Messages

16

Reel to Reel Tape Machines / Re: J-Corder decks vs. A810

« on: November 24, 2009, 10:19:30 AM »

I have first hand experience with the Studer A810, the Revox PR99 and the Technics RS1520.
Unmodified the Studer A810 beats the other two in all areas hands down. However to get a good A810 expect to pay a pretty penny for a professionally maintained unit. There are a lot of A810s out there for still significant prices that are in very sad state. Those machines were real workhorses and many of them are totally worn out.

The PR99 is interesting because it is in the basis a real Studer, but by concept totally stripped down to a bare minimum. Unfortunately they didn't do a particularly good job on the I/O electronics. The REC/Playback core of the machine and the heads are well designed. I have modified several of these decks to use only the core circuitry. I have also further improved those circuits to bring them up to modern audio standards. (you can read about that in other threads on this forum)  That makes it a good playback machine and an excellent recording machine, certainly outperforming the stock Studer A810.

The Technics RS1520 has a very good tape path, but the stock electronics are really disappointing. Also the recording head is quite disappointing. As a playback only machine with modified or external electronics you can get a good performance from it. For recording it is not the best choice because of the limitation of the recording head. It may have been OK for 1970s consumer tapes, but with an Agfa 468, you can loose as much as 6dB headroom compared to a Studer/Revox recording head.

By far the best performance I get is from the Studer A810 with custom external playback electronics. That really brings out the excellent characteristics of the A810 transport.

17

Reel to Reel Tape Machines / Re: Problem with Revox PR99 Mk II

« on: November 16, 2009, 11:41:26 AM »

Hi Kantik,

I bet you have your "tape dump" button pushed in. the one next to the "reel size" button below the editing block.

18

Raw Tape / Re: ampex 671

« on: September 15, 2009, 04:28:29 PM »

I bought a bunch of Ampex 671 tapes some 20 years ago. I used them for recording not very critical material on 3 3/4 and 7 1/2 ips.

The performance of the tape is actually quite good for a Double Play tape. Like with all DP tapes the headroom is limited and the output level is quite low. (Actually a necessity to keep the print through at reasonable levels.) The bandwidth of these tapes is actually quite excellent.

The good news is that the mechanical tape moving properties of the 671 are better than any other DP tapes I own. Even better news is that after 20 years those tapes are still as playable as they ever were, without any noticeable degradation in mechanical properties or sound quality.

Somehow I wish I had made many of my live recordings on this tape, because the (much better?) tapes I used back then are now all gone because of major irrecoverable Sticky Shed Syndrome. Somehow a limited quality Ampex 671 sounds a lot more attractive now then a 457 that comes to a grinding halt after only 30 seconds play.

I really get the impression that over the next 30 years these 671 tapes will still be as playable as they are today. If only I would have known that 20 years ago.
 

19

General Discussion / Re: SO - who'se going to Rocky Mountain?

« on: September 15, 2009, 12:49:15 AM »

I will be there.

20

General Discussion / Re: Ideal upper frequence response.........

« on: September 15, 2009, 12:40:26 AM »

At 30ips the bottom octave of any tape machine is pretty severely compromised compared to 15ips. In fact some bass response degradation is already noticeable between 7.5ips and 15ips.

Tape formulas of the 1950s and 1960s would saturate substantially at higher frequencies. By running the tape at 30ips most of this saturation effect would be shifted above 15kHz. A very useful tradeoff against the loss of bass response for that time.

The 'modern' tape formulas show very little saturation below 15kHz even at 15ips (only with good recording heads!). So running the tape at 30ips doesn't really help anything in that area, but it still compromises the bottom octave.

With modern tape like the RMGI468, 15ips will give you a better copy of the original signal than 30ips will.

21

General Discussion / Re: Odd tape dilemma...

« on: August 23, 2009, 05:27:50 PM »

Tj,

Do you know where these tapes originally came from? In the German broadcast industry it is quite normal to have a B-wind. Most of the Telefunken M12 and M15 machines, the standard machine for the German broadcast, were configured for B-wind. After Telefunken discontinued their tape recorder production, Studer developed a replacement machine, custom made for the German broadcast industry, the A816. This machine, based on the A820, also has the heads on the outside of the tape.

In your case I would first rewind the tape and then play it back with a half twist in the tape. After that you're set.
(It is best to use a machine that has quite some distance between the reel and the first tape guide.)

22

Reel to Reel Tape Machines / Re: SonoruS modified reVox PR99 /B77

« on: August 09, 2009, 05:45:49 PM »

Andrew,

If you'd analyze most amplifier circuits in general you'll see that the power supply is partly or often even completely in the audio path.  On a few of the cards in the PR99/B77 the +21V supply voltage is hardly buffered which means that the audio signal goes all the way through the power supply card before it returns to ground. To avoid that, I'm putting large power supply decoupling capacitors on the individual boards and add small resistors in series to avoid the power supply board being in the audio path.

