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Modified Tuner Report

KT-7300 | FT-5500 MKII | KT-7550 | DA-F20 | ST-3636 | KT-5020

This page isn't designed to be just another subjective review of FM tuners. The goal is to acknowledge the DIY efforts of all enthusiasts. Our goals are to, one, help bring it all together; two, give a short subjective opinion of the sound and rate the tuner; three, measure DX upgrade efforts when applied; and last but most important, let the builder explain the mods and his or her thoughts.

The Rules

1. No DX measurements will be made on any tuner not modified to improve its DX capabilities.
2. Most tuners will be tested for sound quality on strong signals using Jim's normal formula (tastes), which are spelled out below.
3. The overall sound quality ratings will be on a 1 to 5 scale, with 1 being Jim's favorites and 5 being his least favorites. This might create clusters with, say, 3 tuners in the #1 position, 4 in the #3 position, etc. There are five categories designated A through E describing what Jim will be listening for, and each tuner will be rated 1 to 5 in each of those categories.

A - Bass: Deep, punchy. Gives a good foundation to the music.
B - Midrange: Good ambience, low-level information, air.
C - Highs: Natural, sweet, extended without unnatural brightness or added hash.
D - Focus/Soundstage: Realistic images. Focus says it all. Obviously not available on all recordings, just as other criteria may not be. The more diffuse the sound, the lower the rating.
E - Dynamics: Punchy, not boring. Lively sound that helps you pretend it's real.

4. On tuners with DX upgrades, no ratings will be involved. Just A/B, off the air statements/measurements against the L-02T.

Here's a demo presentation: The Kenwood L-02T
A - Bass: 1
B - Midrange: 1
C - Highs: 2
D - Focus/Soundstage: 1
E - Dynamics: 1
Overall rating: 1

Kenwood KT-7300 (2/13/05):

The Kenwood KT-7300 rates well before and after mods. Score below.
A - Bass: 1 - after mods: 1
B - Midrange: 4 - after mods: 3
C - Highs: 3 - after mods: 2
D - Focus/Soundstage: 1 - after mods: 1
E - Dynamics: 2 - after mods: 2 plus
Overall rating: 2

Well, that was simple enough, but numbers don't tell it all. But I do plan on leaning toward the unforgiving with the numbers. I thought it would be good to start off this page with a tuner the "everyman" can afford. You probably need to read the Shootout review first, before this review. The good news after mods is that we still kept the good, punchy bass. Originally the highs were forgiving and sweet, but not that extended. The parts changes helped this area a small amount. Long listening sessions were never irritating and always a pleasure. After the mods, the sound through the midrange was more open and airy. Not mentioned in the Shootout review was that the KT-7300 had a well-focused sound. Imaging was top-notch and realistic. But... the bad news is, I just couldn't squeeze out the delicate harmonics and ambience of the L-02T and other, more expensive tuners. A/B tested against the L-02T, the modded KT-7300 was almost like listening to the same music in a lively room or an acoustically well-damped room. So that missing information was lost somewhere other than where my upgrades were applied. If (A) bass and (D) Focus/Soundstage are your bailiwick, this tuner may be for you. So, were the upgrades worth it? Definitely. You get a lot of good sound for your money with this tuner even before the mods, and a notch or two better and longer tuner life after mods. jim...

See the DIY Mods page for information on DIY audio section and power supply mods for the KT-7300.

Hitachi FT-5500 MKII: X-Rayed (6/12/05)
Ray has sent this tuner to Texas twice, in January '04 and February '05.

Ray's Hitachi FT-5500 MKII: January 2004
First report. With the only mod being Black Gates in the audio path, the Hitachi's overall sound was very smooth. Bass and dynamics were on the tame side. There is better to be found. The midrange was less focused than the best and the treble was extended but not unpleasant. Nothing to make me walk over to turn it down - very listenable.

Sonic rating:
A - Bass: 3
B - Midrange: 2
C - Highs: 2
D - Focus/Soundstage: 3
E - Dynamics: 3
Overall rating: 3

Rather than argue or complain, Ray took Jim's constructive criticism to heart and decided to try to better his favorite tuner's sound.

Ray's Hitachi FT-5500 MKII: February 2005
Second report. Along with the Black Gate upgrade, the tuner now has the full RFM treatment of passive de-emphasis, added buffer IC circuit and direct wiring to the jacks. These mods are diagrammed here.

