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My adventure with modding a Tascam 38. (Paging Jim Williams!) Recorders, Players & Tape Machines
Old 20th August 2010
  #1
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Talking My adventure with modding a Tascam 38. (Paging Jim Williams!)

Some time ago I read on Tape Op where Jim Williams spoke about modding his Tascam 38 by doing some various mods to the cards that are used as part of the recording and playback process in the Tascam 38.

One of the upgrades mentioned was the National LME49720 as a replacement. Another which really intrigued me was the removal of the Tamura step up transformer, bridging the connection and changing the size of the resistor going from pin 2 (to ground) on the opamp to a 91 ohm or lower resistor to get the gain back to unity. Jim mentioned that this would improve the playback section to no end. (Thus he has my attention on this).

I would love it if Jim would chime in here with any pointers or helpful tips about implementing the better opamps that are out there in this situation.

To Jim Williams: in your post you didn't mention if you did your standard method of putting a bypass cap in place across the power rails or the use of a (de)coupling cap. I was curious if the LME49720 would function appropriately without oscillation as a drop in replacement without the need for these additional components?

I figured I would also point out that I would try to keep a running diary on this mod since it may be of interest to other Tascam reel to reel owners.

I want to try the opamp swap and losing the transformer (along with changing the resistor etc) before I go about recapping the channel card completely to see what kind of differences I can find when I do an A/B comparison between 2 channels.

As well Jim you mention that the relays can be replaced?

Do you have any recommendations as far as a good quality relay for this application? I think you mentioned it was 16 pin dip.

What are you thoughts about beefing up the PSU filter caps?

Any other things that you did to the Tascam 38 that might be worth mentioning?

Thanks


PS I already have the channel cards out and packed away, since I'm moving to Philadelphia in a few weeks and I need to transport the 38 to my new job. I read that taking out the amp cards is a good practice for long distance trips (4 and a half hours).

Peace
Illumination
Old 20th August 2010
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OK, it looks like the OPA2134 would work in the amp cards without any oscillation problems. However I still might be interested if using bypass caps or a coupling cap would improve using it sonically.

Peace
Illumination
Old 20th August 2010
  #3
Smile

It may be imagination, but isn't Jim's core business performing mod's on gear, and other than suggesting a few things for you [after already outling the process in print], isn't it a bit unfair to expect him to give you detailed descriptions of how he does his mod's? He isn't really in the DIY biz. He seems to give very freely alot of his hard earned personal knowledge [and insight], so I think we should tread lightly on him... Maybe some tech's who aren't in the mod biz could chime in and help you?

Also in a 15+ year old machine I would re-cap it as well, so you can really see what is happening with your mod's...and do the ps.

On the other side, posting your experiences would be wonderful for the 100's of 38 owners out there. I'm into bigger formats, but many of the GS community would love to see a DIY/How to.

Good luck with your project!
Old 20th August 2010
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Quote:
Originally Posted by tubeaudiofan View Post
It may be imagination, but isn't Jim's core business performing mod's on gear, and other than suggesting a few things for you [after already outling the process in print], isn't it a bit unfair to expect him to give you detailed descriptions of how he does his mod's? He isn't really in the DIY biz. He seems to give very freely alot of his hard earned personal knowledge [and insight], so I think we should tread lightly on him... Maybe some tech's who aren't in the mod biz could chime in and help you?

Also in a 15+ year old machine I would re-cap it as well, so you can really see what is happening with your mod's...and do the ps.

On the other side, posting your experiences would be wonderful for the 100's of 38 owners out there. I'm into bigger formats, but many of the GS community would love to see a DIY/How to.

Good luck with your project!
Well he'd made this list of things he did a while back in response to someone on Tape Op, it was several years ago to be exact.

Seeing as how he really liked his deck and he consistently has been very helpful and informative about modding equipment if you want to DIY, I figured he would contribute to this thread. I mean that's really his thing. I'm just curious to hear it from the man himself.

All others are welcome to contribute as well by the way!

Peace
Illumination
Old 20th August 2010
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I've put LME49860 (the higher voltage version of the 49720) in my Tascam MS16. With any high speed opamp, it's ALWAYS a good idea to use psu bypass caps from each power rail pin to ground - it's also a good idea for standard fare opamps like the 5532, etc. It prevents any ultrasonic oscillation that can cloud the audible frequency spectrum, and it simply allows the opamp to function better. I would not recommend using them without the bypass caps.
BTW, psu bypass caps are also called psu decoupling caps.

