Opening up a TL Audio FAT TRACK to swap Tubes

[ion]

hi all

i recive the Fat Track, had not no chance to really re build my setup yet and send some audio through, but i am positive i want to swap the cheap stock tubes against some quality NOS 60s Mullards or Amperex ones...

well... now i am checkin the build of the unit... and i am really clueless how to open it up to do the swap.... i even opened up a Ghost 24LE Desk once to change jumpers... wasnt a big deal.. but i have no idea for this one.

would i have to remove all Pot knobs and unmount the faceplate?

 

[Kingston]

That thing is filled to the brim with chips. The tube is just there to add a starved plate fart sound to all your material. It's basically there for marketing purposes only. A better mod would be to bypass the tube entirely and think about swapping in some better opamps in critical spots.

If you didn't understand much of that, I think it would be best the leave the unit as is.

 

[ion]

yeah, well i know that TLA is a lot of marketing etc...

but they also get a lot of bashing... and tbh i just tried it out, stock as it comes and it doesnt sound bad at all!

EQ is really good aswell, and really i dont see many alternatives in this size and and compact concept wich i need

when you are allrady at bashing... do you think the SSL X-Desk has anything to do with what SSL is known for?  :

 

[ion]

Hey Kingston

can you give me something like a proof it is a starved plate design in there?

this does mean it runs at very low voltage and hardly get the tubes working at all right?

but again, HOW do you know? do you know it for this and thier recent pieces, and the mixers, or are you only asuming it because you opened a 15 years old "classic" of thier cheapest series?

please elaborate

i tried it out here and it doesnt sound bad like i said, nothing like the Culture Vulture of course, but its dual triode design after all

so i am thinking of putting quality tubes in there, but if they get used 3% that d be quite a waste of course

oh man... i REALLY dig the work concept and size of this thing.... thats the main factor, i dont see alterntavies

 

[kooma]

actually schematics are in gmail, ht was something like 180V.
..but dunno if that really makes this one any better

 

[ion]

hey dunno what you mean by shematics are in Gmail

neitehr i do know what you mean with "ht" ???

so you are saying the tubes run at 180V ?

can you please confirm this "for sure"

because in that case it makes some sense to put some NOS goodies in there compared to a Voltage below 100V where i would feel like wasting money because they wouldnt be used in thier full potential

thanks a lot for the input, its sometimes hard to get constructive comments on this... i spoke to Bowie (Christian) quite a specialist and he also says a lot of that GS TLA bashing is from ppl who want to sell thier own products or that of thier mates etc... i dont say TLA isnt responsible for thier image but there is a lot of "jumping on the bashing train" really!

so i thank you for a constructive comment instead of "get a Studer kiddo"  ;D

 

[Adky]

I did check out the schematic , the Tube should be running at 185VDC according to the schematic. i own a few TLA stuff, they sounds ok but a bit to the "dirty" side in tone quality. go ahead  swap those Tube to some nice one , some NOS GE is good,but for today choice i use JJ or EH gold pin, they are easy to get and not bad.  if it is a AX7 usually are , you can try a AT7 or AY7 or even a U7 , also you should think about upgrading those OP-Amp chips as well, i do see a lot of RC4580 and TL074 on the EQ, you can swap with better chips such as OPA2132 or OPA4134(quad) , then also swap out those 100uf caps in the signal path to the nicest caps you can get, BC caps and Slimic II are nice choice if sapce are avaliable try WIMA or RIFA MKP cap or even go both way ,according to my experiences, but that much mod will sure tax out your power supply , do also consider get that beef up too do check the rectifier in the PSU to see are they Fast recovery type if not swap them too. good luck with all that.

 

[ion]

;D ;D ;D i love you DIY junkies

but you are probably right

okay first i am happy to hear about the Voltage... so not "straved plate fart" as i thought (...) you wrote the same on KVR Kingston... i like information and "warn a brother" but this stripped down generalized Version on the edge to misinformation doesnt help anyone.

about further modding it, well as much as i like the idea of "cleaning" this thing up a bit... by far ALL i have had experience with is recapping 2 Neve 1272 Preamps... and to be honest my soldering is not the finest and i was give all the right caps back than rom valued Prodigy Member API, so i didnt even had to find out what caps and where to...

i dont know if i am capable of this... about OPamps i am abosultly clueles... no idea how they even are mounted.. my guess is they are sticked into a system like... lets say CF Cards into a slot?
or do tehy also need soldering?
my biggest issue is, i cant read shematics man, and i wouldnt know what parts to get and wich to swap/ where to put em in...

or would you say this is really an easy job with the Fat Track?
damn i am not even sure how to open it ( and i opened a 24 ch Board completly...) but i suppose the top cover and all knobs have to be removed?

anyway thanks mucho for this info!

 

[Adky]

Alright! I usually will start from the bottom, but without the actual picture of it I can't help much, I usually will just take everything off carefully and then group the screws or write them down so I can put it back. generally if you are not good in soldering , I suggest you get some junks to pratice on first or don't bother. it take times to pratice your skill level up.
Good Luck .

 

[bootyfox]

Ok, I posted this over at gearslutz, but maybe this was too geeky for them over there. Just wanted to share my findings after opening up my Fat Track and maybe someone has some suggestions for eventual upgrades/mods for this:

The schematics for this unit are finally online at the TL website, so I decided to take this thing apart, see how it works and check if there's room for improvement (normally there is).

What I found:

There are almost 100 (!) electrolytics spread over the different audiopaths. 91 of them are coupling electrolytics at 100uf 25v / 85degrees. Manufactured by Samwha. I guess replacing those with some low esr types like panasonic fc might be a good idea.