Sonic rating: Before and after second set of mods.
A - Bass: 3 - after mods: 1
B - Midrange: 2 - after mods: 2
C - Highs: 2 - after mods: 1
D - Focus/Soundstage: 3 - after mods: 1
E - Dynamics: 3 - after mods: 1
Overall rating: 1

What were those lyrics Dinah Washington sang?
What a diff'rence a diy makes
Twenty-four little changes
Brought more fun to the music
Where there were no dynamic ranges...

OK, I'll stop. This is definitely a different-sounding tuner. A better sense of dynamics is now there. I'm using the word dynamics here to describe a more lifelike, exciting sound: a sense of more layers, more gradations between loud and soft passages. The "new" Hitachi delivers a quick, clean, punchy sound. It still remained enjoyable hour after hour. The illusion of real music is now easier to imagine. The bass goes deep with better punch. The highs remained natural and extended. The midrange is now well-focused, clean and clear. What mod or series of mods improved this over the original? I can't guess, maybe a combination. Ray's circuit changes and additions made significant improvements. Kudos.

I had to throw the FT-5500 MKII into the ring with the L-02T. You've heard this before, but I could live with either of these two. The Hitachi matched up against the L-02T well in bass, focus and dynamics, and its highs were more extended. On some recordings, the L-02T had slightly more ambiance and air around voice and instruments. It's always a pleasure to find a tuner that gives the L-02T some competition, and it's always a pleasure to listen to a great-sounding tuner! I hope and trust that will be the case quite often on this modified tuner page. jim...

RFM's response:

WOW, and thanks Jim, for a very good and, IMHO, honest evaluation. My first impression of the modded tuner, after ~30 hours of break-in, was YES, there it is, better separation, depth, and extension of both ends of the audio spectrum. I attribute the improvements to a combination of low output Z and use of passive de-emphasis."

Q (Bob): Ray, I forgot, did you measure this one for flatness when the mods were done?

A (Ray): Yup, got an F3 of 2114 HZ or 75.3 µS. I calculated the circuit as 4.7K R355 and 3.3K R353 paralleled as source Z along with ~100 ohm in the MPX amp. CP302 measured 43 ohm through it so I lumped all this as effectively 2K in series with the 6.8K. The two 100K act as 50K in parallel with the cap and thus effectively paralleling the source Z of 2K + 6.8K. This works with the .01 µF cap to give a calculated de-emphasis value of 74.8 µS.

Kenwood KT-7550 (10/7/05): A collaboration between Jim and Ray

I'm glad I waited to review a modified KT-7550 [the same tuner as the KT-7500 - Editor] for this page until after Ray put in his two cents and caps. The mods include those listed on Jim and Bob's DIY page plus Ray's passive de-emphasis mod. Ray's mods should be on our DIY page shortly. This sample has not been aligned but seems to be in better-than-average alignment.

I've modified 35 or so samples of this tuner over the last four years. With Ray's latest input, maybe we can retire the project. It can't get any better, can it? This tuner gives a pleasant, laidback sense of wholeness, of oneness to music from the lowest bass through the highs. The bass through the midrange seems more in step as compared to KT-7500s done before this latest mod. It was a good sign when I kept putting down the A/B switcher and notepad to just listen. Whether I listened for 30 minutes or three hours and 30, I still came away with that good feeling of time well spent. The L-02T seemed to have a bit more focused midrange in comparison. There was also slightly more background noise compared to the L-02T, on problem stations. The bass, now, holds its own with the L-02T. The mids are smooth and sweet and I couldn't ask for better highs.

If you're not worried about a certain look or owning THE megabuck tuner of the month or some collector's piece, this tuner, modified and aligned, should satisfy all your FM needs. It will mine. A highly recommended new mod added to the older mods. Before this finalized review, this tuner was shipped to Ray for final tweaking and testing. His words are at the end of the review. jim...

