Eccentric pickup measurement - UK Vintage Radio Repair and Restoration Discussion Forum

Bufo Bill · 20th Feb 2021, 4:41 pm

I thought some of us interested in Vinyl sound reproduction might be interested in a little illustration of the vast array of techniques we use in categorising our hifi. As many will know, equalisation curves were not standardised until after the war. One of the things I love about my Quad QCII Preamplifier is that it can reproduce these curves, and we'll return to my Quad shortly. Even today, compliance of cartridges can be measured in various ways. One thing i thought was fairly standard was the measurement used for cartridge output in mV, using a speed of 5cm/ per Second (I think that's correct).

But even this was not always standard throughout the history of our hobby.

The Acoustical (Quad) QCII Preamplifier is widely known for having a range of plug in adaptors for tailoring the "Gram" input to various types of cartridges, for example a cartridge with a 16mV output and up to 50KOhm impedance or a 4mV cartridge with an impedance of up to 100KOhm. Up until recently I used an AKG P8ES, rated at 3.75mV @ 5cm/ sec. The pickup adaptor was rated at 4mV, up to 100KOhm impedance, and I was very underwhelmed with the performance. I had to turn up the volume control so high that a hum could be heard at all times.
In my ignorance (as a newcomer to electronics) I thought that the impedance must be the problem, but given the correct ingredients (a rainy afternoon, a handful of resistors, a soldering iron) I soon discovered this not to be the case.

Reading through the QCII literature, I finally found the answer to the low volume.

Quad Acoustical were measuring the voltage at 3cm/sec! So by that standard the output was 2.25 mV.

I am now using a modern Rega cartridge with a higher output, and volume problems are a thing of the past.

You live you learn, thanks for reading.
Cheers from Bill.

barretter · 21st Feb 2021, 9:21 am

The 33rpm vinyl LP wasn't introduced until 1948 (in the USA, later here) and even then there were various equalization curves until the gradual acceptance of the RIAA standard after 1954.

Radio Wrangler · 21st Feb 2021, 12:43 pm

The QCII pre-dates "meaty" cuts, the Shure audio obstacle course disc, and the cartridges needed to navigate it.

David

20th Feb 2021, 4:41 pm	#1
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Eccentric pickup measurement I thought some of us interested in Vinyl sound reproduction might be interested in a little illustration of the vast array of techniques we use in categorising our hifi. As many will know, equalisation curves were not standardised until after the war. One of the things I love about my Quad QCII Preamplifier is that it can reproduce these curves, and we'll return to my Quad shortly. Even today, compliance of cartridges can be measured in various ways. One thing i thought was fairly standard was the measurement used for cartridge output in mV, using a speed of 5cm/ per Second (I think that's correct). But even this was not always standard throughout the history of our hobby. The Acoustical (Quad) QCII Preamplifier is widely known for having a range of plug in adaptors for tailoring the "Gram" input to various types of cartridges, for example a cartridge with a 16mV output and up to 50KOhm impedance or a 4mV cartridge with an impedance of up to 100KOhm. Up until recently I used an AKG P8ES, rated at 3.75mV @ 5cm/ sec. The pickup adaptor was rated at 4mV, up to 100KOhm impedance, and I was very underwhelmed with the performance. I had to turn up the volume control so high that a hum could be heard at all times. In my ignorance (as a newcomer to electronics) I thought that the impedance must be the problem, but given the correct ingredients (a rainy afternoon, a handful of resistors, a soldering iron) I soon discovered this not to be the case. Reading through the QCII literature, I finally found the answer to the low volume. Quad Acoustical were measuring the voltage at 3cm/sec! So by that standard the output was 2.25 mV. I am now using a modern Rega cartridge with a higher output, and volume problems are a thing of the past. You live you learn, thanks for reading. Cheers from Bill.

21st Feb 2021, 9:21 am	#2
barretter Heptode Join Date: Jan 2006 Location: Todmorden, West Yorkshire, UK. Posts: 870	Re: Eccentric pickup measurement The 33rpm vinyl LP wasn't introduced until 1948 (in the USA, later here) and even then there were various equalization curves until the gradual acceptance of the RIAA standard after 1954.

21st Feb 2021, 12:43 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: Eccentric pickup measurement The QCII pre-dates "meaty" cuts, the Shure audio obstacle course disc, and the cartridges needed to navigate it. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done