TG1 - advice from any one who has built it...

[jplebre]

shouldnt the LM317 be positive? not negative?

 

[late]

Anyone have used Hairball 8020 meter?

To adjust the metar, use 500R-1k 10turn pot in parallel. But how?

 

[jplebre]

Anyone have used Hairball 8020 meter?

To adjust the metar, use 500R-1k 10turn pot in parallel. But how?

You needed to have another pot in paralell so you could compensate the amperage, as well as some place to put the meter in series to see if you are actually going for 1mA

Found post here: http://www.groupdiy.com/index.php?topic=37400.msg653727#msg653727

Edit2: haven't done it yet. I'm busy for the next few weeks so I'm hoping week after next one I get to do this.

 

[jplebre]

OK new developments on my issue - more info on what the problem actually is:
It seems all is fine but the compressor is compressing signals at -2dBu. If I actually feed a sine wave to a signal under -25dBFS (on my sound card, callibrated for -20dBfs) there's no loss

Now, before I thinker with anything, could someone please confirm if this is this normal?
If it's indeed an issue I'm thinking it's probably a calibration issue: either with AOT 3/4, 5/6 (it does make a difference in the overal level if I'm in limit or compression) or unity gain with AOT1,2?

I'm more inclined to think AOT3/4 5/6 because When switching to THD, all is good (no loss no matter what level) so I'm guessing it's either around VT9 (make up stage on signal path) or something related with the sidechain.

Also, if someone could confirm this based on experience with chandler/original/festers:
- when using Hold, the top of the potentiometer changes voltage as well. SHould it remain fix at 10v and only the wiper change voltage?
- Hold control not doing much. (note: i don't have the meters working yet, so I can't actually see. But by hear, only the last 3 steps really do a difference).
- Original attack time speed quite slow (both on Lim/Comp mode?)

Compression is sweet. If you are holding off building this guy don't as it's pretty "special"

If you guys could help confirm the above would be a great help on the troubleshoot process

Thanks

 

[imo]

yes, thanks Harpo. I couldn't find any ref on the relay and had way too big of a resistor in there.
I have the relays working. I have the voltages straight at all the test points on the main board. I did notice however that the current on the negative side of the 24v rail is low. I measured 120mA on the +24 side, but only about 55mA on the -24 side. This is with only the main board hooked up. No AC signal
the 4898 is B 19.9 E 20.4 C 9.3
The 4910 is B .6 E 0 C 9.3
the voltages seem right with the emiitter of 4910 at ground, and the base .6v above it. I just wanted to double check before i went any further.
Thanks
Ian

 

[jplebre]

I want to ask if everyone has cracked the code on:

1). +/-20v
JP1...6, TP+20v, TP-20v
2).Unity gain
Initial gain is set by AOT1,2
3).Distortion w/o compression
minimum distortion adjustment AOT 7,9
4).Distortion at 20dB GR
distortion under hard compression adjusted by AOT8/10, usually 10R is fine
5).Com threshold
Com threshold adjustment: AOT3,4
6).Lim threshold
Lim threshold set by AOT5,6.
7).Check: reqresp, max gain, min gain, S/N, timeconstants.

I've been PM'ing several members and my feeling - either because they admited or from their "I guess so" or "I think that" is that the above is not straight forward.
There are members here that said that they went around in circles adjusting. Now, I'm having a bit of a hard time even understanding where to start as some things - even w Igor's description - don't make much sense to me.

I would love if it got to the point where we could maybe do some sort of a meta post on this where everything get's explained a bit better.

You all know my problems on this. Signal get's dropped to -6VU if the i/p signal is higher than that. Hold does very little except for the last few steps - every other step seems to simply bring signal further down. On Limiter mode, the signal is slightly higer (by about 4dB) than the -6VU on compress. On THD mode the signal keeps a consistent level.

Now, here's the bits that are hazy:
2) Unity gain - but AOT1,2 is on the sidechain. So how exactly does it impact on gain?
on my example, disabling sidechain (THD mode) is ok signal wise, but compression engaged the level is way too low. No gain make up is present on VT9 (which should be happening according to EMI docs
So what is this? a make up? an offset for the threshold?

