- 积分
- 1300
- 在线时间
- 1761 小时
- 最后登录
- 2020-1-21
- 阅读权限
- 70
- 精华
- 0
 
- UID
- 373636
- 帖子
- 853
- 精华
- 0
- 经验
- 1300 点
- 金钱
- 870 ￥
- 注册时间
- 2011-8-1
|
英版黑胶网，Vinylengine , 楼主是Lockyer Dog, 今年初有一联串讨论，如何使用R-C将联接MM/MI唱臂线的电容等化为零，从而广延顺平唱头的频响。似向G版请教下。先谢了。
Here's a simple method for avoiding response effects of phono cable and built in phono preamp capacitance , specifically the interaction with MM/MI cartridge inductance. I make no claim as to whether to do so is a good thing or not, and note cartridge manufacturers quite possibly intend there to be a certain interaction and resonance response. However, in the cause of the great ultra low phono cable capacitance pursuit, and avoidance of that well known cable capacitance resonance, the method presented here at least allows one to test how ‘near-zero capacitance’ might perform, in a very non-invasive and straightforward way.
It's a means of 'nulling' almost all cartridge loading capacitance/cartridge inductance interaction in the audio band, and allows near-zero capacitance performance for more or less any normal phono preamp/cable arrangement. It works without modification to cables, phono preamps or cartridges, and can be implemented in an RCA 'loading plug', the same way as R loading is commonly varied, using RCA Y adapters.
I've modelled it for cartridge inductance 400mH to 700mH, and for total loading capacitance 150pf to 600pf, where the standard internal preamp load is 47k. That covers most likely cartridge/cable/preamp combinations. The results are pretty good, as illustrated below.
All one has to do is add this network across to the existing RCA connection :
Here's a table of suggested optimal R values for the modification. These values are optimal when modification inductance is approx the same as cartridge inductance :
javascript:;
For values in between, interpolate the nearest values. Where there's a 'x', the unmodified response is more accurate, so the modification isn't beneficial. All suggestions are predictions based on simulations. The usual caveats apply !
Level 2
If one obtains 100pf true total loading by using low capacitance phono cables (or even pnorris' true zero, or flavio81's armboard/headshell preamp), modifying (reducing) preamp internal C loading value, and modify the preamp to have 100k R loading, then the following frequency response plot is predicted, for the modification marked up on the plot below :
Reduce capacitance as far as possible (it's hard to get below 100pf with a seperate preamp/cable arrangement as you know). In this case, aim for 100pf total. Take advantage of increasing preamp R loading to 100k. Then add the extra network shown as a sketch on my most recent plot. For example, using a RCA Y connector as a pass through, as previously.
Ba-da-bing (in principle) !
My bad, I can see I wasn't clear that the extra network shown needs to be added across the phono connection, after reducing total loading capacitance to 100pf and increasing R loading to 100k. Values shown are good for for a 2M like, high inductance (700mH) cartridge.
It's a good idea to work with c 400mH or lower cartridges if 147pf is lowest achievable total C.
I created constraints to make tabulation of component values manageable. Lowest achievable C unlocks the best frequency response for high inductance cartridges, it really needs to be c 100pf total to achieve the curves I did with 700mH. I managed to achieve 100pf measured without going exotic though. I'll include 147pf as a table value - but 'you can't defy the laws of physics, captain', it's a passive circuit and has no gain, can't put back what isn't there ! 500mH cartridge should just be fine with 147pf and an L2 mod. Will suggest component values shortly. |
-
|
发表于 2011-9-21 13:48
楼主
MM/MI唱头一般都要在其两端并联一个负载电容器，这个电容器与唱头的电感并联谐振在高频以提升高频响应。唱臂线的电容（这个电容可能与负载电容器相比很小）实际上也是并联在唱头两端的，只要在确定那个负载电容器时把唱臂线的电容也考虑进去不就可以了吗？不过考虑是这样考虑，并没有实际测量过。