I have seen some people built 834P with alternative input and output tubes but I never heard them. I personally tried all imaginable 12AX7-type tubes (AZ, AT, AU, 6N2P and many others) in 834P. Some other triodes were king of better “here and there” but I very much like the result that I got with my present settings and I keep using it.

In my corrector the input and output tubes is a smooth plate 12AX7 Telefunken (selected for better sound as the all different). As the middle tubes I use a broken pair of 7025 Sylvania. This is kind of a mystery story. I bought this pair for $1 at MIT fleamarket juts because I did not used the Sylvania’s 12AX7 and wanted to try them. When I placed them into my ML2 then they were not impressive not to say that they were bad, very bad. That Sylvania pair did something bizarre on tube tester. On my tube tester the 12AX7 and 7025 use the same settings and the normal “full charge” transconductance of new 12AX7 usually around 1700. I never saw before any 12AX7-family tubes that measured more then 1950. However, those Sylvanias pushed 3750…

Anyhow, when I placed those Sylvanias into the second stage of my 2834PT then my love to this corrector started to grow immensely and I really do not remember how my 834P sounded with other tubes. I believe I put those Sylvanias into use in 2000-2001 (The corrector still produces a flat response with 112pf and 330pf). I really hate to see what happen when this pair will die. However, because I heat juts opposite half of tube I will flip them from right to left channel… I think I’m all set to rest of my live with this pair of 7025 and I really have no motivations to try anything else with this corrector.

Rgs,
Romy

Dear Brian

Is it double the gain at V1?

It does not sound like that, but I can not hear any distortion even when running them at full scream straight into the amps.

Volume that I listen to is at volume that I always listened to. So I can't say the the improvement I heard is due to increased volume.

I was hoping that someone else could try this simple mod to confirm what I heard. I have very little enthusiasm to go back after the improvement I heard.

Cheers

The very much non-definitive EAR 834P Modification Guide
by Loesch Thorsten

Hi,

Given that Romy already let the proverbial Cat out of the Bag (pun intended) I think I may have to make good here....

The EAR 834P is a very simple, but rather smartly designed Circuit, implemented by EAR in a rather skinflint fashion. It's performance is pretty good for the outlay asked here in the UK (where the MM input only Version in basic black sells for under $ 600. I would not recommend the version with the build in MC Stepups anymore (I used to for a while as the build in transformers are pretty resonable), but for the difference in price between the two versions you can get VERY MUCH superior Stepups that you only need to wire up. More on that later.

The result of the skinflint implementation is that while it offers rather good performance, it is being held back in performance by a number of "cost accountant" parts as well as some potentially smart features, that to me simply don't quite work as well in reality as they should in theory. Still, given the brutally simple design and implementation the sound this thing makes is a credit to TdP's abilities to design effective, commercial products.

But hell, this is supposed to be the "Modification Guide", not an Ode to TdP. The notes below come from scratch building EAR 834P copies, the odd mod to units owned by others and conversations with fellow modketiers. In general the improvements from the measures suggested below is NOT subtle. Credit for the majority of things in here should go to many and varied people (the list is too long to print and some prefer to be known just "Friends" or "Associates" or "Aquaintances" (you know who you are), errors, omissions, gaffes, spelling mistakes and other such are mine of course, solely mine.

In order for what I write to make sense I'll link in for now a Circuit Diagram of the 834P, it may soon have to disappear due to copyright issues, so download and save it now in case you don't have it.

There seem to have been some recent revisions to the Unit. I know about many a unit without C2 and some have an extra resistor in series with the output, supposedly to kill oscillation with excessively capacitive cables.

Tube rolling and the application of major overkill external tube regulated supplies has been discussed already. I'll not again do that in detail, peruse the archives please for details and many views especially on the tube rolling.

Forever onwards EAR and to the stuff for which you have to be able to use a Soldering Iron.