3) distortion w/out compression. does this mean common mode rejection?

5) 6) Thresholds.
But what should these be set to? 0vu? +4? +10? -10????
Am I understanding correctly that the Hold would be slamming the quiescent amplification forcing the signal to hit the threshold?

I'm struggling to understand what the unit should be doing, therefore struggling to know how to troubleshoot

Am I alone?

 

[late]

LL1540 is compatible with 10k:10k configuration? Just need use 12k resistors.

Like here is suggested connections:
http://www.lundahl.se/pdf/1540.pdf

jblebre: I also would like to know more about that calibration procedure.

 

[jplebre]

the document you have states that each primary is 610 and each secondary is 800ohms
Not sure this would do if you are going for 10k:10k input for 1:1 gain i/p - o/p solution

 

[jplebre]

Should the nominal +10vDC (near R115*/R63, "live" end of hold pot) stay put?
Looking at the schematic, seems like it should remain +10vDC regardless of the position of the wiper for hold control, but then again there is some sort of feedback to the base of VT20 so I'm not sure.

Can someone confirm if the 10vdc should remain fixed or vary depending on the position of the hold pot?


EDIT: following Fester's TG fix, there's an extra cut that needs to be done. The trimmer resistor side "1" goes to the 270ohm resistor. This needs to be cut as well.
I can now measure a fixed 9.7v ish on the hold circuit, regardless where the wiper is. The wiper now does it's thing correctly.

The CV voltage seems to be fixed at about 5v. Shouldn't it follow the hold control?

Thanks

 

[imo]

I consider it a small miracle, but i have a somewhat working 500 series TG1. I agree that we should aggregate some standardized setup procedures. I have the right voltage as per Igor's notes. I've also got my meter going (used a 1mA meter) but beyond that I'm trying to decipher the original schematic with voltages(hard to see) to see if everything is in line. Right now the only thing jumping out to me as out of line is this: i have 13vDC on the top of the hold pot where it should be 10. The 500 series has both an input pot and a hold pot(as well as a hold trimmer). I've been messing with the trimmer/pot combo to see what effect it had, but still somewhat unsure.
Igor's instructions are pretty cloudy. He says to set unity gain with the hold control in the middle(doesn't mention anything about the 10k hold trimpot). and to move the hold control around until you get unity(with AOT1 trim). That seems pretty loose..Is this really the way you calibrate this unit?

Any setup comments, general comments about the circuit would be VERY welcome!

 

[jplebre]

if it's anything like the rack unit, the hold trimmer should be set to one of the sides. so it doesn't add parallell resistance.
You can use this trimmer to match for stereo operation.

Where are the documents for the 500 series? it might shed some light on the issues I'm having

 

[imo]

Here are where the files are: https://drive.google.com/folderview?id=0B9HeCk99hJfqYXRyTWppcjJIVm8&usp=sharing

So, I've been tearing this thing back apart, trying to properly calibrate it. In one of the many dismemberments, i have done something...Not exactly sure.
I am able to see a signal all the way to the input of C21/R65, which is the collector of the output transistors(4898 and 4910). the voltage is dropping to around .7vDC, which is down from 9-10(which is where it should be). The obvious sign is that the transistors are blown, right? I checked them with my transistor checker and they both check fine though. ?????
I was going to order the MJE2955TTU and MJE3055TTU, but these are only available in to-220. would this do with good heatsinks?
Everything was working previously, so i am assuming they must have sourced too much current and died?
I guess i'm looking for a confirmation before i desolder for the 4th time<g. Any ideas?
Thanks
Ian

I had them mounted originally with mica insulators underneath. There is a solid connection to the collector through the screws

 

[imo]

I have another question regarding the meter:
I was able to set up my 1mA meter via the diagram. I used a 2k resistor in series to the positive terminal of the meter, and then the 200r trimmer and 22r resistor. I was able to trim the meter to full scale deflection at 2.4mA. In circuit the meter is barely registering at any settings. My schematic has a 200r trimmer already installed with the 22r. Do I measure my test rig and then set the trimmer for the same resistance that i am getting at FSD?
Thanks
Ian

 

[jplebre]

My schematic has a 200r trimmer already installed with the 22r.

