G-Sun

Re: Symmetrical FET
« Reply #40 on: September 29, 2014, 11:55:25 AM »
Gustav: I see the kit is removed from you shop.
Is it still coming, or has there been some change of plans?

I haven't looked through the BOM closely. Many hard-to-find items/ many vendors if buying just a pcb?
HJFP2, ssl9k, Harrison Ford Filters
My music


Re: Symmetrical FET
« Reply #41 on: September 29, 2014, 12:13:46 PM »
Gustav: I see the kit is removed from you shop.
Is it still coming, or has there been some change of plans?

I haven't looked through the BOM closely. Many hard-to-find items/ many vendors if buying just a pcb?

Just one "hard-to-find" part - 4M7 dual gang pot, which can be found at Reichelt.

Alpha seems to have lost my original order for pots, so I have to wait another 3 months, which is why I took it down.

Gustav

G-Sun

Re: Symmetrical FET
« Reply #42 on: September 29, 2014, 03:13:27 PM »
Gustav: I see the kit is removed from you shop.
Is it still coming, or has there been some change of plans?

I haven't looked through the BOM closely. Many hard-to-find items/ many vendors if buying just a pcb?

Just one "hard-to-find" part - 4M7 dual gang pot, which can be found at Reichelt.

Alpha seems to have lost my original order for pots, so I have to wait another 3 months, which is why I took it down.

Gustav
Ok, thanks for the info!
HJFP2, ssl9k, Harrison Ford Filters
My music

djfatum

Re: Symmetrical FET
« Reply #43 on: October 14, 2014, 12:01:40 PM »
potentiometer 4M7 anyone knows where it can be purchased ?? :-[

G-Sun

Re: Symmetrical FET
« Reply #44 on: October 14, 2014, 12:09:37 PM »

Just one "hard-to-find" part - 4M7 dual gang pot, which can be found at Reichelt.
Gustav
HJFP2, ssl9k, Harrison Ford Filters
My music

djfatum

Re: Symmetrical FET
« Reply #45 on: October 14, 2014, 01:23:18 PM »
I found only the mono version   :-[

Re: Symmetrical FET
« Reply #46 on: October 14, 2014, 01:36:27 PM »
I found only the mono version   :-[

PO4S-LIN 4,7M

Gustav

djfatum

Re: Symmetrical FET
« Reply #47 on: October 14, 2014, 03:40:27 PM »
Thank you for your help   8)

Andrzej

Wayne

Re: Symmetrical FET
« Reply #48 on: October 15, 2014, 11:46:46 AM »
Hi All

Total Noob question, Im still learning but im getting there... slowly! Ive been putting one of these boards together, I'm just putting in the last parts and was wondering about the values for the program regulator resistors - is there a formula to working these out that i am missing?

Many thanks



gyraf

Re: Symmetrical FET
« Reply #49 on: October 15, 2014, 12:37:45 PM »
Quote
" program regulator resistors"

What do you mean?

Jakob E.
..note to self: don't let Harman run your company..


Wayne

Re: Symmetrical FET
« Reply #50 on: October 15, 2014, 12:43:35 PM »
ahh i think i might have worked it out, on this board in the PSU section there is 4 resistors marked K and R with no values, but having looked a touch harder, from what i understand they are the resistors for setting the output voltage for the 317 and 377.... (first time I've done this part my self)

So for what i understand the out put voltage of these needs to be +18v and -18

would a value for R be 240ohm and K be 3k3...?

Cheers


Wayne

Re: Symmetrical FET
« Reply #52 on: November 04, 2014, 12:36:39 PM »
cool so just powered up my build seems to be working :)

Anyone go any tips on how I calibrate the VU's on this?

Cheers

Wayne



Re: Symmetrical FET
« Reply #53 on: November 05, 2014, 11:12:55 AM »
cool so just powered up my build seems to be working :)

Anyone go any tips on how I calibrate the VU's on this?

Cheers

Wayne

I just did some work on the assembly guide, and Ill do a small calibration guide.

You should be able to use the 1178 manual for stringent calibration, but to get you moving..

In the section of the PCB marked "meter circuit", you should see 4 trimmers.

The ones marked "ZERO (R/L respectively)" at coordinates S2 and S8 will adjust the 0dB point on your VU.

