When to apply reverse RIAA/78 turnover

[DrDave]

When in the typical restoration sequence of an old 78 should the equalization be adjusted to remove the RIAA curve put in by the preamp and apply the 78 turnover.

I've been doing it after rumble/low pass, impulse and median filtering.

Some day I will buy an adjustable preamp if I can find one at a reasonable price. Also the manual talks of choosing stylii of appropriate size. Where do you get those? So far I have only found 1 for my cartridge. I think it s 3 mil and the shape is not specified.

[Craig Maier]

Re: When to apply reverse RIAA/78 turnover

If you transferred a 78 recording via an RIAA preamplifier and you want the sound to have the proper frequency response balance, you need to reverse the RIAA curve and add back in the correct turnover. The paragraphic EQ in the Diamondcut products has the presets to do just that. As for styli, the company that I use is Stanton. The Stanton 500 cartridge is available with a myriad of larger styli. I think that the company is in NY (perhaps Long Island - at least that is what comes to my mind.) As for preamplifiers, we have designed one that does exactly what you are looking for. We are in pilot run right now and doing the final engineering evaluation of this run. These units will be sold via our website. The preamp is in a 19 inch rack X 1.75 inches (1U) in height. It includes all of the various turnovers and rolloffs that are required and also the ability to play hill and dale recordings without haveing to re-wire your phono cartridge. I expect that we will start taking orders in about two months.

[DougMac]

Re: When to apply reverse RIAA/78 turnover

I haven't heard anything about the pre-amp you're planning to market. What's the latest news?

Thanks, Doug

[Craig Maier]

Re: When to apply reverse RIAA/78 turnover

There are some very long lead time parts in the product. For example, the rotary switches are semi-custom parts and I have been informed will not be available for about 16 more weeks. That is the best information that I can provide you at this time. When the product is in stock, we will have a bulletin on our homepage indicating as such. Thanks for your patience.

[rfc]

Re: When to apply reverse RIAA/78 turnover

Craig - I hadn't planned on 78 restoration but I came across a job requiring 78 restoration. I only have a Philips 45/33 rpm turntable. Can I record at one of these speeds and adjust the speed to 78 with the DC software? If not, what 78 rpm turntable do you use?

[Beautman]

Re: When to apply reverse RIAA/78 turnover

Just a suggestion on the topic:
Perhaps future versions of the software can include some additional paragraphic presets for more playback equalization curves, such as ffrr and early Columbia lp.

[Craig Maier]

Re: When to apply reverse RIAA/78 turnover

The speed change filter will facilitate fractional speed mastering of 78's. Record them at 45 RPM and then find the speed change preset to convert it to 78. Also, you will find more details on this subject in the manual. Keep in mind that you also need a special stylus for 78's. LP stylii will work very poorly, if at all.

[Craig Maier]

Re: When to apply reverse RIAA/78 turnover

Beautman,

Do you happen to know the turnover and rolloff frequencies for Columbia vinyl and ffrr?

[Beautman]

Re: When to apply reverse RIAA/78 turnover

You can find a number of settings listed at
www.vadlyd.dk/English/RIAA_and_78_RPM_preamp.html

and
www.shellac.org/wams/wequal.html

I've also seen several 1950s home preamps that had at least one of these settings in addition to RIAA and flat. I'll keep a lookout for further information.

[This message has been edited by Beautman (edited 03-08-2001).]

[Craig Maier]

Re: When to apply reverse RIAA/78 turnover

If an acoustical recording was transferred to your hard drive with an RIAA preamplifier, then the correct process is Reverse RIAA. Acoustical recordings, by their very nature, had no intentional turnover frequency. For later electrical recordings, you can find a listing of the common turnover frequencies in the Diamond Cut Users guide shown as a function of record manufacturer.

[Dan McDonald]

Re: When to apply reverse RIAA/78 turnover

For acoustic phonograph records (like cylinders, Edison Diamond Discs, etc.), is the correct procedure simply to "reverse RIAA?" There seem to be a lot of options.

For later (but still early) recordings, how do you know which turnover freq is appropriate? Do you just go by listening?

Dan McDonald

[Dan McDonald]

Re: When to apply reverse RIAA/78 turnover

Thanks, Craig.

A couple of more questions:

1) Are audio recorders typically built with a flat response? I have a number of recordings made from the audience at concerts and wondered whether any correction was required.

2) I have some open-reel commercial recordings from the late 1970s. I checked and the pre-amp section of the receiver I am using for restoration work (a Sony from about 1980) indicates that the phono inputs have RIAA equalization but the aux (where tape recorders, etc are plugged in) do not. I guessed from that that commercial open-reel recordings probably do not have any equalization built in, but wasn't certain.

Thanks

Dan

[Craig Maier]

Re: When to apply reverse RIAA/78 turnover

Aux, or line level inputs on audio amplifiers have no fixed compensation like the Magnetic phone EQ input. Tape decks use an internal (usually NAB) eq curve for recording and playback to improve the s/n of the tape. This is transparent to the user as the tape deck handles the encoding and decoding of these curves. Only in the event that you are taking a signal directly off of a tape head do you need to use EQ. If you were doing that, the Diamond Cut Paragraphic EQ has a reverse NAB curve to decode this signal. Never use this curve if your tape deck has its own electronics, which is the case with 99 percent of the recorders out there.

[Dan McDonald]

Re: When to apply reverse RIAA/78 turnover

Thanks Craig - now two more related questions, if you don't mind.

I have a Pete Seeger concert recorded on a mono home open-reel machine in 1955. If I play it back on a fairly nice Revox (ca. 1985), it sounds like the Revox is probably adding some EQ into the tape; would the old home reel machine from the early 50s have used the same or a different eq?

Similarly, I have some rock concerts recorded with mono cassette recorders in the early 70s or late 60s. If I play these back with a late model cassette machine, will the eq match fairly closely or will these be off in some way?

Thanks,

Dan McDonald

[Craig Maier]

Re: When to apply reverse RIAA/78 turnover

Early home magnetic tape recorders, including models from the 1955 time period often "rolled their own" internal EQ. As long as the tape was played on the same machine that it was recorded, this lack of standard was of no consequence. The NAB evenually established a standard curve EQ curve for each of the speeds used. I am not sure when this standard was invoked, but I would guess that it took hold in the 1960's. AS for home disc recorders like the Recordio (I had one when I was a kid) these thing made crude recordings from a built in radio or through its crystal mike. The "cutter" was driven by a piezoelectric element of large, but very crude construction. I do not recall the exact schematic of the device, but I do recall that there was a seperate amplifier used to drive the cutter. I do not know if it had a turnover curve, but I do remember that its output was transformer coupled to the cutter. That would give it a natural turnover at some frequency determined by the magnetizing inductance of this transformer coupled with amplifiers output resistance driving it (2 x pi x Lm / Rp). As for other machines like the Victor pre-grooved recordings (which we own about 60 of) they were of earlier vintage and used a magnetic cutter. I have no idea if they had any turnover curve. I do know that they had lotsa distortion, however!