Flat Phono Preamp and Inexpensive: Mutually Exclusive?

[Wigwam Jones]

I am generally looking about for a FLAT phono preamp for my Pilot Console project. The idea is that I'll want to play 33 / 45 RPM records with RIAA EQ and older 78 RPM records with other kinds of EQ. I am sort of planning to run the phono output into an onboard PC, and do EQ in software instead of through the phono preamp.

So, looking for non-RIAA phono preamps, I find expensive units. Nothing in the 'cheap' category, though. All the cheap phono preamps seem to have RIAA built into them and can't be defeated.

I realize I could apply a reverse RIAA curve in software and get back to an approximation of flat EQ, but if I'm going to be listening RT, then I'd have to re-apply EQ for the correct curve and that could be a hassle.

So, anyone happen to know what sorts of phono preamps might be out there without RIAA and for say LESS than $50? No need to link to those which cost several hundred dollars, they're out of my budget entirely, although I do appreciate that they're probably quite superior in every way.

 

[Wigwam Jones]

Could you build one? I wonder if you might find a kit cheap. It's just a straight signal amplifier, right?

I think I may have to build one, but all the schematics I see seem to have RIAA built in, and I'm not technical enough to be able to spot it and take it out again. I have read suggestions about using a microphone preamp, but the input impedance is WAY different.

It seems the 78 RPM guys who are into digitizing have the same problem. I read a lot of complaints about the lack of non-RIAA phono preamps, but the only ones anyone seem to come up with cost pretty much the world (from my point of view). I realize that $500 for a flat phono preamp is 'cheap' to some, but to me, it might as well be a million.

 

[Brett a]

I think I may have to build one, but all the schematics I see seem to have RIAA built in, and I'm not technical enough to be able to spot it and take it out again. I have read suggestions about using a microphone preamp, but the input impedance is WAY different.

It seems the 78 RPM guys who are into digitizing have the same problem. I read a lot of complaints about the lack of non-RIAA phono preamps, but the only ones anyone seem to come up with cost pretty much the world (from my point of view). I realize that $500 for a flat phono preamp is 'cheap' to some, but to me, it might as well be a million.

Sorry, I deleted my post thinking it really wasn't going to be helpful. But we can go with it.

I think what would be good to know (if you were to build or improvise) is what are the desired input and output measurements. Then it's just a matter of connecting the dots.

But maybe someone will be along to actually answer your question.

 

[Wigwam Jones]

Sorry, I deleted my post thinking it really wasn't going to be helpful. But we can go with it.

I think what would be good to know (if you were to build or improvise) is what are the desired input and output measurements. Then it's just a matter of connecting the dots.

But maybe someone will be along to actually answer your question.

Well, I'm not certain of any one way yet. But here are my thoughts.

In a standard LP system, the workflow is:

LP-->Phono-Preamp-->Amp-->Speakers

And in such cases, the idea of the preamp (either stand-alone or part of a traditional preamplifier or even build into an integrated amp or receiver) is fine. It's how I listen to my vinyl records now. Assuming I wanted to digitize them, I take a tape out and run it into a Behringer ADC and then to my PC via USB input. That's great when I want to listen without digital processing.

If I wanted to listen and record digitally, then it seems I could loop back with a DAC from the PC to the preamp and then back to the amplifier, like a tape loop or an EQ loop in the old days. But that seems unnecessarily complex for what I'm wanting to do.

Imagining that I use a PC in my console to take the place of a preamp's typical functions (outboard USB sound card to amp), then the goal would be to pop up the MM low-level input from the phono but without applying EQ to it.

So, workflow would be like this:

LP-->Phono Preamp (without RIAA)-->ADC/USB-->PC-->USB DAC-->Amp

I believe a MM phono output is 47K impedance, and 2-5 MV power. The typical line-level output is .7 to 2.5V, so basically I'm looking to amplify from 5mv to 2V or thereabouts, straight, no EQ applied.

 

[JoeESP9]

Have you considered a microphone preamp? One of them should have the gain you need without any built in equalization.

 

[Wigwam Jones]

Have you considered a microphone preamp? One of them should have the gain you need without any built in equalization.

I have considered it, but I'm not an expert on the differences between microphone preamps and phono preamps. It would appear (from Google) that the input impedances are wildly different. 47K for phono versus 470K to 1M. Again, just repeating what I'm reading online. It would be nice if it was that simple, though. Microphone amps are available relatively inexpensively, although many provide phantom power which I do not need and many are single-channel only, whereas I need stereo.

 

[TerryO]

I built a HagTech "Bugle" Phono Stage for about $50 after our Audio Club (Pacific Northwest Audio Society) had a Phono Stage Shoot-out.

First place went to a Custom-Built $10,000 Phono amp. Second place went to the "Bugle" (approx. $50.00). The rest of the 12 entries followed as 3rd, 4th, etc. All of them cost between $1500- $2500 and were less than 3 years old.
The following day I ordered my "Bugle"!

At the time that the Bugle was to be played, we all knew it was a gag and we were all laughing. After it was finished, there was complete silence...talk about being taken by complete surprise! Forget the price, it's a very, very good phono stage!

Best Regards,
TerryO

 

[Wigwam Jones]

I built a HagTech "Bugle" Phono Stage for about $50 after our Audio Club (Pacific Northwest Audio Society) had a Phono Stage Shoot-out.

