New Build started. Guitar and amp (Now with sound clips!)

[strelok]

Got the large components populated today. PT and heaters wired up. Found most of the terminal strips I need. Just one short. Should be able to turn up one more hopefully.


[img2976]http://i.imgur.com/y9ovZqR.jpg[/img]

[img2976]http://i.imgur.com/bnPfxkj.jpg[/img]

[img2976]http://i.imgur.com/qNcvMHr.jpg[/img]

http://imgur.com/a/P8W5t

[strelok]

Got the amp up and running tonight. Sounding pretty good. Has a bit of a fuzzy sounding oscillation at low volumes so going to have to start probing to see where its coming from. There's a few things that ended up being closer together than I had originally planned so hopefully its just a wire that needs to be moved around. Just haaad to design my own layout First thing though will be to shield the grid wire coming out of the tone stack. Was running low on time and wanted to get it running before it got ridiculously late. Didn't have time to get the VVR hooked up but everything is installed and I wanted to test it without it first.

[img2976]http://i.imgur.com/pY3ffH5.jpg[/img]
[img2976]http://i.imgur.com/LDWThr6.jpg[/img]
[img2976]http://i.imgur.com/GuBSRSy.jpg[/img]
[img2976]http://i.imgur.com/hZXNDX4.jpg[/img]
[img2976]http://i.imgur.com/SrfRWga.jpg[/img]
[img2976]http://i.imgur.com/xyjb84n.jpg[/img]
[img2976]http://i.imgur.com/k2DtPvI.jpg[/img]
[img3968]http://i.imgur.com/2IAXOg6.jpg[/img]
[img2976]http://i.imgur.com/XUg2LZ9.jpg[/img]
[img2976]http://i.imgur.com/NZU67q1.jpg[/img]

[strelok]

Well more good news. Its not an oscillation after all. I suspected last night it might be the shitty speaker laying around the shop that's been used and abused quite a bit as a test unit. So I brought my 112 cab in today that has a Scumback G12M-65 in it and all the weird noises disappeared. Not only that it sounds fucking awesome. My layout turned out to be okay after all! Will get sound clips up in the near future.

[strelok]

Got the VVR hooked up today. Works great. Next thing will be to add a grid stopper to the PI and see if I can't get rid of some of that nasty distortion typical of this circuit at higher gain settings.

[rp]

Looks great, don't doubt it sounds good. I never got around to commenting that your layout looks perfect and should not be the cause of any trouble. As long as the grounds are right there's simply too few wires to interact. Report back on that PI grid resistor, if you hear anything. I might do it to mine.

I might swing that cathode bypass cap on the output to the other side of the resistor.

Hope you don't have to spend dad's retirement yelling at him to turn it down

[strelok]

Thanks! I didn't have much time to work on it tonight, but I did notice that the preamp voltages are rather low. Not so surprising as the overall B+ is much lower to accommodate the 6k6's. About 295v coming out of the VVR, 250v on the screens and roughly 190v to the preamp. The amp is rather brown, which I do like very much but it would be nice to get some more high's and clarity out if it too. So I'm thinking I'll just change the 22k resistor going to the preamp filter node to something like 1-5k as 230-250v is about where the preamp b+ sits in a regular deluxe. Of course, I'll always have the VVR to dial it back down too.

The opposite thing starts to happen from what I thought with the VVR. Past a certain point when you turn it down further the amp seems to clean up some. Probably because the first couple stages just can't amplify as much to drive the rest of it. Upping the preamp voltage will hopefully help a little with this as well.

I'll keep y'all posted on that and the grid resistor changes once I get to it tomorrow. I'll check on that cathode resistor and see how hot its getting, should only be dissipating a watt or two, and the cap sits a half inch or so above it with the resistor planted firmly on the chassis. I may still move it anyway.

Hope you don't have to spend dad's retirement yelling at him to turn it down

That would be great if it where the case. I miss hearing my dad play guitar. He was one of the main reasons I started. Besides I'm on the other end of the country, so I won't really have to worry about it.

[Ken Moon]

Very nice - I love me some true PTP

You really went the distance with making your own chassis, too!

You should be proud

[strelok]

Me too, I used to think it was a primitive and inferior way of building until I started my current job about a year and a half ago. We build tube stereo amps entirely PTP. Up until that point I had only really worked with PTP repairing tabletop radios that were generally a huge rats nest. Working this job has given me a chance to experience PTP done 'right'. It certainly has influenced how I think about how I build my own amps. I've really taken to PTP for prototyping and low volume building. Obviously a well designed PCB can't be beat for high volume production. But man after dealing with having to pull up eyelet boards on my SE express to get to this or that and make fairly minor changes, PTP makes a lot more sense in this context and if you don't like the circuit you can pull all or parts of it out and totally re-do things without much consequence.