 

23

Reel to Reel Tape Machines / Re: The best reel to reel Revox transport

« on: June 08, 2009, 10:09:32 PM »

I agree with Steve. The pinch roller may look good, but if it has been treated with alcohol in the past it may have dried out unevenly. The sidebands you see are indeed a bit strange. You would normally see 4.8Hz sidebands of the pinch roller at about -30dBc and 13.9Hz sidebands of the capstan itself at about -50dBc. The second harmonic of the pinch roller is normally just visible at around -50dBc I do my measurements normally at 1kHz with a RBW of 1Hz. The mains frequency shouldn't really be visible as a mechanical effect. It may be caused by some intermodulation elsewhere in the machine, especially since you seem to see the second harmonic of the mains frequency.

24

Reel to Reel Tape Machines / Re: The best reel to reel Revox transport

« on: June 07, 2009, 12:09:39 AM »

The PR99 would normally be the preferred way to go, especially if you carry out the few simple mods that I describe in my article.

That said, if your plan is to use the machine for playback only through external electronics, the story becomes a bit different. The audio electronics on the A700 are really bad. The stock A700 sounds about as bad as a stock RS1500. However from a mechanical point of view the A700 is really good. It shares its transport with the Studer B67. That transport was developed in the early 1970's but is remarkably modern in performance. The tape handling of the A700 is about the best I've seen except for the large studio machines A80 and A820. The A700 has tape tension control under all circumstances including during braking. You can, without exaggeration, put a plastic 3" reel on one side and a 10.5" metal reel on the other side and maneuver the tape perfectly without ever creating tape loops or over stress on the tape. This functionality all comes from an ASIC that Studer had developed especially for this transport. Must have been an enormous investment in those days.
If that ASIC breaks, you're dead in the water, but I have never seen that problem or heard about it, so it is probably a relatively low risk.

Furthermore, the A700 does have a scrape roller, but if you use 468 tape there is almost no scrape flutter in the first place.

So, if you are planning to bypass all the audio electronics, the A700 or even better the Studer B67 is a very good choice. They normally will be at least 10 years older than most of the PR99s, though.

25

Tape Tech / Re: Resistors used in PR99

« on: May 31, 2009, 06:21:58 PM »

Andrew,

The later Revox machines used mainly Beyschlag resistors. The older machines were Roederstein if I'm not mistaken. Both brands don't exist anymore since both were absorbed by Vishay. The earlier Roederstein resistors were crap, so you wouldn't want to use those anymore. The Beyschlag resistors were very good. In any case I recommend the MRS25 resistors (formerly Philips) for replacement. They are very comparable to the original Beyschlags. You can easily get the MRS25 from Digikey.

If you are interested, here is a link to an article I wrote about using the B77/PR99 for the Tape Project Tapes.

http://laocaudiosociety.com/tech.html

26

Tape Project Albums - general / Re: Favorite TP tape to play for audiophiles and guests

« on: May 29, 2009, 11:43:59 AM »

In my opinion the Arnold Overtures is the best recording of the lot, but musically it is less interesting and it is indeed less suitable for demonstrations.
In second place, for me, is the 'Exotic Dances'. Also a really great recording. Good demo material as well.
In third place for the recording, but definitely my number one demo tape is the 'Suite Espagnola'. It has some fantastic dynamics and it excites almost everyone, whether they like classical music or not.

27

Reel to Reel Tape Machines / Re: SonoruS modified reVox PR99 /B77

« on: May 22, 2009, 10:29:46 AM »

With the Sonorus modification the PR99 or B77 has different EQ's for the two speeds. At 15ips, the machine records and plays back with IEC EQ. At 7.5ips, the machine records and plays back with NAB EQ.

On top of that there is the option to have the machine play back 15 ips tapes with NAB EQ, by plugging a dongle into a connector on the back. There is no 15ips NAB recording option.

Concerning mechanical upgrades. I haven't done much in that area. The only very minor mechanical modification in the Sonorus PR99 or B77 is the bearing in the left rolling tape guide. The original SKF bearing is replaced by a heavier and smoother Minebea bearing. 

28

General Discussion / Re: The SACD vs Tape Challenge

« on: April 13, 2009, 11:11:10 AM »

just two examples luxman D-06 and esoteric SA-50 - both support DSD natively
http://puresuperaudio.blogspot.com/2009/03/new-high-definition-pure-audio-players.html

Hiro,

Both the Luxman and Esoteric SACD players are fine machines. They support DSD, but the actual DAC chips (PCM1792A and AK4392) first use digital filtering to control the high frequency noise and then convert the data to a PCM like multi bit sigma-delta data to convert it back to analog. The PCM inputs on those chips go through a different digital filter but end up on the same multi bit sigma delta DAC. I'm sure both chips do a good job, but it is unclear whether these DAC chips will perform equally good on all DSD coded data streams.

