You can use a separate RIAA preamp and connect that to the "regular" preamp, or make a kind of "integrated preamp" and connect a separate RIAA stage within the same chassis.
Gee, why didn’t I think of that? 
The point I was trying to make was that many of us of a certain age and those still playing vinyl would consider an “RIAA phonograph EQ” stage as essential to a “pre-amp”, and regardless of voltage gain and any additional signal processing, etc, absence of such would classically the device as a line stage. But of course that’s just peevish semantics on my part, and the lexicon of this hobby is certainly not something on which I think there is accord.
Back to the subject of Tom’s primer, I think at minimum a pre-amp/control front end should accommodate all source signal types and levels likely to be used, and that as the RIAA EQ curve was established almost 70yrs ago, the math for target for playback compensation has already been done, and it’d be a relatively simple task to design a modular daughter board for that function. No doubt far more complex designs have started out sketched on the back of an artisanal crafted IPA soaked beer cozy.
Of course when you deep into the weeds of non-mainstream phono cartridges - Moving coils most notably- you can quickly get bogged down by issue of input impedance and capacitance.
A fond memory of my first serious separates system - QUAD 33/FM3/303/ESL57, was the user adjustable phono and tape level plug-in “adaptor” PCBs. The line level buffer and phono EQ circuits were also on plug-in boards but they required removal of sleeve to access. While the use of space saving DIN signal connectors and the rather limited functionality of the 33 wasn’t to everyone’s taste, and the low output level required to match the 303’s input sensitivity reduced its compatibility with other brands, I always considered the quirky little pre-amp to be quite a fun piece, and certainly never hurtful to listen to. By comparison the Aerospace grade designed AGI511 or earliest Dayton Wright sounded more than a bit too glassy and “detailed” for my taste, and where the first hint that specs don’t tell the whole story.
Of course, while it’s always nice when small manufacturers such as Tom solicit customer feedback as part of their R&D process, ultimately there are a lot of moving parts involved, and they’ll need to make decisions based on their assessment and risk tolerance.
The point I was trying to make was that many of us of a certain age and those still playing vinyl would consider an “RIAA phonograph EQ” stage as essential to a “pre-amp”, and regardless of voltage gain and any additional signal processing, etc, absence of such would classically the device as a line stage. But of course that’s just peevish semantics on my part, and the lexicon of this hobby is certainly not something on which I think there is accord.
Back to the subject of Tom’s primer, I think at minimum a pre-amp/control front end should accommodate all source signal types and levels likely to be used, and that as the RIAA EQ curve was established almost 70yrs ago, the math for target for playback compensation has already been done, and it’d be a relatively simple task to design a modular daughter board for that function. No doubt far more complex designs have started out sketched on the back of an artisanal crafted IPA soaked beer cozy.
Of course when you deep into the weeds of non-mainstream phono cartridges - Moving coils most notably- you can quickly get bogged down by issue of input impedance and capacitance.
A fond memory of my first serious separates system - QUAD 33/FM3/303/ESL57, was the user adjustable phono and tape level plug-in “adaptor” PCBs. The line level buffer and phono EQ circuits were also on plug-in boards but they required removal of sleeve to access. While the use of space saving DIN signal connectors and the rather limited functionality of the 33 wasn’t to everyone’s taste, and the low output level required to match the 303’s input sensitivity reduced its compatibility with other brands, I always considered the quirky little pre-amp to be quite a fun piece, and certainly never hurtful to listen to. By comparison the Aerospace grade designed AGI511 or earliest Dayton Wright sounded more than a bit too glassy and “detailed” for my taste, and where the first hint that specs don’t tell the whole story.
Of course, while it’s always nice when small manufacturers such as Tom solicit customer feedback as part of their R&D process, ultimately there are a lot of moving parts involved, and they’ll need to make decisions based on their assessment and risk tolerance.
Attachments
And now that the dispensaries for such artisanal crafted IPAs have reopened, that design process could conceivably begin.
I do have a couple of pages of notes from reading the relevant chapter in Doug Self's Small Signal Audio Design.That doesn't need to get super complicated. Add a DIP switch to choose from a set of values and leave one switch setting open for DIY tweaks.
The main challenge is the silly low output of the MC cartridges. Lots of low-noise gain is needed. Thankfully I have a full kit of Linear Systems' devices so I could conceivably design something good...
I won't do design by committee, but it is probably time for a short market survey to narrow down a few options. I'm definitely interested in what you folks think should be the next addition to my portfolio. I can probably come up with some other questions too. I'll drop a link here and elsewhere once I have the survey ready.
Tom
I resemble that quote. Well down the rabbit hole. Far enough to need multiple phono stages for experiments. But I should note impedance and capacitance is only really an issue for MMs. MCs (and Grados) are far easier to please. Just reduce noise. As cartridge output decreases abandon voltage amplification and go current.
But I am moving away from an RIAA stage. I have miniDSP as my preamp and it can do RIAA to stupid accuracy for free. Added bonus of making certain vinyl die hards look at me in a funny way
But I am moving away from an RIAA stage. I have miniDSP as my preamp and it can do RIAA to stupid accuracy for free. Added bonus of making certain vinyl die hards look at me in a funny way
I don't want to get in between you and the people who look at you in that funny way. But if you use anyhow a DSP how often do you use that? Do you use it exactly one time per record and then you save your records digitally? And next time you want to play whatever is on that record just use your digital file?
