fet boy

[fucanay]

[quote author="Samuel Groner"]With respect to the hum problem: if it's the same in both channels it is likely that there's too much ripple on the supply line. If it's more in the channel closer to the PSU it's probably rather just induced hum. Try rotating the transformer as a first means.

Samuel[/quote]

It's the same on both channel according to the analyzer I use in Logic. Both channels have noise at about -55db at the lowest gain setting, then during the rotation it gets a small amount better before getting really bad.

I tried rotating, putting it outside the case, and another transformer and performance is the same. I put the PSU board up bout 5 inches outside the case sitting on a cardboard box. I tried putting another 1000uf cap after the regulator. I still don't know how to use my scope, nor do I have proper probes, so I don't know how I'll find out about ripple at this point.

Grrrrrr.

Matt

 

[Samuel Groner]

Then read a tutorial on how to use a scope--it's not that hard and will save you literally hours and days while troubleshooting. For audio you often don't really need fancy probes, cut a BNC cable in half and use some alligator clips.

I don't know how I'll find out about ripple at this point.

In the meantime just connect the PSU out to your audio in--you'll quickly see whether you have ghosty silence or full-scale hum... Just to be sure that there won't be any damage us a 1k series resistor between PSU and input as well as an AC-coupling capacitor (of a few uF, observe polarity!).

Samuel

 

[3nity]

In the meantime just connect the PSU out to your audio in--you'll quickly see whether you have ghosty silence or full-scale hum... Just to be sure that there won't be any damage us a 1k series resistor between PSU and input as well as an AC-coupling capacitor (of a few uF, observe polarity!).

Samuel

PSU out to Preamp in??

 

[Samuel Groner]

Just stright to your AD.

Samuel

 

[fucanay]

Ok, the grounding scheme above works to kill the oscillation. If you are using the same PSU as I am, then a bigger smoothing cap is in order. I just put another 1000uf cap in series with the one in the schematic and the noise improves greatly. I think more would make it even better, but it's size would probably make it have to be mouted off board. I also reduced the voltage dropping resistor to 10 ohms to give it more room for regulation.

Much better, but not perfect yet.

Matt

 

[Samuel Groner]

If that additional 1000 uF helped your transformer has a too low secondary voltage or your regulator is messed up. Why do you refuse to look at the DC output of your PSU..?

Samuel

 

[lofi]

[quote author="Samuel Groner"]

I don't know how I'll find out about ripple at this point.

In the meantime just connect the PSU out to your audio in--you'll quickly see whether you have ghosty silence or full-scale hum... Just to be sure that there won't be any damage us a 1k series resistor between PSU and input as well as an AC-coupling capacitor (of a few uF, observe polarity!).

Samuel[/quote]

proper fu*king idiot request here sir, but any chance of a drawing to show exactly what you mean? dont want to fry any of my ad's and to be honest, i am likely to do that

sorry

Iain

 

[fucanay]

[quote author="Samuel Groner"]If that additional 1000 uF helped your transformer has a too low secondary voltage or your regulator is messed up. Why do you refuse to look at the DC output of your PSU..?

Samuel[/quote]

I haven't refused to do anything. I'm doing the best I can here.

I have the proper voltages at my PSU output. My regulator is no longer getting too hot and have been replaced twice already. My transformer isn't too low, it's a little too high and has been lowered with a 10R resistor to keep the reg cool, but there is about 30.5 VDC there to regulate down to +24.

So my tranny secondaries are putting out plenty and my regulator is regulating. What else could it be?

Matt

 

[fucanay]

Ok, I tired the alligator clips on my scope again, the way I did it before and what I thought was ripple on the output of the PSU is now gone with the second 1000uF cap.

Before I go mad looking for the source of the residual noise, how do you go about measuring the db of the noise itself? I think the noise is really only audible at the highest gain settings. And there is really too much gain on this thing to be usable for me anyway.

Matt

 

[3nity]

My LM317 its getting too hot too! i'm using a 12-0-12V transformer wired in series to get 24V.

Now MAtt you did put a 10R/1 watt resistor in series between the Diode bridge and the 1000uf/35v?
Did you cut out the trace? huh?
Thanks.

 

[fucanay]

[quote author="3nity"]My LM317 its getting too hot too! i'm using a 12-0-12V transformer wired in series to get 24V.

Now MAtt you did put a 10R/1 watt resistor in series between the Diode bridge and the 1000uf/35v?
Did you cut out the trace? huh?
Thanks.[/quote]

No, I just shortened the leg of the bridge and attached the resistor between the bridge and the board. And then, if there is too much ripple add another 1000uf cap before the other one.

This is how it looks on mine:

Does that make sense? And I do still have a small heatsink on that regulator, but I'm not totally sure it needs one.

Matt

 

[3nity]

What could possibly happen to the Fetboy circuit if powered and no ground at all?

I ask this question cuz i poweres mine and CS1 and CS2 got very hot and RS1 looks like it passed out!

 

[fucanay]

[quote author="3nity"]What could possibly happen to the Fetboy circuit if powered and no ground at all?

