MM flat preamp … i need a set of fresh ears
Posted: Thu Sep 12, 2019 6:10 pm
hi all, longtime lurker finally posting…
i have 2 of wayne's MM preamps, 1 MC preamp, and the switcher/EQ board. all i gotta do is some metal work… duh.
one of the MM preamps will be dedicated for mono. i have several ortofon mono carts—a CG 25, a CG 65, and an SPU Mono [how is that for an oxymoron—SPU stands for Stereo Pick-Up, so here we have a Stereo Mono Pick-Up…] the CGs are low Z with 6 ohm coils and 1.5 mV output).
this SPU Mono is not a "true" mono cartridge; the two coils are rotated 45° so it does have vertical compliance, but the coils pick up only lateral movements. according to ortofon, the coils have 100 ohms DCR and are said to produce 3 mV @ 1khz/5cm. ortofon recommends a load of 47k. the lead out wires of the coil are paralleled at the 4 headshell pins so that the cartridge can be used with a normal stereo phono input. if the cartridge–as recommended–sees two 47k phono preamp inputs in parallel, the effective load would be 23k5. which still seems high to me.
in order to find out the optimal load, i ripped an old verve mono LP ("ella and louis", a very early mono pressing) with different loads. because of the missing metal work, i used the mic preamps of my metric halo ULN-8; channels 1+2 were modified to 10k input, channels 3+4 to 47k.
if i only connect one channel of the cartridge to the phono preamp, the cartridge "sees" the nominal 47k or 10k. with both channels connected, the load is paralleled i.e. 23k5 and 5k. as i also have a decent 1:5 MC step-up transformer, i tried inductive loading, too—1 channel into 47k equals 1k8 reflected load, both channels 900 ohms, and using the 10k inputs, the reflected load is 400 and 200 ohms.that makes for eight different loads from 200 ohms to 47kohms. i have uploaded the files as mono wav in 96/24 to my server; the file is pretty big with 1.1gb… here's the link: <http://www.rintelen.ch/download/ella_mono_wav.zip> (guaranteed virus-free; i think wayne can vouch for me)
what i would like to ask is if you could listen to the files and let me know your opinion, which loads sounds "best". (i have listened to the files so often that i can't trust my ears anymore…)
each of the 8 tracks starts with a 1k tone from a test LP; i tried to set the recording gain so that 1k is at around -22.5 DBFS. this reference tone is followed by 10 seconds of pink noise and then two songs from the LP. the files were not de-clicked because i noticed that the clicks change their sound with the load. the files were recorded flat with 192khz/24 bit, then RIAA-eq'd in DSP with 7dB make-up gain and resampled to 96khz. as is, the loudness of all 8 tracks should be within ±1 dB; if you use the 1k tone, you can normalize the level even better.
i have noticed that with loads between 47 and 5k i could pretty much use the same gain. but once the load was 900 ohms or lower, i had to adjust the gain. going from 400 to 200 ohms required 2.5 dB more gain. the cartridge begins to sound thick and a bit sluggish at these loads, but i noticed that the clicks are less pronounced at 200…1k8 than with lighter loads i.e. the load really damps the generator.
(it has been my experience that inductive and resistive loading of MC cartridges is not the same. with resistive loading i try not to go lower than 5 to 10 times the generator impedance, with inductive loading some cartridges work fine with 2 x the impedance—e.g. an ortofon SPU with 3 ohm impedance sounds punchy and dynamic with 9 ohms reflected inductive load but a resistive load of less than, say, 25…30 ohms just kills the sound. that's why i "dared" to load the SPU Mono down to 2x its impedance.)
thank you all in advance for downloading and listening!
i have 2 of wayne's MM preamps, 1 MC preamp, and the switcher/EQ board. all i gotta do is some metal work… duh.
one of the MM preamps will be dedicated for mono. i have several ortofon mono carts—a CG 25, a CG 65, and an SPU Mono [how is that for an oxymoron—SPU stands for Stereo Pick-Up, so here we have a Stereo Mono Pick-Up…] the CGs are low Z with 6 ohm coils and 1.5 mV output).
this SPU Mono is not a "true" mono cartridge; the two coils are rotated 45° so it does have vertical compliance, but the coils pick up only lateral movements. according to ortofon, the coils have 100 ohms DCR and are said to produce 3 mV @ 1khz/5cm. ortofon recommends a load of 47k. the lead out wires of the coil are paralleled at the 4 headshell pins so that the cartridge can be used with a normal stereo phono input. if the cartridge–as recommended–sees two 47k phono preamp inputs in parallel, the effective load would be 23k5. which still seems high to me.
in order to find out the optimal load, i ripped an old verve mono LP ("ella and louis", a very early mono pressing) with different loads. because of the missing metal work, i used the mic preamps of my metric halo ULN-8; channels 1+2 were modified to 10k input, channels 3+4 to 47k.
if i only connect one channel of the cartridge to the phono preamp, the cartridge "sees" the nominal 47k or 10k. with both channels connected, the load is paralleled i.e. 23k5 and 5k. as i also have a decent 1:5 MC step-up transformer, i tried inductive loading, too—1 channel into 47k equals 1k8 reflected load, both channels 900 ohms, and using the 10k inputs, the reflected load is 400 and 200 ohms.that makes for eight different loads from 200 ohms to 47kohms. i have uploaded the files as mono wav in 96/24 to my server; the file is pretty big with 1.1gb… here's the link: <http://www.rintelen.ch/download/ella_mono_wav.zip> (guaranteed virus-free; i think wayne can vouch for me)
what i would like to ask is if you could listen to the files and let me know your opinion, which loads sounds "best". (i have listened to the files so often that i can't trust my ears anymore…)
each of the 8 tracks starts with a 1k tone from a test LP; i tried to set the recording gain so that 1k is at around -22.5 DBFS. this reference tone is followed by 10 seconds of pink noise and then two songs from the LP. the files were not de-clicked because i noticed that the clicks change their sound with the load. the files were recorded flat with 192khz/24 bit, then RIAA-eq'd in DSP with 7dB make-up gain and resampled to 96khz. as is, the loudness of all 8 tracks should be within ±1 dB; if you use the 1k tone, you can normalize the level even better.
i have noticed that with loads between 47 and 5k i could pretty much use the same gain. but once the load was 900 ohms or lower, i had to adjust the gain. going from 400 to 200 ohms required 2.5 dB more gain. the cartridge begins to sound thick and a bit sluggish at these loads, but i noticed that the clicks are less pronounced at 200…1k8 than with lighter loads i.e. the load really damps the generator.
(it has been my experience that inductive and resistive loading of MC cartridges is not the same. with resistive loading i try not to go lower than 5 to 10 times the generator impedance, with inductive loading some cartridges work fine with 2 x the impedance—e.g. an ortofon SPU with 3 ohm impedance sounds punchy and dynamic with 9 ohms reflected inductive load but a resistive load of less than, say, 25…30 ohms just kills the sound. that's why i "dared" to load the SPU Mono down to 2x its impedance.)
thank you all in advance for downloading and listening!