care for my little girl. Everyone wants you to book 5 days a
week...but that is another story.
I've got preamps that can do some of this I assume, and the turntable
a Thorens TD-147. It's opamps are dated and include the following:
MC34001 Single Opamp
LM324 14 Pin opamp
BC547 Transistor
BPW34 OSRAM, Si PIN Photodiode, suitable from 400nm to 1100nm.
Still available? Yes, cannabas' bandwidth is about center in that range.
4x1n4150 = Bridge.
I've got the following pre amps with their Phono sections:
Audio Research SP3A1 & SP-10 along with a Marantz 3250.
However I'm not a design guy, I'm more of a nuts and bolts kinda guy.
Do we want to review schematics build something into these or keep it
external and interface to one of these?
I don't want to Hijack the thread, but I do need more information to move forward.
Its kind of not so fun to build the wrong something then find it won't work out.
As I look through various threads, sites, forums, many are out there for review
yet many are not supported by any measurement data so how do we sort it
all out.
It also seems that most of the designs, boards, kits are for MC cartridges.
So do I look at Walt Jungs stuff? Nelson Pass? Look at various Handbooks?
Find Samual Groners research?
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tabarddn51
Super Member
Hi Spike, Well that's the thing with DIY, you have to take your B***s in your hands & jump. The plus side is this unit can be built for a little over $100, if you can do your own box & use batteries to run it. I am currently trialling a P/S for it that cost me under $30 to sling together and it quieter than my 2 x SLA batteries. That is not much of an outlay considering, it is one of the very best sounding phono stages out there. I know from personnel experience it sounds better than a kit EAR834 + SUT and also the Pass Pearl 1 + SUT. Hopefully in a couple of weeks I can compare it with a Pearl 2 that does not need a SUT.
Happy deliberations, Cheers Derek.
Happy deliberations, Cheers Derek.
So, are you actually asking for mods to the AD797MCPRE board that will make it compatible with a MM cartridge and not a dual purpose design? It's not that difficult to mod the board- it's just a couple of opamps per channel after all, and the output stage contains all the RIAA "stuff".Thanks for getting back Derek, Wyn Sachin.
I guess making the phono amp switchable between MC & MM kind
of defeats the purpose of the project with the ready made board,
unless a simple switch etc can be improvised somewhere.
Otherwise is designing and laying out a brand new board
configuration in which I have no experience doing.
I have a few very nice op amps in PDIP as I've said, including
the AD797. LME4990 (adapter) the tin can versions of LME49710,
LME49720. LT1468, a smattering of OPA134, OPA2134,
and some of the other LT devices. I'm just not experience
with them yet.
I was a tube guy then got into test and measurement and ran
into some problems trying to upgrade some HP test gear. So
I went back to school to learn electronics and should finished up
with a little Electrical Engineering Technology: Associates at my
local community college next semester or next fall depending on
the if I can handle the course load and find a two day afternoon
day care for my little girl. Everyone wants you to book 5 days a
week...but that is another story.
I've got preamps that can do some of this I assume, and the turntable
a Thorens TD-147. It's opamps are dated and include the following:
MC34001 Single Opamp
LM324 14 Pin opamp
BC547 Transistor
BPW34 OSRAM, Si PIN Photodiode, suitable from 400nm to 1100nm.
Still available? Yes, cannabas' bandwidth is about center in that range.
4x1n4150 = Bridge.
I've got the following pre amps with their Phono sections:
Audio Research SP3A1 & SP-10 along with a Marantz 3250.
However I'm not a design guy, I'm more of a nuts and bolts kinda guy.
Do we want to review schematics build something into these or keep it
external and interface to one of these?
I don't want to Hijack the thread, but I do need more information to move forward.
Its kind of not so fun to build the wrong something then find it won't work out.
As I look through various threads, sites, forums, many are out there for review
yet many are not supported by any measurement data so how do we sort it
all out.
It also seems that most of the designs, boards, kits are for MC cartridges.
So do I look at Walt Jungs stuff? Nelson Pass? Look at various Handbooks?
Find Samual Groners research?
USMC Spike
Well-Known Member
Wyn, Thanks for getting back on this. So as I understand is, yes, that is what I was asking.
So, from what I understand then the AD797s can't be used in the first stage.
I'm trying to figure out what this design's source is/was?