The ones marked "TRACK (R/L respectively) at coordinates S4 and S7 will adjust the meter throw/tracking.

The two remaining trimmers marked "Q-BIAS (R/L respectively) at coordinates A5 and D5 set the FET bias.

Gustav


Greg S.

Re: Symmetrical FET
« Reply #54 on: December 13, 2014, 09:05:32 AM »
Hi Guys,
finally I wanted to denoise my early built Sym Fet.

Does someone know,
Are there some wrong printed parts?

1  At The Pre Amp e.g. are 3 30K for each Channel,
Gustav told me to use 30R, same at his built guide.
2  Why are there 2200-4700uF at the Lundahls?
I mean, the 1176LN got there 470uF
The original didn't got one!
I mean, never ever use a C direct into the Signalpath,
If you want to block DC, use something like this



3  Did some checked why there are Labeled 4 Ratios and at the Lorlins got 3 Connctions?

Re: Symmetrical FET
« Reply #55 on: December 13, 2014, 12:33:09 PM »
Hi Guys,
finally I wanted to denoise my early built Sym Fet.

Pots differ from my set-up, may be a wiring issue, and it may be worth looking at the grounding done, toroid set-up, heavier connection for ground from XLR, see if you can tap into the board on any problem area and draw a clean ground to chassis, etc. I have no discernible noise in my builds, so it should be possible with the board you used and implementation of similar wiring and mounting.

Does someone know,
Are there some wrong printed parts?

1  At The Pre Amp e.g. are 3 30K for each Channel,
Gustav told me to use 30R, same at his built guide.

Because its printed wrong on the silk screen, it was corrected in the info, yes.

2  Why are there 2200-4700uF at the Lundahls?
I mean, the 1176LN got there 470uF
The original didn't got one!

You can probably use a lower value, but its just to make sure we block any DC, and avoid creating an audible filter at the same time. Its what I had when I tried it out.

I mean, never ever use a C direct into the Signalpath,

C = electrolytic capacitor?

Never, like the output of 1176 you mentioned? :)

I also added electrolytic capacitors in front of the pots to avoid scratchy pots (google it, seems to be a common problem on the original). You may leave those out too for a more pure path, if you wish. Make sure to check for DC on the output.

3  Did some checked why there are Labeled 4 Ratios and at the Lorlins got 3 Connctions?

Sounds like you referred to the original schematic for the output cap, you could easily do the same for this.

Hope that helps!

Gustav
« Last Edit: December 13, 2014, 01:10:01 PM by Gustav »

just.sounds

Re: Symmetrical FET
« Reply #56 on: February 02, 2015, 09:18:05 AM »
I almost completed one of these puppys. Nice sound !! on one channel....

One problem one channel seems to POP the output cap (before the trafo) one output cap was making acousitical sound and another one started to leak fluid....

Any guess what could cause this? The input/gain reduction on this channel is looking fine. Opamp is fine output transistors are checked and replaced so there must be a short somewhere. but i can not find it yet.


mike76

Re: Symmetrical FET
« Reply #57 on: March 25, 2015, 03:59:02 AM »
Hi,

I was wondering how much current is necessary for the device? Would approx. 300mA be enough? How would I get to know how much is enough (from theory or calculating)?

Thanks guys and girls.

Re: Symmetrical FET
« Reply #58 on: March 25, 2015, 05:09:33 AM »
I almost completed one of these puppys. Nice sound !! on one channel....

One problem one channel seems to POP the output cap (before the trafo) one output cap was making acousitical sound and another one started to leak fluid....

Any guess what could cause this? The input/gain reduction on this channel is looking fine. Opamp is fine output transistors are checked and replaced so there must be a short somewhere. but i can not find it yet.

Are the transformers mounted? And did you measure DC at the output on the channel with a problem ? (before the blocking cap).

Gustav

Re: Symmetrical FET
« Reply #59 on: March 25, 2015, 05:12:05 AM »
Hi,

I was wondering how much current is necessary for the device? Would approx. 300mA be enough? How would I get to know how much is enough (from theory or calculating)?

Thanks guys and girls.

You could measure the current draw on the circuit. I can't remember it to be honest, and it doesnt seem like I made a note of it.

Any reason why you need the exact draw?

Gustav