Author Topic: Revibe Build (Read 24214 times)

sluckey · « **Reply #100 on:** September 23, 2016, 10:25:58 pm »

Try clipping in that test filter cap across node B cap and then node C cap. Make any difference in either position?

EKDENTON · « **Reply #101 on:** September 24, 2016, 09:24:03 pm »

Okay I tried that, and I had some sparks when connecting the cap to B and also C. It didn't do that when I was testing with the capacitor before when I had the bad capacitor. I checked and I did have the cap connected with the correct polarity. Playing through it the distortion was still there and I also noticed that the vibrato had stopped working. I took voltages of V4&5 and for some reason I only had 87v on pin 6 - V2. So I don't know if connecting the cap had anything to do with that or if it was a coincidence? Anyway I tried the JJ, Tung Sol, and a China made 12ax7. All those were way too much hum. So I had a Sovtek and it is quiet and the voltages are back to normal.

sluckey · « **Reply #102 on:** September 25, 2016, 08:27:00 am »

It's normal to get some sparks when connecting a filter cap into a live power supply circuit. You also should discharge the cap before moving from one B+ node to another. It's very common to just touch the positive lead to chassis. Expect a small firecracker spark.

What guitar are you using to test the revibe? Got another?

EKDENTON · « **Reply #103 on:** September 25, 2016, 10:46:59 am »

Yes both electrics I have do have pretty hot pickups, so I have an acoustic that has a weak piezoelectric pickup under the bridge. It also distorts. I'm going to get a scope from a friend today. If you can tell me what points to connect it maybe I can determine closer the problem spot. I am wondering if because I made the board smaller than it should be by mistake all my leads are short and resistors are very close to turrets. Soldering that close.....possibly overheated something?

sluckey · « **Reply #104 on:** September 25, 2016, 11:39:31 am »

Get a signal generator too if he has one. You will need a clean 400Hz to 1KHz sine wave to apply to the input jack. Amplitude should be about 0.2v to 0.5v peak to peak as viewed on the scope at the input jack. Signal path is simple. You only need to trace input jack, V1B grid, V1B plate, v4 grids, V4 plates, output jack.

I suppose it's possible you have overheated some component. But the workmanship looks good. And you did verify all the resistors, right?

Download the new version of my schematic. It will come in handy when tracing circuits. You may have to hit reload or refresh to get the new version.

http://sluckeyamps.com/revibe/revibe.pdf

EKDENTON · « **Reply #105 on:** September 27, 2016, 05:19:37 pm »

Okay I had a hard time figuring out this signal generator but i think i had it set on 1Khz. The first photo is on the grid of V1B, the second photo is on the plate of V1B it looks basically the same as the grid but about about half the size. Checking anything on V4 is difficult because of the vibrato. When i set the pots full CCW i'm getting a single horizontal line. when I change the intensity or what i call depth pot the horizontal line moves up and down with the speed changing with the pot and switch. (photo 3) The same behavior is at the output jack. So I thought i would be seeing a sine wave with some clipping or odd behavior but i am seeing a good sine wave up to V4 then I do not know if what I am seeing (this horizontal line) is normal or if it is the issue that i am having with distortion.

shooter · « **Reply #106 on:** September 27, 2016, 06:44:09 pm »

If I've followed the ball, this test should be done with only V1 AND V4 plugged in, on other tubes, is that correct?

sluckey · « **Reply #107 on:** September 27, 2016, 07:21:09 pm »

Just looking at scope pics is not very useful. We need to know the measured voltage at the input jack, grid of V1-B, plate of V1-B, both grids of V4, both plates of V4, and the output jack.

Pull all tubes except V1 and V4.

Set the output of the sig gen so the voltage at V1B grid is .5V peak to peak. That's measured from the most positive peak of the sine wave to the most negative peak of the sine wave. The signal voltage at the plate of V1B should be considerably BIGGER than the signal on the grid. The signal voltage at the grids of V4 should be about the same (maybe a little less) as the signal voltage on the plate of V1B. The signal voltage on the plates of V4B should be BIGGER than the signal on the grids. And the signal voltage at the output jack should be much less than the signal voltage on the plates (due to the 330K/10K voltage divider. Ideally, it will be about the same amplitude as the voltage on V1B grid.