The LME's are a world apart from the awfull JRC4558's that were in my MS16. It's like night and day - clear and detailed, no longer murky and dark. The MS16 doesn't have transformers, so I can't speak to that mod.

BTW, the opa2134 is no longer available in a DIP8 package. If you want to use it you'll have to get a SOIC to DIP brown dog adapter.
Old 20th August 2010
  #6
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Quote:
Originally Posted by mexicola View Post
I've put LME49860 (the higher voltage version of the 49720) in my Tascam MS16. With any high speed opamp, it's ALWAYS a good idea to use psu bypass caps from each power rail pin to ground - it's also a good idea for standard fare opamps like the 5532, etc. It prevents any ultrasonic oscillation that can cloud the audible frequency spectrum, and it simply allows the opamp to function better. I would not recommend using them without the bypass caps.
BTW, psu bypass caps are also called psu decoupling caps.

The LME's are a world apart from the awfull JRC4558's that were in my MS16. It's like night and day - clear and detailed, no longer murky and dark. The MS16 doesn't have transformers, so I can't speak to that mod.

BTW, the opa2134 is no longer available in a DIP8 package. If you want to use it you'll have to get a SOIC to DIP brown dog adapter.
I have to look at the cards again as well. The National still looks promising if not expensive.

On your MS16 were the JRC4558s in the recording path as well? Or just the playback?

Thanks for the information btw.

I read that on some cards finding a good ground plane can be a PITA which is why I was curious if there was a good drop in replacement that wouldn't require that. Ah well...Off to digikey I go.

Peace
Illumination
Old 20th August 2010
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expensive???? $2.78 ea.
Order LME49720NA Parts Online, Download Datasheets, View Manufacturer Info at Avnet Express

The JRC's were in the record and playback amplifiers. 3 of em per card, 16 cards, that's 48 opamps I replaced!!! And two .1uF ceramic caps per opamp, 96 of em in all that I added to the back of the pcb!!!

I also doubled the capacitance value of all the PSU electrolytics and added .1uF ceramics in parallel with those. Funny thing is that my rec/play cards had a space on the pcb for the electrolytic bypass caps, they just didn't spend the 2 cents per cap to put any in!!!

Finding the ground plane is quite simple. Look at your schematic to see where it comes in the card, and use a continuity meter to make sure you've got ground before soldering to it. Or you can just look at the bottom of the pcb...usually the large areas of copper are the ground plane. But if you're unsure of how to find a ground plane, you might want to refer the work to a qualified tech.

You should actually be more concerned about your desoldering skills. IIRC the tascam pcb's are not thru-plated so it's really easy to lift traces, and since none of the opamps are socketed, you have to desolder each opamp leg, which puts alot of heat into a single area. If you don't do alot of soldering, I wouldn't recommend jumping into something like this.

BTW, I'd highly recommend installing sockets. And getting some heat shrink for the legs of the bypass caps, because the reach to ground for some of em goes over other traces that you don't want them getting shorted to.
Old 21st August 2010
  #8
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Quote:
Originally Posted by mexicola View Post
expensive???? $2.78 ea.
Order LME49720NA Parts Online, Download Datasheets, View Manufacturer Info at Avnet Express

The JRC's were in the record and playback amplifiers. 3 of em per card, 16 cards, that's 48 opamps I replaced!!! And two .1uF ceramic caps per opamp, 96 of em in all that I added to the back of the pcb!!!

I also doubled the capacitance value of all the PSU electrolytics and added .1uF ceramics in parallel with those. Funny thing is that my rec/play cards had a space on the pcb for the electrolytic bypass caps, they just didn't spend the 2 cents per cap to put any in!!!

Finding the ground plane is quite simple. Look at your schematic to see where it comes in the card, and use a continuity meter to make sure you've got ground before soldering to it. Or you can just look at the bottom of the pcb...usually the large areas of copper are the ground plane. But if you're unsure of how to find a ground plane, you might want to refer the work to a qualified tech.

You should actually be more concerned about your desoldering skills. IIRC the tascam pcb's are not thru-plated so it's really easy to lift traces, and since none of the opamps are socketed, you have to desolder each opamp leg, which puts alot of heat into a single area. If you don't do alot of soldering, I wouldn't recommend jumping into something like this.

BTW, I'd highly recommend installing sockets. And getting some heat shrink for the legs of the bypass caps, because the reach to ground for some of em goes over other traces that you don't want them getting shorted to.
Thanks for the tips!



