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

[echotodd]

A picture of the guts.

 

[tommypiper]

...and I used some Carnhills I had laying around for the outputs.  ...

What model Carnhills did you use and how are they wired?  (sorry if I missed it earlier, I looked and didn't see a mention of it...)

Congrats! 

 

[echotodd]

They're VTB1148s wired 1:1.  Thanks!  I started it a long time ago and kind of got stuck on the options.  I'm still mulling over trying Ed's 1166 on the outputs but it sounds so good right now!  

 

[briomusic]

They're VTB1148s wired 1:1.  Thanks!  I started it a long time ago and kind of got stuck on the options.  I'm still mulling over trying Ed's 1166 on the outputs but it sounds so good right now!  

hi echo,
how do you wire the 1148 1:1? I didn't think it was possible with 1+1:1.7+1.7? according to the carnhil design guide it's never 0dB voltage gain....

also what are you using on the input? sowter?

cheers
briomusic

 

[echotodd]

I really need to drink the coffee BEFORE I post.  It's wired in series giving me +4 on the output.  I probably should trade them out for 600:600 ohm xmfrs, but it sounds so good.  The inputs are gardners 10k:10K.

 

[maxwall]

From the BOM

4   *       1/4W MF 1%       R205, R206, R207, R208  A1, A2 RELEASE        
10  *       1/4W MF 1%       AOT1, AOT2, AOT3, AOT4, AOT5, AOT6, AOT7, AOT8, AOT9, AOT10

Testproc:
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.



* = ?

A lot of requests on this , is there any indication what starting values should be for these  ?
seems this is a source of confusion with most builders. Looks like a good place for trimpots.

 

[crisotop]

have a look at festers notes (txt file, that came with the bom), it's all in there

 

[maxwall]

From mb_schem

AOT 1/4/6 ........not used
A.O.T. 8 ........Not used

From test procedure above in txt file.

AOT 8/10 ......10r


somewhat difficult to follow, seems test procedure is only directly related
info on this, the body of notes do not go into much detail about AOT values.
Its seems these values will be different will each individual unit or the
values would be published.

 

[crisotop]

pm'd just in case you missed the notes file

 

[maxwall]

yes, missed the notes file , thanks.

 

[wmtunate]

Here's what I used:

A.O.T. 8 = not used
A.O.T. 10 = 10R
aot1 = 330R
aot2 = not used
aot3 = 47k
aot4 = not used
aot5 = 3k
aot6 = not used
aot 7 = 3.3k
aot 9 = 68k

 

[warpie]

does anyone have issues with R77 (56 Ohm) resistor?
I'm using a 1Watt one and still runs hot.

thanks
michael

Sorry to bring this up again but I'm still having the same problem. Just wondering how hot is on other people's units (?)

thanks again,
michael

 

[echotodd]

Check to make sure you don't have any of the pins shorted on the output transistors.  That'll make it get hot in a hurry.

 

[echotodd]

Mark,

Did you ever find out more about the time constants?

Todd

 

[warpie]

Check to make sure you don't have any of the pins shorted on the output transistors.  That'll make it get hot in a hurry.

thanks for the advise echotodd but unfortunately that's not the problem. I start to believe that there's something wrong with the power supply, although I'm getting all the voltages right and the circuits seems to work fine...  :

 

[echotodd]

Thanks Mark,

I'm good with the release times.  It's the attack times I'm wondering about.  I suppose it's mostly nit-picking as it just sounds great, but I'd like to know.

warpie,

what are you using for output transistors?  Is it happening on one channel or both?

 

[warpie]

warpie,

what are you using for output transistors?  Is it happening on one channel or both?

On both channels yes.
I'm using MJE2955T and MJE3055T. I have omitted C3 and C4 though but I don't think that's the problem.
I'm using a JLM PSU (AC/DC)

 

[echotodd]

I using the JLM myself.  I wanted a dedicated source for my meter lamps so I'm sure you're fine there.  Why eliminate the caps at C3&C4? i'm not super great with my electronics know-how but, especially C4 provides an AC ground path for both the MJE2955.  My guess is that you have a stability issue that's causing MJE2955 to draw excessive current and looking at the schematic it seems like C4 is a pretty good place to start.

 

[warpie]

I using the JLM myself.  I wanted a dedicated source for my meter lamps so I'm sure you're fine there.  Why eliminate the caps at C3&C4? i'm not super great with my electronics know-how but, especially C4 provides an AC ground path for both the MJE2955.  My guess is that you have a stability issue that's causing MJE2955 to draw excessive current and looking at the schematic it seems like C4 is a pretty good place to start.

I don't have any spare caps at the moment. I only found a 200uF (50V) lytic and used it as C4 but the problem remains.
It runs hot even with a 2W resistor... :

I'll get some caps asap but I don't believe it will solve the problem...

 

[echotodd]

Once again, thanks Mark!  I think the addition of the Auto attack setting threw me and should probably just have come to the logical conclusion that nothing was really changed in the faster attack settings.  I don't really find myself using the slower settings anyway!

Warpie,  Sorry man, I wish I could be more help!  Have you checked D15 and D14?  What are you reading at T_OP?