Fostex 3180 Reverb Schematic?

Anyone have it? I had a channel go bad on one. Thanks

-kdawg

I have a service manual for it somewhere, should be quite easy to find as the cover is green!
Stephen

3180 Shematic - from the service manual :wink:

I've found a scan I did a few years back, it's 643Kb - let me know your email address and I'll send it.
Stephen

thank you! I'm always amazed at how fast people reply on here...

Turns out there was only a bad pot anyhow, but has anyone ever investigated to see if there is a way to reduce the noise/hiss from the design?

-kdawg

[silent:arts] - you saved me the trouble! I knew someone would need that manual one day. Do you have the schematic for any Fostex compressors? I can't remember the numbers.
Stephen

Stephen,
the service manual from the 3180 is the only one I have from fostex gear.
btw, I have one 3180, but never used it - should I give it a try ?

I'm still looking for the service manual - particularly any calibration methods.

Also - I was staking a stab at reducing the noise floor. I replaced all JRC4558 opamps with OPA2134, didn't help as much as I hoped. The "Dry" knob I can turn up full with an acceptable noise floor, but the "Reverb" knob all the way up is quite noisy (Yes I know that isn't normal usage, but I wanted to see where it's at). This is with no input also.

I read some docs at http://members.tripod.com/~roymal/ultimate.htm but I'm not sure what the best point to adapt this might be. The Fostex is not running the opamps at full gain like this site shows, would setting up U6 / U204 like this help? Thanks

-kdawg

Hi! Do any of you still use this forum or know where I can find the schematic for the 3180? This forum is over ten years old and doesn't contain the original links anymore.

Anyone solve the noise floor problem on this thing?

Any tips?

jaakjensen said:

Hi! Do any of you still use this forum or know where I can find the schematic for the 3180? This forum is over ten years old and doesn't contain the original links anymore.

Anyone solve the noise floor problem on this thing?

Any tips?

Click to expand...

Lots of love here for old fostex these days...  I'll take a stab at it a bit later tonight.

Ok so looking quickly at this...
Recap all electrolytics
The psu seems to be only +/-12v... There is probably a great reason for this (which you will have to discover) but the some of the opamps can run on +/-15 or slightly more and probably sound better esp if you've already changed them for something fancy.  Quieter I would imagine.
C101/201 could be changed for something more polypropylenish.
Feedback caps on u101 and u6 are probably ceramic right now.  Fkp caps or polystyrene would improve sound quality.

Of you have a lot of noise you might have a going bad transistor.  Was it always noisy or did it get that way recently?

Thank you so much for the insight Enginefire! I really appreciate it.

A total re-cap was my first thought. I was also considering adding a few larger caps across the supply rails of each op-amp IC to help with noise from the power supply.

Where are you seeing the +/- 12 V from the supply? I'm wondering if removing the transformer from the unit and replacing it with an external DC power supply might help with the noise. The transformer is so close to the output jacks... can't help but think there might be some interference/noise there.

Can you tell what the original op-amps are from the circuit in the schematic above? I could peek inside to see what they are but a parts list would be wonderful.  The one-page document posted above is just the schematic. Was there a parts list or anything else that came with that schematic? Would love to find the whole service manual if I could get my hands on it.

From the owner's manual, it seems like these things have always been nosiy. -35 db noise floor is what I'm getting on my end at the moment but the Owner's manual says something more in the range of -35 db to -50 db. I just picked it up late last year and am hoping to revive it! I'm hoping to push it down to -60dB. That will make it actually usable in the studio.

Any other ideas?

[silent:arts] said:

3180 Shematic

Click to expand...

You're the best Silent Arts~! Thank you!

Hey jaakjensen
I'm thinking 12v because of the regulator chips..78m12 and 7912.
Watch out for c5 and c6 they shouldn't be increased they stabilize the power regulators so they don't oscillate.  There is another thread going on right now about the compressor from this same era the 3070.  OP increase the value of these caps and they kept blowing.  Keeping them at 10uf is good. 

Check their distance from the caps before and after.  Tgry are probably on long leads.

Modding the psu is a big job but might bring you improvement of the power transformer is interfering with the reverb tanks.  Really doing it proper is huge.  You would need the 12v for the ics that need it Plus 15-17 for the fancy replacement chips... A lot of work plus lot of potential for really wrecking the thing .  start with a recap.  C1 and 2 can probably go to 1000 or even 2200uf if it fits... But I would change the regulators to more modern versions rates for 1.5A (ti makes them I think).

All the op amps should be listed on the schematic on the lower right.

From what I can tell the signal to noise ratio should be -62 from the reverb under load... What kind of noise are you getting at -35?

I am turning the reverb up all the way up to be 100% wet and then bringing up the input signal until the compressor starts working or until I start hearing the squirty-spring sound (usually those happen at the same time). The input signal is dead silent but the reverb channel is very noisy. Like... noise floor white noise.  Not 60 Hz electrical hum. I will see what I can find for lower noise drop-in Op-Amp replacements. Modding PSU is the last thing on my list to try. I'm hoping to try re-capping and other component swapping before I do anything like that.

I got one of those, same noise problem. Never measured, but unusable when mixing etc. "Designer mistake"?

Definitely a designer mistake. I think one of the problems is that none of the Op-Amp ICs have decoupling capacitors (based on the schematic provided above). If one were to decouple the supplies on every IC, I believe it would drastically improve the noise floor. I'm just having a hard time determining where ground (0 V) is... most of the IC's are powered with +12V and -12V for the rails, and one cap would need to be added between +12v and ground and a second between -12V and ground to decouple the supplies. Anyone disagree?

Not correct, opamps typically have high power supply rejection. This unit has two sections, a drive amp and a recovery amp. You need first to work out where the noise is being introduced. Then work out how to reduce it. Is the spring getting the correct amount of drive? If you disconnect the recovery amp from the spring, does it get quiet? Apply sensible fault finding techniques, and you will get your answer.

Agreed - power supply caps aren't gonna fix a bad gain/impedance structure. The cost reduced design of the Fostex 3180 has probably prevented them from using a low noise amplifier to handle the pickup coil of the reverb tank, and that IMHO is the most fruitful way to reduce the total device noise. Driving the reverb tank is not gonna be that tough using a simple IC op amp, but the pickup coil is going to be a low impedance, low level source, not much different than a ribbon mike. Typical low cost IC op amps will have an equivalent noise impedance of around 1 or 2kΩ, and if that coil is closer to 50-100Ω, then there's a lot of noise from the electronics that does not have to be there.

Not sure which reverb tank they used, and what the source impedance of that pickup coil is, but chances are that a newer, low voltage noise op amp such as the LME49710 might work well, or perhaps the even lower voltage noise AD797. Another idea is to use a low noise common emitter discrete stage wrapped inside of an op amp feedback loop to reduce noise even further.

While this sounds slightly complex, it actually might not be that difficult. Given that one is replacing an 8 pin DIP package, a new carrier board could be made containing a low noise discrete front end and an SO8 package op amp, and it'd likely be easy to get it to fit into something close to an 8 pin DIP footprint. Bias current induced dissipation might be a problem with a very low voltage noise discrete stage, but a little 'glue-on' heatsink might make this work well enough.

Of course, there may be some silly design problems at the driving end of the device, but my vote is to provide the slightly expensive low noise pickup amplifier stage that Fostex chose not to provide, in order to grind the noise down, to the limits of the reverb tank that Foxtex chose.