I've read the RIAA Phono Preamplifier section from Jung, W. (2002). Op Amp Applications, Analog Devices, Inc. (ch 6.11 - 6.27).
I'm not certain how to modify the board for other devices, that is the devices that I have.
LT1115, LT1028, along with the Ultra low noise unity gain buffer LT1128.
LME Series: LME49990, LME49870, LME49710HA, LME49720HA,
OPA 134, OPA1641.
Thanks,
So, from what I understand then the AD797s can't be used in the first stage.
I'm trying to figure out what this design's source is/was?
I've read the RIAA Phono Preamplifier section from Jung, W. (2002). Op Amp Applications, Analog Devices, Inc. (ch 6.11 - 6.27).
I'm not certain how to modify the board for other devices, that is the devices that I have.
LT1115, LT1028, along with the Ultra low noise unity gain buffer LT1128.
LME Series: LME49990, LME49870, LME49710HA, LME49720HA,
OPA 134, OPA1641.
Thanks,
See post #1185 in this thread for the provenance of the original design.
Yes, Walt always did do good work. Well worth reading.
The biggest problem with the AD797 as a MM input amp is that the input bias current is very high. MM cartridges generally have coil DC resistances in the 1k+ region- for example the Shure M97 is 1.55k- and it becomes hard to configure the AD797 so that the output offset is not very high- possibly several mv- and hence the output voltage from the RIAA amp could be c.4v. This is still within the acceptable operating range of the output opamp with 1v RMS out, but it's hardly ideal. In my opinion, you'd be better off trying an amp like the LME49710 which will actually give you lower noise and much lower offset and similar distortion.
Also, with the AD797 input amp if you were to disconnect the phono input at any time while the amp was active the output would likely go to one of the rails which I can't believe would be a good thing for your speakers...
So, this is what to do. Replace the ImpR/L pot with a fixed 47k R. Leave off the input cap (C25/C26).
Set the first opamp GainR/L pot to the max (2k), replace the 47ohm R (R1/2) that goes from the input inverting terminal to ground with 820ohms. Don't make any of my previously recommended changes- which will leave a very large ultrasonic peak in the gain at about 3MHz- or just add a 2200-3300pF cap from the non-inverting input of the 2nd opamp to ground (output opamp side of 390 ohm R (R9/R10)).
This improves the overload characteristics of the amp significantly and also helps to eliminate RFI interference issues.
This will give you a 1v RMS output at 1kHz for a 5.5mv input.
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USMC Spike
Well-Known Member
Hi Wyn,
I visited the #1185 post. So if I understand correctly, do not make any of those changes from that post.
Change the first ICs to LME79410, and leave the 2nd IC as is (LME49990).
Would I still want to add the 2200-3300pf cap to ground? Since I don't have the schematic
I'll assume it's/their in series after the 390 Ohm R at R9/R10 to ground.
Okay time to buy the boards, find the BOM order parts etc.
From what I recall, these will fit a case I can get at Fry's. A bit of sleuthing around for me,
the usual kind of stuff. Once I get everything else I'll keep y'all appraised.
thanks,
I visited the #1185 post. So if I understand correctly, do not make any of those changes from that post.
Change the first ICs to LME79410, and leave the 2nd IC as is (LME49990).
Would I still want to add the 2200-3300pf cap to ground? Since I don't have the schematic
I'll assume it's/their in series after the 390 Ohm R at R9/R10 to ground.
Okay time to buy the boards, find the BOM order parts etc.
From what I recall, these will fit a case I can get at Fry's. A bit of sleuthing around for me,
the usual kind of stuff. Once I get everything else I'll keep y'all appraised.
thanks,
Use LME49710 for both parts. Add the cap to ground at the junction of R9 (R10) (390ohms) and the non inverting input (pin3) of the output amp- which is I believe what you are referring to.
You could also add an appropriate cap at the input- c25/c26. I originally suggested leaving it off, but it's probably best for you to add the cap- the issue is that your cabling etc. can add anything between 50pF and 200pF, which makes meeting a specific capacitance in the 150-300pF target a bit iffy- but if you just want to have something in that range then a 100pF cap would likely be close enough.
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USMC Spike
Well-Known Member
Wyn, I think I've got it. It should look something like these.
I'm trying to reconcile the difference between them.
I tried to get a good look at your schematic from post #1335, but even
when enlarged I can't read it (even with my "reading:" glasses.) Can you
post a larger pic please?