Step 1:
=======

Replace C1 and C7 with SCR/Angela/Mundorf/Audyn Tinfoil & Polypropylene Cap's NOT with Hovelands (IMHO). The MIT/REL Polystyrene & Tinfoil or their Tinfoil & Polypropylene may be as good or better, I have not extensively tried them. If you don't have the greenbacks for even SCR Tinfoils mentioned above, try Arcotronics KP 1.72, which I quite like.

If your views differ from mine use whatever capacitors sound "right" to you, may they be TCC Visconol, Vitamin Q or Jensen PIO or even Hoveland. It's your Money and your Phonostage.

Remove C5, R6 & R7, then bridge R7 with a piece of high quality wire. If you want to be sure to stop any possible tendency of oscillation in the cathode follower place a 100 Ohm carbon composite 1/4W Resistor in the R7 Position C5 and R6 remain omited. If you wish to retain an ECC83 for V3 change R9 from 68K to 120K. If you plan to change the V3 to a 12AU7/ECC82 or at least 12AT7/ECC81 leave it as is in Value.

If C3 & C4 are already silver mica (they where in some Units I came across) leave them as they are, if not try finding good quality NOS non magnetic Silver Mica Units, 1% tolerance to replace them. If C2 is present, and you find the sound of the unit a little too laid back, perhaps lacking in definition and extension of very high frequencies remove it. I like the sound MUCH better without C2. Again, other folks like other Capacitors, make your own selection, but PLEASE do not put some "selected Wima MKP's" in there or crapola like that.

The RIAA Capacitors are among the most sonically critical in any Phonostage, so don't treat them as afterthought, but as the main thing. No Skimping. The Capacitors MUST have 1% or better (lower) tolerance and ideally better than 0.5% matching between channels. I like silver mica (non magnetic) best, tinfoil & polystyrene second tied with magnetic silver mics units. Normal Aluminum Foil Polystyrenes of extended foil construction are another big step down, the generic styroflex are pretty awfull and polypropylene & aluminum foil completely useless, but that is just my personal view.

Step 2:
=======

Replace C6 with Elna Silmic 100uF/6.3V or if you must Black Gate 100uF/6.3V. The SG Series Sanyo Os-Con's can be used too, but I like neither the tone of the Os-Con or the BG's, they sound a little sharp, etched and aggressive to MY ears. Again, it's your money and unit. Some people liked BG's on the Cathode a lot. Go figure.

Step 3:
=======

Change over C8 and C9 to larger value, "known good" sounding electrolytics, I'd be tempted to specify at least 100uF/385V Nippon Chemi Con (radial leads) VX series, these will be a VERY "tight fit". Also find a way to bypass them with at least 0.47uF Wima MKP04 or better (tight fit again). You could use Black Gates again, or Elna Cerafine if you can find them, the Cerafines I quite like, the Black Gates I don't like that much.

If I'd build another unit from scratch I would use a pair of Ansar
Supersound 32uF + 32uF 400V, but these are 4" long and 2.5" in diameter, no way you get them inside the original EAR case. And they cost around 50 Bucks each too.... ;-)

They are available from Cricklewood Electronics in London, you'll have to e-mail them for details.

http://www.cricklewoodelectronics.com/

If you modify an existing unit retaining the on-board supply change D1 & D2 to soft switching, superfast types and place a 100 Ohm 2W Resistor between the transformer HT secondary and the Diodes.

In a scratch build unit I actually would/do use a 240-0-240V Mains transformer and a Valve Rectifier (6X4/EZ90 or 6CA4/EZ80/EZ81), and make two electrically independent supplies, with the HT Rail in the EAR split up between the channels, so that C8 and C9 doubled up, R13 doubled up but changed to 200/220K per channal and R14 doubled up and changed to 20/22k per Channel.

Transformers and rectifiers realy belong into a seperate chassis, so C10 and on are off board, I'd recommend per channel a filter chain using 3 pcs each of 510 Ohm Resistors and 3 each of Nippon Chemic Con 47uF/450V Axial Electrolytic Capacitors (Radioshack in the US sells them) or better for that. Of course such an external unit may be added to an original EAR and the HT MAY be split up there too as detailed above if the original supply is stripped out to make room.

