Fisher X-1000 integrated - Welcome

[audiodon]

This continues to be exciting and educational.
I look forward to how the EFB turns out to run the tubes in a cool manner, not only for the performance enhancements from tubes that work in a linear region and don't run hot but also because I can consider the final tubes going into the output stage to be final tubes for years and possibly decades of enjoyable trouble-free use.

Here's a link to the X-1000 and EFB thread:
http://www.audiokarma.org/forums/showthread.php?t=544769

 

[dcgillespie]

Epilog

With the installation of EFB(tm) in the X-1000, the last of its performance opportunities has now been addressed. That effort can be found in this thread:

http://www.audiokarma.org/forums/showthread.php?t=544769

With the exception of the phase inverter and phono preamp circuits, there are now no circuits that have not been heavily altered, or more likely, completely removed and replaced. And yet, in spite of all the re-engineering, the X-1000 still remains a Fisher at heart.

I have written before that the mystique of Fisher is much more that just its "sound" -- but also encompasses its look of class, and the way it operates: Whatever is was designed to do, a Fisher just does it very well, without muss or fuss. Smooth, capable, dependable, and polished are a few of the descriptors that come to mind. I think Don used "poise" as a descriptor as well. These are a combination of concepts that Avery stood for that helped to make Fisher uniquely what it was, such that the actual circuitry used to achieve the end goal was secondary. Put another way, the specific circuitry didn't make Fisher what it was, but the particular combination of its timeless good looks, the features provided, how well it operated, the pride of ownership, and yes, its sound, did. As long as these concepts are kept front and center with any Fisher project, then whatever it is will retain its Fisher heritage at heart.

And so it is with this X-1000. This unit retains all the elements that endeared the Fisher brand, but simply brought them up to the 21st century within what the basic technology can offer. The classic good looks are still there: nothing externally has physically been altered. So are the features: Original features that today are less than useful have been replaced with ones that can offer real benefit in today's audio world. So is the smooth operation, which is now even better: This unit is now so quiet and electrically unassuming, that you could easily forget it is operating if no source is playing.

From a sonic perspective, there is a great feeling now that this unit knows no limits: Bass material is delivered with authority and definition, without any sense of strain or limitation. High frequency detail is crystal clear without any impression of veiling nor tendency towards shrillness, and power just seems limitless: You never get the impression that the end of power is in sight. The X-1000 now sounds the same at any power output level, whether in a personal setting, or at an outdoor block party.

These are my impressions of course, but it is Don's that count, so a detailed accounting from him matters most. As I have stated before, this unit is now worthy of standing on its own with regards to the delivery capability in the lower regions, so I hope he will give it a chance to do that before automatically defaulting to his normal sub based operation.

The most notable impact in bypassing the tone controls is the restoration of the lowest bass octaves. With material that contains such energy, the effect is quite noticeable. This, along with the removal of the built in permanent LF filter, and improved output stage performance is what gives the re-engineered X such new found authority and definition in this region.

The extended HF response and resulting improvement in transient detail cannot be discounted either. It is the accurate reproduction of this kind of detail that helps define the sound stage, locate various instruments and vocals within the performance, and make the presentation sound alive. No doubt that everything was being reproduced before, but now, the improved response provides a focus on the presentation that simply was not there before.

The Preamp Out/Power Amp In jacks have proven to be most useful not only on the test bench, but in the listening room as well. Where as the original unit came off as a single device, the revised X is now a superb performing independent preamp and power amp unit that can be connected together as one, or separated as needed. In my listening tests, I used the X's preamps to drive my triode power amps in my listening room, as well as different preamps to drive the X's power amps to excellent satisfaction.

The new tape input/output and monitoring facilities are a welcomed change which now provides a true signal loop for any external device to use, as is the separation of the Monitor and Aux circuits, with the new recording output buffer capable of driving a small speaker if an appropriate matching transformer is used.

Having the output Common terminals at ground level now is also one of those little improvements that is so nice to have. In the lab, ground loops though Common output connections and the AC ground system are now avoided, and in the listening room, you no longer have to worry about shorted Common leads or common ground switching systems. You can actually use the Common terminals as a ground connection now, too.

With the inclusion of EFB, the original performance of the output stage can be had with greatly reduced quiescent current levels for cooler operation and long tube life, or, greatly improved performance can now be had by maintaining approximately the original current flow specification. The bias controls have been redesigned to allow enough range to cover both of these operating points for most tubes.

