Old era 78 replay circuitry

[rontech]

I am not sure if this is the right place for this; however.

I was wondering that in the days of 78 rpm shellac discs prior to late 50's, what was provided ( circuitwise ) for replay characteristics? Then we had a radiogram plus two table radios which had P.U. inputs.

All the sets were, at various times, used with pre war magnetic and post war "crystal" pickup heads. (No turnover 78 / lp types )

I do not recall the music sounding particularly different from our records compared to records broadcast by the BBC. ( Long time ago though ! )

[Herald1360]

Not a lot in most cases! PU inputs often went literally straight on to the top of the volume control sometimes without even any switching to mute the radio side.

For early '50s hifi you could look at what Quad did in the QC2 preamp, but you'll have to be prepared to draw your own circuit to see exactly what's going on, since there's a lot of switching and plug in adaptors to find your way round!

[barrymagrec]

Most of the record companies had their own characteristic for 78s, as they did for LPs until the RIAA standard came in.

Some hi fi units had various settings for different characteristics, including Quad and Leak but if you can get hold of the DTN Williamson / GEC book on high quality sound reproduction it includes a pre amp design with quite a lot of different settings and some description of the characteristics, if I remember correctly, I have a copy but I currently have no idea where it is.

[Peter.N.]

Most early radio's that had 'pick up' or 'gram' sockets on the back had them wired direct to the volume control. I don't think that equalising had been thought about much in those days.

Peter

[Edward Huggins]

Many amplifiers that did not have pre-equalised settings, would often feature a "scratch filter" mainly for use on 78s. Indeed these can be easily built as a small cased unit and added ahead of the volume control. It can be readily removed when not needed for LPs to avoid insertion loss.

[dave walsh]

Indeed Peter and I suppose that there wasn't really that much of a Hi Fi perception then when people readily accepted a [now "mellow and nostalgic"] sound reflecting the limited fr range of the reproducer perhaps? There were significant differences in EQ used and there is a lot of equalisation literature plus dedicated pre-amps [I have one] as things got more sophisticated later but how much this reached the general public is debatable. As long as the sound seemed acceptable [and picture quality in early TV] it was the access to either, then, that was the main focus for the punter not the engineering standards. Ironically though, I often find the sound quality on 78's to be very good. Perhaps based on the old record/tape general principle that the faster it goes around the better quality.

When I put together my first RP "lash up" as a youngster it was probably not very good but sounded amazing and more importantly, was available to ME. My friend used to do excellent cassette compilations in the 80's but when I asked him how he transferred the 78 rpm material he said "What special stylus?"

Dave

[Hartley118]

You've asked an interesting question.

The early magnetic pickups used mechanical design to give some approximate equalization. For example, the HMV design illustrated was popular throughout the 1930s.

The armature suspension was pretty stiff, but the head had high mass, resulting in an in-band low-frequency resonance that gave an LF boost roughly compensating for the LF cut in the recording characteristic.

At the HF end, most 78s had no pre-emphasis, and some boost was desirable. This was provided by the resonance of the moving mass of the armature and needle chuck with the compliance of the needle and its contact with the record groove. This would typicall peak around a few kHz and there was no ambition to reproduce above 5kHz.

If the resulting flat-ish response emphasised too much surface noise, capacitors were sometimes switched in parallel with the pickup as a scratch filter. Together with the inductance and resistance of the pickup, a reasonably steep cut filter could be created. We have to bear in mind of course that the preferred end result was normally a mellow sound and only a few emerging 'quality enthusiasts' would tolerate hearing surface noise in order to listen to more of the detail in the recording.

Post war, more science was introduced into pickups and their equalization. The head labelled RGD is a relatively sophisticated Garrard 'Lightweight' magnetic head with sapphire stylus fitted to a Garrard RC60 autochanger from a 1940s RGD radiogram. RGD took some trouble over equalization, illustrated by the pictured cluster of Rs and Cs connected betweeen the pickup and the feed to the amplifier.