I'm trying to reconcile the difference between them.
I tried to get a good look at your schematic from post #1335, but even
when enlarged I can't read it (even with my "reading:" glasses.) Can you
post a larger pic please?
Attachments
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I'm not sure I understand the question. Are you asking what the difference the topology makes?
The first design- the "putting the RIAA deemphasis in a single feedback loop"- is, in a sense, the optimal configuration- best noise, dynamic range, and immunity to overload.
It does, however act as a unity gain amp at HF which is not optimal in my opinion as it leaves a path for RF to get through and cause issues.
It is also a frequency dependent feedback design, and some people dislike it on principle.
The design shown also has a gain of only 35dB- or about x56- which would only give you 310mv RMS @1kHz for a 5.5mv signal, not the higher gain you need, and to avoid compromising the HF gain flatness you need a second gain stage.
The second is a so called "passive RIAA" design- it has a fixed gain stage followed by a passive "filter network" which acts as the de-emphasis- then it has a final output gain stage to recover the gain lost in the network plus whatever additional gain you need. It obviously still has lots of feedback- it has two opamps in fixed, low, gain configurations after all- but some people prefer it this way. The two opamps are configured as the same gain- which is normal for reasons I won't explore.
It has inferior noise, dynamic range and immunity to overload than the first design, but it does provide immunity to RF getting through.
I think it also has relatively low gain, but without running a simulation I can't say exactly what.
My own preference is something different- a mixed design with two opamps. The input amp has the HF pole in the feedback, followed by an additional RF rejection passive pole between the gain stages, and finally the LF equalization stage. In my opinion it gives the best of all worlds, but that's neither here nor there.
Back to the suggested AD797MCpre changes.
I believe that this was the original design- I know the component names are not fully consistent with the board.
This needs to be modified to swap out the AD797, to increase the input gain to somewhere around 2.5-3.3 (R15 becomes 820 to 620 ohms), to add an additional RF rolloff (the 2200-3300pF cap), to increase the input R to 47k, and reduce the input cap to 100p.
In both cases rawinp is the input to the board and to the right of the 390ohm resistor (R9) is the non inverting input of the second opamp.
USMC Spike
Well-Known Member
Thanks absolon, I tried wading through that thread.
If I understand correctly I can use the AD797MCPRE board that Wyn described with the devices
that I have listed and Wyn has been kind enough to take the time to describe which he recommends
and what part changes should be made.
Wyn, then I would go with what you suggest with the following:
I assume that we are getting to that with this board and the 2 x LME49710HA devices
per channel. So, at least here with this board that would be a jumping off point.
I have an idea of the power supply that I want to use.
If I understand correctly I can use the AD797MCPRE board that Wyn described with the devices
that I have listed and Wyn has been kind enough to take the time to describe which he recommends
and what part changes should be made.
Wyn, then I would go with what you suggest with the following:
I assume that we are getting to that with this board and the 2 x LME49710HA devices
per channel. So, at least here with this board that would be a jumping off point.
I have an idea of the power supply that I want to use.
USMC Spike
Well-Known Member
deleted and placed in the post above.
I can't delete this post though.
I can't delete this post though.
I made some RIAA corrections to the AD797MCPRE earlier which reduced the nominal error by about an order of magnitude while improving the RF rejection. I can't say that my suggestions we're met with unbridled enthusiasm, which is fine...
Well, if you want I can explain the differences between the various approaches in terms of overload etc. and give detailed instructions on how to convert the AD797 board to the mixed design. I've done this previously for a friend who wanted a 2.5mv input configuration and I could easily do it for 5.5mv.
If you want you could start a new thread. I redesigned/explained in detail the Leach MC preamp for someone before and it was done in a new thread.
http://audiokarma.org/forums/index.php?threads/the-leach-moving-coil-pre-preamp.838004/
absolon
Super Member
I think a substantial number of these were built by people who enjoyed the construction aspect but didn't really understand the elemental principles of how the circuit worked and consequently didn't feel comfortable modifying it or troubleshooting inadvertent errors. These threads on the CNC and AD797 preamps are very informative but as Spike pointed out, with post counts in the thousands, they are getting very unwieldy and difficult to follow.
I missed the RIAA corrections you made. If you could approximately date them, that would make it easier for me to track back and find them.
