Hamptone HJFP -help thread

[G-Sun]

I couldn't find a dedicated help-thread for the Hamptone HJFP, so I'm creating one.

This should apply for:

• Hamptone HJFP2, 2ch full kit
• Hamptone HJFP1, 1 ch kit

Homepage: www.hamptone.com
Manual: http://www.hamptone.com/support.html

 

[G-Sun]

So, I've built a Hamptone HJFP2
and are having a few issues:

- Pad ch 1 is not working
- 48V led ch 1 is not working
- Ch2 has 5db or so more noise than Ch1, and it's too much
- 2 of the top-panel screws, front, are not going in
- XLR out is not clicking in (Should they?)

My config is low gain (-6db).

Sound: Sound is good
Shootout/files here: http://www.gearslutz.com/board/gear-shoot-outs-sound-file-comparisons-audio-tests/675026-preamps-hjfp2-ua610-onyx.html
However I was a little surprised the sound was so "driven/distorted", and I'll go for the +3db gain/cleaner mod (I'll post back how it goes.)

So, does anyone have tips for sorting my issues?

+48V led is either gone, or are soldered backwards I guess
And I'll check the xlr-mounting, if they're all the way inn.

 

[grantlack]

Try moving or shielding the leads of that on/off lamp on the front and see if your noise figures improve. I'm assuming it's running off AC. Do you have the parallel outputs wired? They look like the wiring would have to pass awful close to the power transformer, keep that routed as far away as possible. LED is likely reversed as you predict, check soldering around the pad for shorts or cold joints.

 

[Davo]

in regards to the noise... rotate your toroid... I've got the tube version of this and found it particularly susceptible to toroid noise even
with the steel shield... if it's still noisy, might try some mu metal around the toroid

 

[G-Sun]

Thanks folks!

Try moving or shielding the leads of that on/off lamp on the front and see if your noise figures improve. I'm assuming it's running off AC.

Nice, I'll try

Do you have the parallel outputs wired? They look like the wiring would have to pass awful close to the power transformer, keep that routed as far away as possible.

No, not yet.

LED is likely reversed as you predict, check soldering around the pad for shorts or cold joints.

Yes

in regards to the noise... rotate your toroid... I've got the tube version of this and found it particularly susceptible to toroid noise even
with the steel shield... if it's still noisy, might try some mu metal around the toroid

Nice tip I'll check it out

 

[G-Sun]

Ok,

- Pad ch 1 is working. Resoldered the joints around the switch and that did it
- Checked ch1 48V led, it's dead. I'll order a new one
- The xlr-out-thing is just the xlr-connector on my cable -my other cables are fine
- Remounted the xlr, and panel seems to fit now  ;D

Noise is still there:
Ch1: -73,5dbFS
Ch2: -68,2dbFS
Full gain, reading is into my soundcard

I have cleaned the boards, moved the lamp-wires a little.
I'll try rotating the toroid.

Not bad  :-*

 

[G-Sun]

I've now modded channel 2 to:
R10=20k, R12=2,8k

Files here

I really can't hear any difference.
Think I'm going back to stock.

 

[Gus]

IIRC there was a fetboy thread and a number of other posts about this preamp.

 

[G-Sun]

IIRC there was a fetboy thread and a number of other posts about this preamp.

Thanks! I've looked around and couldn't find anything on this specific subject.

In the papers Scott describes that the bias in the HJFP is around 55% of the DC voltage, and that lowering it would make it more linear, increasing it would make it more distorted.
But, it's unclear to me if this is something I can adjust myself.

 

[Gus]

Search the web for things like for jfet biasing, how to bias a jfet, Vishay app notes, look for the book"The Art of Electronics".  read about transistor circuits.

Jfet circuits will cause people issues if they do not understand some things about jfets, things like how they vary and how to adjust the circuit and/or select the jfet for the circuit.

There are/were posts about this circuit with good information.

 

[G-Sun]

Search the web for things like for jfet biasing, how to bias a jfet, Vishay app notes, look for the book"The Art of Electronics".  read about transistor circuits.

Jfet circuits will cause people issues if they do not understand some things about jfets, things like how they vary and how to adjust the circuit and/or select the jfet for the circuit.

There are/were posts about this circuit with good information.

Thanks! I think an unguided mod is a little over my skill-level
Maybe later