The Fisher Phono Preamp, and RIAA

yeah, nothing to really worry about. The accuracy of the invert circuit also plays into the measurement but I doubt you'd hear +/- 1 db deviation from ideal.
 
hello I am newbie

I plan to buy a phono stage pre amp but, I am appreciate with this Fisher CC-3000 Pre amp that have 3 phono inputs including setting of resistance, if comparing with common phono stage pre amp, does this Fisher CC-3000 can beat that? Please give me suggestion and information also comparison.
Thank you
 
liem - What's wrong with the Fisher? We can't tell you what to get if you don't tell us what's missing from the Fisher.
 
liem - What's wrong with the Fisher? We can't tell you what to get if you don't tell us what's missing from the Fisher.

No I mean, how good is the phono section of Fisher CC 3000 if comparing with common phono stage pre amp like Pro-Ject, etc...
 
Pro-Ject makes several preamps. Which one do you want to compare to?
I mean If this Fisher CC3000 compare with NAD Pp14 or Musical Fidelity VLPS or Pro-ject Phono Mini, is there any big difference in sound quality?
Using Fisher CC3000 as just phono pre amp, is that will produce quite clean and clarity sound from turntable?
Assumed that turntable in perfect condition
Thank you
 
only one way to find out is to a/b em. with a highish output cart and the right capacitence cable etc the fisher should do pretty good. My fav with my fishers is a goldring 1042 that outputs 6.5mv.
 
liemjerry; Try this search and you'll get quite a few links on AK regarding the SQ on the CC-3000. IT's a SANYO/FISHER from the 80's/90's and not too many guys here in this forum would have heard of it. But it's part of the "family" so we'll try to help as much as we can. Google this.......... fisher cc-3000 preamplifier site:audiokarma.org
 
A lot of this is over my head.

Fortunately my tech is aware of some improvements for my 500b.

He changed out the coupling caps and then reset the bias for me so far. That made a noticeable improvement in sound quality. He also ensured the selinium rectifier was replaced.

Next he mentioned he could make improvements to the phono stage. That will be next. Based on his work so far, I cant wait.

Great to have this forum with so many highly experienced folks weighing in.

Like I said, a good part of it is over my head, but I understand enough to help me get the most out my vintage equipment.
 
Might want to ask exactly what he plans to do with the phono stage. Stock its pretty good, and with Dave's revision to the phono PEC it gets more accurate but otherwise I'd be very leery of tinkering in there.
 
He will replace inferior ceramic coupling caps with metalized polypropylene caps.

I agree, the stock 500b is pretty good. I use mine with a Denon DL103 through an sut with very good results.
 
The new caps are burning in nicely. Took a few hours but I'm hearing good improvement.

I recommend this change to folks with Fisher 500b's that have ceramic caps in the phono section.
 
INTRODUCTION

Over the years, I have generally defended the Fisher phono preamp design -- not to extol its absolute EQ accuracy, but simply to say that keeping it in perspective, it is not all that bad at all, and in fact, very much in keeping with the performance of that from many other manufacturers of the day. I've also defended the design against a rather (in)famous modern day review by a well known expert, as executed in a 500C receiver, wherein he rather summarily trashed their performance, based on testing conditions that were capable of anything but accuracy.

In the early days of stereo where the RIAA curve's beginnings can be found, most manufacturers (including Fisher) didn't even provide specifications of EQ compliance, rather choosing to simply indicate that their unit offered a setting to produce the RIAA EQ curve. Where it was given (HH Scott for example), "good" compliance was indicated by a response curve that was specified as being within +/- 1 db of ideal. In the succeeding years of those heady days, the best manufacturers tightened this specification to produce within +/- .5 db of ideal as accuracy drew more attention, but measured accuracy within +/- 1 db was still quite common. Remember, the engineers of the day did not have CAD capability (let alone a computer), or even a pocket calculator for design work! All they had was a slide rule, chalk boards for group work, and pencil and paper for their notes and personal calculations.

On the production end of things, the early stereo units (including Fisher) often employed discrete components in the EQ networks, which just as often, were often not high tolerance components, let alone matched between the channels. Some manufacturers (like Dynaco for example) did use close tolerance parts. But most (including Fisher) simply used standard 10% components, which then added their own flavor of error into the mix. Of course, time and use then further works its own brand of error into these components as well.