Martin

[RojDW48]

Very interesting post, Martin. I have an HMV 2001 RP with a fascinating 'turret' style speed change arrangement on its Plessey TT. Under the turret there are different arrangements of components for different speeds that switch in and out as you change the speed. So someone was thinking about these issues in 1952 at least. I'll see if I can dig out the data and post it.

[rontech]

Thanks for all the replies, very informative response.

The main record player used by my father was a Garrard RC4 autochanger. When I was very young ( 4 -7 ish ) the pu head was a Garrard magnetic one, seem to remember a permanent magnet and a coil inside the head shell. The head was removable by turning through 90 deg. Later, a crystal unit appeared., I think it had a manufacturer's label "Rothermel / Brush" on the base . The case in which it was fitted had the Garrard logo stamped on the top and had the same arm fitting as the magnetic ones. I recall about this time steel needles were banished and fibre "needles" were used. There was also a device with a chuck to hold the needles and enabled them to be "sharpened" by rotating them against a strip of sandpaper. I think the sharpener was made by Imhofs of London.

The result was a dramatic reduction in surface noise and of course a nice "mellow tone"

All the electronics in those days was from the 1935 - 1938 period. ( HMV, Marconiphone and RGD.

[RojDW48]

Found it! The equalisation bit of the HMV 2001 RP

[Ed_Dinning]

Hi Gents, a 50's edition of Radio Constructor had a comprehensive preamp/ equalisation stage and listed component values for many different makes of 78's and pick-ups.
I should be on line in the Rad Constr site

Ed

[dave walsh]

The 1956 Dynatron Windsor RG10A, offered on 1/8/18, was very interesting.
The Amplifier photo shows three options 78/Hi-Fi/LP.

Chas Miller designed a home brew valve amp with 78's in mind and it was in three editions of The Radiophile [1989] when it [almost] combined with Radio Bygones. Chas had several switched EQ options in that as I recall.

Dave

[dseymo1]

I remember owning a preamp which offered perhaps half a dozen switchable eq options to suit the various record manufacturers' products. Don't remember now what it was, though.

[kalee20]

F Langford-Smiths's 'Radio Designer's Handbook' gives several equalisation curves. The RIAA had only recently agreed a standard, for use with 33rpm records being developed, and as others have said, there were many characteristics around.

I built a magnetic pre-amp with 6 different switchable characteristics (one being RIAA, one being completely flat). It worked well, but trying to gauge which characteristic a given record was recorded with, was a bit subjective!

Really old, pure acoustic recordings would, of course, be even harder to pin down. Just use the tone controls till it's as good as you can get!

[Ted Kendall]

Originally Posted by kalee20

I built a magnetic pre-amp with 6 different switchable characteristics (one being RIAA, one being completely flat). It worked well, but trying to gauge which characteristic a given record was recorded with, was a bit subjective!

Tell me about it. One thing which makes this easier is to have three switches, one for the bass rolloff, one for the mid-range kink and one for the top rolloff. If you leave the outer two open and adjust the mid first, then get the other two sounding right, the process is fairly straightforward, with practice. Even with the right curve, some trimming with tone controls is usually needed. The point is to get as close as you can with simple curves, so that the downstream tone controls don't have to be worked as hard and therefore give better results.

Originally Posted by kalee20

Really old, pure acoustic recordings would, of course, be even harder to pin down. Just use the tone controls till it's as good as you can get!

The acoustic recording process is essentially a combination of resonances, so there is no deterministic replay curve. However, the same procedure works well - adjust the curve controls until things sound roughly right, and then tweak to taste. A good third-octave graphic is my tool of choice here.

[Peter.N.]

