Thanks alot Peter.

I'll give that a try. Right now I'm so excited..I got mine working. I took the power up really slow with my variac and damn'd if the power light and the LEDs didn't start lighting up. And no smoke or sizzles so far. I just tried channel 1 and it sounds great. My initial reaction is that it seems to have a bit more punch than my GR MP-1NV and my ~Seb~ vmp-4000e, and definitely more that my m-audio omni pre's. Channel 2 does have a bit of extra noise (hummmmm) so I think I'm going to have to unhook the pilot lite and put some kind of shielding around it.

Does anyone know how to solder/attach a copper coupler onto the back of the faceplate like Scott suggested on 2/15/04? I still can't get it to hold on.

Mark

I take it all back. Now the power transformer IS smoking. And the coating has mostly melted off the outside of it. I now see that the red and the green wires from the toroidal power transformer were touching/crossed where they attach to the power supply PCB.

Also, there is a black bubble coming out of the top of the B30 rectifier. What the hell could that be? Anyone have any advice/suggestions for the newbie?

Oh well. Hopefully I can get some new parts soon and repair it. Looks like the transformer came from Digikey and the rectifier came from Mouser. It sure sounded nice for a few minutes. It had a really hot sound.

Mark

What are the red & green wires?

Replace the rectifier, not worth messing around with a dodgy component.

Peter

Thanks Peter.

The red and green wires come off the transformer and attache to the PCB. From the diagram/schematic, it appears that they go to the B30 rectifier and then on to the rest of the phantom power regulator. Ohhhhh...that's why the rectifier fried. I think I'm acually starting to understand this.

I ordered a new transformer from Digikey and a new rectifier from Mouser last night. Can you think of anything else I might have to replace? Nothing else appears to be damaged. I guess I should look at the resistors and capacitors that come next in the chain. The fuse didn't blow either.

Mark

quote:

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Originally posted by markmazoo:
Thanks Peter.

The red and green wires come off the transformer and attache to the PCB. From the diagram/schematic, it appears that they go to the B30 rectifier and then on to the rest of the phantom power regulator. Ohhhhh...that's why the rectifier fried. I think I'm acually starting to understand this.

I ordered a new transformer from Digikey and a new rectifier from Mouser last night. Can you think of anything else I might have to replace? Nothing else appears to be damaged. I guess I should look at the resistors and capacitors that come next in the chain. The fuse didn't blow either.

Mark

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Sorry to hear about the problem but glad to hear you are starting to understand. I had a few valuable "Ah-Ha" moments during assembly myself. It was a good learning experience.

Yes, Peter. Thank you very much for helping out as much as possible. I know its tough without the full compliment of schematics and such. I thought that was what was meant by loading. I have had to do that before on other projects but for some reason I doubted on this one. Thanks again.

Keep us posted markmazoo

(I wonder how Stubabdub is doing?)


Jason A.

Mark

Looks like the mains transformer secondary shorted out. Good idea to use heatshrink tubing so that there are no exposed connections, ESPECIALLY on mains voltage connections! I get cold shivers when I open some of the older tube amps & there are all these exposed tag strip connections with 600v DC on them! OK, rant mode off......

What is the value of the mains fuse? This should have blown way before the rectifier started to bubble. I would have thought that this would be about 250 mA or so.

In a cct as critical as a mic pre, I would also replace the smoothing & bypass caps, everything between the transformer & the voltage regulators.

Peter

The only fuse I see is a Littelfuse 313 series SLO-BLO 2 amp, 250 volt fuse. It looks like it is between the power entry module and the power switch. Am I missing something here? It looks like it would only protect from a surge from the wall outlet.

Good idea on the caps. Looks like there is only one ( C33; a 470 ohms 100 watt radial aluminum electrolytic miniature cap) between the transformer and the voltage regulator on the 48vdc phantom power regulator.

Mark from KalamazoO

Looking at this pic

http://www.hamptone.com/HJFP_PSU.jpg

The front left cap 470uF/100v cap will be for the phantom supply. The 3 (Xicon?) caps on the right hand side are the ones to consider replacing.

Also check the values of the resistors on this board.

Can someone confirm the capacity of the fuse? 2A sounds quite a large figure.

Peter

I verified the 2A fuse with Scott.

Here's what he said "in general, if you short out transformer windings, you will burn it up. The failure probably caused enough added current to burn out the part, without exceding 2A. You can reduce the fuse to 1A, but on occation it might pop during power up, which is why I went to a 2A".

Just in case anyone else was struggling with the installation of the shield around the pilot light. I thought it had to be soldered to the face plate to be effective. Scott mentioned the following hint as to how to mount the copper coupler around the pilot light...

"If you attach the ground wire to it, and twist it with the other wires, it pretty much stays in place. A piece of 3M double sticking tape (the stuff you use to hang pictures with),stuck onto the pilot before sticking it on also helps. Or you
can wrap some tape around the pilot, increasing its diameter..."

I was also struggling with the layout of the point to point wiring between the power supply switch, fuse holder, transformer, and the power line filter. The photo of this wiring doesn't show the wiring in close enough detail to copy it directly, although there is an excellent schematic of the power supply assembly as well as the detailed instructions. I did notice that there is a better photo (on the Hamptone website) of the tube amp power supply assembly in the HVTP2 Chassis Assembly Photos. I'm assuming this is exactly like the HJFP2 JFET power supply.