First place went to a Custom-Built $10,000 Phono amp. Second place went to the "Bugle" (approx. $50.00). The rest of the 12 entries followed as 3rd, 4th, etc. All of them cost between $1500- $2500 and were less than 3 years old.
The following day I ordered my "Bugle"!

At the time that the Bugle was to be played, we all knew it was a gag and we were all laughing. After it was finished, there was complete silence...talk about being taken by complete surprise! Forget the price, it's a very, very good phono stage!

Best Regards,
TerryO

Thank you for that information! Looks like quite a cool kit. However, although it certainly appears to be very flexible in terms of building it with the desired EQ (RIAA, Decca, NAB, etc), I don't see anything about having NO equalization. Do you know if that is possible with this kit? Thanks again!

 

[dumptruck]

I would think between Hagerman and Elliot, at least one of them would be happy to instruct you on how to add a "flat" mod to their phono pre, assuming you were buying the boards from them.

 

[Jon_Logan]

A High Z mic preamp should do the trick. 40dB of gain should be about right.

When you talk about "flat", you mean a lack of designed eq, right? Be cause the frequency response will be affect by the load resistance and capacitance that the cartridge is "looking into".

If you get a high Z mic preamp with a 470kOhm, or some high input impedance such as that, just load the input (to ground with 220~330pF and a 47k resistor. With a very high input impedance the passive components will dominate and set the input impedance.

 

[Wigwam Jones]

A High Z mic preamp should do the trick. 40dB of gain should be about right.

When you talk about "flat", you mean a lack of designed eq, right? Be cause the frequency response will be affect by the load resistance and capacitance that the cartridge is "looking into".

Yes, I mean without the RIAA eq curve that nearly all modern phono preamps have built into them.

If you get a high Z mic preamp with a 470kOhm, or some high input impedance such as that, just load the input (to ground with 220~330pF and a 47k resistor. With a very high input impedance the passive components will dominate and set the input impedance.

Thanks! You'll have to explain "just load the input" to me. I have no idea what you're talking about. If you can break it down for me, I'd really appreciate it.

 

[dumptruck]

He means just take a 47kΩ resistor from the center pin "hot" input and short it right to the negative. Since the input impedance is far higher than 47k, the cart will "see" the load as just the 47k in parallel. I'm not sure I see this as making much sense if you don't already HAVE a mic preamp, though.

 

[Wigwam Jones]

He means just take a 47kΩ resistor from the center pin "hot" input and short it right to the negative. Since the input impedance is far higher than 47k, the cart will "see" the load as just the 47k in parallel.

Oh, that's cool. Thanks!

 

[tblob]

The old Shure M64 phono preamp will do phono(RIAA), tape(NAB), or flat.
It can also be obtained cheaply and can easily be "hot-rodded" with higher quality components.

It a good discrete circuit, and most of the music you heard on FM Radio in the 70's and 80's was probably amplified with this preamp.

Also, as an owner of many microphone preamps (some of them quite expensive), I can vouch that it is not really the right way to do things due to improper impedance.

 

[Robinhawaii]

Would the 78 be mono? I would think a UTC transformer would give you the gain needed. If mono, you would only need one (?) which should be in the $25.00 range, well within budget.

Take care,

Rob

 

[DougMac]

I have two suggestions. The first is the Tracertek CTP-1000. This is what I use. It does a good job, it's certainly good enough for 78s. It's all analog.

Another one to check is the Parasound Z-Phono USB. It has both analog and USB outs. The flat EQ is only through the USB port. I'm really thinking about getting this. I've seen some excellent reviews, then I've seen some from those who are disappointed and complain the power supply is noisy.

 

[shelly_d]

Wigwam:

Just about any audio grade Op Amp will do it for you. A flat gain amp can be made with 2 resistors, an op amp and a power supply. Input impedance is set by another resistor and, if needed, a parallel capacitor. I'm not home right now so I cannot post a quick schematic but you would probably want about 40 to 50 dB of gain.

Here is a link that has the general schematics on it. The one you would want to use is on the right, non - inverting.

http://www.elexp.com/t_gain.htm

To add the termination resistor it would run from the + input to ground. Any input capacitance you would want to add would be in parallel to the the resistor. In the diagram if R1 = 180K and R2 = 1K would would get 45 dB of flat gain. You would want to use the highest voltages that the Op Amp is comfortable with, typically +/- 12 to 15 volts.

Hope this helps you.

Shelly_D

 

[fiddlefye]

How about a pre with a tape head (NAB) input? That would be flat I presume and could be loaded to get things just right. I've owned a few of them over the years. Dyna PAS3 maybe do it?

 

[Wigwam Jones]

The old Shure M64 phono preamp will do phono(RIAA), tape(NAB), or flat.
It can also be obtained cheaply and can easily be "hot-rodded" with higher quality components.

It a good discrete circuit, and most of the music you heard on FM Radio in the 70's and 80's was probably amplified with this preamp.

Also, as an owner of many microphone preamps (some of them quite expensive), I can vouch that it is not really the right way to do things due to improper impedance.

Thanks, that's great information!

 

[Wigwam Jones]

Would the 78 be mono? I would think a UTC transformer would give you the gain needed. If mono, you would only need one (?) which should be in the $25.00 range, well within budget.

Take care,

Rob

I was wondering about those, but alas, the changer won't just be for 78s, but for stereo 33 1/3 and 45 as well, so I'm looking for a one-size-fits-all kind of approach if I can find one. Thanks!