To me such a supply sounds much better on pretty much all accounts compared to the original. I have tried both a completely split supply (two transformers and all seperate from there on) and "semi" Dual Mono Supplies that have a common Transformer and rectifier and split up after that.

I have found (not only for the EAR and other phonostages) that if only one main supply exists the arrangement originally used in the EAR is the better one. If you have two complete seperate supplies, bring the two grounds together near the Input, to signal ground and split the PSU Rail as discussed above, taking care to return the negative side of the second added capacitors directly to the same point where the original capacitor is connected.

Step 4:
=======

Place a 1 Ohm 2W Resistor between the LT winding and the Diode Bride D3, ideally replace D3 by individual schottky diodes. This will reduce the LT Voltage. If it is at around 34V already you can leave R16 (33R) alone, otherwise adjust the value until you get 34V across all the heaters together.

As the heaters are in series in the original EAR 834P it is essentiall if you "tuberoll" to make ABSOLUTELY CERTAIN that the used Valves have identical heater ratings. Some special quality Valves have got higher heater current draws and thus should not be used in the EAR.

Step 5:
=======

For the last few bits try changing Resistors, I agree this is seriously now in the margins, but I still find quite material changes in sound with changes in resistors. The ones with largest impact are:

R1
R2
R12

Also the series resistor in the output if fitted has been reported as quite critical.

Also with some notable influence are:

R3
R8
R9
R10

You are likely to even hear small changes from the other remaining resistors, but these will be quite small.

Depending upon the desired "tone" use whatever gives you what you like, Vishay/Caddock for detail, Allan Bradly (need to be temperature cycled in the oven to stabilise their value and then selected afterwards R2 and R12 are value critical) for warm and fuzzy vintage sound or Kiwame for a sound almost as cosily warm but slightly more modern, Rhopoint non inductive precision wirewound for a "neutral" sound, but the Rohpoints sadly don't come in 750k. I guess I myself would use Caddock/Vishay R12 and Rhopoint for the rest.

Step 6:
=======

If you have the MM/MC Version bypass the internal Stepups and the switching, on all versions you may find that higher quality RCA connectors (Cardas would be my take) may improve the sound further.

As MC Stepup I would at this time recommend the Stevens & Billington TX103, depending upon the needs of your cartridge set up for a 1:10 or 1:5 Stepup. The lower stepup ratio is preferable if your pickup has enough output. The S&B TX 103 vs EAR has been discussed here previously, no need to get into more details. You get the raw transformers and wire them up, finished. Mine are still withut case, just raw transformers with wiretails.

I hope this info is of use to someone, I appreciate feedback from those that have done the mods and remember, YMMV, presented here are ideas, part choices and procedures that make sense to me, they may the polar opposite from what you like.

That said, a suitably modded or scratch build EAR 834P plus a pair of Stevens & Billington TX-103's will give tremendous performance for the final bottom line investment and is likely to embarrass some of of the higher cost "spread" that is around in the High End.

Later T

There are many ways to deal with EAR-843PT. To my ears it works wonderfully, this in my case it coupled with Expressive Technologies ET2 transformer that probably takes in totally new league. I kind of so addicted to this transformer that I even run even the high output 3mV cartridges into it, but it would be a totally different subject. The interesting fact is that as many phonostages I have tried no one sounded with ET2 as beautiful as with EAR-843PT. The key of feedback circuits is to set up a proper HF equalization of the open loop and in case of the EAR-843PT (that do not use fast tubes to begin with) the equalization it taking place naturally due to the nature of the 12AX7.

Anyhow

I perfectly in peace with the way how rebuilt EAR-843PT works with mica caps in feedback loop. Still, if you wish to take the EAR-843PT up to ridicules but beneficial extreme than you might try to work with feedback caps.