Peace
Illumination
Old 22nd August 2010
  #9
Smile

Sorry Langston:
I re read my post, and I was rather harsh. I wasn't in the best of moods that AM, my apologies.

Best of luck!
Old 22nd August 2010
  #10
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Quote:
Originally Posted by illacov View Post
OK, it looks like the OPA2134 would work in the amp cards without any oscillation problems. However I still might be interested if using bypass caps or a coupling cap would improve using it sonically.

Peace
Illumination
Shame the 2134 isn't available as a DIP anymore. However, I can recommend using the OPA2604 in the U 102 position (the IC that feeds the record head when the 38 is in record mode) as it has more current 'oomph' than the 2134. I noticed that hotter peaks were recorded cleanly with the 2604 than with other ICs I tried (2134, and the Analog Devices OP 275) when doing mods on a Tascam 32. (The 32, 34[b] and 38 all use the same basic audio cards, with just some small wiring differences in the cards for the 34 and the 38.)
Old 23rd August 2010
  #11
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Quote:
Originally Posted by Ampex 354 View Post
Shame the 2134 isn't available as a DIP anymore. However, I can recommend using the OPA2604 in the U 102 position (the IC that feeds the record head when the 38 is in record mode) as it has more current 'oomph' than the 2134. I noticed that hotter peaks were recorded cleanly with the 2604 than with other ICs I tried (2134, and the Analog Devices OP 275) when doing mods on a Tascam 32. (The 32, 34[b] and 38 all use the same basic audio cards, with just some small wiring differences in the cards for the 34 and the 38.)
Did you keep the step up transformer?

I was kind of wondering if it imparts anything work keeping when I do the upgrade. My personal thing is to not ditch a transformer if its bad but to install a better one. However Tamuras are not all that bad, but it would be cool if a person could install Jensens in their place or Cinemags. Without knowing the turns ratio and primary/secondary impedances of the step up tranny on the card I'd have to send it out to someone for analysis.

What were the mods that you did to the 32? You mentioned the opamp that feeds the record head but I'd love to know more.

On a side note, one of my little fantasy ideas for this thing would be to bypass the card in general for record and playback; instead it would be awesome to feed a preamp right to the record head and to get a feed right off the repro head. However that would be a much more drastic mod vs just upgrading opamps and recapping the unit.

I'd seriously like to know how the tone of unit is effected by upgrading the opamps and possibly removing the transformers.

I really dig the 38 to begin with but in a perfect world I'd love to have the ability to hit the tape hotter for a better signal to noise ratio but still retain that tone that I dig off the deck.

I don't want this to get closer to sounding like a analog to digital converter lol, I just want more pure tone if at all possible, but without sacrificing the flavor of the unit.

Peace
Illumination
Old 23rd August 2010
  #12
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Quote:
Originally Posted by illacov View Post

I'd seriously like to know how the tone of unit is effected by upgrading the opamps and possibly removing the transformers.

I really dig the 38 to begin with but in a perfect world I'd love to have the ability to hit the tape hotter for a better signal to noise ratio but still retain that tone that I dig off the deck.

I don't want this to get closer to sounding like a analog to digital converter lol, I just want more pure tone if at all possible, but without sacrificing the flavor of the unit.
If you want to hit the tape harder, you'll have to mod your bias section. There was one film cap I changed in the bias section of my MS16 which allowed me to bias to +9 (where the stock MS16 can only do +4).

By changing to higher speed opamps, you're not really altering the tone at all. (the tonal signature of a piece of gear is inherent in it's circuit design. you can improve clarity and improve fidelity, but altering the overal tonal sound of gear is not really what changing opamps and recapping does). What you're doing is improving the depth, clarity, and detail that your machine can capture. It's the difference between muddy, smeared sounding audio and detailed, hifi audio. Hi fidelity analog is freakin amazing! My advice: install sockets so you can swap out opamps and see which ones you like.

There is absolutely no possible way that it'll sound like an A/D convertor.
The real flavor of a tape machine is the tape, and that isn't modifiable - thank god! By improving the sonic characteristics of your rec/play section you're actually allowing the real character of the tape through, whereas before you weren't really hearing the full sound of the tape because your reproduce amplifier was smearing the sonics.
Old 23rd August 2010
  #13
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Quote:
Originally Posted by mexicola View Post
If you want to hit the tape harder, you'll have to mod your bias section. There was one film cap I changed in the bias section of my MS16 which allowed me to bias to +9 (where the stock MS16 can only do +4).