While we're in the off-topic weeds here, it sounds like there might be a market for a flat frequency preamp with variable gain and cartridge loadings (MM/MC) to feed a sound card/usb adc. You would then input the captured file for digital RIAA application on a PC app. Pure Music units come to mind, but I expect it would be a trivial card for Tom. Hard to know how many of us might go for it.
Like Tom I use a miniDSP as the active crossover (and in my case the preamp, not sure about him). So it's always there and RIAA EQ is a couple of PEQs and job done.
Let me find the spreadsheet. Like all my projects, by the time I finally get them running I have forgotten. It's less than you would think.
Oddly Hans Polak came up with exactly that last year. For MM you can phantom power it no problems, MC generally needs a bit more. I have a focusrite Scarlett to try this out in (mumble ) years if I ever clear the backlog.
Two words:
QCAD: QCAD - QCAD: 2D CAD
ModuShop: Modushop by Hi-Fi 2000 | Contenitori per Elettronica | Electronic Enclosures | Hi Fi Chassis
Gianluca will be happy to send you the CAD drawings of the chassis you need. Then you just draw where you want the holes, and voila, you have a chassis. It's not the cheapest solution, but man is it ever nice to just have to turn the screwdriver and have an amp built in an afternoon instead of in a weekend. Granted, I tend to build more than one, so maybe my perspective is different.
Tom
QCAD: QCAD - QCAD: 2D CAD
ModuShop: Modushop by Hi-Fi 2000 | Contenitori per Elettronica | Electronic Enclosures | Hi Fi Chassis
Gianluca will be happy to send you the CAD drawings of the chassis you need. Then you just draw where you want the holes, and voila, you have a chassis. It's not the cheapest solution, but man is it ever nice to just have to turn the screwdriver and have an amp built in an afternoon instead of in a weekend. Granted, I tend to build more than one, so maybe my perspective is different.
Tom
Yup, those Modushop chassis are about as foolproof as you can get. The Ghent Audio case for 3 channel ICEPower was a breeze as well. While custom machining and printing doesn't come cheap, after hacking a raw Slimline case for Hypex, I'd decided that woodworking is a lot easier than metal bashing. The DIYAudio ACA1.5(?) chassis was a bargoon AFAIC.
But that would cause me to admit total failure in my goal to have the amplifiers integrated into the speaker stands and require a renegotiation with SWMBO. Not quite ready for that. Give me another 3 months maybe
I noticed the default configuration of the Modulus-86 provides 10x gain (20dB). I have a LM3886DR right now, with the default gain of 20x (26dB). My LM3886DR is hooked up to a B1 buffer, and I listen to 8 ohm floorstanders with a sensitivity of 91dB. Loud listening has the volume of the B1 about half open so there should be some headroom. Do you think I need additional gain on the Modulus-86, or maybe on the universal buffer that I'm putting in front of it?
I understand that this is also depending on the sources. I want to focus on the best result for the future, but it won't be any fun if my current setup won't provide loud enough listening levels. In the future I plan to build a balanced DAC which should provide the 1.8v input voltage. Right now I have a cheap logitech bluetooth box though (which could be worse). I'd be prepared to get a commercial DAC/streamer to bridge the gap if it's affordable (recommendations welcome).
I understand that this is also depending on the sources. I want to focus on the best result for the future, but it won't be any fun if my current setup won't provide loud enough listening levels. In the future I plan to build a balanced DAC which should provide the 1.8v input voltage. Right now I have a cheap logitech bluetooth box though (which could be worse). I'd be prepared to get a commercial DAC/streamer to bridge the gap if it's affordable (recommendations welcome).
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You can build the Modulus-86 with 26 dB gain if you'd like. Just swap out one resistor (R14 if I recall correctly - it's mentioned in the design doc).
That said, 20 dB gain would provide better gain structure. I generally don't find I need additional gain. My LXmini and Modulus-86 now serve TV/home theatre duty and the volume on my MiniDSP SHD driving them rarely makes it above -30 dB.
So unless you need the amps to have the same gain, I would build the Modulus-86 with its default 20 dB gain.
Tom
That said, 20 dB gain would provide better gain structure. I generally don't find I need additional gain. My LXmini and Modulus-86 now serve TV/home theatre duty and the volume on my MiniDSP SHD driving them rarely makes it above -30 dB.
So unless you need the amps to have the same gain, I would build the Modulus-86 with its default 20 dB gain.
Tom
Thanks for the quick answer Tom. I needed to know that last piece of information before placing the order at Mouser. I hate it when I need just two resistors and have to pay shipping for that. All parts are now in transit, except my Modushop cases. I need my back panel connectors to measure them before I can make a CAD drawing and send it to them. Thanks for the tip on that, I knew about the option but not about open source CAD software. Maybe it's a bit less "DIY" but who cares, I didn't mine the ore for the copper either.
If your order ships from Mouser in the US, expect it to be delayed. Part of the delay is due to the recent "extreme weather event". I also think they're making some changes at their facility. They've made a lot of changes to their shipping materials lately and I've had orders take 3-4 days to ship even before the weather hit, which is unusually slow for them. They normally ship the same day if I order before 3-4PM.
At least they've been pretty good about sending out status emails and I'm not in a hurry to get the parts.
Tom
At least they've been pretty good about sending out status emails and I'm not in a hurry to get the parts.
Tom