Also of note is that the inclusion of screen stability resistors along with the new operating conditions provided by EFB make the output stage very stable regarding any tendency towards output tube arcing. The unit was received with a blown cathode resistor on one output tube, and I have seen pics of other X-1000s with the same damage. Indeed, the original design encompasses many of the conditions that make the tubes ripe for arcing. The re-engineered X reduces that possibility by leaps and bounds.

Finally, after all the work and testing, I found last night that there is still one opportunity left to be addressed in this unit: The channels are reversed on the headphone jack! This is a common complaint today with Fisher equipment, as no standard existed when these units were built, so yet a little more bench time will be needed to correct that issue. After that, some more tests, and then a trial run on my friend's AR-9s. Those suckers are so inefficient that I call them space heaters, as that's about how much power it takes to drive them. Still, the X was offered to drive such speakers, so the test should be interesting.

The remaining details and tube testing should be finished up early next week, and then the listening tests with the AR-9s. Hopefully then, by the end of next week, I can start packing this unit up for return shipment.

Dave

 

[audiodon]

To paraphrase Paul Harvey, "stay tuned for the rest of the story".

 

[dcgillespie]

Details, Details

The wiring to the rear mounted headphone jack on this version of the X-1000 has now been corrected to the standard in place today -- which is no small feat being as the jack is the top most jack on the rear panel when sitting upright, meaning it is the hardest to get to with the unit inverted. Not that you need an X-1000 to drive a set of headphones mind you, but honestly, with the super quiet performance of the unit now, coupled with very good tracking of the original volume control, and now the channel designation being correct, it is a very pleasant experience. In any event, to not correct such a basic wiring error in view of everything else that has been done to improve the unit would just be a crime, so the correction has been made.

The plug immediately below it (sitting normally) was for connection to a SpaceXpander unit to allow remote control of that device by way of a control on the front panel of the X-1000. That wiring has all been removed of course, leaving the jack -- which is also a 1/4 inch stereo phone jack -- connected to nothing now. If desired, it could be appropriately wired in parallel with the existing headphone jack to provide two headphone jacks as the later versions of the X-1000 provided -- although the later versions relocated these jacks on the front panel. In any event, this is an option I will leave for Don to do if he is so inclined.

With that work finished, I then turned my attention to the phono preamps -- not for the purposes of any intended modifications, but rather, to assess their general performance, since some modification work had already been done to them prior to my receiving the unit. And also, as I have commented before, this same preamp circuit, as used in SO many pieces of Fisher gear, generates a full spectrum of comments, from their being the ends of the earth, to being down right godawful. My, my, they do generate strong opinions!

Don had indicated that the phono preamps had been modified for improved sound, but complained that the modification produced lower gain from the preamps in the process. Because of these comments, and because I had recently measured the performance of the identical (but stock) preamps in my modified Fisher 400 (posts #138 and #140 of that thread), I wanted to see what the effect of the modification installed in the X was, using the performance of the preamps in my 400 as a base for comparison.

Pressing Don further, the modification done was simply to replace the PEC RIAA components in each channel with close tolerance discrete components, using the same stock values as those offered within the PECs. The word "simply" is a bit of a misnomer here, as this effort, along with a general recap of the preamp unit, required the entire preamp unit to be removed, which is hardly a simple task in this unit.

Measurement was accomplished by sampling the preamp signal at the Recording Output jacks. As a side note, using these jacks now provides super accurate results of phono preamp response measurements in the modified X, since it now includes buffer circuits between the internal signal path, and any outside world equipment connected to the Recording Output jacks. Therefore, any equipment connected to these jack will not load down the signal to artificially alter the response curve.

Below 10 kHz, the response of the modified preamps was within .1 db of that which I measured from the phono preamps in my 400. Above 10 kHz however, there was a definite improvement in conformity up to 20 kHz. Where as the response drooped notably in this region in the preamps in my 400, the modified preamps in the X remained within -1 db to 20 kHz.

With this improved response, there is also much more evidence of the T3 error in the RIAA response curve that Fisher chose not to address . This is an error created in two stage feedback network type EQ designs, that creates an ultrasonic spike above 20 kHz. Because it is ultra sonic, most manufacturers chose not to address it, with the idea that any cables connecting the turntable, and connected to the tape output jacks would tame it anyway. This is certainly true, but of course this virtually always went much too far, seriously attenuating the response of the preamp circuits above 10 kHz, in the process of taming the T3 error. In any event, with the increased accuracy afforded by the discrete components, coupled with the on board buffer stages now included (normally used externally to obtain accurate measurement results anyway), the limitations of the original network are exposed. Again however, I must emphasize that this error occurs above 20 kHz, so the previous discussion is more theoretical in nature, rather than producing any real world sonic consequence with respect to vinyl reproduction.

