advertisement


EAR MC4 SUT with a Quad 34 mm phono input.

H

HeinzR

pfm Member
This forum offers a wealth of information on how to adapt the Quad 34 to modern mm cartridges, starting with changing to a standard input capacitance of 47 pf or approx. 100 pf, among other possible measures. Does this only apply to mm cartridges? In my case, I have an MC cartridge, Orthofon Venice with 5.4 ohm output impedance that is plugged into the 6 ohm MC input of the EAR MC4. What is the ideal input capacitance value of the Quad 34 for an SUT of this type? Or should I also use a 47 pf cap as if it were a mm cartridge?

Does the total capacitance comes „through“ the SUT, starting with the cartridge and the tonearm cable, or does only the capacitance behind the secondary coil count, which would then be smaller in total? So I would perhaps chose an even smaller value than 47 pf?
 
MC cart's are basically immune to changes in cap'. How they sound is very much influenced by impedance.

The major problem with SUTs is that they are very much personal in taste and how they sound is also very much influeneced by what MM stage they are feeding.
 
My combination of the SUT with the MC cartrige sounds wonderful in the mm input of my MC C22CE. With the Quad 34 in the mm input it sounds a little too muffled. Actually exactly as it was sometimes described here in the forum for mm cartridges before people changed to 47 pF input capacitance on the Quad 34. That's why I thought it might help in my case too.
 
Interesting.
Way beyond me now though.
Hopefully someone with far more understanding than me will comment on cap' and imp' effects/influence on the sound of SUTs into MM stages though.
I am interested to learn too.
 
HeinzR said:
This forum offers a wealth of information on how to adapt the Quad 34 to modern mm cartridges, starting with changing to a standard input capacitance of 47 pf or approx. 100 pf, among other possible measures. Does this only apply to mm cartridges? In my case, I have an MC cartridge, Orthofon Venice with 5.4 ohm output impedance that is plugged into the 6 ohm MC input of the EAR MC4. What is the ideal input capacitance value of the Quad 34 for an SUT of this type? Or should I also use a 47 pf cap as if it were a mm cartridge?

Does the total capacitance comes „through“ the SUT, starting with the cartridge and the tonearm cable, or does only the capacitance behind the secondary coil count, which would then be smaller in total? So I would perhaps chose an even smaller value than 47 pf?
Click to expand...
Whether one is running an MC directly into a MC phono input, or a pair of transformers into the far higher resistive network of a MM stage, the ultimate frequency plot of MCs is mostly* affected by loading resistance. With step-up transformers, there exists an increase in gain, however this is combined with a reduction of the MM phono input resistance. This reduction is calculated by dividing the MM input impedance by the square of the turns ratio. For example, 47k becomes 470R with a 1:10 turns ratio, e.g. 47000/(10^2) = 470. By extension; 1:20 = 120R, 1:30 = 50R, 1:40 = 30R. Quality of transformers vary but the basic loading rule applies. What one generally wants is the best compromise between gain and equivalent loading impedance for a given MC giving the best HF response, and this often comes down to experimentation.

With a Quad 34 comes the question of whether or not this has been fully serviced, including the phono card. Regardless, setup transformers will expect to 'see' 47k.

* The sort of capacitance that MM stages typically have won't make a jot of difference, as this need be well up into the thousands to have any appreciable affect, and even then its more of an intersection with how the specific equivalent resistance affects the HF resonance peak that may help with the control of HF resonance (usually at too high of a frequency to hear, though).
 
Thank you, @Craig B for the detailed explanation. What does that mean in practical terms, sorry I'm just an interested layman. I assume that in relation to the input capacitance of the Quad 34, it means that it is very high for an MM cartridge, but that it doesn't matter to an MC cartridge...not even if an SUT is connected in between? But what about the input impedance? If I assume that the Quad 34 is still within its specification, or let us take any other pre amp with a 47K MM input…Does the large reduction in impedance by the SUT mean that the input impedance of the MM phono stage would have to be changed? Or will the downstream circuit of the phono amp be disturbed doing so?
As I said before, the MC C22CE works wonderfully on its phono MM input using the MC4. I also used to have an EAR 864 and the MC4 worked very well. Of course I have tried the four different input impedances resp. ratios of the MC4 but in the respect of high freq. weakness its all the same, the 6 ohms/24 ratio input works best with my MC cartridge.
So many questions...in case the Quad 34 need a revision on the MM phono, which components are critical to replace (except all electrolytic capacitors, which have been changed anyway)? Thanks a lot.
 