I ask this question cuz i poweres mine and CS1 and CS2 got very hot and RS1 looks like it passed out![/quote]

Well, I did fire up mine with no ground at all, but I never checked for heat on the caps. As a matter of fact, I've never tested any cap for heat. Are they in backward or anything?

hopefully, somebody more knowledgeable will stop by and answer that.

Maybe some pics?

Matt

 

[3nity]

I'm not pretty shure but i think i applied 30V when first powered them!
I forgot to trim the LM317 wich i was using to power my 1176!!

I'm gonna change RS1 and see if it burns again!

 

[rodabod]

[quote author="lofi"][quote author="Samuel Groner"]
In the meantime just connect the PSU out to your audio in[/quote]

proper fu*king idiot request here sir, but any chance of a drawing to show exactly what you mean? dont want to fry any of my ad's and to be honest, i am likely to do that
[/quote]

Basically just plug the PSU output into an A/D. If you block the DC with a cap, your A/D will just be seeing the ripple (which sits in the audio range) and will not drive much current as it is feeding into an input impedance of say, 10K. I personally wouldn't do this as A/Ds can be expensive, but if you plugged either of the PSU rails plus the PSU ground onto XLR pins 2+3 separately via a capacitor then this should work. I think I'd use a 'scope instead.


[quote author="fucanay"]
Before I go mad looking for the source of the residual noise, how do you go about measuring the db of the noise itself? I think the noise is really only audible at the highest gain settings. And there is really too much gain on this thing to be usable for me anyway.
[/quote]

Listen to Samuel. Take a proper fault-finding approach; make sure your PSU is good first. With a 'scope, measure the AC component which sits on the DC coming from your PSU. You'll maybe need to whack the V/div. up on the 'scope and reposition the trace to see it.

Other than that, I'd make sure you definitely don't have oscillation problems. Look for any very high frequencies output at high gains (could be tens of KHz). You might also notice a lack of headroom as well as hum on the output.

Noise level is usually measured with respect to programme level; eg. for 50dB of gain, inject -50dBu 1K sine tone and raise gain to measure 0dBu at output. Now mute input by terminating with a 200R resistor. Measure new output level. This is your relative noise level.

 

[fucanay]

[quote author="rodabod"]
[quote author="fucanay"]
Before I go mad looking for the source of the residual noise, how do you go about measuring the db of the noise itself? I think the noise is really only audible at the highest gain settings. And there is really too much gain on this thing to be usable for me anyway.
[/quote]

[quote author="rodabod"]Listen to Samuel. Take a proper fault-finding approach; make sure your PSU is good first. With a 'scope, measure the AC component which sits on the DC coming from your PSU. You'll maybe need to whack the V/div. up on the 'scope and reposition the trace to see it.[/quote][/quote]

Not sure what you mean by AC component. Is that just seeing remnants of the sine wave? If so, the second 1000uF cap I added made the PSU output flat, which was a new development because earlier it was funky lookin.

[quote author="rodabod"]Other than that, I'd make sure you definitely don't have oscillation problems. Look for any very high frequencies output at high gains (could be tens of KHz). You might also notice a lack of headroom as well as hum on the output.[/quote]

Looking at my analyzer in Logic Pro, I do see some stuff in the high freqs and a little in the low. At this point I thought I was only hearing the lows, but maybe it's just louder than the highs.

I'd love to be able to check that definitely. What is the process for seeing oscillation with the scope? I'm scope skill deficient, so I don't know what settings and at what places to probe.

[quote author="rodabod"]Noise level is usually measured with respect to programme level; eg. for 50dB of gain, inject -50dBu 1K sine tone and raise gain to measure 0dBu at output. Now mute input by terminating with a 200R resistor. Measure new output level. This is your relative noise level.[/quote]

I have to think about this one. It's a bit over my head and I think it's premature having just thought about the rest of your reply.

Thanks a ton rodabod,

Matt

 

[fucanay]

Ok, here is what I did. I don't have a proper scope probe and have been using alligator clips. I took the red clip and attached it to an old DMM probe and went probing. First, one of the secondaries on the transformer, Sine-ish shape. Then the PSU outputs, both +24 and +48 flat as can be. Then poked around a little until I got to the drain of Q1 and I got a pulsing fat line. Q5, fat line but no pulse. On the channel where I added a 10k resistor between C2 and the pot, there was only the fat line for a second as I got to the end of the rotation on the pot and then it disappeared, this is on Q1, Q5 on that channel is exactly the same as the other one.

So is the fat line oscillation or distortion?

Matt

 

[lofi]

what ranges are you in Matt?

 

[fucanay]

[quote author="lofi"]what ranges are you in Matt?[/quote]

Oh boy, ummm, I dunno. I just kind of turned the knobs until I got the clearest picture on the scope. My scope has a max setting of 5V so I have to use the position knob to move it down. And I think I had the time/division at .2 ms.

I hope that's what you mean.

Matt

 

[fucanay]

Anyone have an idea of what could cause this? I've been studying the schem and tracing the circuit and I'm clueless.

Matt