quote:

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Originally posted by Don Richmond:
I don't know how many folks are still paying attention to this thread, as I know a lot of you have finished your preamps and are happily tracking away. HOwever, I have only now had some time to get going on my kit, and am at the power supply testing phase with a problem that I'm hoping someone can shed some light on. Everything's been going fine, the posts here have been helpful, I've been careful and it all looks great but: When I test the power supply (without the B-50 rectifier(?) installed - only the B-30) I get 26 volts on what should be the 48 volt conductors and a -5 volt reading on what should be the 25.5 volt ones, and the way I read it there shouldn't be any reading on the 48 volt conductors without B-50 installed. I examined everything closely, polarities all seem right, soldering looks good, can't find anything wrong. Any ideas? Thanks to one and all!

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I didn't read it like that at all. I assume that you would get some voltage across the 48V but you just weren't supposed to measure yet because it WOULD be wrong. I think you are just supposed to worry about one voltage at a time as you install the rectifiers. So if your 24V is reading right then all is well.

At least that's my take.


Jason A.

Gotta quick question. Would a B30 regulator be for 30 volts and the B50 be for 50 volts?

Rade

Thanks for your reply, Jason. My internet was down all weekend, so just getting back here. After much inspection I decided all was as it should be even though my readings seemed screwy so I went ahead with installing the other rectifier, and then all the voltages read as they should. I then finished the assembly and all seems fine. However, I'm using the preamp in the studio today and it seems abnormally low in gain compared to my other outboard pres. I don't have anything big and fancy, but say for example comparing it to an Aphex 107 - I have the HJFP2 running to my Yamaha O1v with a XLR to 1/4" TRS cord, and comparing the mixer input trim levels to where I normally run the Aphex, even with the HJFP2 cranked all the way, I'm having to run the input trims much hotter - say from a little less than 12 o'clock where they usually are to about 4 o'clock. Is this normal? Is there something I don't know about the XLR output of the Hamptone, or how to run it through the mixer? As far as I can tell, both channels of the Hamptone are the same. How do the gain levels seem to you all, and if I screwed something up, any ideas on what? Thanks very much to one and all - DR

quote:

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Originally posted by Don Richmond:
Thanks for your reply, Jason. My internet was down all weekend, so just getting back here. After much inspection I decided all was as it should be even though my readings seemed screwy so I went ahead with installing the other rectifier, and then all the voltages read as they should. I then finished the assembly and all seems fine. However, I'm using the preamp in the studio today and it seems abnormally low in gain compared to my other outboard pres. I don't have anything big and fancy, but say for example comparing it to an Aphex 107 - I have the HJFP2 running to my Yamaha O1v with a XLR to 1/4" TRS cord, and comparing the mixer input trim levels to where I normally run the Aphex, even with the HJFP2 cranked all the way, I'm having to run the input trims much hotter - say from a little less than 12 o'clock where they usually are to about 4 o'clock. Is this normal? Is there something I don't know about the XLR output of the Hamptone, or how to run it through the mixer? As far as I can tell, both channels of the Hamptone are the same. How do the gain levels seem to you all, and if I screwed something up, any ideas on what? Thanks very much to one and all - DR

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I don't have low gain levels. I take the output directly into the computer with no problems even on dynamic and ribbon mics.

Silly question but you don't by chance have the pad engaged?


Jason A.

No - I wish it were that simple. I just tried the XLR out into a dbx 160XT compressor that has XLR i/o and it won't even drive the compressor enough to make it compress at a -10 db threshhold. Something's definitely not right. I was very careful assembling them and both audio cards are certainly the same and the soldering's all good it seems. I remember wondering about the orientation of the transistors as I was putting them in. The ones that have a flat side and a rounded side (with no heat sink) seemed obvious. The ones with a heat sink I put in with the printed side facing away from the back leg of the tripod, if that makes sense. Other than that I felt very solid about everything I did and was quite sure the resistors were all properly identified and all. Any ideas? Thanks and best - Don

Don,

Did you see the update on the tech page over at Hamptone.com? It may have been in response to your question.


Jason A.

Hi there. I just got my JFMP kit yesterday, and I'd like to say that this forum is a beautiful, beautiful thing.

When I put my NPN transistors & darlingtons in, it only then occured to me that they might be polarized, and I didn't see any legible markings that might suggest an "in" or "out."

I'm paranoid that I might've put them in backwards.

Thanks!
-Josh T

I'm working on the tube pre... (as a complete beginner in terms of electronics -

One thing I've noticed is Scott's very specific within the instructions and always mentions when a piece is polarized. So my guess would be if it's not stated in the JFet docs then it's not.

Just my observation... -

I saw that Scott posted a diagram yesterday showing the way the transistors go, and (guess what?) I put them in backwards! I had to desolder them and turn them around. Everything else on the channel boards looks okay...I've had the last couple days off, and everything has been going along at a fine clip

*** BUT ***

I put everything (except the 48v rectifier) into the PSU board, strapped a 10k resistor across the green & red wire, wired the transformer to a 2-prong wire, plugged it in, and got a puny 5.6v measured in parallel across the 10v.

Does anyone know if I am measuring this correctly? I don't have a proper variac but I did bring the power up slowly with a 1/2 assed home job version (a dimmer switch wired in series with an outlet), and there was no smoke, sparks, fire or popping. Just a sad, sad me.