Finally, the other notable difference is that the 1 kHz gain of the stock Fisher preamps in my 400 was clocked at 83, while the modified preamps in the X both produce a gain of 70. While it is unknown what the gain of the stock preamps were in the X before their modification, a gain of 70 would appear to be in keeping with the specifications Fisher originally provided for the X-1000. Their high level input sensitivity specification is .23 vac, while the phono input sensitivity is specified at .0033 vac. This in fact equates to a phono stage gain of 69.7, which is very close to that actually measured.

When the X was initially repaired, a base line of information was developed, where the high level input sensitivity of this particular unit came in at .21 vac for rated output. Since the new line stage amplifiers mimic the original Fisher design in both gain and input impedance, the re-engineered X also requires .21 vac to develop the same power output level. With a measured gain of 70 in the phono preamps then, that indicates that the new X will develop its full rated power output from a cartridge that can develop .003 volt output, somewhat besting the original Fisher X-1000 specification.

Finally, since the discussion is once again response related, when discussing phono preamp circuits, it is always very instructive to show what a square wave looks like when injected into these circuits. However, they cannot be directly injected, because the RIAA response curve would distort their image dramatically. However, if you first inject a square wave through a reverse RIAA network (similar to what the recording process used), and then into the phono input, a properly operating phono preamp will theoretically EQ the reversed square wave back to its originally image at the preamp's output. With how telling square waves are with respect to frequency response, this is a very tough test for any phono preamp to pass, as the opportunities for error are ripe all over the place.

As a side note, witness the rather famous article where the phono preamps of a 500 C receiver were measured. The measurement process used was so poor, that it butchered the results, leading many to believe that the Fisher preamps are a very poor design. The point here is that even the measurement process can indicate poor results if it is not set up properly.

Since the response of the frequencies between 20 Hz and 20 kHz are the only frequencies of concern, two square wave displays of 200 Hz and 2 kHz will properly cover response within the 20 to 20 kHz audio bandwidth. Pics of these square waves then include:

1. A 200 Hz square wave passing through a Reverse RIAA Network, then through the modified phono preamps of the X-1000, with the output sample taken at the buffered Recording Output jacks. This waveform shows really quite uniform response down to nearly 20 kHz, with some phase delay which is nearly unavoidable at the lowest audio frequencies in typical designs.

The response of this preamp, coupled with the extended response of the remaining circuits in there-engineered X will not tolerate any second class turntable installations now. In my listening room, the table is on a cement floor, and no problems were apparent even at elevated listening levels -- but installing this unit in a console setting with a changer unit would be an open invitation to rumble and LF feedback issues. Such a setting would now require a external rumble filter to be included in the tape monitor loop, or the bass controls reduced at the very least.

2. A 2 kHz square wave through the modified phono preamps, using the same setup as described above. Here, the T3 error is clearly seen as a spike on the leading edge. To illustrate just how high the frequencies are this spike includes, backing off the phono level outputs by one numeral (from Max to 9) added enough circuit capacitance from the shielded cable Fisher used in this preamp build to eliminate the spike. Still, the spike originates from using only a two stage FB network to achieve complete RIAA compliance.

The gain and EQ performance between the two channels was virtually identical, which no doubt the discrete EQ components helped to create. All in all then, I would suggest that for those interested in the most accurate vinyl playback, that the use of close tolerance discrete components in the RIAA FB network would make for a worthwhile upgrade.

On to testing the remaining tubes and some final listening tests, and then this project is a wrap!

Dave

 

[audiodon]

The cold light of analysis casts a warm shadow in this case.

 

[buglegirl]

Hiya,

The cold light of analysis casts a warm tube shadow in this case.

Fixed it for you Don.

Dave thanks for finally explaining why those usually overlooked PEC's are not to be ignored.

Frannie

 

[dcgillespie]

Well, this bad boy is all packaged back up (triple boxed) and in the hands of UPS for shipment back to Audiodon. With that I'll close this thread out until we hear from him!

