29-07-2017, 01:27 AM
That’s an interesting comment about the FM3 output level, nominally 100 mV at 30% modulation (316 mV at 100% modulation). For its time, it was probably at the low end of the range, although it was consistent with Quad established practice. A look through H-Fi Year Book 1972 shows a few, such as the Sugden R21/R51, at 0.5 V (presumably for 100% modulation), with 1 V maximum for variable outputs quite common, some in between and one or two even above that level. There was nothing new about that range, though. The Rogers RD Junior AM tuner of 1952 had 1 V available, and the original Leak Troughline of 1955 had 1 V variable.
Quad adopted the 100 mV at 30% modulation convention with its Acoustical AM model of 1953, designed to work with the QCII control unit. Previously, its Quad/R tuner had a relatively low output level, around gramophone pickup level, in part required to fit the interconnection scheme for the original Quad amplifier. However, an additional advantage of doing it that way was that the ratio of AC-to-DC loading was very little affected by the additional AC loading imposed by the amplifier input. Keeping this ratio as close as possible to unity was an important element in minimizing diode demodulator distortion. For a tuner with an unbuffered output that might be used with various amplifiers, the load presented an amplifier input was an unknown variable, so mitigation by tapping down the output was desirable. In radio receivers, the AC loading was a known and fixed quantity, so it was not such an issue. (Although it did become one when interconnection with tape recorders arrived in the mid-1950s – hence the German approach to diode outlets that eventually morphed into the DIN “constant current” standard.)
The 100 mV level still allowed quite a bit of room for the tapping down of diode outputs. In the Acoustical AM case, the diode load was 150k over 4k7, so the additional AC loading added by the amplifier input (100k in parallel with the 4k7) was quite small. And evidently 100 mV was quite workable within the gain structure of the QCII. Quad then retained 100 mV at 30% modulation for all of its subsequent tuners through to the FM66. This tuner output level was mostly associated with control unit radio inputs of 100 k impedance and 100 mV sensitivity. That meant that the tuner would fully load the power amplifier with the volume control at -10 dB, which probably represented a higher volume control setting than for many or even most tuner and amplifier combinations.
The 100 mV convention was used by other makers, both for tuner outputs and amplifier inputs, an example being the Pye Mozart HFT108 FM tuner and Mozart HF10 amplifier. An interesting case was that of the Armstrong 600 series tuners from 1973. These had a “low” output of 100 mV at 30% modulation, which acknowledged an established convention. But they also had a high output of 775 mV at 100% modulation. (The previous 500 series had variable outputs, 0 to 1 V.) By then the 775 mV number was being in seen in domestic audio systems. Of course, it came from professional audio practice, and previous to that from telephone practice, where 775 mV represented the 0 dB level, corresponding to 1 mW (0 dBm) in a nominally 600R balanced pair line. Armstrong did refer to the “high” output as being a “0 dB” output. But as it was not associated with 600R, it was not 0 dBm. (I guess that it could be described as 0 dBu, but that convention seems not to have arrived until the 1990s.) I can’t think of any good reason for the adoption of 775 mV for domestic unbalanced and relatively high impedance interconnections, but it was established number and perhaps its use (along with 0 dB) conveyed an air of professionality. Also around this time, the term “line”, which hitherto pretty much always meant the 600R balanced type, was coming into use for domestic unbalanced interconnects. At one time “high level inputs” was sometimes used as the generic term for amplifier radio/tape/auxiliary inputs, but this seemed to fade out. Maybe “line” also was thought to convey professionality. It may have started with tape recorders before it was applied to amplifiers. For example, the Revox A77 had an (unbalanced) line output, and the Ferrograph Series 7 had an unbalanced 2M2 line input.
When CDs arrived on the scene in the early 1980s, CD players had a standardized output of 2 V full-scale. There may have been some uncertainty as to what the average programme output would be. Quad I think tried CD input sensitivities of 500 and 400 mV before landing upon 300 mV. That meant that a standard CD player, fed into a 300 mV sensitivity input, would produce about the same volume (at any given volume control setting) a as one of its FM tuners fed into a 100 mV input. Extrapolating from that, a tuner with an output level of 1 V at 100% modulation, fed into a 300 mV input, would match a standard CD player volume-wise when that was fed into a 300 mV input.