A cap sonic qualities are mostly derives from the mechanical and electrical characteristics of cap’s dialectic. The dialectic is basically an abrupt termination of a transaction line and the dialectic, being hit by current begin to micro-vibrate, defusing or coloring sound. If you even tried substituted in EAR-843PT with the capacitors that have no-mass dialectic then you instinctually here a HUGE benefits. Practically it is important in the  EAR-843PT case, as the feedback cap are constantly being re-charged. For instance "it" was done in 7788-7721 using air caps in feedback loop:

http://www.goodsoundclub.com/TreeItem.aspx?postID=41#41

So, if the material of dialectic is the bitch then why to use any dialectic at all. Here is when the EAR-843PT-VV phonocorrector comes, where WW stated form 2 vacuum capacitors in feedback. The are wonderful and not very large caps make by Russians for their military needs:

They are smaller then Western caps and have more reasonable size of the contact surfaces, they also cost practically nothing. The values are 100pF and 300pF that is 10% then the EAR-843PT needs. Boosting the feedback resistor does not resolve the problem and the EAR-843PT equalization is quite complex and winded around the entire first stage. Anagnostopoulos Antonis from Greece simulated how the EAR-843PT-VV might look like with 100pF and 300pF:

Feel free to experiment with it.

I personally, due to multiple reasons, am in a process of redoing my analog setup and am trying to convert all my analog to ET2-EAR-843PT phonostages, considering it  as a reference.

Rgs,
Romy the caT

It is nice to see you around, Jim.

A few comments. C1 in my phonostage is .28uF. The higher values were a proposal of Anagnostopoulos. I understand what he is coming form and yes my output stage of power amps will be able to handle the ULF stress. I might try it but I have nothing at this point (sound wise) that would encourage me to do so. The electrolytics in the PS? They are not bypassed, though I have tried. I detected no effect that worth to be bothered, although I religiously do NOT use the Black Gates anywhere.  Removing the C6 defiantly would be nice but I do not know if it might be possible. A grid resistor? I do not feel it is necessary. The 12AX7 is a slow tube and in the current circuit it has no parasitic oscillations. In fact the enter corrector as far from the RF hash as I was able to see.

Not the biggest point: the low voltage operation and particularly operation point of the first stage.  It is very possible that you Jim is correct and the “off the wall operation point” of the first stages is something that makes the corrector to sound so hypnotizing and so musical. I agree that subjectively the 834PT has the largest domination of the second harmonics then any other phonostage I have ever heard.  I had quite a few phonostage and now; parallel to 834PT, I have a very properly operating and very good sounding 2 stages 64dB gained phonocorrector. It is 7788-7721, with 834PT-type of feedback and both cathodes sitting right on ground (as it should be). This feedback 7788-7721 phonocorrector, the 7788-7721 RLC and many others phonocorrectors that I had sounded in a way better then 834PT but here is the irony: I always in the end returned back to 834PT.

I have multiple arms/cartridges combos and as you understand I have a one that I feel does better. Having 3-4 phonocorrector employed at the same time over the course of month and years I slowly moved a better performing corrector to the better performing functional arm (with which I play good stereo records in a good condition). This “moving” is not a fast process as there are always the issues of cartridges loading, real-estate in my rack and so on… Ironically, the 834PT with Expressive Technology ET-2 transformer always, over the time, ended up with my “best arm”. In a way, whatever I do with my analog and whatever phonocorrectors I even had: the connecting to Expressive+834PT always sounded to me like a “return home”.

