Phono preamp without RIAA correction

[Gold]

That is because 1KHz is the 0dB reference frequency. This has nothing t do with turnover frequencies. If you look at the first page of the spec it says "thee disc recording characteristic is defined as the modulation of the groove spiral as a function of frequency (expressed as a velocity ratio)"

So the recording curve shows an increasing velocity with frequency which is constant amplitude.

Cheers

Ian

I said it backwards before. Above 1K it’s constant amplitude. Below 1K with falling frequency response it’s constant velocity.

 

[k brown]

Modern mic preamps are typically engineered to be bridging terminations to low Z microphones or 10x the nominal 150-200 ohm mic impedance. 1.5-2k ohm termination is low for a MM (moving magnet) phono cartridge.

JR

DMP3 Direct In can take balanced or unbalanced; input impedance is 100k.

A simple mod can give any mic pre a similar HiZ input.

 

[Gold]

DMP3 Direct In can take balanced or unbalanced; input impedance is 100k.

A simple mod can give any mic pre a similar HiZ input.

An MM phono cart needs to be terminated with 47k ohm. If not frequency response will be incorrect.

 

[k brown]

Something like the Hafler DH100 phono pre is very easy to build and the RIAA is passive EQ between two flat gain stages.

Parts list shows 5532 for both stages; my example actually had TL082 for 2nd stage (apparently version 1).

 

[Newmarket]

DMP3 Direct In can take balanced or unbalanced; input impedance is 100k.

A simple mod can give any mic pre a similar HiZ input.

You can add a DI input on obviously. But that may not be the best solution in terms of. gain staging / SNR.

 

[Mr. Moscode]

If you want 5532 dual op amps on a small board configured for around 20 db you can find them on Ebay and Amazon for very little $. Change a few Rs and you can get more or less gain.

 

[JohnRoberts]

DMP3 Direct In can take balanced or unbalanced; input impedance is 100k.

A simple mod can give any mic pre a similar HiZ input.

That sounds easy... tag you're it.

FWIW the unterminated input impedance of different topologies varies dramatically but most will be >47k. Some more than others.

JR

 

[ruffrecords]

I said it backwards before. Above 1K it’s constant amplitude. Below 1K with falling frequency response it’s constant velocity.

The curve has the same slope either side of the turnovers so it is all constant amplitude apart from the bit between the two turnovers.

Cheers

Ian

 

[Mr. Moscode]

As for using a stereo phono pickup you'll need to take into consideration that a stereo record is cut so one side of the V groove is one channel and the other is the other channel. In other words the channels are 45 degrees from vertical and horizontal and are 90 deg from each other.

That said it, if the cartridge is held on the instrument the way it sits on a record it will pick up lateral and vertical motion. You would have to tilt it 45 degrees to get pure vertical motion and ignore lateral movement in one channel, and the other channel will contain the lateral and ignore the vertical movement. It you have a skinny cartridge you may be able to mount at a tilt, if not you may have to put something to bridge the space between the needle and instrument. And the cartridge needs be immobile relative to the instrument.

That will take some experimenting to get the balance you want.

You could use 2 amps, one for each channel which would probably lead to some interesting sounds.

I thought about this for a string bass pickup but didn't spend much time experimenting. I use a commercial bass pickup.

 

[Gold]

The curve has the same slope either side of the turnovers so it is all constant amplitude apart from the bit between the two turnovers.

Cheers

Ian

I don’t think that is correct. If it was all constant amplitude the low end would take up all the room on the disc.

The idea is to have the low end constant velocity so 20Hz takes the same amount of space as say 400Hz.

On the top end you want constant amplitude so 20K doesn’t disappear into the noise floor.

 

[Mr. Moscode]

Following up on the cartridge from Gearspace, from Wiki:

While the Stylus only moves horizontally when reproducing a monophonic disk recording, on stereo records the Stylus moves vertically as well as horizontally. During playback, the movement of a single Stylus tracking the groove is sensed independently, e.g., by two coils, each mounted diagonally opposite the relevant groove wall.[42]
The combined Stylus motion can be represented in terms of the vector sum and difference of the two stereo channels. Vertical Stylus motion then carries the L-R difference signal and horizontal Stylus motion carries the L+R summed signal, the latter representing the monophonic component of the signal in exactly the same manner as a purely monophonic record.

https://gearspace.com/board/so-much...does-turntable-decode-m-s-audio-into-l-r.html
So If you want to maximize the vertical, with respect to the cartridge, component of the instruments vibration mix the channels out of phase. you just have to invert the connections on one of the the cartridge's channels. If you want the lateral vibration, horizontal, then hook them together in phase. RE Equalization, you'll have to experiment. You might want to try 2 channel mixing board with eq to experiment.

Post a recording if you have any luck.

 

[Gold]

As for using a stereo phono pickup you'll need to take into consideration that a stereo record is cut so one side of the V groove is one channel and the other is the other channel. In other words the channels are 45 degrees from vertical and horizontal and are 90 deg from each other.

That said it, if the cartridge is held on the instrument the way it sits on a record it will pick up lateral and vertical motion. You would have to tilt it 45 degrees to get pure vertical motion and ignore lateral movement in one channel, and the other channel will contain the lateral and ignore the vertical movement. It you have a skinny cartridge you may be able to mount at a tilt, if not you may have to put something to bridge the space between the needle and instrument. And the cartridge needs be immobile relative to the instrument.

That will take some experimenting to get the balance you want.

