RE-301 noise on reverb

[Marina]

Hello,
This is my first post. I was wondering if anyone would have any ideas about noise on a Roland RE-301. The chorus is fine, but there's a kind of fuzz-box noise in the reverb section.
Thanks,
Marina

[Marina]

Re-301: Noise in Chorus Section

OK sorry, I misinterpreted the problem. Part of the problem is that the unit I'm supposed to be fixing is across town and I can only get there once or twice a week at best. I got a schematic for this thing and spent a couple of hours on it tonight. There are two buttons on the front, one for chorus, one for echo. The customer complains of noise in the echo circuit. Originally he said it was like a fuzz box. I heard that when I first checked it out, but then it went away. I thought maybe I had just inadvertently overdriven the input.

Aparently that wasn't it. The guy is still complaining about noise in the echo circuit. One thing I did find was when the intensity knob in that section is turned up, it makes a noise that builds up like feedback or something. I don't know if that's normal or not. Also, throwing the switch from echo to "single delay" cuts the noise in & out. In with echo, out with single delay. The schematic shows that switch supplying a ground to Q13 gate via a diode, & the block also shows it going to Q16 but I can't see that in the actual schematic. The echo intensity pot is in the source of Q13.

Wish I knew how to load the schemo onto a post here. If anyone can help me out with this, I'll appreciate it a lot. Does anybody have experience with these.. own one, maybe? Could I be barking up the wrong tree? Can anyone tell me if it's normal to get a feedback type of noise when the echo intensity is turned up? I'll try to get more information from the owner as to his experience with the noise. Thanks for any direction you can give me on this.

Marina

[Enzo]

Hi Marina, from up in Lansing.

Click on POST REPLY, or the quick reply button within a post box. If quick reply, then click GO ADVANCED once there.

Type in any text you want, then scroll down a little to see ADDITIONAL OPTIONS. The second section there is ATTACH FILES, so click the MANAGE ATTACHMENTS there.

A window will open and offer UPLOAD FILE from your computer or from a URL. If the schematic you want to post is on your computer, click the BROWSE buttton and find it on your system. For example I just attached a photo from my recent ski vacation...

If the schematic is from some other web site, just enter the URL for it in the box.

ANd of course if the schematic is on another web site, you can always just type its URL into your post.

[tubeswell]

Gotta love that downhill flying freestyle of yours Enzo, but how old were you in that photo? ;-)

[Enzo]

Oh OK, so it's an old photo. here is a more recent one:

[Marina]

Attempted to load schematic from PDF manual. Didn't know how to separate it from the entire manual. Made a copy of the block diagram & then scanned it. Let's see how it worked.

Don't see it in the preview.

Looks like not here. I went through all the steps. Got error message: invalid file.

[Enzo]

If you only have Adobe Reader, you can't separate out a page as far as I know. You could scan a single page if you had a scanner.

How large a file is the whole manual? if it is under 1Mb just post the whole file.

[Enzo]

OK, I have the RE-301 schematic here. Does yours say ET-13 or ET-13A near the top center? Or what date is on the drawing?

The single switch controls transistors, but is not dierctly connected to them. For examplpe Q13, lower left, is controlled by its gate through D5 and R16,17,18. COntrol signal 2 taps in there and you can see its connection upper right on the page to the actual switch.

Do you have and understand a scope?

Noise in the echo? The tape path has three echo playback heads - P1,2,3 - and each goes to its own JFET amplifier stage - Q19-21 - whose outputs are selected by gating through Q23-25 as chosen by the Echo Mode switch. The selected signals are then summed through Q26 and into IC13a and on out to the rest of the system.

If the noise is present when only one playback head is selected, then explore that head and its little circuit. If it doesn;t matter which head or combination of heads is selected, then look more towards Q26 and IC13. Semiconductors are the most likely cause of noise and distortion here.

The IC runs on a split supply, so verify both sides of the +/-14.5v, 14, 15, 16v the voltage is not so critical, but it is impoertant they both be about the same voltage and there be no ripple. And for fuzzy, look for DC offsets on the outputs of op amps. The FETs Q19-21 run on a single supply, but check the voltages around them, if one has DC voltages substantialy off from the others, it is suspect.