A - Bass: 1
B - Midrange: 1
C - Highs: 1
D - Focus/Soundstage: 1.5
E - Dynamics: 1
Overall rating: 1

Ray comments:
"Hi Jim, your JR/BF/RFM/KT-7550 arrived today safe and sound and went straight to the bench for verification. Here's what we got:

Freq. ---- Delta dB from theoretical
100 Hz ---------------- 0
400 Hz ---------------- 0
800 Hz ---------------- 0
1 kHz -------------- -.05
2 kHz -------------- -.10
2122 Hz ---------- -.20
4 kHz -------------- -.40
6 kHz -------------- -.50
8 kHz -------------- -.40
10 kHz ------------ -.40
12 kHz ------------ -.80
15 kHz ---------- -1.70

At the bass end we got -.20 dB @ 20 Hz and -.40 dB @ 15 Hz! Woww, she can woof! Original design should yield -3.0 dB @ ~15 Hz. Now, there's no phase shifting going on at audible bass and maybe that's why you say it's "different but good."

These results show a TC of ~ 79 µS. Very close, I suspect your .0068 µFs might be on the high end of their tolerance which is typical for caps. The rapid drop at the top is due to the pilot filter which starts to affect things at ~ 14.6 kHz. The above measurements do meet Kenwood's spec of +.2 to -1.5 dB. Both channels track very closely.

I think the audio output is a bit too hot at ~ 1.1-1.2 volt average. I suggest changing R62 & R63 from 33K to 18K to reduce the op-amp's gain. Your output wiring eliminated the fixed jack voltage divider causing the high output. IMHO, if you retain your output wiring scheme and reduce the op-amp's gain, you get a big win-win."

Here's an addendum from Ray: "Jim agreed with the suggestion to reduce the audio out voltage and, using his best management technique, gave me 'permission' to do the resistor change out. I then did a personally torturous shootout between this KT-7550 and my own modified Hitachi FT-5500 MKII. Reluctantly, I had to find the KT-7550 slightly better with the difference being more 'air' around wide perimeter images. I think the KT-7550's balanced +/- power supply allows fewer coupling caps in the audio path and thus slightly better articulation."

Mitsubishi DA-F20 (1/2/06): Jim does a DXing shootout

Both Mitsubishi DA-F20's in this review are basically stock. One is pure stock and was used in our Shootout. The other received a new alignment by Bob with new tested, matched ceramic filters.

Sonic rating:
A - Bass: 1.25
B - Midrange: 1
C - Highs: 1
D - Focus/Soundstage: 1
E - Dynamics: 1
Overall rating: 1

This is our first modified tuner report that isn't about subjective sound quality mods, per se. When listened to in wide mode, on strong stations, both tuners were pretty much sonic twins, as we would expect when looking at like transistor tuners. Where the totally stock DA-F20 stumbled a bit was on weaker stations. And tuning. And... well, read on.

I aimed at KTCU 88.7 first. With both tuners switched to narrow mode, the aligned DA-F20 held its own with a good clean signal, while the stock F20 was usually swamped in waves from the stronger and closer 88.5. I used this test on different days and in the evenings too. When both tuners were switched to wide, 88.5 let them both know who's boss. Back to narrow mode: When pulling in 88.7, both tuners only lit 1 of the 5 signal-strength LEDs. The aligned DA-F20 had the stereo and tuning-lock LEDs lit as well, and was happily playing in stereo with an almost hiss-free signal. The stock F20 was dark except for an occasional flicker from the tuning-lock LED, and was giving almost equal time between 88.7's signal and 88.5's.

I wasn't able to find 105.5 in Oklahoma on either tuner, but I found an interesting fact about a well-aligned tuner in narrow mode. Because Dallas has stations at 105.3 and 105.7, one must expect interference when searching for a weak signal at 105.5, and that's what I experienced through the stock F20. No matter how I tried to fine tune, sound from 105.3 or 105.7 always jumped into the room. What a pleasant experience it was to tune to 105.5 with the aligned F20 and get nothing but average background noise. This test was in the morning. Trying the same test tonight, both tuners were much noisier while looking into nothingness tuned at 105.5, but the aligned tuner was still more able to ignore the strong local adjacent-channel stations.

Finally we turn to 88.9. The aligned F20 held an OK signal this evening with the stereo and tuning-lock lamps lit, while the stock F20 had a flickering stereo lamp, no lock lamp and a much noisier signal. Also noticed was that the stock tuner kept muting with the muting button enabled while the aligned tuner wasn't affected. From the start, the aligned F20 felt like a trusted old tool. It was always true when used to best position the antenna or when fine tuning a difficult station. I always felt more confident tuning in the stock tuner second as I searched the airways. As anyone would guess, we highly recommend a good alignment. And the standards for a good alignment are higher today than ever, because so much has been learned about testing and measuring filters from our panel and FMtuners group members.

