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Old Yesterday, 01:05 AM   #3541
AudGuy is offline AudGuy  Canada
diyAudio Member
Join Date: Sep 2018
Location: North Vancouver, BC

Are Q1 & Q2 warming up . . . well, I would say that, NO, they are not. I have not finger detected or measured anything above ambient so far.
I was careful during construction and checked everything closely as I went along, but there could be a cold joint. I will look again.

Are Q3 & Q4 in the right spots . . . of this I am somewhat unsure. The BOM called for Q3-2SK170BL or LSK170B and Q4-2SJ74BL or LSJ74B however, what I received from the DIY store was 4 X LSK170F. I confirmed that all 4 devices were LSK170F and because of where I got them, assumed that these were suitable. This may of been a mistake.

On my behalf, I think this all started with me being unsure exactly what the "source resistor" would be. Studying the schematic did not answer my question. At this point, it was suggested as being R2 but my measurements tended to point at R1 (for whatever reason) so I am confused.

I will post pictures and details of how I am configured later this evening.

thankyou Anand
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Old Yesterday, 01:19 AM   #3542
AudGuy is offline AudGuy  Canada
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Join Date: Sep 2018
Location: North Vancouver, BC
Dennis Hui,

Pictures will be posted a little later this evening.

Z1 & Z2 were IN4733 5.1v devices. Or at least I have ticked them off on my BOM indicating as there being 4 of them. I will confirm from the packing slip.

R7 & R8 were 2026J/1002F devices according to notes I made on my BOM.

I must admit that the term "measure across" is for me, a little bit unsure making.
Does this mean to measure from both end of the measured device, or to measure between one end of the device and ground? I measured between the end of the R1 resistor and ground and see .776vdc on the left and -.774vdc on the right. R2 on both boards measure as about -20.1vdc.

I was able to achieve 0 or near 0 resistance between R10 & Neg.Rail for BIAS and 14 ohms for R9 to ground for OFFSET.

Thanks Dennis,
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Old Yesterday, 01:54 AM   #3543
poseidonsvoice is online now poseidonsvoice  United States
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Join Date: Jul 2004
Location: NC
F6 Illustrated Build Guide

If you received LSK170's and installed them on Q3, Q4, therein lies your first problem. They need to be replaced with the appropriate JFETS in the designated spots as detailed in the BOM. I would reorder from the diyaudio store.

Next, to clarify what 'measure across' means. It means you put one of your DMM leads (i.e. red) on one end of the resistor and put the other DMM lead (i.e. black) on the other end of said resistor.

When measuring across R2 for setting bias, don't worry about the polarity that the DMM reads, just the absolute value. In other words, 0.5V is the same as (-) 0.5V in this instance.

When you are measuring for offset, use another DMM and put the red lead attached to the red binding post (+) and black lead attached to the black binding post (-).

I am assuming that your DMM leads are appropriately attached to the DMM. In other words, the red lead is attached to the "V" terminal and the black lead to the "COM" terminal. Make sure you also set the DMM to read DC volts. Frequently that is designated by a straight line with 3 dashes underneath. AC volts setting looks like a squiggle or mini sinewave.

What value (in ohms) are R7 and R8 in your build? I have a feeling that from your description of 1002F, that they are 10K ohms. Using 3K to 5K ohms may make the bias procedure easier.

One other point. Make it a habit to try to measure each of the passive components so that you do not accidently install the wrong resistor/capacitor on the pcb. Whether it is from Mouser, Digikey or even as a full kit from a known source (i.e. the diyaudio store) I always measure on my own as mistakes do happen (and quite often actually). For example, a 10K resistor and a 1K resistor look exactly the same to the untrained eye. It is important to measure each of these resistors to distinguish them. I do the same for capacitors (up to a certain value like 1000 uf) as well as semiconductors if possible.

Please post pics at your earliest convenience.

Science is not a democracy - Earl Geddes
DIYAudio is a journey not a destination!

