FS: PCBs for TG1 Zener Limiter AVAILABLE!

Help Support GroupDIY:

desol

Well-known member
Joined
Jun 20, 2005
Messages
2,064
Ah, ok....

I know there is demand from this guy for sure... :)
 

orangechili

Well-known member
Joined
May 4, 2009
Messages
232
Location
Daytona Beach, Florida
I got the pcbs and they look great! I had a quick question:

There's a few resistors on the board that have an asterisk by them that I don't see mentioned in the build guide(R15,R39, R40, R66, R71 specificially).  Are these just values that were changed from the original design? Just want to make sure i'm not missing anything  8)
 

fripholm

Well-known member
Joined
May 26, 2013
Messages
305
Location
DE
orangechili said:
I got the pcbs and they look great! I had a quick question:

There's a few resistors on the board that have an asterisk by them that I don't see mentioned in the build guide(R15,R39, R40, R66, R71 specificially).  Are these just values that were changed from the original design? Just want to make sure i'm not missing anything  8)

These were the 'AOT' resistors from the original schematic, which could mean 'adjust on test' or something like that. The asterisks are some leftovers from my first version of the board, when I didn't know how critical they are (I've sold the second!).

Apart from R7, R8 and R56 (see the guide), they don't do much or their value isn't too important. For example, R66 and 71 fine-adjust the +/-20 volt 'rails', but on the 3 boards I built, I always had exactly the right voltage there without any change. If you're using 1% resistors you should be fine...  ;)
 

ChrioN

Well-known member
Joined
Aug 31, 2005
Messages
1,235
Location
Gothenburg, Earth
Got it yesterday but picked it up at the postal office as we speak. Looks great! Which manufactorer did you use? Germans makes everything awesome. Just like Sweden :p (OK OK except IKEA)
 

orangechili

Well-known member
Joined
May 4, 2009
Messages
232
Location
Daytona Beach, Florida
Ok, finally getting around to getting two channels running and had a few questions. I haven't done any fine tuning yet and have a 10k trimmer set to 5k for R7/R8 so if getting the correct values will fix my issues below please let me know.

1. I used 4:1 Cinemag Input transformers and am lacking in overall volume a bit, is there a recommended value I adjust R86, R87 to add more gain back to the unit?
2. The meter takes forever to return back to zero. Is there something I can adjust to make the meter move more freely and not so choppy and slow? Using the hairball 1ma meter(same as don audio one you recommended). Set meter needle just right of 0 like you recommended in the guide. It really stays stuck for a while and very slowly moves back towards zero
3. I notice the output transistors(BD139, 140) are a little hot to the touch when running, i'm using a +28/-28v power supply like recommended. I'm wondering if lowering the voltage a volt or two may help or some heatsinks.

The unit passes audio fine and appears to be working
I haven't messed with the R7/R8 tuning and THD adjustments yet.

 

orangechili

Well-known member
Joined
May 4, 2009
Messages
232
Location
Daytona Beach, Florida
I should also mention there is a nasty clipping when I turn up the output and input controls that sounds like something is not connected properly. I have the same exact issue in both boards. I have triple checked every connection and took my time building it going through the diagram, etc.
 

fripholm

Well-known member
Joined
May 26, 2013
Messages
305
Location
DE
orangechili said:
1. I used 4:1 Cinemag Input transformers and am lacking in overall volume a bit, is there a recommended value I adjust R86, R87 to add more gain back to the unit?
2. The meter takes forever to return back to zero. Is there something I can adjust to make the meter move more freely and not so choppy and slow? Using the hairball 1ma meter(same as don audio one you recommended). Set meter needle just right of 0 like you recommended in the guide. It really stays stuck for a while and very slowly moves back towards zero
3. I notice the output transistors(BD139, 140) are a little hot to the touch when running, i'm using a +28/-28v power supply like recommended. I'm wondering if lowering the voltage a volt or two may help or some heatsinks.

The unit passes audio fine and appears to be working
I haven't messed with the R7/R8 tuning and THD adjustments yet.

Congratulations on finishing your boards  :)

1. R86 and R87 set the gain when the unit is in BYPASS and do nothing when the compressor is engaged. However, in your case with a 4:1 input tranny (~12dB volume drop), both resistors need to be changed to keep the level constant in BYPASS, try 1.8k and 2.2k for R86 and R87, respectively. That should result in around 12dB gain for the output stage, which the signal still passes even in BYPASS, and keeps the input impedance about the same. As I used a 2:1 input transformer, this section was designed for a 6dB volume drop.
The compressor section itself has a gain of around +14dB (when not compressing) which results in an overall gain of +2dB (accounting for your 4:1 input transformer) at the output of the compressor (top of R30).

2. Which value has C33? It slows down the needle movement a bit, but it shouldn't take forever to return to zero. There might be something else wrong. Is the release time also very slow?

3. In my units, the output transistors' temperatures are around 50~60 °C each, which is totally fine without a heatsink.

orangechili said:
I should also mention there is a nasty clipping when I turn up the output and input controls that sounds like something is not connected properly. I have the same exact issue in both boards. I have triple checked every connection and took my time building it going through the diagram, etc.

It's maybe the output stage oscillating. Have you tried a series resistor (try 22~47 ohms) between the board's output connector and your output transformer?

Maybe we should really open a build thread?!
 

orangechili

Well-known member
Joined
May 4, 2009
Messages
232
Location
Daytona Beach, Florida
Good idea on the built thread  ;)

I built both boards with a 22ohm resistor from the output + to the primary high on the output transformer. I may up the resistor value and see if that helps. It's like a big jump near the end of rotation on the output and input pots.

Then there's the meter that basically stays put after getting hit with compression...

What's hard is I have the same issue on both boards.

I just checked transistors orientations and pinouts again and all look correct as well as the off board wiring. I even flipped the polarity on the output transformer secondary wires like recommended in the guide.
 

fripholm

Well-known member
Joined
May 26, 2013
Messages
305
Location
DE
Guys, thanks for your interest!  :)

I will start another run around the end of this month. I am pleased to announce that this time I'll also offer my PSU boards (sold separately) for use with this project or everything else that needs a quiet and stable bipolar power supply.

Will keep you posted!

 

Hobbyist

Member
Joined
Nov 24, 2015
Messages
24
Location
Belgium
fripholm said:
Guys, thanks for your interest!  :)

I will start another run around the end of this month. I am pleased to announce that this time I'll also offer my PSU boards (sold separately) for use with this project or everything else that needs a quiet and stable bipolar power supply.

Will keep you posted!

AWESOME !  :)
 

duantro

Well-known member
Joined
Dec 31, 2008
Messages
755
Location
KCMO USA
fripholm said:
Guys, thanks for your interest!  :)

I will start another run around the end of this month. I am pleased to announce that this time I'll also offer my PSU boards (sold separately) for use with this project or everything else that needs a quiet and stable bipolar power supply.

Will keep you posted!
I'm interested in a few bipolar  psu boards when you get around to it.
 

Latest posts

Top