Bob adds that it's important to know, it was not just the alignment and matched filters that helped this DXer. Along with the first three matched 280 kHz filters, there was a matched narrow 150 kHz filter in position 4. This combination was part of the overall solution for this refined DA-F20 DXer. jim...

Optonica ST-3636 (3/30/06)

Ray modifies:
"1. Defeat opto-lock. Completed via disconnecting switching transistor.
2. Upgrade power supply. Completed, main rectifier diodes changed to Harris fast recovery type. Black Gate filter caps.
3. Upgrade audio caps. Completed using Black Gates from MPX in to output jack feeds.
4. Bypass pilot cancel lowpass filter. Completed. (Good-bad-indifferent, they're out but re-insertable.)
5. Reconfigure de-emphasis. Completed, now resistor, capacitor passive and tested for accurate response curve. MPX's audio gain adjusted and flattened for final output of ~ 600 mV.
6. Reroute output wiring. Completed, eliminating ~ 12" wire & 7" pc traces/channel through the power supply area.
7. Improve IF filters. Not complete, four matched CF's (280-280-150-280) on order. Sockets installed in PC board.
8. Remove RF balun. Completed and F-connector installed. WHEW! I did not install gold output jacks because I'm a second string TIC DIYer and haven't even thought of it. 8:-)) Well, actually, I kind of like the stock Optonica patch-bay, though there is panel room for adding gold jacks du jour.


Bob aligns and listens:
"It is sounding very good. Was in fair alignment as received. Separation was 20 dB wide, 10 dB narrow. Distortion was a tad high, in the 1% range. Reception was OK, not great. I went through it and did my thing. Now it's very good for reception in narrow. It is very open and fast sounding, on some music it may sound touch bright, but that may be poor station processing or source material. Bass is very good, but not what I would call ultra-deep, just fast, and deep. Mids are good. Overall, I could listen to this one for a long time. Drums and congas are fast and detailed. Ray may be onto something with his de-emphasis mod. I really think he should try it again after you [Jim] have it. I also got the front panel off, and cleaned it up inside the glass. It's a pretty nice tuner as it sits here.

I had more trouble than usual with this one resolving the difference in distortion between mono and stereo. It puzzled me, and I ended up redoing the whole filter setup. I put a blue GDT into the single wide filter spot, and matched the other two 280s and single 150 to that. It was much better, but for some reason I did not get the typical .03% distortion in stereo that I easily get on other tuners. I was happy with .1%, so I let it go there. Needless to say, it was not an easy alignment. Stereo separation ended up at 50 dB, which is good for that MPX chip. There is an obvious difference between fixed and variable output, I agree to only use fixed. For DXing, in narrow it is about as good as anything else I have here, which means it's no slouch at all - it really pulls in the stations.


Jim listens and makes notes for TIC:
"This tuner review has been almost two years in the making. Purchased two years ago, it has traveled from Jim to Ray to Bob and back to Jim where it sat, unceremoniously, in my garage until 2006. Sorry Ray, sorry Bob, and oh, so sorry to this very nice revitalized Optonica. In short, Ray went 'Tasmanian' on the power supply, redesigned the de-emphasis network and removed the problematic opto-lock system. And Bob spent a lot of extra time aligning/re-filtering this tuner.

I left the tuner on for several weeks, using it for casual listening from time to time. After all, the poor guy sat unloved and unlistened to for over a year. It needed to warm up and I sure warmed up to it. I 'looked' at Bob's alignment first. The first punishment was to try 88.7 KTCU (10,000 watts) in wide mode. It was a no go as 88.5 KEOM buried the desired signal. But when switched to narrow mode, 88.7 snapped into focus and ignored 88.5. There was occasional background noise but it held a good stereo signal. Very nice. The other 88.7 in far East Texas was also found, but with a very weak signal. I was unable to pull in 105.5 KKFC in Oklahoma. But in narrow, all was quiet when dialed into that frequency. The modified Optonica ignored signals from locals 105.3 and 105.7. One of my favorite stations to use for tests and simply pick on is 107.5 KOAI (16,500 watts). This station seems to boost their bass to warm up their 'smooth jazz.' There has been nearly constant background fuzz for so long that I've almost gotten used to it. Sadly, this station is one of the stations proudly claiming to be high definition. As usual, the constant background fuzz (noise) was there during these tests. It's most noticeable when a DJ is talking. I switched to narrow mode at one of these times and the background noise dropped significantly. If this was because of the low transmitted power or HD radio problems, I don't know. I do know Bob's precise alignment and filter matching did wonders helping make this tuner several cuts above most other stock wide/narrow tuners I've tested.