Input buffers are TL074 opamps, output buffers UTC MC4580L Opamps which don't seem like the cleanest choice to me. I think I counted about 25 of these opamps spread out all over the Fat Track, even the summing amps are MC4580s.
Considering among other characteristics the slow slew rate of 5v/us I am starting to wonder how much of the Fat Track's sound comes from those opamps instead of the tubes - especially when driving it harder.

I do like the sound of the Fat Track a lot, but I think changing opamps to something cleaner and opener might be interesting. If I just wasn't too lazy to do this. So far I've replaced the output buffers and summing amps with LME49720 opamps that I had lying around here. Didn't reassemble it yet though.

A nice thing I discovered: You can simultaneously use two different tubes
in the Fat Track. One of the 12at7 tubes is for the master gain, the other one is only used as additional gain stage for Channel 1/2. So you could for example use one with a darker character for the channel, and a cleaner one for the master or vice versa etc..

I am really wondering why TL Audio chose the MC4580 opamps. Maybe I'm missing something and they are just THE ticket in connection with tube-gain stages?

Anyway, if anyone here has other suggestions for possible changes/upgrades please let me know.

 

[limlo]

Hi bootyfox
that's interesting :  so you mean 1 tube is driven by the master gain knob and 1 by the stereo channels knobs ?
plus the tubeson the mono strips ?

 

[abbey road d enfer]

I am really wondering why TL Audio chose the MC4580 opamps.

The 4580 is not such a bad opamp. Noise is as good as 5532, output capability better than TL0, THD performance honourable and what's wrong with 5V/us ? Even for +20dBu output, it's 3us rise-time; almost irrelevant compared to 14us for a 96kHz ADDA round-trip.

 

[bootyfox]

Hi bootyfox
that's interesting :  so you mean 1 tube is driven by the master gain knob and 1 by the stereo channels knobs ?
plus the tubeson the mono strips ?

Sorry, should have been more specific: The Channel 1 & 2 (with the preamp and eq section) drive the tube marked as V2 on the schematic and the master sum drives the other tube (marked as V1 on the schem).

So channels 3-10 as well as the FX return pass through one tube only - the master tube (V1), and Ch 1&2 pass through both tubes.

Today I actually tested several different combinations of tubes and I finally settled for a Nos GE Jan 5965 tube on channel 1&2 - it has less gain but very fat & crunchy + I can drive it much harder before clipping whatever ICs that follow.
On the master I chose a nos GE Jan 12at7WC tube - that one sounded very nice and brilliant in the topend and not too dirty for summing.
Just for reference:
Other tubes I tried were nos Telefunken ECC81 - sounded almost exactly like the 12ATWC tube, but clipped the output to early due to the higher gain
Nos GE 5751 - they were ok, but somehow lacking the excitement I was looking for. They had a bit more gain in the mid-range which made them feel less thick in the bass-end.

This is fun! Oh, and I changed the eq section - I always felt that the lo-shelf was a bit too muddy & the hi-shelf a bit too harsh, so I switched the caps in top and bottom to wimas at slightly different values. If I remember correctly I replaced the 10nf in the lo-shelf with a 15nf and the in the hi-shelf I put either a 3.3nf or 2.2nf).
The result: Now I'm sharing my bed with this EQ-section! Finally have a real use for it 

 

[bootyfox]

Even for +20dBu output, it's 3us rise-time; almost irrelevant compared to 14us for a 96kHz ADDA round-trip.

Oh, that's good news - I did compare some datasheets and what I was mostly wondering about was the open loop gain / gain bandwidth as well as the slew rate, focusing on the summing/master section only.
I already assumed that the circuit is designed well enough to get the best result with those amps, but quite frankly: I don't think I know enough yet to really make well informed decisions about opamps.
Do you think you could explain your example a bit?
The consensus on most of those "switch the old for the new" threads on various forums seemed to be that "faster equals better". What I never really understood though is in which context/situation an opamp's slew rate starts to actually matter (given that it's in the audio-path)...  ???

 

[abbey road d enfer]

A +20dBu signal has a peak-to-peak value of ca. 22V. With a slew-rate of 1V/us, the rise-time is 22us for a square-wave. That's a very hot signal, a situation that should normally be avoided. 22us is the rise-time of a CD, due to the brickwall filtering at ca. 20kHz. I don't believe anybody ever complained about rise-time of CD's.
In the same conditions, a 4580 has 6us rise-time (the previous figure I gave was for half-wave, which is more likely to happen - think cymbal hit).
The effect of slew-rate starts to be noticeable when it is slower than the rate at which the signal is changing (the first derivative). For a 20kHz sine wave of 22V peak-to-peak (+20dBu rms), the slew-rate is 2.75V/us. Which explains why a TL072 (13V/us), a 5532 (9V/us) and even a 4580 (5V/us) are not particularly different-sounding in this respect.
http://en.wikipedia.org/wiki/Slew_rate

 

[bootyfox]

Thanks a lot for pointing me in the right direction! I think I'm starting to get the picture - guess I got some more reading to do 

 

[limlo]

Hi , reviving a very old thread ...
my fat track died today , i switched it on  it powered briefly for 1 sec and then it died .
I checked the fuse on the back but it's working  so I would like to bring it to my local synths repair technician here in Brussels , since the official service company seems closed , my local audio gear shop closed ... 
i'm looking for the schematics  but all i can find is a block diagram in the manual  and nothing else on what's left of the tl audio website .
can anybody help please ?

 

[Matt Nolan]

limlo - check your personal messages

 

[Bassking]

Heyho! Just to re-revive an old thread: does anybody still have the schematic for the fat track? I'd be very interested in that
Is anybody still using it? It pops up quite frequently and inexpensively in the classifieds...

 

[gyraf]

..uploaded to tech. docs section: https://groupdiy.com/threads/tl-audio.44989/page-2

/Jakob E.