If it already has it, then that's it. You just need the total "right" resistance in parallel to the meter.
But I have to say it wasn't enough that. I need to try what igor said on another post "To adjust the metar, use 500R-1k 10turn pot in parallel."

 

[imo]

I figured it out. I had to temporarily strap a 2k onto the anode side of the diode that is across the meter. I also put a 200r trimmer across the meter in parallel with the 200+51r that is already there. I was able to get the right current at about 42r. Ill keep the trimmer in for now. Its a bit clunky, but it works
I'm trying to get an idea of the range of the hold pot. I am seeing from about 2v to 5.6v on the CV depending on the throw. Anyone see anything similar?

 

[jplebre]

.3v to 5.8v

However, I followed rev2 schematic for igor where the values are logaritmic. So my -10 would actually be much lower than a linear 10k pot.
I'm also having trouble with my signal (almost 20dB) so might not be right.

 

[jplebre]

IMO, thanks for the link. There were pics of the callibration procedure that really helped out!

I noticed Igor's quote on:
t_g, t_e are approx. 3.2V RMS, same amplitude (+/-1%)


Now, on my unit, they are at abou 3.3v RMS same amplitude, but they are out of phase.

Any ideas if this is normal and I am mis interpreting Igor's sentence. If it's not normal, ideas on how this could happen?

J

 

[baadc0de]

Great to know it's not that uncommon...!

I have for now put two philips BC capacitors (1000uF) in antiseries, which gives about 500uF of capacitance but blocks DC both ways. I'll let you know if it helps any.. the output transistors are NOS Motorola ones from electrochronic as are the rest of transistors.

The reason to put in another capacitor - a fake bipolar one - is because in the previous configuration it smoked not only R77 but also a winding on the output transformer (which now reads open). So this is more intended to protect the trafo. If anyone came to a solution to this, please let me know!

One interesting problem for the crowd here, maybe someone has any ideas..

Sometimes, when excessive low frequency information is in the input (such as from a preamp when recording a kick drum or direct bass guitar) and the gain reduction is set to a slow enough attack and quite a bit of makeup, the TG1 starts smoking R77. Could the output transistor pair be somehow to blame? I don't know enough about transistors, but say if one of them faults into being a straight line for a time?

It all works out if I power it off for some time. The output transistors are not heatsinked, maybe I should do that?

Thanks!

Ha! welcome! You're not alone. I've been mentioning this problem for quite a while but unfortunately it looks like a mystery

http://www.groupdiy.com/index.php?topic=37400.msg512287#msg512287
http://www.groupdiy.com/index.php?topic=48297.msg617261#msg617261

I'm pretty sure it's not a heat problem as I'm using heatsinks on the transistors. What transistors do you use?
What wattage is the 56ohms resistor? Do you have good heatsink on the PSU regulators?

In my case a 2watt resistor with a BIG heatsink on the regulators gives me a maximum of around 40C which I suppose it's OK.

Still though, I don't know what causes it.  :

Good luck and let me know. It's been my nightmare for more than two years now  ;D
It'll be good if other people can report too.

Turned out to be a nasty short in the output transistor wiring, that occured only under certain (thermal??) circumstances.

 

[imo]

I think i am having a similar issue with my unit. I am having occasional dropouts that seem to be the output transistors shutting down.
The 500 series is pretty tight for space. Still trying to find a heatsink solution. Right now i have both the transistors off the board with a couple of washers and a nut. That helps a bit and stopped them from shutting down so easily. This is what made me earlier think that i had blown them. I think they were sourcing too much current, and i am now seeing this occasionally when i turn up the hold control all the way up. Is anyone using the TO220 versions of these transistors? I am thinking in this design i could heatsink them better, but it seems that the TO3 is physically a better solution for current and heat.

 

[dirty1_1garry]

Hello TG's guys!

Could anyone of you post voltages on all T_* points of TG schematic with 0.775V input signal?!
Really need to compare!