Thanks!
-Josh T

Hi Josh

Start at the top & measure along the chain...

Put your multimeter on AC Volts & make sure you have 115v on the mains transformer primary. Then check the secondary. Then switch to DC volts & check the output of the rectifier, & so on down the line.

I dont have a schem so I can not be more specific.

Bear in mind that there may be damage to the transistors. They might have been damaged by the extra heat from soldering & desoldering, or by the wrong voltages on the wrong pins when they were inserted incorrectly.

Peter

This is post 150 in this thread... This has become quite the place to be for Hamptoners, eh?

-Dusty

Hey Don & Everyone:

I figured out the -5v thing, and other folks might find this useful as well if they got the kits sent out in early April.

The old instructions accidentally listed installing rectifier B30 twice, a typo that was corrected in the in the issue of instructions I recieved with a pencil note scratching out B30 and inserting B50 where appropriate.

They say to install B30, check the +25.5V supply, then install B50 & check the phantom power.

*

Problem is, B50 is actually the +25.5, and B30 is the phantom.

SO, what I (and apparently Don) did was to install the B30 supply to the phantom, and then check the +25.5V which was not recieving power at all!

** moral of the story is **
cross reference the board layout with the schematic & instructions before you put those rectifiers in! As the original goof was corrected by hand, it's perfectly possible that some typos were corrected properly, and others not. 5 minutes of cross referencing would have saved me 4 odd hours of trouble shooting.

better luck for you.
-Josh T

p.s. Peter in Johannesburg: thanks much for the sage advice, it really helped me calm down & figure out what was going on there.

quote:

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Originally posted by Josh T:
Hey Don & Everyone:

I figured out the -5v thing, and other folks might find this useful as well if they got the kits sent out in early April.

The old instructions accidentally listed installing rectifier B30 twice, a typo that was corrected in the in the issue of instructions I recieved with a pencil note scratching out B30 and inserting B50 where appropriate.

They say to install B30, check the +25.5V supply, then install B50 & check the phantom power.

*

Problem is, B50 is actually the +25.5, and B30 is the phantom.

SO, what I (and apparently Don) did was to install the B30 supply to the phantom, and then check the +25.5V which was not recieving power at all!

** moral of the story is **
cross reference the board layout with the schematic & instructions before you put those rectifiers in! As the original goof was corrected by hand, it's perfectly possible that some typos were corrected properly, and others not. 5 minutes of cross referencing would have saved me 4 odd hours of trouble shooting.

better luck for you.
-Josh T

p.s. Peter in Johannesburg: thanks much for the sage advice, it really helped me calm down & figure out what was going on there.

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Yeah, it's been quite a few pages ago that we originally discussed this typo. I had the original kits before the hand correction. I had to do some deductive reasoning and eventually came up with the right order.

Glad to hear you got it cleared up.


Jason A.

Yep, I'm realizing that now, but I guess since I had the new kit & it had been corrected by hand, I just went with the correction (which was innacurate.)

& hey Jason, thanks for starting this forum & sticking around to help the rest of alon-Josh T

Hey

I've had preamp done for a while now and channel one works great; it always has. I had channel two going fine for a time, but there is a problem with it now. The output from channel two, from my mic and the DI, is distorted and at a lower volume than channel one.

I have gone over the solder connections and can't see any problems, except that I know I have overworked a few of them in my process of making sure I had good joints.

I'm new enough at this that I don't know how to test with a multi-meter to see if I can narrow down the problem to a certain area. Do I test with the power on or off? Does anyone have any ideas what may be causing the distortion? Or how I can test to see where I should investigate more fully?

Thanks......Mark



Mark

quote:

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I'm new enough at this that I don't know how to test with a multi-meter to see if I can narrow down the problem to a certain area. Do I test with the power on or off?

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If you're testnig voltages, then power should be on. If you want to measure individual components like resistors the power off with the PSU discharged.

If one channel is good, then measure each resistor in circuit. Check chan 1 then chan 2 for each component. bear in mind they may not measure the exact value of the component beacause they might be in parallel with another component. The idea is to check one against the other.

If they all measure the same, then power up and check voltages on both channels. Put your multimeter's common lead to ground then measure voltages at various points in the circuit. Again, measure a point in Chan 1 then the same point in Chan 2 & compare the readings. If they differ by more than about 5%, then this might the problematic area.

Peter

Thanks again Peter. You have been a great help all along.

I'll give those suggestions a try tonight and report back Friday.

Mark

I did the suggested testing and got a different reading on channel 2's +48 switch. I may have overheated the +48 phantom power switch(es). One of the LEDs didn't light up, and that was the channel that was distorted. I started fooling with my soldering iron and the LEDs, and next thing you know; both channels are now distorting.

Since neither LED lights up and both channels distort, I'm going to order some replacement switches from Mouser. I'd also like to order a few LEDs but I don't see them listed on the parts lists. Please let me know if anyone knows the LED part number, otherwise I'll email Scott.

Mr. Magoo

Try checking with a dynamic mic, or a mic that does not need phantom. Just to make sure is the phantom supply before ordering more parts. Comes from experience....

Peter

Great catch Peter........from mucho experience no doubt. Dynamic mic has distortion on both channels too. What next?

Mark