In later years, Fisher and others used PECs for the EQ networks, which eased production issues, and also afforded more consistency between the channels and units of a given model. At the time that Fisher made this change, they also took the opportunity to tweak their (by then) almost universal RIAA network design (the X-202 however used a notable variation of it), to tighten the resulting curve produced for closer compliance. It wasn't a major change at all. In fact, it was small enough that so many decades ago when I first noticed the difference in component values, I assumed it more had to do with the manufacturing of all the EQ components into one small PEC package, rather than being the result of improving compliance accuracy. Today however, I realize that the move was indeed one of multiple goals, designed to ease production costs, improve consistency, and improve compliance.

Overall however, when the front end errors from limited design aids were coupled with the back end errors produced from component tolerances (discrete or PEC), its no wonder then that a specification (in the rare cases where provided) -- and "good" measured performance in the lab -- only achieved compliance within a +/- 1 db bracket. Add in also a generally casual attitude towards compliance at the time, and you ended up getting what you got, relying on the better manufacturers to do a better job of achieving compliance, which they did, but which was still only typically within the aforementioned +/- 1 db. With a 2 db (total) spread however, the errors become audible. Today, this can be improved on.

But improving the RIAA performance of yesterday's classics with today's technology can be fraught with its own set of problems. AK is filled with posts of those who have modeled various popular circuits, which they then proclaim as defective because the computer says so. Of course, these same people rarely if ever provide any proof of any such defect, instead relying on the computer to be judge, trial, and jury all at the same time, with their prowess to use it being king.

Done properly, modeling can be a truly wonderful design AID, but should in fact be considered as just that, and hardly be counted on for the final word all by itself -- at least when used with vacuum tube circuit design. Accurate modeling in and of itself requires great knowledge of: (1) The modeling software capability, (2) The hard data it has been programed with, (3) A thorough understanding of electronic circuit design, which affects (4) The accuracy in which the soft data (the circuit to be modeled) has been input into the system.

This is all on top of the realization that the results produced from modeling vacuum tube circuits should be considered as a ball park verification -- one that can be very close if the skill and effort are present to address all the myriad of variables involved -- but still, best used to verify actual results achieved, rather than taken as gospel all by itself. It's like a chain, which is always only as strong as its weakest link. Three of the four areas can be handled with incredible accuracy, but if one is off even by just a little, the results can then be way off from reality.

These requirements then -- for me -- potentially bring into question 99.9% of the modeling results heralded by most diyers which is why I pay only so much attention to modeling results. Instead, I have always preferred to have measured results be the outcome of my efforts -- which is the safe bet, but surely is more time consuming without enlisting the aid of modern design tools. However, I am a creature who is lucky enough to know what I don't know, and since I don't know the intricacies of ACCURATE modeling, I simply don't do it -- but I do endorse it in the hands of those who truly know what they're doing with it.

Against this backdrop, some of you may have followed my efforts recently with a Fisher 400C preamplifier ("A 400C Transformation"), and my goal to have it perform more in keeping with that of a Fisher 400CX/2. To date, those efforts have centered on improving the line stage performance, and eradicating the hum that so many of the stock units display. Along the way, I posted the some scope shots depicting the performance of the modified line stage, which perform admirably now with very little noise. I also posted some scope shots of the RIAA performance of the phono preamps in this unit, which still employed stock, but generally within tolerance EQ components for the RIAA network. They were less than admirable.

To put a wrap on that project, I wanted to address the RIAA results produced. There was not only a discrepancy between the channels, but a notable discrepancy between both of them, and ideal. It just wouldn't be right to have the tail end of the audio chain then perform so well, but not the front end.

As luck would have it, my efforts in working to improve the RIAA compliance in this unit were enhanced immensely by the efforts of George Ronnenkamp, who founded and operated Audio Regenesis. The quality of his work and the products of that company are without equal.

George was indispensable in first accurately modeling the originally 400C phono preamp design (as judged against my own measurements), then comparing it to that produced by the updated design as used in the 400CX(2), and finally modeling the results of my work to improve them, by providing validation of the measured results I achieved.

Modeling the basic Fisher preamp design presents problems from the get go, as apparently none of the modeling programs could properly deal with a grounded cathode (i.e. contact bias) 12AX7 circuit as employed in the second stage of the Fisher design. This was but one variable that had to be chased down, as were things like determining any differences between the reverse RIAA network he was using in his virtual models, versus the real one I was using in my lab. As I said earlier, modeling is fraught with potential problems, let alone those piled on by injecting vacuum tubes into the exercise.

Through out the process then, and parallel with my own real world work, George was independently working on optimum values for the network based on what the model was indicating. Ultimately, the level of conformity we both achieved independent of each other, but verified both by his modeling work, and my real world measurements, was really quite amazing.

Stay tuned!