Thus whereas the Quad 33 and 44 control units had been based upon a “line level” of 100 mV nominal, at which level the input switching was done, the Quad 66 was designed around 300 mV. The radio input, still of 100 mV sensitivity, thus required 10 dB gain before the switching matrix. Quad could have put the 10 dB of gain into the FM66 tuner, but probably did not in order to maintain backward compatibility between the 66 system and earlier tuners.
Generally, though the industry view seemed to be that tuner outputs in the range 775 mV to 1 V (at 100% modulation) would match CD player outputs when fed into typical “line” inputs. The Meridian 200 series provided an example. The 201 control unit line inputs had a nominal sensitivity of 150 mV (although variable). The 204 tuner output was 775 mV, and the 207 CD player fixed output was the standard 2 V. Meridian evidently preferred something like a 6 dB greater difference between nominal input level and input sensitivity than did Quad.
Returning to the case of the Quad FM3, there is a good chance that when used with a non-Quad amplifier, it would seem to be short of output level as compared with non-Quad units plugged into the “line” inputs of the same amplifier. When used with the Quad 33, I guess it would depend what else was plugged into it. I think that it would more-or-less match a standard CD player plugged into the tape input set at 400 mV, or to a radio input via a 10 dB attenuator. You can get some sense as to how Quad approached level matching by noting that the special version of the disc input board with M1 configured for the Shure V15 Type III cartridge had a sensitivity of 3.8 mV. This cartridge was specified to produce 0.7 mV per cm/s of groove modulation. That equates to 3.5 mv at 5 cm/s, typically taken as the average programme level. So, one might expect that the Shure V15 III used with the special M1 input would produce about the same average programme volume as an FM3 plugged into the radio input. But with the V15 III plugged into the standard M1 input of 2 mv sensitivity, it would be 5.5 dB louder for the same volume control setting. Against that, the FM3 might be perceived as being a bit quieter.
In terms of backward compatibility, the Quad 33/303 represented a notable break with the past in respect of the control unit-power amplifier interconnection. This had been 1.4 V for the Quad II series, but came down to 500 mV for the Quad 33/303. My guess is that Quad did not want to complicate the design of the 33 by specifying an output level that would have required a higher supply rail voltage, and perhaps an extra gain stage, whereas there was no real problem with including the extra gain in the 303.
Cheers,
Steve
Quad adopted the 100 mV at 30% modulation convention with its Acoustical AM model of 1953, designed to work with the QCII control unit. Previously, its Quad/R tuner had a relatively low output level, around gramophone pickup level, in part required to fit the interconnection scheme for the original Quad amplifier. However, an additional advantage of doing it that way was that the ratio of AC-to-DC loading was very little affected by the additional AC loading imposed by the amplifier input. Keeping this ratio as close as possible to unity was an important element in minimizing diode demodulator distortion. For a tuner with an unbuffered output that might be used with various amplifiers, the load presented an amplifier input was an unknown variable, so mitigation by tapping down the output was desirable. In radio receivers, the AC loading was a known and fixed quantity, so it was not such an issue. (Although it did become one when interconnection with tape recorders arrived in the mid-1950s – hence the German approach to diode outlets that eventually morphed into the DIN “constant current” standard.)
The 100 mV level still allowed quite a bit of room for the tapping down of diode outputs. In the Acoustical AM case, the diode load was 150k over 4k7, so the additional AC loading added by the amplifier input (100k in parallel with the 4k7) was quite small. And evidently 100 mV was quite workable within the gain structure of the QCII. Quad then retained 100 mV at 30% modulation for all of its subsequent tuners through to the FM66. This tuner output level was mostly associated with control unit radio inputs of 100 k impedance and 100 mV sensitivity. That meant that the tuner would fully load the power amplifier with the volume control at -10 dB, which probably represented a higher volume control setting than for many or even most tuner and amplifier combinations.
