DIY Guitar Amp Comments Thread

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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Fri Jul 08, 2011 3:43 pm

macrae11 wrote:
2. What is gain factor, like what is the scale it's on?


Gain or amplification factor is based on maximum voltage gain of the valve. It differs from model to model for example a 12AX7 has a gain factor of 100 whereas a 12AZ7 has a gain of 60 and a 12AU7 is <20. Wanna simply lower the gain on a stage in your amp, try substituting a 5751 (70) in place of a 12AX7. Keep in mind that these are maximum values and that it is certainly circuit dependent especially on the amount of cathode bypass.
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Fri Jul 08, 2011 3:45 pm

macrae11 wrote:
3. What effect does going through multiple tubes have on this whole scenario.



It's all relative and related. I try to deal with one stage at a time but effectively every stage affects the one downstream of it.
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Fri Jul 08, 2011 3:46 pm

macrae11 wrote:
4. Any RC effect in the power section?



Absolutely, I'll try to touch on that when I fill in the power amp section.
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Re: DIY Guitar Amp Comments Thread

Postby macrae11 » Sat Jul 09, 2011 5:53 am

Alain Benoit wrote:
macrae11 wrote:
3. What effect does going through multiple tubes have on this whole scenario.



It's all relative and related. I try to deal with one stage at a time but effectively every stage affects the one downstream of it.


Ok so my question here, is the effect additive? To put another way, is the next tube circuit just lopping off everything above 13k again, presumably making the low pass slope a bit steeper but not really affecting the tone, or does the cut off point actually get lower?
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Tue Jul 12, 2011 2:36 am

The next tube circuit could add an 8k boost for all you know right now, you'll have to stay tuned for the continuation of the preamp stages. Each stage has it's own qualities dependent on design. What is lost in one stage could be gained in another, pardon the pun.
The inherent interactions are what makes designing challenging, it's a giant balancing act. Prototyping and testing are a helpful tool.
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Tue Jul 12, 2011 2:42 am

Peter Drefahl of Drefahl Audio had this to say;

"Looks like a very sophisticated project, with all those proven-quality components and fine crafting :-)"

Considering his work and his reputation, this meant alot to me.
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Re: DIY Guitar Amp Comments Thread

Postby macrae11 » Tue Jul 12, 2011 7:44 am

Very cool. How did he find his way here?
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Tue Jul 12, 2011 12:09 pm

I was trying to source rather esoteric parts from him for the build, he was curious what for so I gave him the link.
He's a super cool chap.
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Re: DIY Guitar Amp Comments Thread

Postby RoadDog » Wed Jul 13, 2011 8:47 am

...that guy said chap...
A spider wanders aimlessly within the warmth of a shadow....
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Re: DIY Guitar Amp Comments Thread

Postby macrae11 » Sat Jul 30, 2011 3:57 pm

Very cool. Can't wait to see the logo etching.
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Sat Jul 30, 2011 4:15 pm

I immediately liked his treatment of the sketch I made, especially how he chose a font that won't drop the hole out of the 'R' without looking stencilized because the effect was carried over to the 'H'.
You see this will not be an etching like with a laser, water cutting cannot be depth controlled, so the logo will be missing or 'hollowed' from the plate.
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Re: DIY Guitar Amp Comments Thread

Postby Jef » Sat Jul 30, 2011 7:24 pm

Alain Benoit wrote:I immediately liked his treatment of the sketch I made, especially how he chose a font that won't drop the hole out of the 'R' without looking stencilized because the effect was carried over to the 'H'.
You see this will not be an etching like with a laser, water cutting cannot be depth controlled, so the logo will be missing or 'hollowed' from the plate.
That small sliver of metal holding the center of the R-hole :mrgreen: looks like it may be a weak spot and could be easily snapped off. Is it going to be open behind the lettering or will it have a backer plate behind it?
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Sat Jul 30, 2011 8:16 pm

Well it's 1/8" stainless so not very tender. Also yes, it is going to be bolted to the grill.
Also I'm hoping that the gap will be nearly 1/8" wide once the logo is to scale.
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Re: DIY Guitar Amp Comments Thread

Postby Mathieu Benoit » Wed Oct 05, 2011 10:00 am

Monday night, a guitar was plugged into it for the first time.
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Re: DIY Guitar Amp Comments Thread

Postby macrae11 » Wed Oct 05, 2011 10:39 am

Oooh! Details?
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Wed Oct 05, 2011 10:49 am

Well, so far the important things seem to be within nominal ranges. B+ checks out and drops predictably across the nodes. Bias is within a usable range, that was my biggest worry. You can lose a quad in less that three seconds if bias takes a dive. Hum and hiss seem reasonable for now. Clean channel appears to not have enough gain. Overdrive channel is breaking up in a way I don't like so that's where I'm gonna start my troubleshooting and weeks.
Stay toooooned.
Right now I need to step away from it and catch my breath.
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Re: DIY Guitar Amp Comments Thread

