quote:

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Originally posted by stubbadub:
I figured I'd bug the general populous a couple more times before contacting Scott again...

Scott put this revision up on the site recently:

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2/5/04: The instructions for assembling the psu tell you to install B30, test the 25.5vdc supply, then install B30, and test the +48vdc supply. The second B30 should be B50. The idea is you test one circuit, make sure its ok, then test the second. I explain it verbally so I think most people were able to work around it. If you have two meters, you can install both bridge rectifiers (B30 and B50) and bring the two supplies up at once.
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The instructions mention installing the B30 to test the 25.5VDC, then later he says to install the B30 and to test the +48VDC. Jason, according to how you did it earlier in the thread, didn't you install the B50 then test the 25.5VDC and it worked out? Would you say that his site update has the correction backwards or should I really install the B30 first?

The Sweaty Dudes

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Yeah, I saw that and wondered about it as well. Since I didn't load things properly I can't say definitively that my way is right but it seemed to work at the time. Maybe I just didn't look close enough or possibly got lucky. Either way, nothing blew up and every thing worked out in the end.

You are showing more patience than me. I would put both in and call it good if I were in your shoes.

Give us an update.


Jason A.

Hi.

I've just finished putting together my second Hamptone JFET pre. The first kit sounds great, but I'm having a bit of trouble with this one. Channel 1 (the left one as you look at the front panel) is fine, but Channel 2 has a buzz.

I traced the buzz to the pilot light. As soon as I disconnected it, the buzz went away. When I reconnected it, the buzz came back.

Both pre's work well when the pilot is disconnected. Anyone have any ideas?

Thanks,

Marty

quote:

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Originally posted by beal9000:
Hi.

I've just finished putting together my second Hamptone JFET pre. The first kit sounds great, but I'm having a bit of trouble with this one. Channel 1 (the left one as you look at the front panel) is fine, but Channel 2 has a buzz.

I traced the buzz to the pilot light. As soon as I disconnected it, the buzz went away. When I reconnected it, the buzz came back.

Both pre's work well when the pilot is disconnected. Anyone have any ideas?

Thanks,

Marty

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I would tend to look at the light first, simply because there are less things to go wrong. Then move on to the channel if you still have the problem.

* Look at the connection to the switch.
* Look at the connection between the wires on the light and the extension wire. Make sure the connection between the wires are solid and then covered. I soldered them together and then layed the connection back on the wire so I could cover the joint with shrink tubing.
* Make sure your wires are twisted going all the way back.

Again, just me but I would rule out the easy stuff first then move on.

Let me know if you've already tried these.


Jason A.

Mine did that also on one channel at first. Innitially I mediated it by reorienting the di jack in relationship to the power light.

Does the buzz go away if you plug a cord into the di jack? Mine did which led me to:

Check the extra ground wire (not really mentioned explicitly in the instructions) that goes from di jack ground to the ground pad next to the brown wire, this grounds the di jack to the input tranny and in the case of mine was my only cold solder joint.

No noise at all after that.

BTW - my good friend used the pre on drum overheads recording a band at his studio last weekend - he said he loved the sound.

- A

Thanks Jason,

Yes, I've done all those things.

A bit more investigation reveals that the problem is not necessarily channel 2. If I completely uninstall the pilot from the chassis and then reconnect the leads, I can induce a buzz by moving the lamp near the DI jack on either channel. So maybe the lamp is bad...

I'll keep trying...

Thanks ape,

I'll take a look at that, too. The buzz is still there when I have the DI plugged in. I notice that I have the hot pin oriented closest to the lamp, so maybe reorienting the jack will help.

I'll try it and let you know.

Let us know how that works for you - it was my ch.2 that hummed. Before I did the ground fix
it did go away almost entirely just by orienting the hot tab 180 deg. from the lamp.

If you don't mind me asking, why did you build 2 kits?

I've got all my resistors and some of the diodes soldered in the 3 boards. I'm new at this and I have some general questions.

