Welcome, Guest. Please login or register.

April 04, 2020, 10:52:21 PM

Login with username, password and session length

Recent Posts

Author Topic: First Foray Into Amp Building - Please Help  (Read 13761 times)

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: First Foray Into Amp Building - Please Help
« Reply #30 on: February 06, 2015, 04:18:05 PM »
I notice ZT themselves are a bit coy about power;

"Packing 200 watts of power"
"200W Class A/B Power Amplifier"
"Peak Output: 120 dB at 1 meter"

...and don't actually say "RMS".

The "peak" SPL of 120dB wouldn't be all that impressive in a stage amp even if it were sustained.  The moment a sales blurb mentions "peak" you should get suspicious.

There is an old saying about speaker boxes dating from the '50's - "There ain't no substitute for cubic feet".  There is a small industry devoted to trying to convince people that you can get huge sound, bass in particular, from a matchbox.  Well there are good physical reasons to do with the nature of air why that isn't true, and what you are being sold is an illusion.

"Science notwithstanding..." - no Michael Ross of Guitar Player Magazine, science rules okay?

"Pure analog front-end"

As opposed to what?  An analogue front end that has been sleeping around?   8|

It may be a fine little workhorse amp, but it is being let down by being way oversold.

{yeah, yeah, I know, I keep getting told that I evaluate marketing statements that were never intended to be evaluated.}
If you say theory and practice don't agree you haven't applied enough theory.

nipperiodic

  • Regular
  • **
  • Posts: 19
  • Chip Points: 0
    • View Profile
Re: First Foray Into Amp Building - Please Help
« Reply #31 on: February 07, 2015, 03:50:08 PM »
Well, Mr. Fahey, I'll take you up on your offer. I think I've already zeroed in on the most readily available and best bang for your buck, but I'd still like to hear opinions from the pros. Anyways, some data sheets, in no particular order:

Eminence Patriot 820H http://www.eminence.com/pdf/820H.pdf
Eminence Alpha 8A http://www.eminence.com/pdf/Alpha_8A.pdf
Jensen Mod 8-20 http://www.jensentone.com/printpdf/45 *The Jensen links are a little flakey. I had to save the link as a PDF to view the files correctly.
Jensen C8R http://www.jensentone.com/printpdf/30
Jensen P8R http://www.jensentone.com/printpdf/14
Celestion Eight 15 http://celestion.com/productpdf.php?id=8
WGS G8C http://wgs4.com/g8c
Weber Speakers (various 8" clones?) https://taweber.powweb.com/weber/ They have all kinds of variations, but no specs. They also offer reconeing of vintage speakers via their eBay store, if an 8" ever pops up. Maybe someone here knows some of the intricacies of their speakers?

They all look pretty similar spec-wise, although the Jensen's seem to be a little low in sensitivity relative to the others. Given its current price, my pick would be the Celestion Eight 15 ($29 shipped), but I welcome someone telling me why I should opt for something else.

nipperiodic

  • Regular
  • **
  • Posts: 19
  • Chip Points: 0
    • View Profile
Re: First Foray Into Amp Building - Please Help
« Reply #32 on: February 11, 2015, 06:23:51 PM »
Edit: Weird. At least on my computer, my pics seemed to keep this last page from loading correctly. I'll post links to the photos for now.

As I said, I need to get some pics of the cabinet up, so here are some blurry pics of the pieces still in their frames. Note that there is protective paper on the pieces which hides the grain of the bamboo.

http://imgur.com/ULqVVOL
http://imgur.com/NvNVSfH

All in all, pretty happy with how it turned out. I had a chance to dry fit the pieces, and everything lines up about as well as I would have managed with a saw and router. The only booboo is the front panels. I think some gremlins invaded my design software; they are about 1/16" short on one side. I think some creative gluing to the short end will make the mistake unnoticeable though.

nipperiodic

  • Regular
  • **
  • Posts: 19
  • Chip Points: 0
    • View Profile
Re: First Foray Into Amp Building - Please Help
« Reply #33 on: June 07, 2015, 12:47:26 AM »
Well, I'm a little bummed that no one checked in to see if I ever made any progress with this.

I did finally make some progress. I even have some play by play pictures. Unfortunately, the amp doesn't seem to work, so I need some (explicit) help figuring out what's wrong. I imagine it's something simple that I'm overlooking, but who knows.

When I plug the amp in, nothing explodes or gets hot, but the LED fails to light up. There is absolutely no signal being put out to the speaker.