You need to set the vertical input to AC coupling so the baseline does not keep shifting on you. You will have to change the vertical sensitivity (gain, volts/div, whatever it's called) Should not have to change the time base settings, except the trigger level if you are triggering internally on the signal you are looking at.

EKDENTON · « **Reply #108 on:** September 27, 2016, 10:14:24 pm »

Okay all the tubes are out except 1&4, I have the signal generator set for .5v on the grid of V1B peak to peak which is the height of one square on the display. When I switch over to the plate I get a flat line. Looks way smaller. No signal at all on the output jack. What did I do wrong?

You mentioned earlier set the signal to 1KHz but this generator starts at 100 KHz. I was able to get a sine wave to .5v by adjusting the frequency range.

sluckey · « **Reply #109 on:** September 27, 2016, 10:45:42 pm »

Quote

You mentioned earlier set the signal to 1KHz but this generator starts at 100 KHz.

That sig gen is no good for audio circuits.

EKDENTON · « **Reply #110 on:** September 27, 2016, 11:21:18 pm »

Okay I got a workaround. I found a 1KHz mp3 file online, hooked up my phone as a signal generator and adjusted my volume for .5 v. The plate voltage is way higher thanbthe grid as you said...peaks are off the screen. V4A plate is less, V4B plate is about 1.5v. the output jack is about 2/3rds the input

sluckey · « **Reply #111 on:** September 28, 2016, 06:53:28 am »

Quote

peaks are off the screen.

Turn the volts/div knob so you can see the peaks. I like to set the display for about 4 divisions. How much voltage is at every point I asked you to check?

And since you have a distortion problem, what does the waveform look like at every one of those check points? Do you see any sign of the sinewave squaring off on the peaks? Post pics and post peak to peak voltages foe all those check points.

EKDENTON · « **Reply #112 on:** September 28, 2016, 07:55:14 pm »

V1B Grid .5v.@ div .5 Sine wave good
V1B Plate 1v @ div 5 sine wave good
V4_1 1-1/2v @ div 5 and probe at 10x top 1/3 of sine wave flat
V4_6 2v @ div 5 sine wave good.
V4_2 1.7v @ div .5 sine wave good
V4_7 .75v @ div .5 sine wave good
Output jack approx. .5v entire top of sine wave flat

sluckey · « **Reply #113 on:** September 28, 2016, 10:54:22 pm »

Quote

V4_1 1-1/2v @ div 5 and probe at 10x top 1/3 of sine wave flat

Flat top is your distortion.

Carefully measure dc voltages for V4 pins 1, 2, 3 and 6, 7, 8.What are they? Unsolder the 100K that connects to V4-1 and measure resistance. Unsolder 100K that connects to V4-6 and measure resistance.

I still have no idea what your signal voltages are. Please interpret these... "V4_1 1-1/2v @ div 5" and "V4_2 1.7v @ div .5".

EKDENTON · « **Reply #114 on:** September 29, 2016, 09:23:32 am »

Okay i will get the dc voltages asap.

V1 pin 6 would be 5v
V1 pin 7 and the input tip would be .5v
V4 pin 1 is 75v
V4 pin 2 is 1.7v
V4 pin 6 is 10v
V4 pin 7 is .75v
output jack is .5v

I am learning to use the scope as I type this, so be patient. Pin 1 on V4 was peaking way off the screen so changing the division as much as i could to 5v did not even get close to bringing the peak into view so i had to set the probe on 10X. So let me know if I did this wrong:

With the probe at 10X and Div set at 5v the peak to peak of the sine wave is the height of three horozontal bars. My original signal setting was .5v peak to peak at the height of one horizontal bar. at the new setting I measure 1.5v peak to peak. So to find the voltages I did 1.5*10*5 to get 75v.

the photos of the clipping the first photo is at the output jack at .5v then i changed the div to see the shape of the clipping better in photo 2, photo 3 is V4 pin1

sluckey · « **Reply #115 on:** September 29, 2016, 10:12:45 am »

Quote

With the probe at 10X and Div set at 5v the peak to peak of the sine wave is the height of three horozontal bars.