You're welcome, Heinz.

In practical terms, MM phono input capactance has no practical affect with an MC transformer going in. As to input impedance, MC step-up transformers are all specified with reference to a 47k to 50k (old standard) MM input in mind. Spec'd might be an overstatement really, as these simply return a resistance reduction in line with the transformer coils turns ratio as per the formula mentioned previously.

WRT your MC4, the 6Ohm tap isn't actually 6Ohms, that's just an easy to match user choice for any MC with an internal (coils) impedance of circa 6Ohms (rather than having 1:24 printed on, for example). With your Venice being 5.4Ohm internal impedance this is therefore seeing circa 82R loading, i.e. 47000/(24^2) = 81.6. The general rule of thumb for MC loading is 10 times source impedance as minimum, however, Ortofon typically specify 100Ohm as minimum across the board. 82R is fine.

In lieu of the above, there is nothing about your Quad 34 MM phono card loading that needs changing for use with any of your step-up transformers. If your Quad has been fully recapped/serviced then there is always the possibility that it's MM input just doesn't sound as good via an MC transformer as what you are accustomed to. Gain and/or dynamic headroom could also affect things here. Others may have something to say about these aspects.

HTH
 
Thank you very much for your further explanation, Craig. Perhaps you or others can tell me if the MC module of the Quad 34 is worth a try? Even if it means a new investment and to sacrify the SUT. For some reasons I like the Quad 34 very much especially its overall balanced sound at line level, I do not need the last sparkle of resolution but I like the fatigue free performance together with my Quad 606 and 306 in an active configuration with my Klipsch Underground Jubilees (as Roy Delgado at Klipsch named them) as well as with BBC passive designs. As I have two 34 I am wondering if I could change the parts in one of the phono modules to get a MC stage just to test it?
 
Today I had time to try something out with the Quad 34, replacing C1b and C2b with 47pF 50V ceramic types. As expected, there was little or no difference. I read on this forum that people had successfully swapped C18 and C22 from 2.2 uF to 3.3 uF. The aim for them was to lower the high pass filter a little and allow a little more low bass from the phono section. I tried this out after listening to C1b and C2b as thr first measurement. The bass is indeed deeper and more powerful but by no means too dominant. The bass simply sounds more natural. But that wasn't all.
I don't know the technical reasons so well, but believe me or not, the mids and highs really do sound noticeably different with the 3.3uF. It's not my imagination. I had two very different types of music when I was testing records. One was Thad Jones/Pepper Adams "Little Waltz" from 1966 and the other was Chicago 4 "Critics choice" and "Just you 'n' me". The difference between the 2.2 uF and the 3.3 uF is that with 2.2 uF it sounded flat and unemotional. With 3.3 uF, the sound was suddenly more vibrant, emotional and multi-layered. The music breathed so that I am now satisfied and have left it as it is. I don't know why the cap change not only brought deeper bass but also a much livelier overall sound impression and more transparence. May be it still a tad less energy in the highest frequencies but I can live with it quite well.
I listened with Oracle Delphi Mk4 with Turbo power supply, SME V, Orthofon Venice, EAR MC4 on 24 ratio, Quad 34/606 and Stirling Broadcast LS3/6.
 
I have returned to C18 2.2 uF. It was a good sound using 3.3 uF but too much bass on the long term. The C1 on the MM input is now completely removed for connecting the MC via SUP. Now the treble is really there. The MC has a resistance of 5.4 ohms. But the input of the MC4 with only 10 turns for 40 ohms gives the best result in terms of impulse and definition. The main issue was actually that there was any capacitance at all at the input of the phono module.
 
You must log in or register to reply here.


advertisement


Back
Top