Fisher 500, how much can they be improved

[Sam08861]

Ive got a 500b, (Ibba, mcshane kit, all good tubes, etc, etc). which has had most all the mods except the EFB, which will be next.

I've had incremental gains with each mod but wondering where it peaks. Interestingly, it's also become a bit more clinical and perhaps accurate vs a very dark and musical sounding 6v6gt based voice of music push pull amp. Rolled off highs and tubby lows (the VoM), but gosh what fun.

I'm quite happy with the sound, but just got a simic ii and nichicon (power supply) recapped luxman r-115 which has noticeably more detail and a super smooth and clear presence. Actually quite a difference, with much more authoritative and tight bass and great soundstage, really clean highs and ridiculously silky mids. I am re listening to all my music and songs where I wasn't 100 percent certain on the lyrics are crystal clear through this receiver. I realize these particular solid state receivers are a high bar as far as all in ones, but wondering if it's possible for the fisher series to get to this level of smoothness and clarity. I do most of my listening at the first watt level through fairly efficient horn loaded speakers, so I don't think the power overhead an issue. Until now, I never thought I was missing anything and the Fisher was at least equal to the naim system in my car, which is quite good. The differences between them are similar at all listening volumes, but I never turn them up so loud it hurts.

Wondering if anyone has been able to push their fishers to these levels? Or does this push us into SET territory for tubes? I've never had an SET amp, but assuming these raise the bar for tube sound?

 

[Sam08861]

Ps, a/b listening to these on the same speaker using a Niles spk-1 that swaps over when the luxman is turned on. Will the sudden removal of the speakers hurt the Fisher? I've heard these shouldn't be run without speakers.

 

[thornev]

I've been adding mod after mod on my 500-C. When I installed the Unity Gain mod, I got nothing but horrible distortion. One could conclude my build is bad (and given that I'm a novice electronics engineer, quite a plausible explanation), but I checked it over a dozen times. I concluded that it is possible that there are some mods that don't coexist with each other well and that was the cause of the distortion. I haven't tried to prove my assertion however. Have you installed the Unity Gain mod on your device?

 

[Sam08861]

Not sure what the unity mod is. Can you describe it?

 

[thornev]

http://audiokarma.org/forums/index.php?threads/improving-the-fisher-400.511867/page-3, post 41 & 47 & 49, 117 (parts lists).
Also see http://audiokarma.org/forums/index.php?threads/newly-acquired-fisher-400.736364/page-3, posts 58, 60.
My notes indicate those links will take you to discussion about that mod. It supposedly removes any (de)attenuation the Fisher executes in the processing of input signal to output signal.

 

[Sam08861]

I think I understand the gain is being equalized, not sure how the translates to sonic benefits for the Fisher or that it resulted in audible benefits. I'm open to others experiences with this though or understanding if it improves THD, etc. However, not interested in making modifications for the sake of making modifications.

I can see that the discussion shows measurable and proven, directly verified tangible benefits from the EFB components, however.

My original question is whether or not a modified fisher 500 receiver, without turning into separates, can achieve or even approach the level of performance and clarity of the luxman.

The reason I'm asking is this... If it's not achievable, which I'm inclined to believe, I'm going to stop tweaking and enjoy it as it is. If it is, I'd like to continue to get as much out of this platform as I can.

It's like a ford fair lane 500. One could modify the platform (engine, brakes, suspension, etc) but it will never beat a Ferrari LaFerrarri around a track. The high end here would be formula 1 car, and I'm not expecting that. Maybe here and there it might be pushed to beat the Laferrari in the 1/4 mile or some other spec, but the platform is inherently too heavy to corner well and will never be able to compete. Extending this metaphor, is the Fisher 500 a 911 Porsche platform that can be modified to hang with the Laferrari at the track or is it a BMW 635, which can be great but, no matter what isn't going to hang. Formula 1 here is stuff I can't afford (classe, Mcintosh, etc)

 

[thornev]

It was suggested to me that perhaps I have reached the limits of modding and that I SHOULD stop and just enjoy what I have, as you mentioned. And other than tube rolling, that's exactly what I'm doing - enjoying very much the incredible audio of my 500-C. I haven't enjoyed in so many years as much as I do now listening to FM. I have a separate setup for turntable headphone listening and sometimes I send the turntable and CD signals to the Fisher.