The only intentional modification I made was Roly's suggestion of buffing up the capacitor's to 2200uF/16V (to replace the 470uF) and the 100uF/16V (to replace the 47uF). The only other peculiarity is I have the speaker connected via alligator clips since I don't currently have a cabinet to plug into. Probably not ideal, but it's what I've got. Speaking of which, what are the little crimp connectors called that you use to connect speaker wires to the speaker terminals?

So if someone can explain what I need to do to troubleshoot, I'd appreciate it. Pictures to follow.

nipperiodic

  • Regular
  • **
  • Posts: 19
  • Chip Points: 0
    • View Profile
Re: First Foray Into Amp Building - Please Help
« Reply #34 on: June 07, 2015, 01:34:37 AM »
I thought I did a pretty good job with this (I was even a little proud of my work), so it's definitely frustrating that the amp isn't working. Anyways, below are the pictures of the work in progress. Hopefully the pictures don't break my thread again.

Broke the tracks.



Added the jumpers.



Added the op-amp sockets.



Added the resistors and diodes.



Film caps.



Electrolytics.



The backside.



Op-amps installed.



All the pots, switches, and jacks connected.




Enzo

  • Legendary
  • ******
  • Posts: 1903
  • Chip Points: 201
    • View Profile
Re: First Foray Into Amp Building - Please Help
« Reply #35 on: June 07, 2015, 02:00:22 AM »
Well, it is kinda on you to present your results rather than wait to be asked.

Without reading through three pages of an old thread, I am just looking at the previous couple posts.  8" guitar speakers are 8" guitar speakers.  other than to report if one brand blows up a lot, chosing one is always a matter of taste.  My favorite one may not be your favorite, and vice versa.

The little flat blades on the speakers, and the female crimps that fit onto them are called quick disconnects, and also by the brand name Faston.   They come in sizes by width, as well as the size wire designed to be crimped to.  Width is percent of an inch, so the 250 series is .250 inch or 1/4".  Smaller sizes are 205 and 187.  In my drawer I have them called just speaker terminals, but I THINK those are the 205 size, and the 187 being slightly too small.  Readily available from Mouser or similar.

So it sits there dead?  If nothing lights up and no sound is produced, start at the power supply.  Is there any voltage in the circuits?  verify you have mains voltage across the primary of the power transformer.  if that is not there, you have a problem in the power switch, the fuse/fuse-holder, the mains cord, or the mains wiring.

If you are using a batteru or bench supply or adaptor, then verify it is putting out the desired voltage.

nipperiodic

  • Regular
  • **
  • Posts: 19
  • Chip Points: 0
    • View Profile
Re: First Foray Into Amp Building - Please Help
« Reply #36 on: June 07, 2015, 03:21:43 AM »
 :lmao: I was only kidding about no one asking about the project.

Thanks for the info on the crimps.

I did forget to mention that I switched out the battery for a DC jack and am using a wall wart for power. Don't know how I forgot to mention that.

So the wall wart is rated for 12V and is putting out 12.3V according to my DMM. So I guess it's working.

I'll have a look at the rest tomorrow and try to figure out how to measure/check what you asked for.

Thanks for the help.

nipperiodic

  • Regular
  • **
  • Posts: 19
  • Chip Points: 0
    • View Profile
Re: First Foray Into Amp Building - Please Help
« Reply #37 on: June 07, 2015, 12:08:46 PM »
Whoa, it works.

Turns out I had the female power jack wired up (in)correctly. A while ago, I was playing with it on a breadboard before putting the amp together and had figured out the pin out with a DMM. When I went to solder it in, I didn't remember how I had it connected, so I followed a picture I found online. Who knew, the internet can be wrong.

Obviously, I haven't had much time to play with it yet. It gets surprisingly loud.

I think the 500K pot for the pre-amp gain is way too much for my needs. Turning it all the way up with the output volume maxed creates a rumbly/buzzy sound.

Switching the power amp gain switch to max (200X) gives a metal sound, while the other two settings (20X and ~52X gain) are just sort of clean and louder clean. Which I guess makes sense and is probably more useful than not.

The top boost/bright switch doesn't really seem to make much of a noticeable difference to my ear.

All in all, I think it sounds pretty good considering it's sitting unenclosed on a desktop connected to a speaker without a cabinet. Especially considering I didn't electrocute myself, start a fire, or blow up anything. There is quite a bit of extra room on the board, so I would still like to add some sort of tone control (because why not). I also would still like to add an extra diode to get asymmetrical clipping (not sure how to fit this in).

Fun project. Definitely learned a bit. Not sure if this really solves my goal of a super clean amp. Sort of interested in trying to put together an amp with the LM833 Roly mentioned earlier.

Anyways, I'm rambling. I need to get the speaker housed and find something to fit the amp into.

I'll say it again, because I can't say it enough. Thanks for all the help.