Postby macrae11 » Wed Oct 05, 2011 11:20 am

Would it be possible for you to explain these things in slightly more english like terms? :-D

eg, What is B+? I know what bias is, but what would cause it to be severely out of whack? quad? on the clean channel, I'm assuming you're just talking about volume, not breakup? Or are you talking about volume before breakup? Where does the clean channel start to break up? For the overdrive channel, what is it about the way it's breaking up that you don't like? What kind of guitar were you using? What speaker cabinet?
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Wed Oct 05, 2011 6:44 pm

macrae11 wrote:Would it be possible for you to explain these things in slightly more english like terms? :-D

eg, What is B+? I know what bias is, but what would cause it to be severely out of whack? quad? on the clean channel, I'm assuming you're just talking about volume, not breakup? Or are you talking about volume before breakup? Where does the clean channel start to break up? For the overdrive channel, what is it about the way it's breaking up that you don't like? What kind of guitar were you using? What speaker cabinet?


Back in the early days of thermionics, batteries powered the system. The 'A' battery was used for the filament supply, the 'B' for the high tension plate supply and 'C' for the negative bias voltage. Many guitar amps refer to the B+ supply simply as HT as in High Tension.

Any part of the bias supply chain not being up to par could cause it to be out of whack, in my case it was a dead spot in a trim pot from non-use and shelf life.

Quad referring to the quartet of kinkless tetrodes providing the 100 watts of class AB output power in the PA section.

On the clean channel a simple lack of gain affecting both overall volume and break up. I'll know where it starts to break up once I have corrected the gain issue. Likely something as silly as an error in magnitude on a resistor or something.

On the OD channel, the distortion was simply at times non-linear.

The guitar was a PRS stink ash.

The cab was a 1960A.

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Re: DIY Guitar Amp Comments Thread

Postby Jef » Wed Oct 05, 2011 9:29 pm

popcorn
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Re: DIY Guitar Amp Comments Thread

Postby Mathieu Benoit » Fri Oct 14, 2011 12:35 pm

Jef wrote:popcorn

You may or may not know it yet but you are about to deliver an important compenent of the amp.
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Re: DIY Guitar Amp Comments Thread

Postby Jef » Sat Oct 15, 2011 2:39 pm

Mathieu Benoit wrote:
Jef wrote:popcorn

You may or may not know it yet but you are about to deliver an important compenent of the amp.

Yes, the mission was disclosed to me this morning. 8-)
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Re: DIY Guitar Amp Comments Thread

Postby Mathieu Benoit » Sat Oct 15, 2011 6:13 pm

Image
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Re: DIY Guitar Amp Comments Thread

Postby Alain Benoit » Tue May 08, 2012 7:38 pm

This may serve as a teaser update.

Last September I finished the physical construction of the amplifier in question. Did a quick test and found the Clean channel to not be working.
Knowing that troubleshooting would be a whole new mode/chapter I decided to shelf it and clear my head for a bit.
A bit turned into a stretch as I got busy with work and other things.

I recently received a windfall of free time. Steps one through ten were to restore the workshop to a semblance of order.
With a clear head and a clean shop, I started investigating the issue with the amplifier over the weekend.
It soon became apparent that the fault was in the switching circuit, a relatively simple circuit I managed to narrow it down to a faulty opto-isolator.
Even though I tested all the components before installing them this one slipped by due to testing well but apparently being out of spec just enough to cause the fault.

I ordered a new one from a different manufacturer, due in Friday.
Will update.

On the good side besides the faulty LDR that slipped in there, the build seems to be faultless.
The overdrive channel is insane!! Usable gain range is .5 to 11, rare indeed. the MV serves as just that, pure volume w/o changing the tone.
At mid travel the gain gets into a nicely saturated crunch useful for anything from classic rock to metal chugging, going past this point one would expect muddiness but no, it simply gets thicker and richer in harmonics. Lead style playing in overdrive is clean and silky, dime the gain knob for really glassy arpeggios.
Clean channel is responsive, articulate, nicely compressed and reminiscent of a '59 Bassman in it's root tone just cleaner and really spanky.
The crunch mode of the clean channel can give you pure Angus at around 5 or 6.
(I am manually switching to the clean channel by simply shorting the resistive element of the affected isolator.)

IF I change anything in the design based on listening so far it would be to possibly lower the mid center by about an octave and maybe widen it some. Also I may attempt to try and increase the functional range of the depth control in the feedback loop.
I plan to add a NFB defeat switch.

More beta testing to follow.

Stay tuned..............................

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Re: DIY Guitar Amp Comments Thread

Postby macrae11 » Tue May 08, 2012 8:02 pm

Fun stuff. I'd love to do some beta testing/listening when I'm up in a couple of weeks.
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Re: DIY Guitar Amp Comments Thread

Postby Mathieu Benoit » Tue Sep 18, 2012 11:08 am

Hey Alain... I noticed that the preamp section isn't mentioned in your thread. Are you planning on making a seperate thread about that later, or did you omit due to some kind of trade secret?
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