1.On the power supply board, the holes on the right side of D37 and the left side of D35 are VERY close. My solder joints are touching each other here. It looks like they touch on the schematic. Is this a problem? Do I need to try to lift the solder and do-over? If so, does anyone have any techniques/suggestions on how to keep the solder joints separated?

2.When you install/attach the heatsinks to the regulator and the transisitors, are they supposed to be soldered on or just pinched on?

3.When testing the PSU board the instructions say to put a load resistance of about 1-10k across the output. Can you tell me what this means and how this is done? Also, it says to adjust the trimpot to 48vdc. Where and how do you measure the 48vdc? Please be specific as I'm really lost with the use of my multimeter - although I did figure out how to measure the resistors.

4.Number 11 of Integrating the Electonics Into The Box says to check the DC voltage on each 2N5457. Could you explain how this is done?

Sorry to appear so naive about electronics; but I am really enjoying this project and already have learned alot considering my starting from almost zero. By-the-way, I'm sure I'm "part" (hopefully a very small part) of the reason for Scott's red rant (which I see has now been removed); but I am trying to be gracious and am very appreciative of any help that is/has been offered.

Mark

P.S. I have been a lurker on many different forums for the past year, and this is my inaugural post.

Welcome to the board Mark,

The Diode thing was asked a couple of pages back. It's OK if they touch.

Heatsinks are lightly pinched on. The larger ones on the PS board slide/clip on and then go through a hole in the board.

I forgot to put a load on so maybe someone else can share exactly how they did it.

The 48V is measured across the output pads of the PS board. They are labeled on the back of the board G, 24, 48 (if I remember right). Put your black probe (from the DMM) on the G and your red on the 48. Your DMM should be in the ballpark of 48 but probably not exact. Turn the blue pot one direction or the other until your DMM reads 48V.

I didn't test the 2N5457's. Blew right past that one.

Don't feel bad about being a newbie. This Tech forum is geared for newbies. Just scan some of the other topics and look at how much of a beginner I am/was/am. I wish we could keep the interest of some of the more tech minded guys long enough for them to help out a little more but we get by. For me, a good amount of learning has been by simply jumping in.

If you notice, Scott has not only taken off the red warning but has decided to add a couple of sections on basics. Not only do I approve of this approach, I also think it is a smart web move. Any time you put valuable reference material on your site, you keep people coming back and each time your product is in their face.

Sorry I couldn't answer all the questions but hopefully I was some help.


Jason A.

Well... I'm still trying to get the pilot issue sussed.

But a quick question if I may...

If I touch the case on the input transformer (the Altran C-3402), I get a significant hum/buzz on the output of the pre. Is this a symptom of something I've done wrong? Or is that normal? If anything, shouldn't the case be grounded?

And Ape, I got two kits because there are times when I need a lot of pre's going at once. I've been doing a lot of live tracking lately and I just need a bunch of good sounding pre's to supplement what I already have. The Hamptones have exceeded my expectations by a long shot and I'll be ordering two of the tube kits also.

By the way, were you able to entirely eliminate the hum/buzz in Ch. 2, or is it still there?

Thanks.

Beal -

I was able to do that - in my case it was a bad joint to that ground I mentioned - it goes from jack ground to, I think, pin 8 on the input tx. I recall that when troubleshooting I touched the input tx and got a nice hum also.

Are you in a really bad EM environment?

I remember checking other ground and perhaps the tx case for continuity, and i think the ground i keep on about was no attached to the case.

Unfortunately my pre and docs are at home and I am here in corporate world.

I also think the pre is exceptional it's great that you are using them that widely. My home studio, is decent 1/2" 8, DAW, lots o' mics, live room - the fet pre is my gold channel for sure. I'd love to hear your take on the tube when done.

- Ape

quote:

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Originally posted by ape32:
Are you in a really bad EM environment?

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As a matter of fact, I am. Really bad.

