Peter, Thank you for your response. In regard to possibly running the Hamptone at reduced gain to match up with my multitracks unbalanced inputs do you think I will still get as much of the mic pre's color factor ? Does the sound of the pre pretty much stay the same as you vary the gain or does the color factor increase as you increase the gain ? Regards, Dave

You could definitely get more colour from the preamp by turning up the gain!

You could pad the signal using the idea here:
http://www.colomar.com/Shavano/cable_xlr_to_phone.html

or you could wire a 5k pot across the preamp transformer output & run the wiper to the hot input pin & ground one side of the pot. This will give you a variable output.

Peter

Peter, Thanks again for your response. Perhaps I can add the components necessary to allow me to include two unbalanced outputs on the rear of the mic pre. Regards, Dave

Hi All,

Very basic questions here:
http://hamptone.com/to92id-2.jpg
http://hamptone.com/to92id-1.jpg
what do the "EBC" mean? Does it have to do with each one of the leads? Speaking of which, how do I know which one should go where on the board? At least I’ll get the middle one right… The JFETs leads being configured in a triangle already, that is nice. The NPNs, blah.

And from instruction # 4 on the channel board assembly sheet: "Make certain not to mix up the darlington NPNs (ZTX603) with the regular ones (ZTX653). The circuit works with them reverse but not correctly."

Well, in the ‘active devices’ bag I have 4 JFETs (2N5457) and 8 ZTX 603. I can not find any ZTX653’s – which makes me more paranoid and confused. I am stockpiling guns.

Could someone post some pics of each one of the transistors? Thanks for helping me get past this horribly ignorant impasse.

Hi Klem

Without seeing the documentation that comes with the kit, I'll give this a bash.

"E","B", & "C" stand for Emitter, Base & Collector, the 3 terminals of a Bi-polar transistor.

quote:

how do I know which one should go where on the board?

The position of the transistor should be shown on the component overlay of the PCB.

quote:

I can not find any ZTX653’s

Ask for clarification from Hamptone, sometimes kit suppliers substitute parts at their own discretion.

Regards
Peter

Indeed, wrong parts shipped, all makes sense now. Thanks,

Hi everyone,

My brother (who is an EE) just finished building me the HJFP2 kit. I am also attempting to use this preamp with unbalanced gear, to and RNC then into the inserts on an Mbox. The preamp buld looks great and he said it tested out fine. (I am a musician, not at all a tech, btw)

Well I plugged it all in and tested it with several mics (SM58, SM57, At4047, 603s etc...) and it sounds pretty good, clean and open. However, I am hitting useable gain levels at less than a quarter of a turn on the pots. At halfway it is introducing a lot of noise (hiss) into the chain (even without a mic plugged in) and providing more gain than anyone could ever want.

I am wondering if there is something wrong with the pre or if the balanced to unbalanced connections would be causing this. I was under the impression that going unbalanced to balanced could cause a drop in signal, not an increase.

Also in the Mojopie (http://www.mojopie.com/hjfp2.html) review, the reviewer mentions having a similar problem and figured out that the pots were wired backwards, any posibility that this is the issue?

Any help or insights you guys could provide would be of great help. I emailed Scott as well.

Thanks

Well, I did the smart thing and opened it up. (duh) The pots are wired per the instructions, so that likely isn't the problem.

Mark form FMR said that running the balanced to unbalanced connections into the RNC and Mbox inserts would not cause this problem either. I also plugged it into a balanced input and had the same issue.

Anyone run into this same problem?

(too much gain, and hissing if turned up beyond halfway)

Does the Mbox have a -10 / +4 setting in software?

If it does, setting it to +4 would reduce the sensitivity & make the gain more useable.

Peter

Peter, I think you may have nailed it.

There is no way to changed the input sensativity with the Mbox. I spent a lot of time this weekend playing around with the setup and I think the Mbox, particularly the built in headphone amp, may be the culprit. The Inserts also don't seem to be designed to do what I am trying to do.(Digi on the DUC recomends not using the inserts to hook up an external pre, despite what other people have told me)

using the balanced line inputs I am able to get a clean recording without the hiss being there upon playback.(even in the headphones) So I am thinking at the moment that the Hamptone is fine. I'm going to try and take it into the "big" studio where I am interning/assisting this week to see for sure.

thanks for your help.

Sorry to come on board with a problem, but as the tapeop board is down I've been forced to look elsewhere for advice. You guys seem to know your stuff about this preamp.

I finished assembling the HJFP2 last week, and have several major problems, although all the tests on the power supply and on the board (the nine voltage tests per gain stage on the JFET biasing page in the instructions) were within the acceptable ranges.