Dave

 

[audiodon]

The X-1000 is back, unpacked, and I've looked it over and had it running.
I will refrain from comment until I've spent some time with it, but I will say that the updates were worth the effort from my initial impressions.

 

[AlTinkster92]

What a great read this has been, learned a lot as well. Thanks Don and Dave!

 

[audiodon]

When the unit first came back, the first thing I did was to take off the bottom cover and look at how much less circuitry there was under the chassis than there was when I sent it to Dave.
Then I put in the tubes, sparked it up and gave it ten minutes of quick listening on my electronics lab's Rogers JR-149s, sourced from an abandoned project of JohnVF a couple of years ago.
Those speakers use KEF B110s and KEF T27s, just like the fabulous LS3/5A minimonitors the BBC licensed manufacturing of for so many years and also like the KEF 101s have. The Rogers, though, are in an aluminum cylinder with a fairly complex crossover and wooden tops and bottoms. My pair looks like the hack job restoring them was. Since they're for test, they don't need to look good.
A nice pair, wearing socks, looks like this:

My pair of nudies, doesn't even look this good:

They are very cohesive sounding speakers though, as long as you're fine hearing the second harmonic of low frequency fundamentals instead of the fundamentals themselves. They don't have any cabinet resonance in that funky cylinder and their lack of coloration makes them very easy to listen to. In a sense, they are a cheap way to get the sound of modern speakers with very tough components.

In my passing aural glance, playing Martin Sexton's "Diner" from a CD and Blood Sweat and Tears' "I love you more than you'll ever know" from their first vinyl album told me that this integrated amplifier would be a force to be reckoned with.

 

[audiodon]

Timing is everything, and after the tingling anticipation of having the X-1000 return I didn't have time to spend listening to it for a whole weekend! Monday before work I brought the X-1000 into my office area.

Office System Setup:
Lexicon RT-10 Universal Player
Thorens TD-320 modded turntable (an 80s produced sleeper!) with a stock tonearm AT440ML Cartridge.
Spendor SP1/5 minimonitors (a 6" woofer and a Vifa tweeter)
Nordost Blue Heaven speaker wire
Audiodon made Canare RCA interconnects
preamp and amp described later.


On the following Monday, I listened to a single track from an SACD and a single vinyl track on my office system consisting of a Dennis Had's former company Cary SLP-98P preamp and a Dennis Had's Sweet 807 Inspire SET (or possibly SEP) amp.

I'd tweaked up the Cary preamp over a few months because I'd felt it was somewhat rolled off and indistinct in the bass and a bit unpleasantly crisp in the treble, but after my tube and coupling cap rolling I had it sounding pretty much like I want my close-monitoring presentation to sound like.
http://www.audiokarma.org/forums/showthread.php?t=477855

After listening to those two tracks with the subwoofer turned off, I removed the pre and amp from the circuit and replaced them with the X-1000 with the sub off.
I turned the amp on, set the volume to the 9:00 position and heard nothing. I left it for a couple of minutes when something came up I had to attend to.

Then I returned and played the same two tracks.

What arose out of the silence when I played those two tracks again on the X-1000 was a presentation that differed somewhat from the Cary/Inspire setup, having a Fisher like sweet midrange, equivalent extension on both ends of the midrange and effortless dynamic range compared to the previous setup. I will say that more was the same than was different, but I liked what I heard immediately.

The Fisher did what I love the most as well or better than the other gear and it did it right out of the shop without the addition of anything but RCA triple mica black plate 5814s in the 12AU7 positions Dave had created where the 7247s used to be.

I often form my strongest opinions about the sound of things immediately, but it's only upon repeated and sustained listening that I find I can verify and corroborate my initial impressions and decide that I have not been misled by a supernatural first impression.

I now have listened to this Dave Gillespie redesigned Fisher X-1000 for six full work days and at other times for a good solid 70 hours. All I can say is that this unit continues to satisfy. It does not seem to improve, is not ripening, but simply delivers consistently. There have been times when the music ends and I don't even change it. There is no background hiss to prompt me to put more music on.

Sometimes I'm just concentrating on my work and am not really listening and other times the music captivates me. The fact that I can have it on in the background and it plays in a non-fatiguing way or doesn't play provides a level of satisfaction that pleases me.

I've had the unit on for up to 13 hours at a time and have had no problems with apparent heat or hot transformers.

The other point of interest is that I've been finding myself pulling voicing of my gear back from lush towards neutral and non-fatiguing, especially since I bought a new pair of speakers, voiced they way speakers are today, for my reference system. I'd pulled the Cary back towards a neutral presentation.

