Potato Cakes

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1620 on: March 17, 2019, 04:34:02 PM »
Ah, yeah the tolerance could be the reason. I haven't tried measuring the pots, actually. It's not really a big deal, honestly, as I use the very nice metering on my Dangerous AD+ Converter to match if I need to. Though I do actually have a bit of OCD, it's not so much this kind of thing that bothers me unbearably.

Why would it be that a test tone wouldn't work well with these, though? I'm not sure I follow that.

Not sure why that is with a test tone either, but I had a similar conversation with Mike regarding this a while back. I just know that if I use tone to match stereo linked FET Rack units I wind up going back and readjusting when putting something like a drum mix through them, and the positioning of the knobs end up being more closely matched when the program material is balanced.

Thanks!

Paul


Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1621 on: March 18, 2019, 01:08:08 PM »
So, I have a question.

I've built two FET Rack Rev D units and they were ordered not too long apart from each other, though not at the same time.

They both sound great and work correctly as far as I can tell. However, it seems like the taper on the output control is quite different between the two units. I have them set up so that 24 is exactly the same on both units, however if I were to set one to 18, the other would have to be set significantly higher to match the same output. If I go the opposite direction they also don't line up anymore.

Was there a taper change at some point?

The inputs seem to be a lot more closely matched, though I do have to tweak just a little to get exactly the same gain reduction with the same 1k test signal.

The pots have a 20% tolerance (industry standard) and for a single deck 250K pot that can amount to a pretty noticeable difference.  About a year ago we started matching them on stereo units. It's impossible to do that when units are ship separately.  If you want to email us, we can have you measure on of your pots and we can get a matched one for you.

Mike
Hairball Audio, LLC
DIY Parts and Kits
http://hairballaudio.com/shop

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Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1622 on: March 18, 2019, 01:09:57 PM »
Not sure why that is with a test tone either, but I had a similar conversation with Mike regarding this a while back. I just know that if I use tone to match stereo linked FET Rack units I wind up going back and readjusting when putting something like a drum mix through them, and the positioning of the knobs end up being more closely matched when the program material is balanced.

Thanks!

Paul

With a pure sine in the stereo set-up, these seems to be a bit of a phase shift issue that makes them hard to get in stereo.  With actual recorded material it's totally fine.

Mike
Hairball Audio, LLC
DIY Parts and Kits
http://hairballaudio.com/shop

Top secret stuff and upcoming releases:
http://facebook.com/hairballaudio
http://twitter.com/HairballAudio/

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1623 on: March 19, 2019, 02:56:41 PM »
Not sure if there is an answer short enough to give on this here without "read more books, study more," but I have 4 Hairball kits waiting to be unboxed and sort of want to understand more about the circuits before getting into the builds. In particular I'm stumped on what should probably be the most basic thing: identifying the coupling between stages....

Todd Sharp the guitar amp guru (my hero) here in Nashville where I live gave me a short stack of book recommendations last fall and I've been reading old tube/amateur radio texts for the better part of the past year (since after my Lola & Rev.  A initiation into DIY) but realize the 1176 circuit has more going on than I'll be able to fully grasp at first. Just want to get the big stuff....

In the tube stuff I've been reading it has driven home that coupling networks are for  connecting the output of one stage to the input of another and with RC coupling there's been a capacitor across the plate circuit.

When it comes to transistors (at least BJT's), my initial efforts at understanding have understood the base to be analogous to the cathode, emitter analogous to grid, and collector analogous to plate, so the collector would be the output unless I'm totally lost in space (and may be at any moment in time).

So on the Rev. D, I understand from the Orange Drop mod/sales page that C1, C7, C8 and C10 are the coupling capacitors, but when I look at the schematic I'm failing to see the connection from C7 to  collector ---- I see  it to the emitter of Q14, but am not seeing a connection to the V+ line (coupling caps involve low reactance to AC but blocking DC right?? Again, unless I'm lost in outer space), or the collector of anything.  Sort of the same dilemma with C8.

C10 actually makes sense. I can see that connected to collector and also the connection to V+. Last, C1 I can see the connection to Drain of the FET but am confused by where V+ goes on the schematic. I see it connecting to the collector of Q2 but am not tracing it back to Q1 the FET.

I may simply be in over my head so if there's not a short/simple answer to these questions would you have any recommendations for transistor based texts along the lines of the '50s/'60s tube books I've been reading???

Sean

scott2000

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1624 on: March 19, 2019, 05:18:22 PM »
I think the UA 1176 manual has a decent theory of operation section that may help with some questions regarding it if you haven't already read it....... maybe not.....

Interesting question. I'd like to hear more on this as well .....Surely there are some threads around here that discuss good resources??? IDK though......

edit....just saw this.....

https://groupdiy.com/index.php?topic=6329.0


I just Googled transistor theory groupdiy.....Sometimes I have a hard time locating stuff using the dedicated search here and searching google with groupdiy included usually helps......

good luck!

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1625 on: March 19, 2019, 06:17:41 PM »
Thanks. I just got to the 1176 manual from mnats' website (where he links it). I'll go ahead and have a read through the Theory Of Operation chapter.

Mike, if you have any advice on this (even really simple "read this or that book" kind of advice), I'd be forever grateful!!! Look forward to getting into the builds which I ordered last summer (I'm a little slow). I moved across town and have been unpacking boxes for the past 3 months straight but this spring I'll get started on another Lola and three more FET/Racks (all waiting in the shipping boxes temporarily stored in my guest room!). After the past 15 or 16 months it's become very clear I'm not doing any of this as a way to get better gear for cheaper, but that ultimately, I sincerely want to learn more than where and how to solder. It's become a mission (at 36; I feel so old to be starting)

I think the UA 1176 manual has a decent theory of operation section that may help with some questions regarding it if you haven't already read it....... maybe not.....

Interesting question. I'd like to hear more on this as well .....Surely there are some threads around here that discuss good resources??? IDK though......

edit....just saw this.....

https://groupdiy.com/index.php?topic=6329.0


I just Googled transistor theory groupdiy.....Sometimes I have a hard time locating stuff using the dedicated search here and searching google with groupdiy included usually helps......

good luck!

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1626 on: March 19, 2019, 06:26:59 PM »
Scanned your post, sorry short on time.  Sounds like you're assuming all of the transistor stages are common emitter stages, which are indeed the most common. However Q14 is set up as a common collector with the signal on the emitter.  This is most likely used to get a low impedance before the next stage. It has no gain.

C8 is on the wiper of the output pot to block DC before the signal inters the final line amp stage.

Input pot controls the level/volume to the signal amp (and GR amp) and the output pot is the level volume setter for the line amp stage.

Douglas Self has a great book called "Small Signal Audio Design".

Mike
Hairball Audio, LLC
DIY Parts and Kits
http://hairballaudio.com/shop

Top secret stuff and upcoming releases:
http://facebook.com/hairballaudio
http://twitter.com/HairballAudio/