When I turned to Ray's work in the audio section, things continued to be a cut above. I knew things were right when a pleasant, mild feeling of euphoria came over me about an hour into one serious listening session. Endorphins? I think so. Something I've experienced often while exercising and which can be released through other human actions, including, I guess, when one really gets 'into' the music. The sound was fast and articulate with a nice stereo spread and good front-to-back realism on music that was recorded well. Bass was good. The highs were extended and crisp but not artificially bright. Revisiting my comments on the final Shootout, I said 'The [Kenwood] L-02T has a slightly darker and richer tonal character, while the [Burmester] 978 has a slightly airier sound.' I consider those two tuners to be among the best stock tuners out there, and will reference them in future reviews as a sort of yin and yang principle. This is for people who have different tastes in what they perceive as sonic perfection. I would affiliate the modified Optonica with the Burmester.

OK, I see a small problem here. Most often the scores for sonics will be really high on all the modified tuners reviewed, and they should be. Why would I rebuild a tuner and review it unless it turned out really well? Why would Ray or Bob or anyone else? Having said that, my praise to Ray and to Bob could not be higher. Well done, guys. jim..."

Optonica ST-3636 (3/30/06):

Sonic rating:
A - Bass: 1
B - Midrange: 1
C - Highs: 1
D - Focus/Soundstage: 1
E - Dynamics: 1
Overall rating: 1

Kenwood KT-5020 (4/10/06)

The reviewed tuner is the same one described on our DIY Mods page.

How many incarnations does it take for any modified tuner to reach FM Audio Nirvana? Well, it helps to shorten the signal path if the tuner's first incarnation is already a sweet-sounding little tuner as the KT-5020 is. In its first life, it ran with the big dogs, having a sonic character very similar to the L-02T. In its second life with a new OPA2604 op-amp, all Black Gates from MPX to outputs and more mods, it presented a more lively presentation with an extended but natural sound. The bass was still warm and tight, and the midrange and highs were open and exciting with a good stereo spread. I listened and enjoyed it in this configuration off and on for many months.

Several months ago, I found myself shy a Black Gate cap or two while modifying a Sansui tuner for a local pal, so I cannibalized this 5020 of all its Black Gates. It seemed like a perfect opportunity to redo this KT-5020 with Sanyo OS-CON caps, which I'm also very fond of. With parts available, I replaced the Black Gates with Nichicon Fine Gold capacitors and Sanyo OS-CONs after the op-amp. So the 5020 was reborn into its third incarnation. There was a stock KT-5020 visiting the house earlier this year and A/B tests were done. Revisiting the yin and yang principle discussed above in Ray and Bob's Optonica masterpiece, I would say the second incarnation of the KT-5020 with Black Gates sat on the Burmester 978 side of the table, while the stock 5020 sat with the L-02T. But the Nichicon/Sanyo OS-CON mod sat dead in the middle of the table - not too yin and not too yang. As a matter of fact, if great tuners were like really tasty cake, how would you flavor yours? With delicious chocolate ice cream, maybe like I could describe the L-02T? With sweet vanilla like I might describe the Burmester? Or would you choose Neopolitan for a nice flavoring of both? This tuner, in this third configuration, gave me a 'taste' of it all. It has an open airy sound that has a sweeter upper midrange and highs more to my tastes. I don't think the midrange could be any better. It has a great soundstage and very good bass. Now, many of these characteristics were designed in by the good folks at Kenwood, certainly not by my meager parts changes. Flavorings? But I do think I WAS able to flavor this 'tasty tuner dessert' for several different audiophile tastes. And one thing I've learned in our FMTuners group is that one man's chocolate is another man's vanilla. So you DIY'ers, 'eat up your soldering irons and make your own desserts. One last thing: after living with the OPA2604 for several months, I replaced it with an OPA2132 earlier today. I do think I like it better.

Kenwood KT-5020 (4/10/06):

Sonic rating:
A - Bass: 1
B - Midrange: 1
C - Highs: 1
D - Focus/Soundstage: 1
E - Dynamics: 1
Overall rating: 1

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