Last edited by poseidonsvoice; Yesterday at 02:05 AM.
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Old Yesterday, 02:46 AM   #3544
AudGuy is offline AudGuy  Canada
diyAudio Member
Join Date: Sep 2018
Location: North Vancouver, BC
Here is a shot looking straight down at the F6 and another that is 90 degrees around.
I will post some better shots after supper, or tomorrow.

Re the JFET's . . . I though that I was ordering the correct items, but live and learn. I will see about obtaining the correct items.

Thx for answering the measuring across question, terminology can sometimes get in the way.
Attached Images
File Type: jpg F6_TopView .jpg (176.7 KB, 93 views)
File Type: jpg F6_Angle View.jpg (325.2 KB, 91 views)
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Old Yesterday, 03:46 AM   #3545
Dennis Hui is offline Dennis Hui  Canada
Hoopy Frood
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Join Date: Aug 2002
Location: Toronto, Canada
F6 Illustrated Build Guide
AudGuy, unfortunately you will need the new jfets before you can proceed. Your build
is very tidy and I'm sure you will have it working very soon.

We are fearless amplifier builders. A little heat doesn't scare us at all.
- NP 2002
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Old Yesterday, 04:02 AM   #3546
AudGuy is offline AudGuy  Canada
diyAudio Member
Join Date: Sep 2018
Location: North Vancouver, BC

In addition: R7,R8,R9 & R10 are all 10K resistors. I will order both some 3K and 5K with possible replacement in mind for R7 & R8.

My problem is that I did measure all the components that I received to ensure that I got what I ordered. That doesn't help though if I ordered the wrong thing. Mybad...

So the DIY store expects my shipment to take 4-16 days. It will get here when it does and I can resume when that has happened.

Until then, thanks guys much appreciated.
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Old Today, 12:14 AM   #3547
AudGuy is offline AudGuy  Canada
diyAudio Member
Join Date: Sep 2018
Location: North Vancouver, BC
Today I have determined that everything on my two boards is as it is expected to be, with the exception of these two components:

Z1 & Z2 expects IN4733 5.1v BUT I have installed IN5231B devices.
Q4 expects LSJ74B BUT I have installed LSK170B devices.

I have placed an order with the store for the correct set of JFET's that includes the proper LSJ74B devices for the Q4 position.

I don't know whether the IN5231B diodes are suitable or if I should attempt to obtain some IN4733 5.1v devices?

Initial look-see of the boards and solder joints is that there is nothing drastic and maybe one or two joints that could be re-flowed. I will look much closer.

In spite of the need to deal with Q4 I feel a little more confident now.
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Old Today, 09:14 PM   #3548
silver89 is online now silver89  United States
diyAudio Member
Join Date: Jul 2017
Hi Everyone

I am so thankful for this forum and been loving the reading and learning. I'm a noob building my first amp starting with the F6 with Z1, Z2 3 green led and 3.3k R7 and R8 mod. Having an issue and need help diagnosing. Got one board up and running stable, biased to .499mV and offset at 0.0V. Second board is the issue. D1 LED not lighting up. A few measurements are below. Seems like something at the trim pot P2. Adjusting P1 offset changes comp voltage values downstream a bit but adjusting P2 bias does nothing. Thinking bad P2 but not sure if it could be something else. Reflowed P2 and nothing. If p2, can I somehow test while still on the board? Can get more measurements if needed but some of the terminology is over my head but still trying to learn. May not be able to get back today since it is my daughter's B-day but thanks in advance.

Rails 24v
Z1, Z2 - 5.85v
R7, R8 - 18.3v
R2 - 0mv
R1 - 4.5mv
Q1, Q2 - 24.9 deg C with no temp change after turn on
Attached Images
File Type: jpg IMG_7818.jpg (779.8 KB, 2 views)
File Type: jpg IMG_7817.jpg (511.6 KB, 2 views)
File Type: jpg IMG_7819.jpg (748.1 KB, 2 views)
File Type: jpg IMG_7820.jpg (670.0 KB, 0 views)
File Type: jpg IMG_7821.jpg (705.6 KB, 0 views)
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