The 100 mV convention was used by other makers, both for tuner outputs and amplifier inputs, an example being the Pye Mozart HFT108 FM tuner and Mozart HF10 amplifier. An interesting case was that of the Armstrong 600 series tuners from 1973. These had a “low” output of 100 mV at 30% modulation, which acknowledged an established convention. But they also had a high output of 775 mV at 100% modulation. (The previous 500 series had variable outputs, 0 to 1 V.) By then the 775 mV number was being in seen in domestic audio systems. Of course, it came from professional audio practice, and previous to that from telephone practice, where 775 mV represented the 0 dB level, corresponding to 1 mW (0 dBm) in a nominally 600R balanced pair line. Armstrong did refer to the “high” output as being a “0 dB” output. But as it was not associated with 600R, it was not 0 dBm. (I guess that it could be described as 0 dBu, but that convention seems not to have arrived until the 1990s.) I can’t think of any good reason for the adoption of 775 mV for domestic unbalanced and relatively high impedance interconnections, but it was established number and perhaps its use (along with 0 dB) conveyed an air of professionality. Also around this time, the term “line”, which hitherto pretty much always meant the 600R balanced type, was coming into use for domestic unbalanced interconnects. At one time “high level inputs” was sometimes used as the generic term for amplifier radio/tape/auxiliary inputs, but this seemed to fade out. Maybe “line” also was thought to convey professionality. It may have started with tape recorders before it was applied to amplifiers. For example, the Revox A77 had an (unbalanced) line output, and the Ferrograph Series 7 had an unbalanced 2M2 line input.
When CDs arrived on the scene in the early 1980s, CD players had a standardized output of 2 V full-scale. There may have been some uncertainty as to what the average programme output would be. Quad I think tried CD input sensitivities of 500 and 400 mV before landing upon 300 mV. That meant that a standard CD player, fed into a 300 mV sensitivity input, would produce about the same volume (at any given volume control setting) a as one of its FM tuners fed into a 100 mV input. Extrapolating from that, a tuner with an output level of 1 V at 100% modulation, fed into a 300 mV input, would match a standard CD player volume-wise when that was fed into a 300 mV input.
Thus whereas the Quad 33 and 44 control units had been based upon a “line level” of 100 mV nominal, at which level the input switching was done, the Quad 66 was designed around 300 mV. The radio input, still of 100 mV sensitivity, thus required 10 dB gain before the switching matrix. Quad could have put the 10 dB of gain into the FM66 tuner, but probably did not in order to maintain backward compatibility between the 66 system and earlier tuners.
Generally, though the industry view seemed to be that tuner outputs in the range 775 mV to 1 V (at 100% modulation) would match CD player outputs when fed into typical “line” inputs. The Meridian 200 series provided an example. The 201 control unit line inputs had a nominal sensitivity of 150 mV (although variable). The 204 tuner output was 775 mV, and the 207 CD player fixed output was the standard 2 V. Meridian evidently preferred something like a 6 dB greater difference between nominal input level and input sensitivity than did Quad.
Returning to the case of the Quad FM3, there is a good chance that when used with a non-Quad amplifier, it would seem to be short of output level as compared with non-Quad units plugged into the “line” inputs of the same amplifier. When used with the Quad 33, I guess it would depend what else was plugged into it. I think that it would more-or-less match a standard CD player plugged into the tape input set at 400 mV, or to a radio input via a 10 dB attenuator. You can get some sense as to how Quad approached level matching by noting that the special version of the disc input board with M1 configured for the Shure V15 Type III cartridge had a sensitivity of 3.8 mV. This cartridge was specified to produce 0.7 mV per cm/s of groove modulation. That equates to 3.5 mv at 5 cm/s, typically taken as the average programme level. So, one might expect that the Shure V15 III used with the special M1 input would produce about the same average programme volume as an FM3 plugged into the radio input. But with the V15 III plugged into the standard M1 input of 2 mv sensitivity, it would be 5.5 dB louder for the same volume control setting. Against that, the FM3 might be perceived as being a bit quieter.
In terms of backward compatibility, the Quad 33/303 represented a notable break with the past in respect of the control unit-power amplifier interconnection. This had been 1.4 V for the Quad II series, but came down to 500 mV for the Quad 33/303. My guess is that Quad did not want to complicate the design of the 33 by specifying an output level that would have required a higher supply rail voltage, and perhaps an extra gain stage, whereas there was no real problem with including the extra gain in the 303.
Cheers,
Steve