To my ears the Expressive+834PT has some beautiful softness, grace, sensuality, elegance and charm that I never able to get form other sound sources, (with exception of FM). In addition the Expressive+834PT is the only know to me correctors that do not make analog to sound tacky. I understand the Guy’s comment about the “syrupy euphonic mess”. In a way it is correct. However, mess is not something that comes from a phonocorrector but something that comes from the entire playback. The Expressive+834PT, being soft space-wise, graceful, sensual, elegant and charmfull still, from my point of view possess all necessary elements that would be identifiable with the most “high precision” phonocorrectors-performers. However, the Expressive+834PT does not demonstrate those elements, does not advertise them and use it’s potentials very sparely and only when music calls upon it. Listening the Expressive+834PT is like me playing tennis against a world champion who, if he wishes, might keep me winning but who has under the hood so much “potentials” and so much capacity that it would be not even decent for him to win while he is playing against such a player as myself. In the end, I know what “syrupy euphonic mess” is but for whatever reason my analog playback does not sound like a “syrupy euphonic mess” when it driven by Expressive+834PT. There are some folks among the posters of this site, who were in my rooms and I do not think that anyone even thought that my analog results as “syrupy euphonic mess”, nor do I.

I really do not have any agenda by “loving” the Expressive+834PT. In fact I relay would love that other phonocorrectors (and particularly those that I have built myself) sounded better then Expressive+834PT. Unfortunately it is not a case. Interesting that in past I took my Expressive+834PT to a few other listening rooms and I was not able to see as interesting result compare to other phonocorrectors as I hear in my listening room.

Finally there was in interesting story about the Expressive+834PT sound. Near 70 years ago Sergey Koussevitsky and Stern rehearsed with Boston symphony and Koussevitsky was screaming and cursing in English, Russian, German and French demanding that the a specific phrase of the Stern’s violin should be opening up with “a fantastic sound”. Isaac Stern asked: “ Maestro, what would fantastic mean and how you would like me to play the phrase”. “I do not know but it should be fantastic”, - Koussevitsky replied. The fan part that at the premier that Stern’s phase did sounded “fantastic”, although nether Isaac Stern, nor Koussevitsky, nor the entire Boston Symphony still had no idea how and why it was as it was. To me, the Expressive+834PT has the same “fantastic” sound. It is very possible that it comes form the distortions in the first stage but I would afraid to loose it if I ‘fix” it. There are many good performing phonostages out there. There are not a lot that do the Stern/Koussevitsky's “fantastic sound”….

difool wrote:

What is the benefit of using 834PT in dual mono over a stereo 834PT?

That is a good question and I asked myself it numerous times. My current standing is the benefits are purely intellectual as I am not able to observe the applied benefits. I do not say that the tangible appalled benefits do not exist – I just say that I do not think that I was able to catch them.  The idea initially was that in order to get rid of any crosstalk across the channels and to improve the stereophonic imaging each channel should be completely isolated and do not use the half of the same tubes. Running two separate 834P default phonostages with MM needle did give some very-very minor advantage in imaging department – much less that it would be expected but detectable if to search for it. With ET magnetic the entire imaging presentation changes and as far as I could remember I did not detect any sensible difference between one and two correctors.

Still, what I went for custom made 834PT I decided to keep the separate PS and separate gain stages, the same I will be doing in my “End of Life" phonostage:

http://www.romythecat.com/Forums/ShowPost.aspx?postID=5856#5856

…which will be juts repackaging of what I have now. Is it necessary? I do not think so. Is it conceptually better? Yes it probably is. The other side benefit is that each half of 12AX7 has own performance (gain, cathode emission etc…) and if you have the juts a half of the tube then you might find the exact tube that you need. In case of use right and left side of the tube for two channel you need to be too lucky…

So, would I advise to go for 2 separate channels? Nope, I feel that it is unnecessary. Will I combine the channels in my “End of Life" phonostage? Nope, I will keep then separated. Will I combine the channels if I build the 834PT again? Most likely I would.