By changing to higher speed opamps, you're not really altering the tone at all. (the tonal signature of a piece of gear is inherent in it's circuit design. you can improve clarity and improve fidelity, but altering the overal tonal sound of gear is not really what changing opamps and recapping does). What you're doing is improving the depth, clarity, and detail that your machine can capture. It's the difference between muddy, smeared sounding audio and detailed, hifi audio. Hi fidelity analog is freakin amazing! My advice: install sockets so you can swap out opamps and see which ones you like.

There is absolutely no possible way that it'll sound like an A/D convertor.
The real flavor of a tape machine is the tape, and that isn't modifiable - thank god! By improving the sonic characteristics of your rec/play section you're actually allowing the real character of the tape through, whereas before you weren't really hearing the full sound of the tape because your reproduce amplifier was smearing the sonics.
Nice!

Hopefully somebody can clue me into the cap in the bias section so I can do the same thing on my 38. I'll look at the cards and see what I'm into.

I think the LMEs look promising at that price point.

If there's indeed some nice film caps that can fit on the board, they're going in for sure!


I'm still curious about those transformers hmmmm.....If there was a way to add some really nice ones in the stock trannies place, because there's quite a bit of room inside the deck to do something like 8 Jensens. The return from the tape heads would have a low impedance I'm guessing?

Thanks!

Peace
Illumination
Old 24th August 2010
  #14
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For grins, on that 32 of mine, I'd removed the original transformers, and wired in a pair of old Beyers I'd removed from a gutted tube PA mixer. (The mixer had 8 of them; they coupled balanced low impedance signals to grids of 6267 preamp pentodes. Sounded a little 'truer' than the original transformers did.
Old 24th August 2010
  #15
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Quote:
Originally Posted by Ampex 354 View Post
For grins, on that 32 of mine, I'd removed the original transformers, and wired in a pair of old Beyers I'd removed from a gutted tube PA mixer. (The mixer had 8 of them; they coupled balanced low impedance signals to grids of 6267 preamp pentodes. Sounded a little 'truer' than the original transformers did.
You wouldn't have the turns ratio on those would you? Or the primary and secondary impedances?

Where did you mount the transformers? Those Tamuras are TINY!

Damn this is turning into a pretty geeky affair!

Peace
Illumination
Old 24th August 2010
  #16
Smile

Might be the Beyers trannies that were offered on Ampex tube mixers [Mx-10, Mx-35, etc], I have a few, I will try find the info on them. They are quite small... You can search the Mx-10 threads here and on other forums [google], some people like'm, some don't, but they are small enough...
Old 24th August 2010
  #17
PRH
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Quote:
Originally Posted by Ampex 354 View Post
Shame the 2134 isn't available as a DIP anymore.
They list as active on the TI web site.

Paul
Old 24th August 2010
  #18
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Quote:
Originally Posted by PRH View Post
They list as active on the TI web site.

Paul
Ah, you're right. I wonder if they released a new DIP8 version, as the ones now available at Digikey and Avnet have the PA suffix. The older discontinued ones have the PAG suffix.

I could have sworn they didn't make them in DIP8 anymore though, because I was building a piece of gear a few months back that I wanted the 2134 for, and everywhere I looked they were either discontinued or out of stock. I ended up having to use the SOIC version, which I just hate surface mount components with a passion!
Old 28th December 2010
  #19
Gear Addict
So how did your project turn out?

2-3 years ago a Tascam 32 found its way to my place. I'm finally starting to look at. Seems like it's in need of a recap as the "tone" is very midrange-y. That could just be because of the junk tape that's threaded on it.

At any rate...I've got a reel of ATR tape on the way and might look into getting the electronics cleaned up.

The transformer is listed as having an 18db step up and if I'm right...That's a 1:8 ratio. It's fed from either the Sync or Repro heads based on the controls.
Old 12th February 2013
  #20
Gear interested
 

I too have read about this mod to the Tascam 38 and I have a question if possible?
When Jim Williams mentions replacing the opamp's on the Tascam 38 card. Does he mean the JRC5089 and the JRC5023 or just the 5089?
Old 12th February 2013
  #21
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Quote:
Originally Posted by edthebear View Post
I too have read about this mod to the Tascam 38 and I have a question if possible?
When Jim Williams mentions replacing the opamp's on the Tascam 38 card. Does he mean the JRC5089 and the JRC5023 or just the 5089?
I'm not familiar with the 38. But I'd recommend peeping the schematic and seeing which ones are in the audio path.
Old 12th February 2013
  #22
Gear interested
 

Many thanks I will give that a try!
Old 13th April 2013
  #23
Gear interested
 

Are you going to change all the electrolytic caps to other values or are you going to keep the stock ones? Thanks!

