perrew wrote:

Romy, I might be confused with the passive and active, but from my understanding you prefer your active 834PT to the passive RC network and passive LCR networks. You also prefer the passive LCR to the passive RC. So 834PT>LCR>RC. If I got it right a RL network will be similar to a LCR from needing a capacitor for the ground and then additional capacitor for the amplifier stage unless the amplifier stage is direct coupled or you can use a Transformer in between, which need to be matched. If the biggest advantage from the LCR network is the RIAA curve is not altered from change in tubes is not such big advatage any longer why then choose the increasing complexity of the LCR over the simpler RC? P

Perrew,

We need to keep a perspective on what we are talking about. There is a different about what we prefer and what we use. What I prefer is RL filtration and in context of RIAA it gets converted into LCR filter. Theoretically it is possible to avoid the final cap at the bottom as well and use only pure inductance filtertration:

http://www.RomyTheCat.com/TreeItem.aspx?PostID=644

…but the pure inductive RX ides has own issuers.  That is what I “prefer” but it is not necessary what I use. We trade opinions about conceptual advantages but we do not justify that that what we use. I do use a phonostage with feedback, I like it very much and am not going to change it to LCR. (I have then LCR phonostage as well). My feedback phonostage is a different type feedback, the one that use native tube’s Miller capacitance to write the curve. Still, I have no experience to evaluate METHODOLOGICALLY PROPERLY the advantages of my type of RIAA vs. LCR RIAA.  To compare two completed phonostages does not signify a lot about the advantages/disadvantages of a given RIAA filtration method.  So, my position is my feeling that LCR might be adventitious and it is what I “prefer” as better RIAA filter. Still, I use my feedback RC, so what, who said that what I USE must be what I prefer?

Romy the Cat wrote:

I never had a lot of trouble with high transconductance tubes. I use the EC8020 a lot. Stefano, you might look into this EC8020. I never seen it but just looked into the datasheet and it looks very interesting tube and it might be better candidate to your phonocorrector’s fist stage then the WE 437A. I generally, under other equal conditions, prefer Telefunken/Siemens tubes to any other tubes. My second choose would be the older British tube and only then I would look into all of those RAC/WE/Raytheon. Of cause it is a gross generalization but … I am comfortable with this generalization.  Thomas Mayer wrote: This is true for RC RIAAs, not for LCR RIAAs. This is one of the big advantages of the LCR technique. The network has a constant 600 Ohms input impedance, if it's terminated by the proper 600 Ohm value. Variation in the driving tubes rp does only affect the loss in the network, but the loss is always the same over the frequency band. So the RIAA curve will not chabge when the tube detoriates or when tubes are changed. That is not necessarily true. I think any passive RIAA would not be a subject of curve variation with tube aging. Moreover, I would take this argument even further. Even if we have a feedback RIAA, where the gain of the open loop is in the task of direct shaping the RIAA curve, than I feel that aging of the tube and minor change of their gain is not truly a practical issue. There are a lot of people out there who go totally crazy with writing the accuracy of the RIAA curve with .05dB precession. I feel that it is absolutely not necessary. If you want RIAA precession then have your corrector to run multiple curves as 50% of records out there are NOT RIAA pre-equalized. It is not to mention that there was a huge deviation in the RIAA equalizers during the cutting of the records. From what I see the .25dB-.5dB accuracy is plenty for normal record playing. The MC R loading, MM C loading, VTAs, the cartridges themselves give much higher discrepancies then .25dB. so, if you look how the small tubes change gain with time then in most cases it is not significant to affect RIAA too mach. Unless your LP is the only source you use and unless you run your phonostage a few hours each day I would not feel that the tubes aging might be a factor in RIAA running away. The Cat

twogoodears wrote:

Actually a N.O.S. EC-8020 "diamond" is worth EUR 500+ ea., an STC 3A7167M is fetching EUR 750+ ea. (I own one N.O.S. sampler with original carton box, bought by chance for cheap, years ago) and WE 437A is at "only" EUR 350+ ea.... the only tube to be still commercially available is the Western Electric's, at USD 750 ea. (EUR 501,88)...

You got to be kidding? If the prices are in this scale then I would have problems. Perhaps not becose it is too expensive but become there is absolutely no assurance that the given bought tube will be able to work in your phonostage according it noise characteristic. I would agree that probably it worth to buy them ONCE to trey what they are all about but if I have a devise that I would really upon then I prefer to have a few spare tube. I would say for phonostage that I might settle you would need to have at least 3 pairs of tested replacement tubes for me to feel comfortable. The most ridiculously expensive tube I ever paid it was a pair of new RE604. I tested what the hype was all about and went for another tube. Now, if I did select the RE604 to stay in my amps then considering the power tube go south faster I would probably need to get 3-5 tested pairs of them to feel comfortable. It has nothing to do with rational or sanity, it is how my sick mind works. According to Zodiac I am a Cancer and like any crabs we Cancers always build the stash of possessions, otherwise we do not feel comfortable…. So, to have 3 workable pair of WE437A I would need 8-10 pairs of “random” WE437A. That sounds bitey… from another hard if  your Thomas claims that  EC-8020 is very stable then you would need just 3 pairs of them…

twogoodears wrote:

Tube market is quite strange: considering that a Telefunken VF-14 with original carton-box for Neumann U-47 classic microphones reached USD 1.000/1.200 ea. price-tags the WE 437A's appears like true bargains;-)!

And you know that 90% of this cost is not from the people who NEED them and know what to do with them but from the people, who hear the hype, buy them to learn what the hype all about. I think it would be a good idea to large dealers of NOS tubes to have trial stock of tubes.  I would not mind for instance instead of buying all those tubes that I have bought for my Milq MF channel to pay let say $500 for a weekend and to have an assortment of different tube send to me to try. Perhaps it would be a good business for somebody…

twogoodears wrote:

Now, I would probably go for WE416B or C or WE417 or Telefunken EC810F, not because I'm disatisfied with my actual LCR/WE437A, but because the cost involved in tuning and maintaining to specs, or simply obtaining the correct balance between right and left channels in such a design proved to be quite expensive... always less than any medical surgery, anyway;-)

BTW, the WE417A that I used have a habit to change gain very fast and very erratically, so if you match then NOW it does not mean that it would be matched in 3 weeks or in 3 month. I presume that WE437A will behave the same.

twogoodears wrote:

Herr Mayer and myself agreed and - all considered - that's what I ended with... a nicely sounding LCR phono stage, much better than my previous vintage preamp.

I do not know what previous vintage preamp you used, whatever vintage preamps/phonocorrectors I have seen they all where crap. In what you do you need to have a very perspective about what you are trying to accomplish. Mr. Mayer and anyone else on the technical side who might assist you with building of your phonostage are endlessly blind in what they do. They build just a phonostage as an absentminded instrument and it is up to you to make this inattentive tool to serve your purpose. You do not really need a phonostage but you are trying to construct a special sound. The knowledge that your technical associates have in design audio might not be in direct relation with your sonic objective. The DIYers would go over zillion topologies, tube and options without respect to Sound. It shall be your job to discriminate result, to navigate what they do in the direction where it shall go and eventually to say to yourself: “stop, here is where I have got what I would like to have.”

BTW, the hoodlums who are interested about Inductive RIAA might fins this link useful:

http://digilander.libero.it/paeng/inductive_riaa.htm