When I said "there are no true DSD DACs" I meant that as far as I know the original beauty of DSD didn't fly because you cannot convert DSD back to analog as intended.

The original thought behind DSD was to create a 1 bit data stream that basically contains the audio information in analog form, but since it was digital data you could still store it on digital storage media. 
In the basis that original thought is still valid. If you take the digital DSD data stream and you hook that up to the analog input of you amp, you will actually hear the music. (Try that with PCM.) However the trick is in the details. DBX brought out a 1 bit sigma delta digital recorder somewhere in 80's that used a non-dithered and non-noise shaped A/D process. The drawback was that the S/N ratio was only about 50dB. But since this was DBX they combined that with their compander noise reduction system to get something like 100dB. It worked but was not suitable as a standard.
DSD is basically the same, but it uses enormous amounts of negative feedback and dither to move the noise below 20kHz to the area above 20kHz. From a digital point of view that works OK, however it has now become practically impossible to distill the analog information straight from the DSD stream. Even the slightest timing and transition imperfections will bring a significant amount of the noise that was moved away from the audio band back in. In the end if you can get 60dB S/N you're doing very well.

So what I have seen as practical solutions in all DSD DAC chips as far as I know is that the DSD principles are abandoned and the DSD stream is first converted to a multi bit PCM like delta sigma signal exactly the same as is done with high res PCM.

All these tricks make DSD about as vague and uncontrolled as our beloved analog media. Great fun, but not very practical.

29

General Discussion / Re: The SACD vs Tape Challenge

« on: April 07, 2009, 01:51:00 AM »

Arian,

regarding compatability with DSD, i have a few comments.

on the playback side; i've not heard an SACD player that is superior on one label but not on all labels. it's either better or it's not.

OTOH certain pro DSD ADC's did sound better than others. i was an EMM Labs owner for 7 years and there is no doubt that SACD's recorded thru EMM Labs pro ADC sounded better than the dCS pro ADC. and the EMM Labs mastered discs did sound better on EMM Labs consumer DAC's. dCs mastered discs also sounded better on EMM Labs consumer DAC's. Ed Meitner was involved with Sony/Philips in the creation of the first pro audio gear for DSD recording. Andreas Koch (who also did digital design for EMM Labs) worked with Sony/Philips in the creation of the DSD format.

even though SACD's mastered on the dCs were not quite as good (in general they had less pleasing high frequencies), those SACD's still sound very good. i think that over time there are fewer 'non-optimized' SACD's. i've not purchased one for 3 or 4 years which had any edge. i think that dCs has improved their ADC.

i think another problem with SACD is that some DAC's convert DSD to PCM prior to analog conversion (mostly this was older SACD players). it's not hard to find out which players do what and how.

like anything; there is SACD 'done right' and SACD 'light'. PCM also comes in many different flavors of filtering and upsampling, it's not unique to SACD.

mikel

Mike,

I have played for a while with both the EMMlabs and the modified Luxman in my system at the same time and it was very clear that some SACDs performed better on the EMMlabs while others performed better on the Luxman. The noise shaping algorithms of DSD on the recording side is vastly different from one SACD recording to another and the different playback systems handle that very different. This was very audible and also very measurable. I could measure noise floor differences of up to 20dB. Most of the time in favor of the EMMlabs but sometimes the Luxman was just as good, depending on the SACD used.
I was making analog recordings of SACDs at that time using my virtual surround process. Except for the noise that was very different, also the depth of the soundstage was remarkably different between the EMMlabs and the Luxman and again depending on the SACD the EMMlabs or the Luxman could be clearly better in that respect. So I ended up making some of the recordings from the EMMlabs and others from the Luxman.

Concerning DSD to PCM conversion, I think that is one of the flaws of DSD. As far as I have been able to find there are no true DSD DACs. All of the existing DACs will convert DSD to some level of PCM in the actual DAC section. I have spend quite some time trying to design a real DSD DAC, but I failed because there is a practical limitation you cannot get around. The only way is to start filtering in the digital domain and abandon the true DSD stream. Again if there is a real DSD DAC out there I would really like to learn more about that.

30

General Discussion / Re: The SACD vs Tape Challenge

« on: April 06, 2009, 11:26:54 AM »

Mike,

Thanks for the equipment suggestions. I am still very interested in SACD despite the inherent flaws, because it has been adopted by some serious audio labels and there certainly are very nice recordings available on that medium.

DSD, because of its analog nature, is very suitable for continuously ongoing improvements and may even have the potential to become the best recording medium in the end. There is however the danger, even more so than with our analog recording media, that there will be significant mismatches between recording equipment and playback equipment for DSD. You can already hear (and measure) large differences between DSD recording algorithms used by the different music labels. It is very conceivable that DSD playback equipment depending on the algorithms used there may favor a certain recording algorithm.
(Maybe we end up with three different SACD players in our systems, each one dedicated to certain music labels.)