And should they all have bypass caps?
Old 3rd August 2013
  #24
Gear Head
 

This is a very interesting post and one I am interested in finding out more about. You see, I work on these machines all the time and do currently do repairs on them. I was a Lead Technician at Chicago Factory Service. I have had a lot of mixers come in back then where people changed to higher slew rate Op Amps and never did any compensation and we put them all back stock when the Op Amp they put in all burned out due to oscillation.
There are improvement to be had on these machines as they were built on an assembly line to make a profit. I like the characteristics of the LME49720 IC and can see where that could improve transient response lower noise and increase bandwidth. I am kind of new here but have been doing Electronics repair for better than 40 years. I have worked at Sony and Teac and have a BSEE.
If you guys would state more specifically about the mods this would help and I could try some of these and get back to you. I do get Tascam units to sweep all the way to 50 KHz in some cases at 0 Vu and 15 IPS. I am kind of known for servicing these things in the Chicago area.
Old 12th August 2013
  #25
I'm glad this got a hit a week ago... after recording digital I am looking to move to tape with the tascam 38 I bought not too long ago.

Just for kicks, I am hoping to record a 5 song cover EP on tape. Very interested in getting the best sound of this bad boy, and any more updates on the modifications, success stories, horror stories, and a bit more detail where/what/why for someone who hasn't had too much experience replacing components would be great
Old 12th August 2013
  #26
This gentleman has a few more updates, but I'm not savvy enough to understand exactly what all these adjustments entail. skywave perhaps you can enlighten me?

It seems relatively straight-forward, however I'm reviewing the schematics to understand Jim's statement "remove the resistor from pin 2 to ground on the opamp". Not sure where this resistor is located in the picture provided, which is why I'm going to look at the Tascam documentation I have to see if I catch where this may be.

q: will all three opamps pictured be replaced with the same opamp described? or only the one next to the step-up transformer per channel?

Cooper Sloan - Olympia, WA
Old 13th August 2013
  #27
This seems to me to be a hybrid schematic of what Jim (green) and Cooper (blue) were mentioning (red being common between the two)...

I found it hard to understand what Jim was talking about with regards to Coopers' schematic diagram, till I did a bit more research on the Tascam 38 schematic.

The "R103" seems to have been confused by Cooper to be the resister to alter, whereas it is "R115" that is connected by the opamp to ground mentioned by Jim.

The only addition I see, making this a hybrid schematic, would be to change the electrolitic capacitor "C102" to a stronger 470uF compared to the one provided by Tascam, and leave the R103 at 330ohm alone.

Would this hybridization run too hot and ruin the deck? By correctly replacing the R115 connected to pin 2 (as shown in the diagram I provided below) with a 91ohm resistor, does that negate the need to recap C102 with the 470uF?

Anywho I'm no Electrical Engineer... these were my undereducated $0.02
Old 13th August 2013
  #28
Woops, here's the picture
Attached Thumbnails
My adventure with modding a Tascam 38. (Paging Jim Williams!)-tascam-38-upgrade.jpg  
Old 13th August 2013
  #29
with proper colors
Attached Thumbnails
My adventure with modding a Tascam 38. (Paging Jim Williams!)-tascam-38-upgrade.jpg  
Old 30th October 2013
  #30
Gear Head
 

Thanks to orenradio for the schematics and reason all these so called modifications are. Too many people approach me with can I do this mod and that mod and I say give me the schematic and they have none. In this, if a schematic is not available for the mod it is a waste of time to talk about such a mod. Modifications can also go in the other direction as well so even though high grade parts are used if the results is not documented what's the point.
If a guy tells me it sounds better I say in what way? I want to see number and proof on the test equipment otherwise I am putting in parts that are nothing more than snake oil.
Yes, I have recognized better op amps in deck electronics for some time and now we are talking a Op Amp of 55Mhz Ft. So far I have not seen too much proof that these really make a vast improvement. Remember that the circuit is only as good as it's weakest link. Once I do, I am all for putting more advanced circuits into a machine- but I want to know why.

I see the last part of the circuit is changed from a gain of 10 to 241 and thus 47 dB. Does his have any side effects? Noise?

On the Filter supply caps- remember the deck was made for profit not for the best performance possible. In this I consider either 50% increase in capacitors or maybe double. I have done some machines when asked and they did not have a problem with this. The capacitors of the same value these days are about 1/2 the size of the older 20 year old ones so space is not an issue.
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