Firstly, one channel does not work at all, although I've checked and double checked and the two cards have been assembled identically (also, point to point). phantom power works. The gain pot seems to work as noise increases when something is plugged into the di. Ocassionally if I play really hard the output will jump up to (i assume) normal level. I was thinking cold solder, but they all seem to be fine.

Secondly, neither channel's xlr inputs work. I've run a 1khz at -6db line level signal through them, and with the pads out, at full gain, the signal is barely audible on the output, and barely shows on the meters in protools. Thats the main problem. On the working channel, this signal comes up strong on the di jack (instrument level selected), but when the pad is engaged (for line level) I can't get as much output level as on the input, even at full gain.

I guess there's more than 1 thing going wrong here.. I have been corresponding with Scott but I'm hoping one of you may be able to point me in the right direction as well. I will try to get the "working" channel functioning 100% first, then I can narrow down whats wrong with the other card.

Thanks, Mike

Hi Mike

Sounds like you need to trace the signal stage by stage to find the problems.

Have a look at this page for an excellent guide:

http://www.diyfactory.com/data/mbsignaltracing.htm

Regards
Peter

Hi All-

I just finished building the JFET kit, all DC voltages measured good. All functions of the audio channels work properly (+48, Pad and Phase). I am getting noise that sounds like 60 cycle hum/buzz that is in both channels but mostly in channel 2. I re-twisted the 4 wires on the transformer (incoming AC mains) and rotated it to reduce the noise as much as possible. It did make a difference, but the noise is still there. When I connect mics and turn up the gain, channel one is almost acceptably quiet but, in channel 2, the noise gets louder with the signal. After reading some of the FAQs on Scott's site, this pre-amp should be quiet, absolutely quiet, right? I am going to re-check the resistors on the step attenuators, re-check all the point to point and visually scan the audio boards for any bridges, flux etc. If all is okay, what do you guys think would be the best approach to finding a possibly failing component?

Any help would be greatly appreciated. BTW, I built the tube pre a couple of years ago and it is awesome!

-Steve

Hi Steve

Any pics of the inside?

How have you grounded the pre? Star grounding is the best way.

What mains transformer have you used?

Regards
Peter

Hi Peter-

Sorry I didn't reply to your message sooner. I was expecting an email notification from the forum that I had a response to my question.

I am using the xformer that came with the kit: TE62065, 22VAC x 2 25 VA toroidal (text from parts list) from digikey.com

I have grounded the pre via a lug from the ground at power entry to chassis per instructions. I definitely have 60 cycle coming out the output along with some harmonics. I have seen this in Digicheck software using my RME card with the spectral analyzer tool. Rotating the toroidal changes the characteristic(causes more/less harmonic noise depending which direction).

Scott had me check the regulator voltages on the power supply and both measured right on the money. I actually untwisted the mains in on the xformer from the switch and the noise got a little quieter...go figure.

I can take a couple of pics if you think that would help. I've never posted pictures on this forum before so bear with me.

Thanks for any help you can give. I really appreciate it. I'm gonna email Scott more details after Thanksgiving.

-Steve

OK, keep us informed as to what Scott says.

If you need to post pics, http://www.photobucket.com is a good site.

Regards
Peter

hi. first time posting. i've built a HJFP2 a few months ago and have been using it ever since. just the other day, the right channel mic input got the flu and decided not to output properly. the signal is barely audible now at full gain. the phantom works and the DI/LINE work fine. i'm recording some stereo piano in the next couple of days and really have to figure this out. any suggestions would be greatly appreciated as I'm a total newbie(building the preamp was like paint by number, verified several times before soldering) at this. thanks.

Bottlebeet

The DI jack socket, is it a switching type, the type that cuts out the mic, when plugging in the DI?

If it is, it could be the switch contacts are either dirty or not making contact. Try inserting a shorting jack (tip & ring connected together, dont use a mono jack) & see if this cures the problem. If it does, then the problem is with the switch.

Peter

quote:

Originally posted by Peter Cornell:
Bottlebeet

The DI jack socket, is it a switching type, the type that cuts out the mic, when plugging in the DI?

If it is, it could be the switch contacts are either dirty or not making contact. Try inserting a shorting jack (tip & ring connected together, dont use a mono jack) & see if this cures the problem. If it does, then the problem is with the switch.

Peter

wow fast reply. in new developments, the DI/LINE and the mic are now both suffering from very quiet outputs. checked all the solder joints... any other suggestions?

also when i press the inst/line switch i get some heavy action on the meters. still very quiet like a 60db pad has been applied to the right side of the hamptone. any other suggestions?

greatly appreciated