 

[larryderouin]

The mods that have been discussed actually improve what FISHER "screwed up" due to price points, or do away with redundant or obsolete features and establish current features that make the FISHER receivers compatible with newer accesories. The unity gain is actually a buffer unit between the volume control and the AMP output section, that allows when incorporated with the re-routing of the Space expander jacks into Pre-Out / Main IN jacks use of modern high impedance sources. Most of the mods you have on the 500B or C are Safety and reliability mods. EFB takes the relibility mods a big step further and reduces the quiescent idle current down to less than 55%, maintains a plate to screen voltage ratio at all times. As far as comparing it to a Luxman S.S. that's really Apples and Oranges. You can probably get it close to the performance of the luxman in practically all specs except Wattage. But you'd still have Apples and Oranges.

If Dave gets on here he can explain it better than I can.

 

[Sam08861]

Thanks Thornev and Larry, I’m re reading more carefully to understand better and your note is very encouraging. I did see from the handwritten schematics that we now get a pre out and amp in. This is great. The luxman has this feature too. Will be fun mixing and matching preamp and amp sections to see how the various combos sound. Almost like having separates. (Ok I will concede that is just playing around

Also see the tone controls etc, can be bypassed. The newer receiver has a cd direct (bypasses volume control, tone control and input selection) and tone defeat feature that seem similar in that ‘unnecessary’ items are removed from the signal path.

Brothers after the mods from other mothers, but understand they are apples and oranges.

I also see that the measured wattage increases, adding some headroom as well.

 

[Dave451]

Guys,
Dave explains very well what the purpose of this mod is in the "Improving the Fisher 400" thread, where he introduced the mod that he says will be effective for the 500C and 800C as well. The link is provided by Thorne above, along with a link from my post describing my experience with these mods in my 400.

Note particularly posts 37 and 41. 37 in particular describes the theoretical and practical basis for the mod which is to deal with the "Miller Effect" high frequency roll off caused by how Fisher designed the interface between the tone control amp and the power amp driver to improve the stability of the circuit. The amp does this, as Larry mentions above, by dealing the the impedance mis-match between these sections, particularly at mid-level volume settings. Another side benefit is the utility of using higher impedance sources when changing the 'space expander' jacks to a 'pre-amp out/amp in' set up.

I have my modified Fisher 400 (with the op amp mod) and a stock 400 in the listening room right now and I can tell you the difference in HF response and clarity are pretty remarkable, with considerable improvement in the modified amp. Of the mods that Dave developed and discussed in this excellent thread, I think the biggest sonic improvement comes from use of the op amp to resolve these issues, even more so than the driver circuit mods ('removing the noose, etc') discussed further along in the thread.

Thorne, it's too bad you're unity/op amp mod is creating distortion in your 500C. There must be something amiss, as I performed all the mods shown, including op amp, driver circuit revisions, EFT and IBAM (all, in fact, except re-purposing the space expander jacks) with only improvement in operation.
Good luck with your work, guys!

 

[Sam08861]

Thank Dave,

Post 37 was immensely helpful. What is being said in the 1st paragraph is exactly what I'm hearing. The output on the oscope is a great depiction. Setting aside some time to study the whole thread with the schematics in front of me. I'm a hobbyist in my understanding and was jumping to simply copy the mod, but see that an understanding of the fundamental scientific basis will be essential in assessing effectiveness and modifying to address my units specific circuits.

 

[thornev]

Dave451, Yeah I was bummed about my Unity Gain/op amp mod distortion. It's probably something wrong with my build or the way I connected. Since you stated how significant the improvement is, maybe I'll take it up again. I addressed my issues in this thread if you would be so good to check to see if you can see something wrong: http://audiokarma.org/forums/index.php?threads/questions-about-treble-boost-mod.820408/

oh you already did discuss ! It looks like I never displayed my board so I've attached pics.

 

[Sam08861]

Thornev, did you verify the polarity of the electrolytic (big and small black ones) capacitors? These can only go one way, unlike the resistors and mica capacitors. Same goes for the diode.