Today (well I guess its technically yesterday at this point ) I installed a 332k grid stopper on the PI, seemed to help a bit with the nasty distortion and got a bit more usable range out of the volume knob. Went up to 500k to see if it would help more but didn't make too much difference and seemed to suck the life out of the amp a bit. Hard to explain exactly how, but I didn't like it. Maybe I'm just hearing things haha. Went back to 332k.

I kinda like the nasty overdrive though. With these old circuits I think you just gotta take them with there flaws to a certain extent. Start changing a bunch of things around and its not really a deluxe anymore. Granted I've already done considerable changes, but its still a deluxe circuit at heart for the most part. Besides I don't expect it will be used at that high of a gain level, its just supposed to be a nice classic rock amp. And the weird crazy compressed fuzzed out overdrive is there too if you want it. Its a nice novelty.

Played around with the preamp voltages a bit, ended up just sticking with the stock 22k dropping resistor. I like the lower voltages on the preamp better it turns out. Gives a more spongy feel to the overdrive.

We were out of 1k5's for the cathode resistors when I built the amp so I used 1k's. Swapped them for 1k5's today. Didn't make much of a difference but I figured it would be good to get the correct values in there. Also just tried to tidy things up a bit. A few cable ties here and there. Also installed shielded wire to the grid of V2a as the amp was picking up a little buzz. Wasn't too bad but I knew that's where it was coming from as it went away when the tone control was all the way down. Amp is now full on stealth mode with only a slight bit of hum/hiss with everything dimed, thanks to the metal film/oxide resistors.

Pretty much ready to call her good. The only thing is there is a low frequency tremolo sounding oscillation coming from, I think, the output section. I didn't notice it on the scope in any of the preamp stages if I remember right when I scoped it out, will have to double check. But its there on the output. Its not too bad, kinda actually like it. Gives it a swirly sound on the decays of low notes. Don't hear it on the A string or higher. Speaking of scopes I measured the power output as well. Around 6-7 watts clean and about 12-14 full tilt, for reference.

[img2976]http://i.imgur.com/pSA7ujd.jpg[/img]

[strelok]

Fixed the low frequency wobble in the power supply last week. Been kinda out of it since as my allergies have been kicking the crap out of me with the early end of winter. Somebody I worked with suggested the wobble was not an oscillation but a inter modulation from the power supply. Sure enough the frequency of the wobble changed with different notes played through the amp. He suggested putting a small cap before the VVR, all I could find was 33uf which might have been overkill but it cleaned up the issue and didn't really seem to impact the sound of the amp much. Once I get to feeling better I'll get some sound clips recorded and put them up.

Also looks like I will have to add caps in series with the input and v2a grid as I'm getting DC scratch on the guitar pots now.

[strelok]

Finally got around to recording some sound clips this weekend. They didn't come out sounding as good as I would have liked but they're decent. Probably could have used to back off on the gain a bit. Settings where tone control maxed, and both channels at up around 3-4. SM57 on the speaker and a AKG214 a few feet away for some room tone. Didn't really have time to play with the mic placement just set it up and went. Sorry for the sloppy playing.

[Structo]

Does that have a granite look to it?

[strelok]

Granite? I assume you're talking about the powder coat? Its actually more of a matte black, at least in person. I think the reflection from the flash is what gives it that look in the pictures. The finish is called wrinkletex if I remember right. So its got a bit of a texture to it.

Btw what do ya'll think of the sound clips?

[TUBEDUDE]

Sounds nice, I'm sure dad will be pleased. Even crunchy the volume is low? Good job!

The finish is appropriate, as wrinkle, and hammer tone finishes were on many chassis back in the day.

[strelok]

Yeah it sounds pretty good until you get the VVR down past about half. As you turn it down it seems to loose a bit of liveliness. Its not unbearably loud cranked up all the way. But it does make my ears feel fatigued after about half an hour or so. The recording was made with the VVR maxed fwiw.

As to the issue with the tubby/fuzzy distortion I came to the conclusion that its caused by blocking distortion on both V2A and V2B. Adding the grid stop on V2B (PI) helped but didn't get rid of it completely.

I noticed that when different preamp tubes where put in V1 (12at7, 12au7 etc). The undesirable distortion still came on at the same spot on the volume knob; about 3/4 of the way up, despite the gain being much lower. So my conclusion is that its caused by the fact that the bright cap/tone control is no longer having much effect as the volume is cranked and so the relative amount of low freq. coming through is much higher. I decided to experiment with some RC values in series with the grid. I did various combinations of 332k and 221k resistors with 330pf, 1000pf, and also no cap and found I liked 332k with no cap the best. I may yet try a smaller value for the cap, 100pf or so just to see if that will help the brightness issue when the volume is dimed.

Also I learned that if you add a cap in series with the input (to eleminate DC scratch when the VVR is low) its important to move the 1meg grid leak in between the cap and grid. Otherwise the grid has no DC reference to ground and the amp will start to cut out at lower settings on the VVR.