You could use 2 amps, one for each channel which would probably lead to some interesting sounds.

I thought about this for a string bass pickup but didn't spend much time experimenting. I use a commercial bass pickup.

I'm not sure what your point is? In a disc recording system Input = Output with all the caveats of an analog system. If you play with the the angle the stylus contacts the disc you will get odd and heavily distorted results. The vertical/lateral encode and decode is a function of the way the cutterhead/phono pickup is constructed. The output of the cutterhead drive amps is Left/Right. There is no sum/difference encode/decode in lathe electronics or a phono preamp.

 

[ronchinoy]

Grab a schematic off any old Akai Amp from the early 80s. And have a look at their Phono Section.
That is what I did when I wanted to make my RIAA complaint pre amp.
Only problem is finding this old ICs. they used. But when it comes to sound I really liked the Akai Phono sound.
Another option would be to look at headphone amps. There are some mind blowing designs and work done here.
I would think a Head Phone amp is nothing but an amp without RIAA filters. One design so impressed me I think it was called the O2. That I was thinking of building it and adding RIAA filter to it.

 

[thomasdf]

I am amazed by all the interest here, thanks a lot ! Love this place and the debates / ideas, chiming in !

To tell you a bit more about what I have in mind : on another thread I showed interest in building an plate reverb (the old school EMT way)

I'm still investigating this, and really would like to try a pair of Audio Technica (entry level) audio cartridges (bang for the buck !) attached and decoupled to / from the metal structure, the stylus on the plate. Why ? I don't like piezo pickups (tone, mechanics, the vibrations they tame, the impedance) and I realized a phono cartridge might be a good candidate : 20hz - 20Khz response, fine dynamics, beautiful and delicate tone, and the list goes on. Vox even made some spring reverb with record pickup in some of their amp with the spring soldered to the stylus ! So why not ?

I'd like the freq response to be as flat / smooth as possible so I can have some room for hi / lo cut and EQing / gentle tone shaping, I am afraid RIAA would be too boomy and dark... but I'll have to do some trial & errors. Anyway I plan to EQ on the way in, and probably deess too, in my experience it can help a lot.

Back to electronics : so far I like the 5532 design because I have plenty, and it seems clean and not overly complicated to setup. The amplifier part will be a Class D mono 60W amp I have here, it doesn't have to be loud but I wanted it to have some kind of "autority" in the signal reproduction, and lots of headroom.

Next step is trying an repro amp with a cartridge on various surfaces / angles and if it sounds interesting or promising ... getting to the metal work.

While doing some Googling, I found this funny video :

Audio is out of phase (obv) and I don't know why he didnt try with other material than his little box, but you'll understand why it made me what to persue in that cartridge as contact mic way

 

[gyraf]

..try doing an analysis of how your system frequency response behaves "as-is", then map out what response emphasis you'd always want - and at last, what response parameters you'd like to tweak on a case-to-case basis (i.e. its control panel). IIRC, EMT had emphasis/deemphasis in the 140, dunno about the goldfoil.

 

[ruffrecords]

I don’t think that is correct. If it was all constant amplitude the low end would take up all the room on the disc.

The idea is to have the low end constant velocity so 20Hz takes the same amount of space as say 400Hz.

On the top end you want constant amplitude so 20K doesn’t disappear into the noise floor.

I don't understand that. A 20Hz wave of a given physical amplitude on the disc takes up no more room than a 20KHz one.

Cheers

Ian

 

[thomasdf]

..try doing an analysis of how your system frequency response behaves "as-is", then map out what response emphasis you'd always want - and at last, what response parameters you'd like to tweak on a case-to-case basis (i.e. its control panel). IIRC, EMT had emphasis/deemphasis in the 140, dunno about the goldfoil.

It's true that's there's quite a lot going on : https://www.barryrudolph.com/recall/manuals/emt140.pdf

EDIT : now that I think about it, maybe it could be interesting to pickup with a RIAA preamp and drive the plate with a reverse RIAA just like cutting a record ?

 

[Newmarket]

I don't understand that. A 20Hz wave of a given physical amplitude on the disc takes up no more room than a 20KHz one.

Isn't the point that in music there is much more energy in the lower frequencies so the amplitude of a 20Hz signal will always be much larger than a 20kHz signal ? If this were reproduced 'flat' on disc then the low frequency excursion would be excessive whilst the high frequency signal would be very small (so poor SNR) ?
Happy to be enlightened if my understanding there is too basic.

 

[13engrsapper]

There are lots of example circuits for RIAA preamps in the older transistor and tube manuals. You could build one and leave out the compensation. Personally I would just buy a Danner Cassette line amp - look at the tape machine amps too.. and modify it to my needs if it was a one-off thing - it's already got an enclosure and board, most likely transformer coupled, and a properly functioning circuit on day one- a great start for little money. Build your own external compensation board if need be.

 

[zamproject]

so far I like the 5532 design because I have plenty, and it seems clean and not overly complicated to setup.

then have a look at the simple Studer phono amp/eq

now that I think about it, maybe it could be interesting to pickup with a RIAA preamp and drive the plate with a reverse RIAA just like cutting a record ?

That's my first thought, can be a start to try RIAA, then maybe adjust the emphasis/de-emphasis EQ curve
Probably the plate naturally do emphasis by how energy travel through the alloy ?... test should be made.

I'm also thinking about mono cartridge ? you only get one axis movement (Lat) which can have pros/cons depending of your implementation.

Cheers
Zam