At one point I pulled the pre/amp (former spacexpander) jumpers out and connected the Cary preamp and ran it for an afternoon with the EL-34 power amp section of the X-1000. I didn't hear a lot of difference between the Fisher pre and the Cary pre. To me, that means my voicing work on the Cary pulled it towards neutral, the same way that Dave has done with his square wave testing. In fact the presentation was so similar that the next workday I simply left the Cary in place and used it as the preamp all day.
It's interesting to me when things converge that way.
That's all for tonite. More later.

 

[AlTinkster92]

This has been a great read, will be re reading it to learn all I can, thanks Don and Dave.

 

[audiodon]

Tube Rolling in the phono stage
The phono stage consists of two tubes in the V1 and V5 positions at the far left of the chassis. This is in a modded phono stage listened to after Dave's tests in #http://www.audiokarma.org/forums/showpost.php?p=7154187&postcount=124

There's an input selector switch shared, in concept if not exact execution, with the X-202, X-202-B, 400-C pre, 101-ST and possibly a couple of TA receivers where there's an input selector switch with multiple sets of standoffs and wafers inside and two phono tubes on top, always on the extreme left of the chassis when the chassis is right side up.
I did my homework to verify that Dave did not change the function of these 12AX7 tube positions.
He changed the functions of V2, creating recording output buffers.
He changed V3 to make the channel A and B line amp.
He changed V6 to make the linestage/control output buffers.
As far as I know, he did not change the functions of these two positions, V1 and V5.
That takes care of all five 12AX7 positions in this amp.

I will state up front that the changes were relatively small and I found this section only lightly to moderately sensitive to tube rolling.

The track I used was a 45 RPM version of XTC's "Grass" from the album Skylarking.
Tubes used and impressions:
1. RCA USA made 60s style short plate 12AX7s labeled CM with 1964 date codes:
These tubes went with the amp and came back with the amp.
Good quiet linear tubes.

2. Psvane 12AX7-1 triple-mica
I bought these on BT.
Very quiet smooth tubes. Good bass and extended treble. Very smooth and linear. A top choice.

3. Raytheon triple-mica black plate 5751s.
I bought these on BT:
Great smooth bass, extended treble with lots of shimmer. Not the best choice in this circuit, these tubes would shine in a darker sonic environment. Possibly the best bass in the group for this phono stage.

4. Sylvania triple-mica 5751s:
I bought these on BT.
Good even Sylvania presentation, but did not take particular advantage of the eerie holographic sonic image these tubes can throw in certain circuits.

5. Eico/Mullard 12AX7s:
Surprisingly lively for the supposedly dark Mullard tubes. I was looking to tame the treble a bit but these tubes did not do that as much as expected. Great bounce and body. Kick drum not as distinct as most other tubes.

6. Telefunken 12AX7s:
Good overall balanced presentation with just a hint of that Tfk sparkle, but not glorious enough for me to think these have to be the tubes in this position.

7. Heath/Mullard
These are my favorite ECC83 style Mullard tubes with codes 846 and 1022 stamped sideways. These are my reference Mullards since I don't have any 10Ms.
Rich in body and texture with great treble. Same issue as the Eico/Mullards on the bass . . . not quite as distinct and tight.

8. RCA '50s style long chalky black plate 12AX7s labeled Silvertone.
Silvertone is right. Great tubes. Did nothing wrong. Also added nothing exceptional.

9. Sylvania long gray plate 7025s. These look like every long plate sylvania with yellow, green or red ink and have long been my go-to tubes in Fisher phono stages. Well, this is no exception. I continue to be astounded at how overlooked these tubes are.
I left them in because 7025s are supposedly tested for low-noise and I just love the presentation they give.

10. As a spoiler, I put my Tim DePavarincini designed EAR 834P phono stage with three of my favorite RCA triple-mica black plate 5751s in as an outboard phono stage. I ran it into the Aux-1 input.
This was another BT purchase.
This phono stage, as one would imagine, has just so much poise, depth of bass, sweet extended but not forward treble, superior imaging, fabulous midrange, and utter silence in the absence of input, it did two things:
1. Show the exquisiteness of what phono can provide, to this day, when the recording is good, the playback equipment is good, and the phono stage is good.
2. Show just how good the Fisher phono stage is.
I've said for quite a while that, when tended to, the Fisher phono stage can be quite good, though it is not world-class in this day and age. I still find that true. It gives up some bass extension to the best, and shows that additional attention is possible on the shades of imaging in treble for those discerning listeners with a pocketbook to match, but it's a good phono stage.

