All things G1176 - the new "repost" thread.

[bradb]

Regarding these clone 1176s and gain, perhaps those of us who have a TON of gain are using Jfets that just happen to have a ton of gain?

Is there a difference between the jfets used in the originals and these we're supposed to be getting?

Have there been incremental improvements in gain on the clone jfets over time?

I'm going to try going for a lower gain jfet (or pair).

 

[pxpx83]

Found the problem with my 1176 (trimpot for q-bias and zero adj not working). I used the wrong hole for the spot labeled 18 on mnats version of the pcb. I have a small trimpot, but I used the hole meant for a large size trimpot.

Just gotta calibrate it and she's done! :grin:

 

[gyraf]

Brad,

The 1176 simply has a ton of gain. They all do. Look at original specs. No error in this.

But if I understand you right, your problem may be that you have too low a threshold - and that has to do with FET cutoff voltage.

Jakob E.

 

[bradb]

Hi Jakob,

The overall gain on my unit is fine I think... Actually I generally have the output fully cranked to the max while using the 1176.

The problem I have is low threashold... (BTW, I have Lundhals on the input and output, PSU voltage is fine, everything has checked out in the past, and I've used it successfully, I've just cracked it open recently to aid with meter issues on an LA2A project and decided to address this input threshold issue) Here is my calibration technique...

CW output, CCW input, CCW the Qbias pot, CCW the attack, CW the Release, 20:1, Bypass mode. Protools input of -1dB, 1000Hz, Sine. Reading the output of the 1176 into protools using that bomb factory meter plugin. I raise the input pot until i get 0db on the protools meter (if 0 on input is 7 o'clock, i maybe get to 8:30 on the input when the output goes to 0dB!!), turn CW the Qbias pot until the protools meter reads -1dB and then i call it calibrated. 8:30 on the input pot corresponds to my threshold.

Is this correct? Do I need to do other steps before this? The other calibration procedures calibrate the meter to track and zero the meter, so they are independant correct? (i do these steps too, btw)

Last night I popped in some of my other FETS that I had left over after matching, the threshold point is completely the same regardless of FET.

If i could get my threshold at like 12 or 1 o'clock, that would be cool.

Do i need to do some voltage probing?

Thanks all!

 

[al_p]

Hi

I was thinking about this low threshold problem. I was looking at the data sheets for the BF245 and noticed that the A B and C version have different ranges for Vgs and Idss. How do these specs affect the threshold? At all? Sorry my thoery chops aren't good enough to know what this means exactly to the circuit.

I was thinking about ordering a bunch of Bs and Cs, but don't wanna waste time and money. Can anyone comment on this?

thanks

 

[bradb]

I just took a look at the data sheet:

IDSS drain current VDS = 15 V; VGS = 0

BF245A 2 - 6.5 mA
BF245B 6 - 15 mA
BF245C 12 - 25 mA

Looks like the A version is the tamest of all 3 of these. I don't think the B and C are going to help us here.

 

[rbaker]

I'm building my unit without the input transformer---(I might add it in later)

I thought I read that the parts with a * on them should be left out if building it this way...I just want to be sure I'm correct and also that I'm finding all of the parts.

the ones circled in red?

[/img]

 

[sintech]

rbaker,

You're spot on, leave them out for a no input trafo build :thumb:

 

[imo]

Just wanted to add again that i am having the same threshold problem and that it is limiting the usability of an otherwise lovely sounding unit. I am using the Lundahl input transformer and have tested a bunch of different FETs to match them. I simply can't get the unit above 10% on the input, and then have to completely open up the units output to get a workable level.
I have done the output mod to double the output, as well as the cut to lessen the ground buzz. This all works great, now if only to find a way to tame the threshold, the unit would be brilliant.
It might be worth it for those of us having the problem to compare what we have, what type of input, balanced or input tran, voltages, etc/
I am surprised that there is no other way than the FET itself to affect the threshold, but unfortunately my understanding of the circuit isn't comprehensive enough to find another way to address this
Ian

 

[bradb]

Ian,

Some of us are having the same EXACT issue. I have mnats' board, Lundahls on the i/o.

I have the same threshold problem, my output is always cranked too!

should we all post some bias voltages?

 

[al_p]

Hey Brad, Ian, and anyone else with this issue.

Here are my measurments. The DMM I am using is the cheapest you can get. Measurements above 20V have no decimal place.