Romy the Cat wrote:

That is a good question and I asked myself it numerous times. My current standing is the benefits are purely intellectual as I am not able to observe the applied benefits.

hagtech wrote:

First, it seems like the tubes are starved.  They are running very low current.  The 12AX7 is also at low voltage.  I'm guessing they are running at about 0.3mA at 65V plate.  This operating point is way down in the muck, where the transfer curves are anything but straight.  This will result in a LOT of even harmonic distortion.  Hey, maybe that's ok, maybe that's what makes this stage musical.  Here's some ideas to think about: 1)  Rebias the tubes to higher current and voltage.  I found the 12AX7 to like 1mA with 140V or more on plate.  And 5mA for 12AU7.  Unfortunately the B+ is pretty low, so you don't have much room to play with.

Jim slightly mistaken considering that the first stage in default EAR-834P sits at 65V. I borrowed one and measured - it was 79V. Dima feels that lower operation point of the first stage is not big deal as the tube runs very low voltage on grid. Perhaps the specific harmonics of that low operation pint do crate some values of this phonostage. However, how low would it be in order the corrector do to have operational problems?  According to Dima it all depends from the specific type of 12AX7 used. As Dima explained in some 12AX7 with low plate voltage some of the electron dispatching from cathode has no enough “juice” and some of them retire on grid. This creates small grid current. That might not be a big deal in other case but what Dima explained to me is that the grid current in this case acts like low impedance load that actually shunts the loading resistor. As the result the cartridge instead of 42K for instance sees 5K that is very-very low and that would provide a very strong HF roll-off for any cartridge.

Dima, made an experiment and some of the tubes that he tried had the grid current at 65V, at 80V not of them had the problem. When he had grid current he reported that his phonostage was rolling off (it was not phonostage itself but the severally over-dumped cartridge via the grid’s shunt) at 7kHz. Would it explain the Guy’s syrupy euphonic mess?

Anyhow, I measured my both old and new 834PT and not of them have retired on grid electrons. Dima proposed to measure with very high sensitively (at least .0001V) the voltage on the first stage grid. If there is zero then there the first tube has the grid shunt. My corrector has Telefunken 12AX7 and it begins to have voltage on grid at 52V. Some other tubes that I tried crated voltage on grid from 48V to 65V, interesting that one GE tube did not have the grid’s voltage even at 40V!!!

Anyhow, Dima proposed to run the first tube pate between 80V and 100V to be on the save side. The low voltage on plate is not the problem that I experience but I thought to post it as a warning for other people to understand the nature of a potential problem.

Recently, I have become aware of a strange phenomenon after lifting the tonearm at the end of the run-out groooves. The record surface noise keeps going when the stylus is no longer in contact with the record. I am using a Garrard 301 with SME 3009 II improved with a Denon 301 cartridge. This is feeding an EAR834P which has been modified by removing C5, R6 & R7 and replacing C5 with a link. I've also upgraded the signal path capacitors, and am using Mullard ECC83 tubes and an Amperex ECC82 tube.
 
While in itself this phenomenon would appear to be benign, it occurs to me that while listening to records the level of surface noise is probably being raised by this unidentified noise, and thereby reducing resolution. I've tried replacing tubes, and replacing the C5 link with a 100ohm resister, but without any improvement.

I have owned a couple of 834P's in the past, and don't recall experiencing this phenomenon. Neither preamp was modified, other than by tube rolling. Can anyone explain what is happening, and perhaps offer a solution?

Happy listening,

Freddy

Freddy, it has most likely has nothing to with phonostage but it might be what I call “Compliance Noise”. Read the flowing posts:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PostID=8427

http://www.goodsoundclub.com/GetPost.aspx?PostID=8724

Is it what you are experiencing?

Romy,

 New member around here great website! I have what is probably a silly question about the above EAR schematic. I've been in the planning stages of scratch building a phono stage and have been looking at a few designs and just want to be sure I have a proper complete schematic of each design. I like simple and this EAR design looks to fit that bill. But anyway on to my schematic question. I can discern everything okay on the schematic but one small area near C2 10pF and what looks to be C3 100pF is whited out. Does the connection line from R4 2M and C2 10 pf just continues down and connect to C3 100pF? It makes sense to me but I just want to be sure no other component is located in that whited out(erased) area. 

                                                                                                       Thanks