Dave

To amplify what Dave says here. Bear in mind, a firm the size of Fisher Radio, HH Scott, Harman-Kardon, or even McIntosh Laboratory or Marantz Company at best could afford something like one Friden mechanical Calculator or something close to it, for any kind of serious number crunching which engineers could share as a department. Even these Friden mechanical calculators on the high end were something like just over $1,000. Slide rules were heavily used, and lots of manual, intensive manual calculations and their attendant drudgery were performed by design engineers. The fact that Fisher phono stages were as excellent as the best of them are, I give amazing credit to Fred Mergner and his team of engineers. Consider these added thoughts carefully. Minicomputers were not yet affordable for most if not all electronics firms, let alone the advanced calculators like the first Hewlett-Packard electronic scientific calculators introduced in the latter part of the 1960's. It's amazing that the best of audio gear in the golden age can still be discussed here as we do, and withstand the test of time the way it does. Food and fuel for thought here.
 
I plan to implement this revised RIAA circuit in my X-100-B. I have a few questions I was hoping the brain-trust here would weigh in on:

1. Are there reasons not to use polystyrene 160V caps in the 680pF position (2 in parallel for 1360pf), or are there special considerations to keep in mind if using polystyrene rather than mica? (sound quality? orientation? I think the marked end of these theoretically indicates the outer foil lead)

2. Both sets of caps I have on hand have axial leads. Any issue with that? I know there has been discussion that smaller components with shorter leads are preferable. Size-wise, my caps are comparable to the digikey-published dimensions for new, radial lead mica caps.

3. I'm thinking I'll just cut out the PEC board altogether and direct mount the new components (rather than perf board), eliminating the tape EQ section and bypassing the EQ selector switch in the process. Has anyone done this? Can they provide any helpful hints, pictures, things to watch out for, pro tips, etc?

4. I figured that while installing this mod, I might as well delete the rumble filter at the same time. Based on Professor Gillespie's input on this thread (https://audiokarma.org/forums/index.php?threads/fisher-400-rumble-circuit.573440/ ) I'll be replacing the 0.022uF coupling caps in the phono section with 0.047uF caps (k42y2 PIO 500V) but clearly the X-100-B and 400C don't share the same line amp circuit components. No 1000pF caps anywhere in the X-100-B, let alone the line stage. There are some 680s in the tone control section, but that's about it. Can anyone weigh in on if the X-100-B just doesn't have a 2nd stage rumble filter?

Many thanks!
 
Klamsoss -- Taking your questions in order:

1. Component accuracy is the important element here. People will debate which type of cap sounds best long after you and I are long dead and gone. It is by far the circuit however that determines how well a given design performs and sounds, and all the circuit knows is component value. It has no idea what the components are made of. To be sure, you want to use quality components to minimize noise, maximize stability of value, long term dependability, etc., etc., etc. Neatness of work also counts. But the relation of component composition to sound quality is largely a personal emotional thing, and little more. I've participated in way too many double blind testing sessions (on both sides of the equation), whose outcome settled this for me long ago.

2. You simply want to use caps that are size appropriate physically for the space allowed, and configuration appropriate for the application. The use of overly large super-duper save the world caps only invites interaction with other circuits and components that never occurred originally, and the use of component packages that don't fit the application only encourages a less that ideal build. The use of quality parts that are appropriate by package and size is the best way to help determine a successful outcome to any project.

3. It's common to eliminate the PEC and hard wire the RIAA EQ section permanently into the circuit. Everybody's approach to accomplishing that will be different. Just make sure that the new EQ "package" is neat and tightly constructed to maximize its intended job, and minimize any undue influence either from or to it.

4. Already answered.

I hope this helps!

Dave
 
Finally polished off my iteration of this mod. I used double sided foam tape to stick my board to the inside of the chassis in the front controls cavity.
Listening to it, I'm actually astonished at how much of a difference it makes.
Thank you, Dave!

Pictures
1. My board. Everything is matched to 0.1%, though my 2.15M resistors @2% only got me down to 2.14M
2. Installed, stuck to the inside of the slanted panel covering the controls cavity.
3. The board, visible inside the control cavity, next to the rest of the phono stage.
 

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Very nicely executed! Glad you found the modification to be such an improvement. To maintain the high level of EQ accuracy you now have, remember that the only thing that should be connected to the recording output jacks is the high input impedance of an external buffer unit to drive any external device you might wish to supply a signal to.

Congrats on you successful project!

Dave
 
Dave in the attached document the RIAA mod looks as shown in the attached file????.

Let me know

Regards
I'm revisiting my RIAA in Fisher 400 and noticed that 15Meg resistor originally connected between #1 and #2 legs is omitted in the revised circuit. I've re-read the whole thread and found no mention of this omission. Can anyone comment?
 
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