For now, I'm just leaving the pilot unwired as the pre's seem to be working fine when they're not attached to the circuit.

I have sessions today and tomorrow... first time I'm trying the JFET's on things other than acoustic guitar and vocals. We'll see how it goes!

Thanks!

[This message was edited by beal9000 on 02-12-04 at 02:32 PM.]

Anyone know the size of that preamp circuit board?

Bear

If you are still fighting the lamp induced buzz, Scott has posted a fix on his site.

quote:

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2/15/04: NOISE INDUCED IN CHANNEL 2 FROM PILOT LIGHT.

Someone brought to my attension a few days ago that they noticed an increased noise floor in channel 2. This person bought two HJFP2 kits, and told me one unit was fine, the other had noise in channel two. Though I had not encountered this (I tested this during design and found no induced noise), I pulled all the pilot lights we had here (47), and tested all of them in circuit. What I found was 5-7 of them did in fact induce noise to a varying degree ranging from barely audible to quite noticeable. I selected the worst two, and found that the induced noise was also a function of the DI jack and pilot light orientations, and by rotating the two you could hear the noise get louder/softer.

SOLUTION: Basically all you need to do is shield the pilot by sliding a clyindrical piece of metal tube over the pilot, and ground it to the chassis. With the worst pilots I found, it totally eliminated the noise. The picture below shows a HVTP2 we built up here with the shield in place. The shield shown is a 5/8" ID (inner diameter) copper coupler for water pipe, available at True Value hardware store for 29 cents. Even if you don't have the noise problem, I would suggest doing this since it can't hurt. Make certain the tube is snug against the front panel, and can't make contact to either side of AC. I also tried a piece of thin sheet metal, and a 0.005: thick piece of Mu Metal wrapped into a tube, both also removed the noise.

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Jason A.

hamptone_light.bmp (22 Kb, 215 downloads)

Mystery solved! That is certainly interesting.

Bear - it is 100mm wide by about 140mm (140 is an estimate)

BTW -
Further application testing - 2 sessions as mic amp for stereo full-range overheads (2 different bands, using Glyn Johns 4 mic setup) mics AT4050s - great clean, sweet sound.

sorry I can't post any of it, I was just assisting on one of the sessions and have no access to the recordings.

Is anyone here considering DIYing this modulke? I have one on my breadboard just waiting for power parts

- Ape

Has anyone done some serious comparisons between the Hamptone and 'standard brand' pres?

quote:

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Originally posted by Henry:
Has anyone done some serious comparisons between the Hamptone and 'standard brand' pres?

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You might try here
http://studioforums.com/eve/forums?a=tpc&s=1436041581&f=1826095781&m=9436014855


Jason A.

Yep... the fix that Scott posted on his site solved all problems with my pilot light issue.

By now, I have compared these pre's with my Avalon 737 and Amek 9098s. I've also checked them against a Great River ME-1NV. The Hamptones compared favorably with all of them.

They just sound great... impressive high-end detail with plenty of warmth and punch. I wouldn't hesitate to try them out in any situation.

Can anyone point me in the right direction as to how to get the 5/8" ID copper tube to solder onto the back of the faceplate? I just can't get it to stick.

Also,I have been hoping that someone would answer the question in my earlier post about how to put a "load on" when testing the +25.5 output in #2 of testing the PSU board?

Thanks

To load a power supply, just solder a 10k resistor across the output. So, in this case, solder a 10k from GND to +V (25.5v?? I do not have the schem...) Then switch on & check the voltage.

To check the voltage, set your multimeter to the relevant DC Volts range (probably 200v), put the black lead on the GND connection & the red on the +V connection. i.e. across the 10k resistor you had soldered in. Read the voltage. Similarly, check the 48v supply as well.

If you are using a 1/4 w resistor this may get hot within a few seconds. Just check the voltage & switch off & disconnect the 10k.

The reason for adding a load is beacause some voltage regulator chips will give an erroneous reading with no load.

Peter