Sorry if you already knew that.

 

[thornev]

I did, Sam. + to ground, right? I believe I would get no sound if I had them reversed. Thanks for checking and certainly let me know if I'm wrong. Thorne

 

[Sam08861]

That's right per the schematic, and the stripes usually indicate the negative legs..

The only other thing I can think of is to check the orientation and pin out of the IC. Or that the IC is faulty. You might try swapping that out. I think you should be able to get a socket for the IC so that this would be easy to swap out in the future. Also the diode is directional and you might check if the ground wire is making good contact with the chassis

If you could label the bottom of the board it might make it easier for folks to comment, as it's hard to know where the component legs come out. One other thing, I learned on small circuits like this is to check each resistor before installing. Probably overkill, but I've had faulty new resistors in the past that were the culprit, and took me forever to figure out.

Might be easier to build a new circuit on a breadboard to test things out before committing to solder. Or if the components are cheap enough, rebuilding the circuit, rather than having to desolder.

 

[thornev]

I bought 2 of all components (more in some cases) and the pics above are "take 2" so I will have to order more for a "take 3". Since I'm not the greatest solderer it is possible I burned something in the chip when soldering the other components. Soldering the chip was tough so I like the idea of using a chip socket.

As for the diode, I've got it with the striped end facing away from the rest of the components on the board.

Thanks, Sam, for your feedback. I'll think about doing a "take 3". I do have a powered breadboard, but it has adjustable voltage, not adjustable current, and I'm not sure I'd know how to provide the correct amperage to the breadboard. Without hooking up speakers, I don't know that I'd be able to tell if the circuit is working correctly. I am getting an oscilloscope next week, but I'm still reading about how to use it to test for correct circuits.

 

[Sam08861]

For the breadboard, I don’t think you need a powered item. Just use long wires to hook it up to the connection points on the receiver, with the speakers hooked up.

That way, if it doesn’t work, you can turn off the receiver, make corrections to the circuit and then turn the receiver back on to retest.

Also, alligator clips on the ends of those long wires may make it easier than soldering/de soldering twice.

Edit.. ps, some would recommend a power strip to turn the receiver on/off to save wear on the volume knob.

 

[Sam08861]

You might also find this useful. I did.

https://learn.sparkfun.com/tutorials/how-to-use-a-breadboard

Edit...

Also, I got one of these type of kits as the various size wires and colors made hookup easy as they have stiff ends + the arduiono is a fun learning tool. (Link below)

And the kits also have a number of common resistors and diodes, etc. I'd shop around as there are hundreds of these kits on Amazon eBay, etc that have different combos of stuff. The components might be low grade, but usually work fine to prototype and are a handy supply in a pinch.



https://www.amazon.com/Elegoo-EL-KI...D=61fQsYALc3L&preST=_SX342_QL70_&dpSrc=detail

This is the one I got....

https://www.amazon.com/dp/B00CXMMDZ...zl&pd_rd_r=0EQ882DH4NEJVSS5SG6K&pd_rd_w=efgFZ

 

[thornev]

That's sort of what I did. When I tested it, I didn't make permanent connections. But on a breadboard I can move parts around. The problem is that I thought I had it correct so how would I know what to try differently? I'll add markers to the trace points and post later.

 

[Dneprrider]

Dave451, Yeah I was bummed about my Unity Gain/op amp mod distortion. It's probably something wrong with my build or the way I connected.

I have been following this and your original thread posting about the problems you have encountered with the unity gain circuit add-on modification. Many contributors have provided good advice, but there are still some unknowns. Is it the build of the add-on board or how it is connected or both that is the issue? There is perhaps another approach to take, which removes at least one of the unknowns. However it requires a fellow AK user with experience building this add-on board to build another board for thornev and provide some actual pictures of the correct wiring interfaced to the receiver. Starting out not everyone is easily able to translate schematic wiring to soldering wires to components under a chassis. My take on reading the original post was that there was a lot of confusion on how to and where to connect this new board. So having some high-resolution pictures of it hooked up would benefit the wider community at large. I hope I am not stepping on anyone’s toes here but I see this as a possible way forward.