Roland Space Echo needs help

[DeepSpace]

Greetings gang!
I have an old Roland Space Echo RE-201. Now I know these things have a reputation for being noisy, but this one seems to be beyond the acceptable threshold in terms of hiss. With nothing plugged into the inputs and all input volumes down it still creates a wall of white noise that is...well...impressive to say the least. Additionally, there seems to be an impedance issue in that a guitar volume control behaves quite differently when run through this unit than it does plugged straight into the amp. Sort of like the taper of the volume pot changes. I dunno, maybe this is standard behavior for this unit but I somehow don't think so. I have the service manual for these, but nothing is jumping out at me as faulty so far. Anybody have any experience with these?
Thanks!

[Liam]

The instrument input pot is much too low a value for guitar in these IIRC. Can't remember what I changed it to in my old RE201, but I changed it for the same reasons you're talking about. It "sucked tone" really badly too, which was also improved by fitting a bigger value pot.

My one was actually pretty quiet. Try changing the echo and reverb volumes and see if you can narrow down where the hiss is coming from.

[DeepSpace]

Hey Liam,
Thanks for the reply! Looking at the schematic, it looks like that inst. volume pot is a 10KB. I think you're right, that seems way low to me. Do you recall the value you changed to? I'm thinking it really needs 50K at least. I'll see if I can isolate the hiss on rev or delay this weekend and post.

[Liam]

I probably would have used 250K or 500K, something similar to a guitar volume pot. There's a bypass cap on the back of the pot as well IIRC, you'll probably need to change that as well. Sorry I can't be specific, modded my RE201 about 8 years back, and sold it a few weeks ago so I can't pull it apart to check it.

Can you post the schem? I've never seen one, and I'd love to know why I could never get the speed control on the motor how I wanted it!

Good luck.

Liam

[DeepSpace]

RE-201 Docs

Sure! I've found this to be the most helpful:
http://www.omegav.ntnu.no/~karlto/diy.html
I'm still slogging my way through it.

[Enzo]

You can make the inputy volume control anything you like, it is just a voltage divider in a Hi-Z circuit. 100k, 250k, sure, why not?

Remember my mantra - any control that affects the noise is after the source of the noise.

Do the bass and treble controls affect the tone of the hiss? If not, then the output stage Q8,9 is noisy, and most likely it is one of the transistors themselves. Or if they do, then do the Echo or Intensity controls have any effect?

Isolate the problem, and I'd bet you find a noisy transistor stage. This is not that complicated a unit, there are only 13 transistors and an IC as far as I can see in the signal circuitry.

[DeepSpace]

I'll check these options out this week and post back. This certainly helps!
Thanks guys!

[Lefirestarter]

Hey DeepSpace

Have you found out what the problem is? I have the same problem on my Re 201. The noise is excessive and i have no knowledge of electronics. If you manage to fix it please tell me how.

Thanks

[DeepSpace]

I'm back on the case guys. Just got back from out of town and got the Space Echo from the rehearsal room. Tone controls do not seem to alter the hiss. So the next step as I see it is to get some freeze spray, open this baby up, fire it up, and hit Q8 & Q9 with the spray and see if the hiss drops or changes in any way. Lefirestarter, check out the schematic and see if you can locate the transistors (Q8 & 9) we're talking about on the PC board. You can get freeze spray at most good electronics stores, (maybe even Radio Shack). If this is foreign to you, you might want to print this thread and take it and your RE 201 to your friendly local electronics wiz. It's kinda fun to watch them grimace and scratch their heads when they see one of these.

[cjlectronics]

I've worked on a few of these. One in particular had a severe hiss problem like yours. I spent hours on it and never did find the source of the hiss. I'm sure you have cleaned the tape path and replaced the tape...correct?

I'm with Enzo, I bet it is a noisy transistor stage or possibly a dirty or bad pot.

Good luck and keep feeding us your findings.

CJ

[DeepSpace]

Thanks for your help guys! Looking at the docs for this, it appears Q8 & 9 are 2SC1000-GR transistors. I haven't actually tested these yet but I'm not having any luck finding replacements for these. I've found equiv. charts for the 2SC1000, but nothing for 2SC1000-GR. Will any good low noise NPN work here? I have to admit that I'm mainly a tube guy and have rather limited experience working with transistors. Do any of you guys have a recommended equivalent replacement for this transistor?

[Enzo]

Yes, most any nice NPN low noise should work. Stick to asian numbers so the pinout stays the same. US types are fine, but the legs won't match up. Not that it is hard to turn the xstr sideways and deal with it, but there are plenty good asian types to choose from, so why bother.

If it were me, I'd slap a couple 2SC1815 in there and see how it sounded. That is a common type I stock just for general use.

I have no idea what the GR means, possibly it is a batch code. In any case, I suppose I would verify the leads are not reversed for some reason. Ther are xstrs with reverse leads for certain applications.

[Lefirestarter]

Hi guys

As my space echo seems to have a similar problem i will ask some questions here. With all inputs down the unit generates a high amount of hiss.

I don't know if it's important but the selector switch for the type of delay is crackling when i turn it but only when turned and i'm wondering if that could affect or create the loud hiss.
The noise seems to be affected by the treble and bass control so i guess the noise must come from anywhere before that. The echo volume know seems to add noise rather than change it. I guess that's just the noise of the tape etc..

I have located the tranistors on the echo board (i think) but how do isolate the faulty one (if it actually is a transistor making the noise) with the freeze spray?
I've never done anything like this before and have tried several electronic shops but no one wants to touch this thing so i have to do this one on my own. ( I live in Luxembourg and it's hard to find people who do this kind of stuff for some reason.).

I would appreciate your help. (sorry for hogging your thread DeepSpace)
Kyan

[Enzo]

The simple thing about freeze spray is you don't have to know what you a re spraying - not at first. Chill areas of the board. If one area responds, then spray smaller areas within that larger space.

BUT that assumes the part will be thermally sensitive, adn that will certainly not always be the case. Freeze spray is just another tool in the troubleshooting arsenal. It may or may not yield a clue. But be sure to try it.

I would be scoping the signal path looking for the niose signal. And I also would substitute transistors readily. They cost a few cents apiece.

[DeepSpace]

Well gang, I'm sorry to say I'm stumped. Changing the instrument input vol pot to 250K is a good tip (thanks Liam!). Unfortunately, I've been unable to locate the source of the hiss. Freeze spray revealed nothing, and I'm unable to pick up the hiss using my scope. I suppose I could just replace all the transistors in this thing but if I'm going to go to that trouble, I'm thinking I should replace all the electrolytics as well seeing as they're well over 20 years old now. Not quite ready for the complete overhaul yet. Only thing I have to go on is one transistor (Q1) seems to be what we tube guys call microphonic. I can tap on it and the tap is amplified and comes through the output. None of the other ones seem to do this. However this is an unlikely source for the hiss issue as the treble and bass controls clearly have no effect on the hiss and Q1 is well before these controls. Anyway, thanks for the help guys! I'll post back if anything reveals itself.
P.S. No prob Lefirestarter. Wish I could be of more help.