Mark

Dear All

I had a "Yah Hooooooo" moment last night when I finally got the HJFP2 working. Looks like most everyone has lost interest in this topic. Hopefully there is someone out there to help me celebrate completion of my first (other than putting together some mic and guitar cables) DIY electronics project.

I got my replacement parts from Mouser and DigiKey. After replacing the mains transformer and the rectifier, I got channel 2 to work. Channel 1 worked but it was very hot one minute and barely audible the next.

After looking closely at the boards and the point to point wiring, I decided to try to redo the wiring from the pot to the board. I had done this to channel 2 before, after I messed up the point to point wiring on that. I had no idea I would have so much trouble with the point-to-point. It was very difficult fitting the small wires into the smaller holes.

Obviously, I didn't have any of that Mogami guitar cable left over. But I did order some cable like that from DigiKey. It was a little smaller diameter, so it was alot easier to wire into the audio board. Plus, I drilled those holes in the board out a little bit.

I'm sure I didn't get the project done in 8 hours, or even 28 hours; as you can see from when I started it on back on the 11th. But I finished the project "this month" at least. Thank goodness for leap year.

Thanks very much to Jason and Peter. And thanks to Scott too for making such a great micpre kit, and for fielding my sometimes way-too-long emails. This thing sounds wonderful. See, this is a "beginners" project.

Mark

I'm here Mark!

Congratulations. Glad to hear you got it going. It has quickly become my favorite pre. Keep us posted on good applications.

I tried to pull out all the stops and insert some purple bananas but they are being a bit stubborn tonight. Here are a couple of yellow ones and you can just pretend they are purple.


Jason A.

Congrats!

You should feel great - If that was my first project I would have had it harder than you did! I hope when you recover you keep the bug - a soldering iron and a multimeter can be invaulable in keeping the home studio alive and healthy.

I also love this preamp, of course, now it makes me want other eqaully nice pieces!

Shoot!

Hey Mark, well done. Now for the next one.....

If some thing is getting hot, then check your DC voltages at certain points like the transistor legs. It should be easy enough as it is a dual preamp. Do this with no input signal present.

What component is getting hot? Anything in the power supply?

Peter

Nothing is getting hot anymore. I've got both pre's working just fine. Thanks again for all the help.

This one was so much fun, I'm saving my $$ to get the tube pre's.

Mark

Hey, well done.

If you're thinking about tubes, you might have a look at

www.geofex.com

Go to the "tube amp faq". It's more for guitar amp work & can be a bit technical, but there are some good pointers regarding safety & first time techniques.

Peter

Hey I'm building the HVTP2 but I had a question I think you guys can answer for me. I've just completed all the assembly and already done the PSU testing and adjustment without the channels hooked up. I've hooked up the channels to the PSU and mounted everything in the chassis and I had a question before I fired it up:

In your units did you guys have continuity to ground from the board to the chassis? Mine does and it appears to be coming through the faceplate/xlr/di connectors. I think this is normal but I don't want to blow anything up before I power up.

Thanks in advance,
Aaron

...it's great to see ya''ll helping each other out on this!

I ordered the HVTP2 tube pre last week after seeing the mojopie review of the jfet and a couple of email/inquiries with Scott.

Much like the other mark, this will be my first DIY project - and it will cool to have this thread to draw on -

quote:

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Originally posted by aaronscool:
Hey I'm building the HVTP2 but I had a question I think you guys can answer for me. I've just completed all the assembly and already done the PSU testing and adjustment without the channels hooked up. I've hooked up the channels to the PSU and mounted everything in the chassis and I had a question before I fired it up:

In your units did you guys have continuity to ground from the board to the chassis? Mine does and it appears to be coming through the faceplate/xlr/di connectors. I think this is normal but I don't want to blow anything up before I power up.

Thanks in advance,
Aaron

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I built the JFET kit and details are beginning to slip the memory but I believe the input power was grounded to chasis so it doesn't seem unthinkable for their to be continuity to ground from the board to the chasis. I don't have the cover off of mine to check but again, its a different pre so take my experience with a grain of salt.


Jason A.

Hey Jason thanks for the reply:

I think as far as grounding through the chassis goes it should be the same between the two models. Certainly I grounded the input power to the chassis but when I check there was definitely ground connectivity from the board to the faceplate then to the chassis. I'm assuming this is happening through the xlr/di connectors somehow but not through anything I did specifically though.

Thanks for the reply though. I'll let you all know when I'm done and have some samples to share.

quote:

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Originally posted by aaronscool:
Hey Jason thanks for the reply:

I think as far as grounding through the chassis goes it should be the same between the two models. Certainly I grounded the input power to the chassis but when I check there was definitely ground connectivity from the board to the faceplate then to the chassis. I'm assuming this is happening through the xlr/di connectors somehow but not through anything I did specifically though.

Thanks for the reply though. I'll let you all know when I'm done and have some samples to share.

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You've got more patience than me. I would of fired it up by now.

Jason A.