[Marina]

The Manual

The manual is 2.8 MB. The attachment uploader was taking exception to the fact that it was a scanned document. Oh well. The circuit that's affected by the switch & the control looks like it's feeding directly into the bias oscillator for the record head - perhaps the ammount of the actual audio in relation to the bias. That would make sense. Do you think because these posts are to an older thread that not many people will read my questions? I'm particularly interested in hearing from someone who might have one of these units, who could possibly tell me if it's normal or not to get feedback or noise when turning up the control.

[Marina]

Thanks Enzo, Lots to think about here. The date on the picture is May 30, 1979. The top of the pages are cut off a little. Don't see ET-13 or 13A, but there are different schematics depending on the serial number. His is the earlier one.

I'm going to have to get back with this tomorrow after work when I can really analyze what you're talking about here. Just want to say I really appreciate all of your suggestions. There is a scope in the shop & I think I know how to use it pretty well. Of course the biggest room in the house is always the room for improvement & I'm sure I have a lot to learn about almost everything.

Great idea about isolating the playback head circuits. I would expect imbalance or noise on the rails to affect the chorus channel as well, but I'll leave no stone unturned to satisfy this customer. DC ofsets on the outputs of the op amps should definitely be investigated. I'll have to look at the circuit for FETs Q19-21 & do comparison checks. Thanks again!

[Enzo]

The ET-13A,which is the 1979 version, is written just above IC12 on th overall circuit diagram. That is within the dark dashed line that represents the circuit board itself.

This thread is not that old, and you are the original poster. ANyone who has interest or something to contribute is aware of it by now. I think the majority of our memners are into tube amps without a lot of experience elsewhere, though ther are some heavy duty service oriented guys as well.

The bias oscillator is in the power supply, pahe 11 of my paper manual. The oscillator feeds the erase and recird heads. The audio signal for the record comes into pin 15 of the PS, from pin 57 of the ET-13 board. That is the output from IC5B that Q13 is involved with.

On any echo machine, if you turn up the intensity enough it will run away-ay-ay-ay-ay-ayayayayayayayyyyyy.

I have something I call the squint test, even though it is not a test. It is one of those can;t see the forest for the trees deals. Hold a schematic out at arms length. Yuo can't see the details, but sometimes the overall flow of a circuit becomes more apparent. This schematic is crammed together and harder to see, but we can try anyway.

The playback heads send their three signals over to three FET amp stages and are mixed and sent on their way by IC13A, as described earlier. That output sugnal goes through C41 through VR7 and on up to the main output stages feeding the output jacks. But C41 also sends the signal to VR6, the intensity pot, where it travels back to Q13 (acting as a switch) and on into IC5B and then into the record head.

The record head puts it back on the tape for the playback heads to pick it up once again and... voila. echo repeats. So VR6 is nothing more than a feedback circuit for the delayed signal.

There is only one bias oscillator, and for that matter only one record head. SO if ANY record function works ok or any echo function works OK, then the bias is OK too. The bias has no way of knowing how many playback heads will be listening.

Isolate the problem. Either the recording is laying a fuzzy sound onto the tape, or the playbacks are fuzzy or the tape is just worn out. Assuming the tape is OK, and if we determine the basic record head system works, we then consider what puts signals into the record head. IC5B does. The input jacks feed IC6 and from there right into IC5B. So if IC5 is OK sometimes, then it is OK, and if IC6 were bad ALL signals would sound crappy.

SO I start to look more at the PB end of things. That is my thoughts so far.

[Marina]

Hi Enzo,
Good circuit analysis. I was able to follow that, and your reasoning sounds right. I see the ET-13 on the diagram I'm using, for the earlier model number, and the date on that page is June 30, 1977. So this machine is almost 30 years old? Wow, I wonder if it has a bunch of dried up electrolytics in it.

[Enzo]

It probably does.

[Marina]

I think the majority of our memners are into tube amps without a lot of experience elsewhere, though ther are some heavy duty service oriented guys as well.

Yeah, I see that now. I'm a tube amp lover. I got hooked on the sound from listening to Kenny Burrell. I own a Blues Deluxe. This is a very cool forum. I like it here.

[Enzo]

Well then welcome to the place, and feel free to hang around after your 301 is fixed.