E B C

Q2: 0.52 1.01 1.70
Q3: 1.12 1.71 12.25
Q4: 11.68 12.24 30
Q5: 4.32 4.75 28
Q6: 28[+0.57*] 28 14.14
Q7: 29 28 14.14
Q8: 13.55 14.15 30
Q9: 13.46 12.87 0
Q12: 3.86 4.39 14.63
Q13: 14.06 14.63 30
Q14: 2.87 3.43 16.47
Q15: 15.96 16.47 30

*meaning E is +0.57 referenced to B

I built the unit completely to project specs, with some mods. Here's where I'm at.

board: Chef's [with ground cuts]
Input: wired as specified by the rev E schematic using a Hammond 850G
Output: LL5402 wired as 1:2
Output Q: BD135/BD136 with pin re-configuration

The unit sounds great, and calibrates properly.

 

[imo]

AL and Brad,
I will try to post some voltages tonight..Thanks for putting them up, will be interesting to see what we get. Also, it seems that all of us are using input transformers. I wonder if anyone had the problem using a balanced unit?
Ian

 

[imo]

Here is my info..
I used Lundahl input and output transformers as well as the BD135 and BD136. I have the output transormer mod for 1:2 output and the hitchhiker cut. Everything else is stock and everything has been calibrated
E B C
Q2: .52, 1.04, 1.78
Q3: 1.16, 1.78, 12.23
Q4: 11.6, 12.2, 30.4
Q5: 4.5, 4.9, 28.6
Q6: 29.2, 28.6, 14.7
Q7: 29.8, 29.2, 14.7
Q8: 14.1, 14.7, 30.4
Q9: 14, 13.4, 0
Q12: 4, 4.5, 14.9
Q13: 14.3, 14.9, 30.4
Q14: 2.9, 3.4, 17.3
Q15: 16.8, 17.3, 30.4

 

[al_p]

Looks like we're in the ball park with each other, and other measurements I've seen. Nothing obviously wacky there.

Has anyone tried 2N5457s for the FETs?

 

[bradb]

just wanna throw an idea out there that just popped into my mind.

we're all using 10k(If i remember right) Log pots on the input. what if that log characteristic is incorrect....

take a look at this:
http://www.efunda.com/math/exp_log/images/exp_log_plot.gif

seems like we have a log characteristic (in blue) , where we may want the exponential characteristic (in red). Maybe this is a clue...

just thinking...

i'll get some voltages posted in a day or so.

 

[astrovic]

Hi all

I'm just starting my first DIY project that isn't a kit - a G1176 (which is why I'm here...) I was hoping that I'd able to build the thing without needing to pester anyone, given the mountains of info on this site posted by the wonderful people here, and on the internet, and otherwise figure it out as I go.

Almost... :grin:

I'm currently waiting on some caps from Digikey, and in the meantime have drilled my front and back panels and am in the process of doing some off-PCB wiring.

I want to ask a simple question regarding the fused IEC connector. I've searched away on this and found a lot of info, but nothing bang on point. The IEC looks like this:

and a drawing of it looks like this:

From the bottom drawing, there are three lugs, one in the top middle (which I know is the ground - it has a "G" next to it) and two on the left. The top-left has a "N" next to it, so I'm sure it's the neutral. The lug below it, by process of elimination, should be the live. However, the "L" for live is on the right-hand side, where there are no lugs.

My belief (but I'm not certain) is that the live lug is on the left as the live pin connects to one (right) side of the fuse, and reaches the lug on the other side of the fuse on the left - hence the live lug being on the left, along with the neutral lug.

Is this right? Given I'm learning about mains voltages here, I'd prefer to ask dumb questions than get it wrong - there's more at stake than a $2.50 IEC :idea: :shock: :idea:

While I'm at it - my torroid has two wires comprising the primary - brown and black. On the diagram on the side of the torroid, the brown is on the top and the black is on the bottom. Should brown go to live and black to neutral?

Apologies again for asking the obvious.

Chris

 

[bradb]

Hey Guys,
After long last, I've checked my voltages and mine are pretty much in line with both of yours.

Still battling!

 

[bradb]

Not to leave you out Chris...

But yes, it looks like the fuse is right after the Live terminal on the plug as it should be. You should get a multimeter and make sure. You will need a multimeter for this project, and basically for getting thru life, so get one.

You always want to switch and fuse on the Live lead. Hardcore dudes switch on both the live and neutral, just to circumvent any idiot housewiring.

good luck.

 

[astrovic]

Thanks Brad - nice to have it confirmed

Yeah, I have a multimeter - just wanted to check before I start making an idiot of myself...

Cheers
Chris

 

[bradb]

to my pals who are having input threshold problems with input trannies...

I'm going to give a try for rewiring my input tranny for 2:1

like here: http://www.groupdiy.com/index.php?topic=15543&highlight=lundahl+input+1176

PRR recommended a 2:1 ratio for the input transformer back when we were discussing it some time ago. 2:1 is what the original UREI units used as well.