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Old 13th May 2019, 10:38 AM   #1
Ian Greenhalgh is offline Ian Greenhalgh  United Kingdom
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Default Technics RS-B605 - can it be modded & improvedŁ

Hi folks

I bought two new decks this month, one I am delighted with, the other is a big disappointment.

Click the image to open in full size.

Both work perfectly, the HK TD4200 makes very impressive recordings, with cobalt doped type Is it makes recordings that are the best I have heard from cassette with clarity in the mids and trebles to die for, in fact, I am blown away at how good the high end reproduction is. Playback is just as good.

The Technics however, really sounds dull, lifeless and muddy by comparison. It is good on playback if I play one of the superb recordings made with the HK in it, it sounds almost as good as the HK, but recording is another story. I bought this deck for the dbx after reading a lot of very positive comments about how good dbx sounds. Well, on this deck, it sounds poor to me, recordings made without it sound thin and brittle, those made with it lack clarity, the bass is boosted but the highs are rolled off to such an extent it makes the recordings sound muddy and bass heavy.

I tried playing back recordings made in the TD4200 in the RS-B605 with and without dbx, without, they sound fine, almost as good as on the TD4200, but with dbx turned on, I am seeing the same thing as recording made with dbx - boosted bass, rolled off treble and a warm, muddy sound with a complete lack of the clarity and openness I am hearing without dbx.

Recording using the same type of tape (cobalt doped type I by Raks) on both decks shows marked differences. I record on the TD4200 with the meter peaking at +3, no NR, quite a bit of negative bias, this produces stunning recordings on these tapes that playback approximately 2db lower than they were recorded, according to the meter. The B605 is altogether different, recording using dbx, I had the levels cranked up, peaking at +6, on playback, the levels were a lot lower, struggling to hit 0db on the loudest passages, I never saw it peak above 0db even once, so it is more than 6db down. As a result I have to crank up the volume on my amp 3 notches to play back recordings made on the B605 and while the dbx has taken care of the tape hiss,the overall quality is a long way from the TD4200.

So, the Technics is, right now, only good for playback. I read about the hideously complex circuitry in the B965 TOTL Technics deck of this series with it's 18 opamps, so I was wondering if this B605 can be improved with some modifications?

The TD4200 has a discrete design with a total of 1 opamp, which is used in the PB amp, I think this discrete design of the electronics is the main reason it sounds so much better than the Technics, so it makes sense to me that modifying the Technics to make the signal path simpler could make it sound much better and get closer to the TD4200 in performance?
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Old 13th May 2019, 01:19 PM   #2
Mark Tillotson is offline Mark Tillotson
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Sounds much more like the recording bias is mis-set on the Technics. If it has a separate record head that might be the issue. Do the heads look worn? Is the record head aligned?



18 opamps aren't going to be a problem if they are working properly, the weak link in a tape recorder is the tape, heads and biasing. However there could easily be issues with elderly electrolytics.
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Old 13th May 2019, 01:38 PM   #3
Ian Greenhalgh is offline Ian Greenhalgh  United Kingdom
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When I got it, the heads were covered in brown oxide. I gave it a thorough cleaning with cotton swabs and iso and they now look fine to me, shiny with no signs of any tarnish or marks. Judging by the overall condition of the fascia, I don't think this deck has been heavily used.


I don't know how to check alignment, I'm afraid. Sadly it doesn't have a manual bias adjust, which maybe a big part of why recordings lack high end as it's stock calibrated to TDK D for type I and I have been using other brands and types which probably need some negative bias adjustment.



There is a large number of people who have modded their B965s to bypass those 18 opamps as it's said to be a poor sounding deck in stock form, despite being the TOTL. After modification, it is said to be one of the very best sounding decks.
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Old 13th May 2019, 06:28 PM   #4
Mark Tillotson is offline Mark Tillotson
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What I found on line was reports of replacing the CD4066's with better modern parts and removing muting transistors. Not the opamps - maybe someone's confused analog switches for opamps?
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Old 13th May 2019, 06:50 PM   #5
Mooly is offline Mooly  United Kingdom
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You need a decent scope before you can even think of looking at the alignment. Signal generation for testing is no problem if you use something like Audacity to make the tones (MP3 or WAV etc) which can then be either burned to CDR or played back via some suitable device.
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Old 13th May 2019, 07:34 PM   #6
dreamth is offline dreamth  Romania
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None of these decks deserve any attention.You have nothing to improve on them.go on Tapeheads.Net Home Page for more information.
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Old 14th May 2019, 08:05 AM   #7
Ian Greenhalgh is offline Ian Greenhalgh  United Kingdom
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I hae one of these cheap ebay Chinese scopes, and I use Audaciy all the time, I have an MAudio Audiophile 2496 soundcard that Iuse to record onto tape often.


Why dosn't this deck deserve any attention? We can't all afford high end dual capstan 3 head ones and what about the simple fun and learning aspect of performing mos? I can always apply the things I learn later to a better deck.
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Old 14th May 2019, 08:32 AM   #8
dreamth is offline dreamth  Romania
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Very few cassette decks offer the possibility to improve on their sound.Most of them are carefully thought taking all the compromises in consideration.Many of us went your way even with more expensive decks with no real audible success.I looked in both schematics already.There's nothing to improve there.
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Old 14th May 2019, 12:42 PM   #9
Ian Greenhalgh is offline Ian Greenhalgh  United Kingdom
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Hmm, that surprises me as I thought there would be quite a bit to gain from replacing the amps and power supply, I would think that manufacturers cut costs in many areas which leaves scope for improvements.
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Old 14th May 2019, 01:22 PM   #10
Mooly is offline Mooly  United Kingdom
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By far the biggest gains are to be had from ensuring the alignment is half decent. Even a budget deck should be capable of giving pretty decent sonics.
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