How good is it?
Well, let's just say that with the outboard EAR phono stage out of the circuit all afternoon while I listened to vinyl, I made no move to put it back in because the Fisher phono stage was fine. To impress my friends on the reference system? Well . . . that might be a different story.

That's all for now.

 

[dannyr]

Thanks for posting your findings. With my done 400 I end up using a Hagtech Bugle instead of the built in preamp most of the time probably because it's easier for me to play with cart loading etc. I'll have to rebuild the the Fisher's phono section fully and revisit it.

Dan

 

[dcgillespie]

Thanks for these very thorough reviews Don. A couple of points I would offer for clarity:

1. All of the actual small signal tubes you sent went right back to you (other than the 7247s as previously arranged), and while here, were carefully maintained in the positions you had originally marked each tube for before sending me the unit. With all the time you had spend with this effort, I felt it was important to maintain that continuity. The output tubes ultimately installed were selected and matched here from a group of Mullard tubes you sent for that purpose.

2. V2 (a 12AX7) is in fact now acting as a recording output buffer for both channels. What is important to note about this tube, is that the internal signal path through the amplifier does not flow through this tube at all. Rather, this tube is "tapped" into the signal path at the appropriate point, meaning that the tube in this position has zero impact on the signal flowing through the unit -- unless of course, the Tape Output/Tape Monitor Input is being used as a loop to include an external signal processor unit. In any event, for any signals routed normally through the unit, a dead short can now be placed on the Tape (recording) Output jacks of the modified X, with zero impact on the sonic presentation of the signals playing through it. If you try that on any other Fisher amplifier/receiver, the speakers will simply go dead -- proving that whatever is connected to the Tape Output jacks in those units will in fact affect the signal flowing through the unit at all times.

3. V3 became the complete left channel line stage amplifier, while V7 became the complete right channel line stage amplifier. In the process of this portion of the modification, these positions were converted to operate with 12AU7 type tubes, versus the former 7247 tubes used in these positions.

4. V6 (a 12AX7) in fact did become the new linestage/control output buffer for both channels. This tube basically operates as an impedance converter, providing no amplification, but does provide a very low output impedance for all signals appearing at the new Preamp Output Jacks. Since either jumpers in those jacks then couple the signal into the internal power amp section, or cables inserted pass this signal onto an alternate external power amp, this tube is therefore always in the signal path. Since it provides no gain however, its impact on the sonic presentation will be minimal.

5. V4 (a 12AX7) is the tone control amplifier for both channels. With the tone controls disengaged, this tube is completely removed from the signal path as well.

6. While the actual phono preamplifier circuits (also 12AX7s) were not altered in any way during my time with the X, the B+ power to operate them was.

The original design of the X included a dual B+ distribution system -- one for each channel -- this to ultimately address concerns in powering the output tubes in the original design. This design had the first stage of phono preamplifiers in both channels powered from the B+ distribution system for the right channel, while the second stage of the phono preamplifiers in each channel was powered from the respective B+ distribution network for the channel they served. This was all part of a greater attempt to balance current flow through the two distribution networks.

With the installation of EFB into the X however, it completely took over control of output stage operation, and in the process, also made the dual B+ distribution system quite unnecessary, and even inferior to that of a good single rail design. Therefore, when EFB was installed, the dual rail approach was completely removed, and a new single rail network was installed.

The effect of this on the phono preamps then is that now each stage within each channel is powered from the same B+ supply point, with those supply points providing virtually the same level of B+ as that of the original design.

I hope this clarifies the function of the five 12AX7 positions with the modified X-1000, and is presented so your tube selection efforts can be maximized for the various functions they serve. Thanks again for such thorough reviews!

Dave

 

[audiodon]

Making it mine again

Thanks Dave.
I had to do a lot of reading and marking down to figure out what tubes perform what functions now. Your assistance adds depth to my chicken scratch comments.

I'm not a big label maker fan, but I do have a Dymo label maker and occasionally put it to use.

I finally made four labels for the X-1000 yesterday.

Two say 12AU7s and are black on white labels so they can cover the existing 7247 silk-screened designations already there.

Two say pre out amp in and cover the spacexpander markings on the back panel.

