12ax7 noise.. which side is best?

[guitarmike2107]

Thanks for the book download that a good one.

I managed to get the hiss reduced, I did two things, one was increase the plate resistor on the input parallel triodes from 68k to 100k for a little more drive. this would not have effected anything hiss wise that I was having problems with.

The other thing I did was tie the three pins of the un-used triode together and connected those to the chassis. the hiss is now acceptable .. or what I would expect.

I do now have a very very faint tick sound. probably related to my linking the three pins together.. think I am going to get my scope out.
EDIT: found ticking to be from power amp/powersupply.. here we go

Picture of the amp in progress below

[greekie]

Mike, where did you get that cool black perf board for the circuit?

Kind regards, Jake

[guitarmike2107]

Hi Jake

I sell it here: http://modulusamplification.com/-FR4...aspx?sid=12886

Not sure who else sells the pre punched stuff, but I am sure you could find it in the states too if thats where you are. though shipping to the states is pretty good for small items, just takes a bit longer.

cheers

Mike

[greekie]

I'm from Denmark, so it's perfect with a UK supplier! Thank you!

Cheers!

[Tonewood]

Excel Workbook for tube data

Merlin and Tubeswell kindly posted a link to it, on another forum if I remember correctly, although Merlin is not the author. Be patient it is a huge acrobat file, some 318 pages long and takes a while to load. Maybe you have read it already?
https://acrobat.com/#d=UjgTcfpvfqvboIiQLKn5rQ
Designing Vacuum Tube Amplifiers, Charles R. Couch 2009

The Excel Workbook that goes with this book is not currently (11/4/10) downloadable.
Anyone here have it and able to make it available here?

Thanks

[martin manning]

I'm interested in taking a look at this Excel workbook too... is there a site where it was supposed to be located? I can't seem to find any reference to the spreadsheet outside of the .pdf document.

[Tonewood]

I'm interested in taking a look at this Excel workbook too... is there a site where it was supposed to be located? I can't seem to find any reference to the spreadsheet outside of the .pdf document.

It is called :vac_tube_amp.XLS
and is supposed to be available here: Free File Hosting, mp3 file hosting, Host, Online Storage for Music, Videos, and Documents

looks like randyc is having problems with the sharing site: "Design of Vacuum Tube Amplifiers" Download - The Jazz Guitar Forum

[martin manning]

Thanks for posting the links. I kept digging and eventually found that site. I don't know why a forum like MEF couldn't have a place to post tools like the one above. They usually don't require more space than a photo, and could be very useful to many.

[tubeswell]

Hi Martin - can you post that spreadsheet here (if you managed to get it) please?

When I tried that link, it said it'd used up all its good graces.

[martin manning]

The download doesn't work for me either. I'm trying to contact the guy, but no response as yet.

[TheTinMan]

Excel Workbook

The link posted above just works <no it doesn't>, you just have to be patient. Please note that you have to wait 60 seconds before the download is available. Scroll down and look over to the right to find the timer and appropriate button in a grey box for the Excel workbook download. Whether you look at the ads during that time is your personal choice

Please note that Randy (the author) added the following when we communicated about the workbook:

A few words of caution: the spreadsheets are not protected so it's possible to inadvertently over-write some of the calculations. (My practice is to use blue text to indicate user entries.) Also, since the spreadsheets were devised for personal usage, no particular care was used to make them friendly to others.

Regarding the original topic, raising the gain of that first stage does have something to do with hearing less hiss. Assuming the noise level is constant, raising the signal level relative to the noise level will make the hiss less noticeable. I suspect this is why some claim that parallel triodes for the first gain stage makes an amp quieter but can't prove it.

Cheers,

Chip

P.S. I have the Excel file but cannot remember how I orignally got in touch with Randy Couch (the author). Given the legal notice at the start of the "book", I don't feel right about posting the Excel file without his permission.

[tubeswell]

Scroll down and look over to the right to find the timer and appropriate button in a grey box for the Excel workbook download.
Chip

Yep tried that - I just get a message saying its been downloaded the maximum amount of allowable times

(I guess if I aint quick, I must be that other thing)

[mooreamps]

Regarding the original topic, raising the gain of that first stage does have something to do with hearing less hiss. Assuming the noise level is constant, raising the signal level relative to the noise level will make the hiss less noticeable. I suspect this is why some claim that parallel triodes for the first gain stage makes an amp quieter but can't prove it.

I did. I wrote a mathematical proof that showed by dropping the cathode bias resistor in half drops the noise factor of a gain stage by approx. 3 dB. This occurs when you use a parallel gain stage instead of a single gain stage. You reduce the cathode resistor from 1.5K to 820 ohms. Adding the extra triode ; just by itself ; has nothing to do with it.

-g

[TheTinMan]

Gary - Thanks! So it's the shared cathode resistor, not the increased gain which reduces the noise level relative to the signal? That would apply to any pair of triodes which share a cathode resistor, not just the first stage. (sorry for stating the obvious - just has some interesting implications IMHO)

If that's the case, does a shared plate resistor also reduce noise?

Cheers,

Chip

[mooreamps]

Gary - Thanks! So it's the shared cathode resistor, not the increased gain which reduces the noise level relative to the signal? That would apply to any pair of triodes which share a cathode resistor, not just the first stage.

Yes, but it is the first gain stage that sets the noise floor of the amplifier. The following gain stages do contribute more, but at a decreasing proportion until you reach the Power Amp.

If that's the case, does a shared plate resistor also reduce noise?

Not as much as the bias resistor. But it is more than just the bias resistor. It is the bias resistor coupled with the value of the input input impedance times the value of the gain of the stage.

-g