Originally Posted by dave walsh

Indeed Peter and I suppose that there wasn't really that much of a Hi Fi perception then when people readily accepted a [now "mellow and nostalgic"] sound reflecting the limited fr range of the reproducer perhaps? There were significant differences in EQ used and there is a lot of equalisation literature plus dedicated pre-amps [I have one] as things got more sophisticated later but how much this reached the general public is debatable. As long as the sound seemed acceptable [and picture quality in early TV] it was the access to either, then, that was the main focus for the punter not the engineering standards. Ironically though, I often find the sound quality on 78's to be very good. Perhaps based on the old record/tape general principle that the faster it goes around the better quality.

When I put together my first RP "lash up" as a youngster it was probably not very good but sounded amazing and more importantly, was available to ME. My friend used to do excellent cassette compilations in the 80's but when I asked him how he transferred the 78 rpm material he said "What special stylus?"

Dave

I did the same and felt the same especially with my big baffle loudspeaker but although most domestic equipment lacked 'top' to say the least there was some very good quality gear available.

In 1954 I worked in London for a firm that sold Leak, Quad and other quality amps and I must admit that although they didn't have the technology available now the sound was superb especially with a good speaker, I say 'a' as it was all mono then. I don't really think I have yet heard anything that sounds better, might be better specified but still doesn't sound better.

Peter

[Hartley118]

In the 1950s and 60s, aside from the high output 'Dansette-style' crystal cartridges, there were some quite decent quality crystal turnover cartridges of modest output. The manufacturers took some trouble to supply equalizing circuits for the best results.

The RIAA disc cutting curve approximates to constant groove modulation amplitude, so the crystal cartridge (an amplitude sensor) starts off with the advantage of a fairly flat response.

However, cartridge manufacturers did supply circuits for correction networks. Here's an example from the Collaro 4T200 transcription unit brochure. My unit is fitted with the Collaro 'Transcription' crystal cartridge, made I think by Ronette, and gives good results playing directly into the 1Mohm gram input of the Pye 39J/H radio featured in my avatar. I never actually bothered with the switched '78' equalization because it sounds OK as it is. The coloration inherent in the 10-inch speaker and cabinet rather dominates with an appealing 'period' sound.

Martin

[bluepilot]

Originally Posted by Ted Kendall

One thing which makes this easier is to have three switches, one for the bass rolloff, one for the mid-range kink and one for the top rolloff.

That's interesting Ted. One thing I can never do satisfactorily is to determine the correct equalization parameters. I always put it down to my ears being too old. I know that the bass was cut and the treble boosted to varying degrees on recording and that these need to be compensated on playback. My preamp just has independently selectable bass boost and treble cut. What exactly is the mid-range kink? Is it something other than what happens naturally between the other two parameters? In practice I do the equalization digitally so how would you specify a suitable filter?

[gramofiend]

There is quite a lot on the internet on this subject and as usual some rubbish! I casually looked for a few pointers and found this which you might like to take a peek at. http://www.normanfield.com/phonopreamplifier.htm
Nowadays we are spoilt for choice for playback transducers/cartridges. I use Shure SC35, M44 and Ortofon OM series cartridges using OM2S styli of several shapes made by Wyndham Hodgson of The Expert Stylus co. I think, for most purposes, what he does not know about stylus manufacture can be quietly forgotten. He does make most of the tips for the American Library of Congress and the BBC to name but two and circuitry can be adapted from sets featured in circuits featured in the radios on the BVWS disc. I am currently working my way through about 17 or so radiograms dating from 1932 to my latest aquisition a Dynatron Queen Anne although that one comes, I suppose, from a time after Dynatron was sold to ECKO and thence to Philips. Beware if you use crystal cartridges to get 'an authentic sound', you may be dissapointed as many of these are by now past their best and may not even work at all! Good luck and above all have fun. There are plenty on here who have all started by experimenting and I guess most of us have made mistakes.
Mike

[Ted Kendall]

Also try this:

Google "manual of analogue sound restoration techniques"

- Peter Copeland's magnum opus on the subject. No circuitry but an exhaustive treatment of the requirements.