I believe that's all I'll do in the labeling on the amp department, but I'll be marking up a copy of the "for the man in a hurry" front panel description and I'll be updating the tube designations sheet.

The process of making this thing mine again is well underway.

I hate that I had to use a colored background label, drawing attention to the label. I would prefer to use black lettering on clear, but that only works on a chassis location free of silk-screening.

I do not feel compelled to do any other tube rolling other than the phono stage. I wanted to see how far I could get the Fisher's modified (replacement of components in the PEC) and waveform tested MM phono stage to go.

Comparing the Fisher's phono stage to an EAR 834P, a purpose built tube phono stage in production for at least 15 years and now retailing at $2500 was an unfair test. But that test does shed light on the Fisher's phono capabilities.
As stated once in another thread, the fact that the Sylvanias ended up staying in the phono stage and the fact that they have tons of gain (close to 1800 micromhos transconductance) on a tester where 1250 is new again points to the phono stage liking tubes with a lot of gain.

 

[chuck802]

Fisher Phono Tube Rolling

Hi Don, while rolling tubes in the modded phono section did you find (or not) the lower gain of 5751s to be an issue at all? I'm asking only about gain, not the quality of sonics - understood from your last post that you like the high gain Sylvies but I am curious. When you have a free minute can you send me a picture of the Sylvania you like? I think I have many but want to make sure we're talking about the same tube - thanks if you can.
As you know many of my Fisher phono stages are so modded - I want to review the B+ change Dave did. Your listening review is very positive.
Thanks Don, nice detailed reviews. -Chuck

 

[audiodon]

Chuck,
In general, I avoid 5751s in phono stages. I tried them in this case for the sake of completeness. I did find slightly lower gain, but not the 30% less you'd expect from a .7mu tube.
I'd read in many places *not one place echoed again and again* that 5751s can skew the RIAA circuit because of their less that 1.0mu when used in phono stages. I take that advice very literally.
In this case I defied that because I had nothing to lose by trying it. The 5751s fared better in the phono stage than I'd expected, but the phono stage does not exploit what the tubes do best. In essence, they're misapplied.
I like all the Sylvanias in phono stages.
There are two main types.
1. Long shiny black ladderback type plates - '50s Sylvanias. Great shimmering highs and nothing lost.
2. Long pinched gray plate 12AX7s with yellow, green, or red lettering. These are common tubes and vastly underrated.
Those are the only two types I am aware of.

 

[audiodon]

Hi,
Here's an epilogue.
I took this unit out of service for an hour and put it on the bench.
Yesterday I fixed a Variac with a bad wiper. This particular Variac has the feature of being able to run up to 135VAC. Here, the voltage strays from a low of 109 to 127.
I connected up the X-1000, ran the Variac up to 126Vac and powered up the Fisher.
Then I checked the small signal tube filament voltages. Everything looked great except for one of the two phono tubes (the two are powered in series from a 24VDC supply) that was running about 25VDC. One tube was only pulling down about 10 volts. I replaced that tube with a duplicate tube, found that replacement tube's fil voltage was 10.1 volts. Then I changed out the other tube and the two evened out about 12.6Vdc each.

While that's a bit higher than ideal, it's certainly within reason for the rare times the voltage spikes up that high here. At normal voltages, it's just below the rated operating point.
Then I ran it down to a more typical 122 volts and the fil voltages dropped right back down to normal.
Then I checked the B+ voltages and everything looked great.

One reason I'd repaired that Variac was to free one up to run the X-1000 exclusively until I can get a bucking transformer built. But I now have two free Variacs.

I put the X-1000 back into its cabinet and put it in my office system on the shelf.

This unit would never have gotten into this kind of condition without the help of the following people:
1. Chuck802 - The former owner of this X-1000 and a dear friend and mentor.
2. thedelihaus - Another great friend who is responsible for the artwork and laser etching that restored the front panel from totally fudged to a joy to behold.
3. Buglegirl - Yet another friend and advocate who supplied the restorable and now lovely cabinet this X-1000 resides in.
4. dcgillespie - The designer and craftsman who took this when I'd decided to shelve it until further notice and turned it into an exceptional component and lifetime keeper. He just stuck with it until everything was done. I credit Dave with a love of solving a puzzle as well as technical expertise and an educational spirit that we all benefit from.

Thank you all.

This unit is my reference benchmark piece. The sound is powerful, yet with great low-level detail and is entirely fatigue-free.

 

[audiodon]

Some beauty shots.