Signal is 3 divisions high and Volts/Div is 5 so the display reads 3x5=15V. And since you are using a 10x probe that 15V display is really 150V. This all assumes that the variable is set to the cal position. Variable must be in cal position anytime you are measuring voltage.

The first photo is named 3.gif. Third photo is named 1.gif. Very confusing to me.

EKDENTON · « **Reply #116 on:** September 29, 2016, 11:06:00 am »

sorry i numbered the photos backwards, should have said the first second and third photo in the order they are posted, rather than by the number of the photo.

I have the scope set in the cal. position.

Also when I set the scope division to .5v then i adjusted my signal tone to be peak to peak just one division on the screen so peak to peak three divisions would be 1.5v not 3v correct?

Also on the dc voltages, do you need them with just tube one and four in, as it is now, or do i need to put all the tubes back in for those measurements?

shooter · « **Reply #117 on:** September 29, 2016, 11:22:04 am »

Quote

three divisions would be 1.5v not 3v correct?

correct

Quote

do you need them with just tube one and four in, as it is now

yes, otherwise you would be "adding unknowns" to the process

EKDENTON · « **Reply #118 on:** September 29, 2016, 11:48:19 am »

okay thanks, wish i had more time to work on it, right now its just a few minutes here and there because of work.
Here are the dc voltages
V4
1. 291v
2. .002v
3. 2.8v
6. 289v
7. .005v
8. 2.8v
Both plate resistors I unsoldered and they check out at 100k
The ones on either side of the 100k also check out at 470k.

shooter · « **Reply #119 on:** September 29, 2016, 08:53:57 pm »

The #'s look good to me, BUT, wait for Sluckey, since he has a working system, mines in a heap.

Do you happen to have a 12AU7 laying around?, if so, put it in V1, then redo your AC (signal) checks.
logic, it's a lower gain tube, to me, your distortion apears more a gain thing than a R or C thing.

EKDENTON · « **Reply #120 on:** September 29, 2016, 09:52:49 pm »

I tried lower gain tubes in all positions but it's the same with any tube. Pin 6 on V1 has a good sine wave so whatever the problem is it is between there and V4 I think. Will see if there is anything Sluckey wants me to check now when he is back.

shooter · « **Reply #121 on:** September 30, 2016, 08:20:21 am »

V4's architecture is over my paygrade for helping Troubleshoot.

It might be fun to unplug the revirb tank, and if you have a RCA to 1/8" cable, jack your phone signal into J3, and see what that sounds like out the revibe and into your amp.

sluckey · « **Reply #122 on:** September 30, 2016, 08:23:32 am »

It'll be very quiet with only V1 and V4 plugged in.

EKDENTON · « **Reply #123 on:** September 30, 2016, 10:11:01 am »

It has a good sine wave at V4 pin 2 so that rules out anything before that point. Then at V4 pin 1 we have clipping. I have checked part values so many times and do not see anything out of place. I think I will replace all of the circled parts anyway just to be sure there is not a bad part. Is there anything else that would cause the first stage of V4 to clip? I have had several tubes in V4 and no matter what tube is there high or low gain the amount of clipping is about the same. Once i get the clipping stopped on that stage I can move on through to the end of the signal path.

Also Sluckey have you put a scope on your revibe to see if there is any of this going on maybe to a lesser degree on your build? I know you have higher voltages because of the different PT. Just stabbing for anything i can think of ....could the lower voltages have anything to do with the clipping at V4?

sluckey · « **Reply #124 on:** September 30, 2016, 11:22:50 am »

I'm gonna check mine with a scope later today so you can compare. You're using 12AX7s for V1 and V4, right. And your input signal is adjusted to .5V peak to peak at the grid of V1B, right?

