Some G9 questions

[Greg]

I have a question about the rotary switches...

I think the GAIN should be shorting, and the INPUT SELECT, LOW CUT, and PHASE non-shorting. Is this correct?

I'll be using a toggle for the mains.

Thanks.

 

[WJS]

I would agree that the input select, low cut, and phase should be non shorting but I believe that the gain could also be non shorting
the first few positions if connected would have the effect of creating a volume dip between each click. this is the result of the resistors being connected in parallel. for the last few stages it doesn't matter if they are shorting within the wiring outside of the switch. if you want volume dips then by all means go for it but i personaly would rather use non shorting.

 

[alk509]

[quote author="WJS"]the first few positions if connected would have the effect of creating a volume dip between each click.[/quote]

Use a non-shorting switch and the feedback circuit goes open between clicks (resistance goes to infinity) and you get a nasty short level boost (a "pop") between clicks.

Peace,
Al.

 

[Greg]

[quote author="alk509"][quote author="WJS"]the first few positions if connected would have the effect of creating a volume dip between each click.[/quote]

Use a non-shorting switch and the feedback circuit goes open between clicks (resistance goes to infinity) and you get a nasty short level boost (a "pop") between clicks.

Peace,
Al.[/quote]

That's what I was thinking. In other solid state circuits I've used shorting switches for gain. So I have one vote for shorting and one for non-shorting. ?!?

 

[gyraf]

Shorting or non-shorting dosen't matter much IMHO, as switch viper is permanently grounded, and individual switch positions are DC-free...

There will be some thumps when switching, but that's unavoidable in an ac-coupled amp with gain regulation at feedback-to-ground like this..

Jakob E.

 

[Greg]

Thanks Jakob :thumb:

I checked all the NA parts suppliers I'm familiar with, and none of them are stocking theTL783 in the TO-220 package. If anyone could help me source this in the US I'd appreciate it. Other than this component, I should be ready to give this project a go !!!

 

[alk509]

[quote author="Greg"]I checked all the NA parts suppliers I'm familiar with, and none of them are stocking theTL783 in the TO-220 package.[/quote]

Do a search.

Peace,
Al.

 

[Greg]

I already did and found alot of useful info about how it works in the G9 circuit, and how it can be used in phantom power supplies circuits, but I didn't see what I was looking for in regards to people not being able to source it.

 

[alk509]

[quote author="Greg"]I already did and found alot of useful info about how it works in the G9 circuit, and how it can be used in phantom power supplies circuits, but I didn't see what I was looking for in regards to people not being able to source it.[/quote]

Hmmm, weird... It took me less than two minutes to find three sources in the U.S. and one in Europe :?.

Peace,
Al.

 

[Greg]

Well I appreciate your help on the matter... Thanks Alk !!! :guinness: :sam: :green: :thumb:

 

[Greg]

Ok, so it's not at Digikey, Mouser, Allied, Newark, or Parts Express. I found a couple other small places but they had big min quantities. Can anyone suggest another supplier for the TL783?

 

[alk509]

Greg, you really need to use the search function of the fora...

Type TL783 in the search box and look at the fifth or sixth post from the top.

Alternatively, you can search for it on TI's website, and they have a list of distributors.

Peace,
Al.

 

[Greg]

I limited my search to "The Lab" only the first few times around, and that's why it didn't come up. I search this forum quite often. I think you should try and and be less condescending in your posts. You could've just said "check the Black Market" and that would have been a simple and great help to me... I rarely search there.

 

[louder]

alo
found a surplus store that has them.
gonna buy some.
best regards
pedro

 

[netcastle]

For those of you who may have read my previous posts on this thread (please don't think I am an idiot), I am led to believe that I have a case of parasitic oscillation plaguing my unit. To sumarize and add a question:

Past gain stage 8 on the left channel and 7 on the right channel I get inaudible oscillations. However, the instrument jack works fine at any gain stage. I've read and reread everything regarding this unit and I am at a loss. I've tried jsut about everything I could that has been suggested in realtion to this problem, including trying new tubes. I just don't know what I am doing. I built this thing with no real electronics experience and while it works and I love the sound I want it to be fully functional.

A relevant peice of info. On my first build I did not have the switching jack in so, obviously, I didn't get a useable signal. But I still got oscillations (extremely audible) when I turned the gain selector to 8 and 7 respectively. Now that it is rebuilt it is useable, but the oscillations persist, only now they have become ultrasonic at the 8 and 7 gain stages (as described).

Tim

 

[gyraf]

Hi Tim,

The oscillation occuring in around one of three or four of the DIY-G9's is still somewhat of a mystery. I don't have a prototype around anymore, so I can't get any further myself for the time being.

My latest suspicion is that it could have to do with electrostatic interaction between some of the large polyester capacitors - that is, that they may interact just by being too close together depending on physical size, dimensions, and mounting.

To check for this, dismount the polyesters one at a time and mount them off-board on a piece of wire. Maybe move them around a bit to check what that does.

BUT - whatever you do - TAKE CARE WITH THE HIGH VOLTAGES - specially if you're not used to work with electronics. There's high voltage on most of the polyester caps.

For eror-checking/repair of the G9, keep an extra voltmeter permanently attached to the 250V line so you have constant monitoring of voltage. ALWAYS remove the mains cable and wait for the HT voltage to go below 40V before doing anything. And don't trust the meter unless you've seen it count down from 250V (or around 245V in this case)

Jakob E.

 

[maxime]

hello,
I 'll be building 2 G9 soon. I'm at the ordering step. I was wondering on where to get nice G9 knobs, as the original don't seem so easy to get.
thanks
maxime

 

[Neeno]

A little bit off topic...

Does anyone know what's the ideal freq. response curve of the G9 using lundahls transformers ?

Neeeeeeeeeeeno :green:

 

[gyraf]

Maxime,

Newark-through-Farnell has the original Thomas&Betts Augat/Alcoswitch PKES-type knobs. Also Musikding.de seems to have some good ones..

Neeno,

It's good enough. Don't worry about it.

Jakob E.

 

[maxime]

thanks a lot gustav
have a nice day