EKDENTON · « **Reply #125 on:** September 30, 2016, 12:31:02 pm »

yes that is correct.

sluckey · « **Reply #126 on:** October 01, 2016, 06:30:45 am »

OK, my revibe is on the bench with only V1 and V4 plugged in using 12AX7s. All pots are max CCW. 0.5V_pp 1KHz test signal at V1-7. My output has compressed (flat) tops too. V4-A is being overdriven. When I back the input signal down to 0.2V_pp the signal is clean at every point from input to output.

Then I replaced the two 12AX7s with lower gain 5751s. With these tubes plugged in I can jack up the input signal to 0.4V_pp with no distortion. Even with 0.5Vpp input the output is only slightly compressed on top.

Real world test with my low output single coil Strat plugged in... Output sounds clean with either 12AX7s or 5751s. I don't have a high output pickup to try.

Try this. Reduce your input test signal to 0.2V_pp. Look at the output with the scope. It should be clean and approximately the same amplitude as the input signal. (I had my probe connected directly to the input and output jacks.) Is it clean?

Bottom line... I think a pair of 5751s will solve your distortion issue.

EKDENTON · « **Reply #127 on:** October 01, 2016, 07:02:42 am »

Okay I will try that and see what hapoens. If it looks better I will order 4-5751's.

If you still have it hooked up could you try the same test with it plugged into your Variac adjusted to where your B+ is around the voltages I have? B+ 322?

I did at one point pull the 5157 from my plexi and had it in V1 and a 12AT7 at V4. I didn't have the scope at that time but I could still heat it.

sluckey · « **Reply #128 on:** October 01, 2016, 12:15:43 pm »

Quote

If you still have it hooked up could you try the same test with it plugged into your Variac adjusted to where your B+ is around the voltages I have? B+ 322?

I did this. Results are identical to the results above except with .5V in the output was about .44V, down from .45v with my B+ at 360V. I don't think your lower B+ is a factor.

sluckey · « **Reply #129 on:** October 02, 2016, 07:53:40 am »

I worked with my Revibe quite a bit yesterday and have come up with a solution for the distortion issue. It's a simple mod that lowers the gain of V1B and V4 and then changes the 330K/10K voltage divider to make the output level the same as the input level. No more distortion with 0.5V_pp input level.

I'll be keeping this mod in my unit. Looks good on the scope and sounds good with my Strat. Mod instructions are in the attached pdf.

kagliostro · « **Reply #130 on:** October 02, 2016, 11:13:09 am »

Ciao Steve

is this mod to be considered a mod to the original project or is to be applied only in particular situations ?

Franco

sluckey · « **Reply #131 on:** October 02, 2016, 12:41:27 pm »

This mod applies to any Revibe that follows the Hoffman schematic or my schematic. V1B and V4 circuits have a LOT of gain. Then there's a 330K/10K voltage divider to knock the signal back down to instrument level at the output. The problem with this is that hot pickups will cause the signal to distort at the plates of V4. This is a permanent mod to my unit and I will be updating the info on my website.

When I built my Revibe in 2013 I dealt with the excessive gain issue simply by using lower gain 5751 tubes. My unit worked fine like this and I had no reason to look any further... Until Ed's distortion problem popped up. I started testing my unit to try to discover the cause of his problem. When I put 12AX7s in my unit to try to duplicate his problem I saw the distortion on the scope with a hot signal (0.5V). V1 was not distorting the signal, but it was supplying a large signal to the input of V4, and this caused V4 to overdrive/distort. Plus, V4 has it's own gain problems, so the distortion was just magnified.

So, I decreased the gain of V1B in order to not overdrive V4 when the input jack has a 0.5v signal (hot guitar). I also decreased the gain of V4 to produce a very clean, but lower amplitude signal at the plates. Finally, I tweaked the output voltage divider to provide unity gain from input to output.

Bottom line, the output signal looks almost identical to the input signal, tremolo effect is still very good, and the reverb circuit is untouched. And you get this with cheap 12AX7s, rather than pricey 5751s.

BTW, I did take a look at Weber's Revibe schematic and noticed he dealt with the V1B gain issue by using split load plate resistors (voltage divider) to decrease the signal being fed to V4.

kagliostro · « **Reply #132 on:** October 02, 2016, 01:44:37 pm »

Thanks

Franco

EKDENTON · « **Reply #133 on:** October 03, 2016, 02:29:45 pm »

Sluckey, thanks for working on this so much and figuring out a mod to get it cleaned up for higher output signals. I will do the mods tonight and check it out. Can't wait.

EKDENTON · « **Reply #134 on:** October 03, 2016, 10:54:54 pm »

Did the mod tonight and it took care of the distortion. With the scope hooked up and using the same settings this input and output signal are the same and pin 1 at V4 has no more clipping. It sounds very good now with either amp using my guitar with active EMG pickups. I think I am done with this one.

sluckey · « **Reply #135 on:** October 04, 2016, 05:42:40 am »

Hey, this has been a tough one. Glad it's finally done. Now just enjoy it. You may never need to build another reverb or tremolo circuit. I've used my Revibe in front of all my amps. The reverb and vibrato are really nice on my clean sounding amps. I don't really care for reverb on the gritty sounding amps but the vibrato is nice.

I'm also glad the distortion problem with high output active pickups surfaced. Back when that vibrato circuit was introduced, there were no high output active pickups so it was never a problem. Your scope work pointed out the problem. Thankfully it was a pretty simple fix. I've left the mod in my unit and am now running with 12AX7s, so our units should be identical, except for the PT, and I don't think the slight differences in B+ is a factor.

Oh, you may want to put that 220K bleeder back in. I now have one across my B+ cap. Those 100�F caps take forever to drain without that bleeder resistor.

EKDENTON · « **Reply #136 on:** October 04, 2016, 10:06:56 am »

Thanks. I learned some troubleshooting techniques in the process. Using my friends scope was fun so I got to looking on ebay and found an iwatsu japan made scope that is in really good condition for $100. I want to learn more about using them. Once I get my cabinet from Mathier I will post a few photos of my Revibe.

Willabe · « **Reply #137 on:** October 04, 2016, 10:31:29 am »

Glad you guys were able to track down the problem and find a cure.

This has been a frustrating quest for you guys but it has also been a great thread IMO.

EKDENTON · « **Reply #138 on:** October 21, 2016, 06:10:10 pm »

I got my cabinet in today. It turned out great. This is a very good tube effects project. it does seem to be finicky about what tube is used in the vibrato circuit. I made a list of 7 brands and only two were usable the other 4 had a loud hum increasing and decreasing with the vibrato. With the right tube it doesn't do it at all. I would recommend it because you can use it with any amp. The cost was pretty low to build because of the small trannies and one output tube. Thankfully Sluckey didn't give up on me getting it fixed and helped throughout the project. Thanks to Sluckey and everyone else that helped out!

sluckey · « **Reply #139 on:** October 21, 2016, 06:43:50 pm »

Sexy!

Quote

it does seem to be finicky about what tube is used in the vibrato circuit.

I did one additional mod that will take care of the picky tube. I added a level pot for the signal feeding V4. Now I can switch between 5751s and 12AX7s with no problems. Take a look...

uki · « **Reply #140 on:** October 22, 2016, 07:24:55 am »

Quote from: EKDENTON on October 21, 2016, 06:10:10 pm

... it does seem to be finicky about what tube is used in the vibrato circuit. I made a list of 7 brands and only two were usable the other 4 had a loud hum increasing and decreasing with the vibrato. With the right tube it doesn't do it at all. ..

Beautiful !!

Please share which tubes did you tried and which ones did work without hum !!

I got similar issue with a vibrato.

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Author Topic: Revibe Build (Read 24214 times)