Sub-mini tube and solid state hybrid amp

[newey]

Longo3-

trying to figure out how to post image.

Image Posting

[longo3]

thanks got them uploading to photobucket now

[longo3]

The burn mark on r13 makes me not want to plug it in again.

[dorrisant]

I will try to sit down tomorrow morning and label the schematic with the proper voltages so you can compare...
dorrisant

[longo3]

The power supply plugged into 110 read 24 volts there was 20 volts after r13 but the hot issue and no sound throughput got me.


I hooked up 1 9volt battery and no heat issue but still no sound.
I hooked up 2 9volts in series that read 18 volts and the lm1875 got to 90 degrees heat sink stayed cool on top, still no sound.
Led lit both ways.

[jcgss77]

May I suggest pulling that resistor out, and installing a new one? Could be it was bad to begin with. You never know.

[longo3]

i have some more of the resistors coming in mail(local radioshack is a joke). I ordered 3 more lm1875's also. there is no resistance on any pin of lm1875 maybe its bad too. does anybodys who got it to work tube glow? mine dont maybe whole kit got static blasted on way here.

[longo3]

new stuff got here today. new resistor in and nothing. new lm1875 and wala music. what a quest.

[dorrisant]

Maybe this will help...

Sorry I took so long to post.

[dorrisant]

I tried not to be redundant so my voltage labeling is minimal... but I did carry the voltages out to the hundredth so you could see the difference over R13... Your readings may be slightly different but it should be relatively close.
Let me know if this helps or if you need more info... sorry if you are frustrated but it might be one of those learning curves that are so important to getting where you want to be.

[longo3]

I Appreciate your time and effort I will print it ,test it, and post my results.
I ordered more lm1875s and more r13 resistors. I put the R13 in and still nothing.
I soldered one leg of the lm1875 at a time. Giving 5 min or so to cool in between.
I soldered it all together at once the first time. Now its off the hook. This amp rocks on a missmatched set of 1970's speakers. I have officially got the wife to come out of the bedroom to yell turn it down with my zoom 2 plus in front of it. I want the tube preamp now to get even more tube sound and they can be ordered with an extra tube to build my own with the other lm1875. thanks again.

[longo3]

It does get to 120 degrees or so after an hour and a half. got a 12 volt fan from computer .

[dorrisant]

Right on! Glad its working for you. 120• sounds about right. Good to know you persevered!

[longo3]

With a toggle switch to bypass R9 the amp has a mean distortion by itself.

[longo3]

I put a 250k pot wired to board instead of 50k tiny now i have a real volume control on outside of amp. no more toggle on r9 neat but dont want to push it.

[longo3]

I know its wrong but i built a tillman circuit minus the 2.2k resistor for more ouput and put it in front of the tube.
To my surprise it gave the amp a much more deep and full tone with the guitar.
The speakers are out of an old set of jensen towers that were no longer practical in there huge box with damaged corners. No better use for the line 6 box.

[dorrisant]

I have a new problem... I scrapped the pepper shredder for a different preamp...

www.diystompboxes.com/smfforum/index.php?topic=87343.20

The schematic is at the bottom of the page.
I cannot get any audio (actually very little) to the speaker... I'm using the K281 from above with the trainwreck with a fake phase inverted. Do the impedances not match? Is the 50k gain pot on the K281 too small? What am I missing?
Please feel free to ask any questions about anything I may be leaving out...
I am running the HT of the preamp on regulated +12V. If you read in the forum posted above you will see that it should work all the way down to +9v.
Any suggestions or incites?

[jcgss77]

I might be way off, but if you haven't already, measure the voltage of the output of the trainwreck, and see how much it is passing on. I think that the chipamps like to see 1 volt there. Don't know if this is what your problem is, but it seems like an easy place to start. I know that earlier in this thread I stated that a stompbox makes a good stompbox, but upon further research it seems that you would probably get better results running your preamp at a higher voltage. If you don't know that already, that is. As far as the value of the pot, experiment unless you like math

[dorrisant]

I checked... I'm injecting 1V p-p at the input. I get 0mV at pin 6 of tube 1...
Some might question lead dress, etc...
I'll post some pics soon.

[dorrisant]

Here are some pics...




I hope that worked...
I'll post this for convenience...

The only differences between my pre and the schematic on the diystompboxes site are 1) the input cap and 2) I replaced R7 with a 1M trimpot. I set it to 150K and left it alone. Once I get the pre running I will tweak it.
Maybe my tubes are bad... In the morning I will go through everything again.

[dorrisant]

Yes, Sozo mustard caps and Dale 1%s... A few extra dollars but I think it might be worth it. Tried a 30v 1a power supply... A little more signal but still not usable. Also noted that when I disconnected B+ from the tubes I got more signal... As if the tubes were killing the signal. I would like to try a higher B+ (200+), but I would have to build something... Maybe that's all it is... But how do the others get it to work on as little as 9v? Maybe I need a booster between preamp and power amp.

[dorrisant]

Update... I found a few things, 1)R13 and R14 were wrong on my board... Changed them to schematic values. 2) Input cap was bad from the factory... Found this when I jumped around it with a clip lead. Suddenly there was sound! I decided to try a higher HT. Tried a noisy old printer power supply... 27v output... Wow... The PS is noisy as hell but when you get past the pops and hum, this thing ROCKS! I will now order a +- 200v transformer and some caps and resistors. It was completely quiet with my original 12v supply (regulated and filtered) but no real over-the-edginess. Way more harmonics and creamy smooth tone at 27v but the noise has to go. I tried a couple of different filter caps but it is too much to overcome with the components on hand. I also changed the gain pot on the K281 from 50k to 1M. Now we are cooking... Or at least going in the right direction.
Waiting for parts... Will post sound clips/video link later.
Big smiles though!

[jcgss77]

Try one of these on that PSU, might filter out a lot of that noise:



I would recommend using filter #4.

[dorrisant]

Great info there jc... Will try to implement tonight!
If all goes well I may post a clip later this week.

[jcgss77]

Don't forget to post that clip!!!!!

[dorrisant]

I put together the #4 filter and it wasn't enough. I put another 240uf electrolytic at the end and that seemed to help even more. It is still noisy but I will leave it alone until I can get a 200+ v supply ordered and built. I installed a switch to allow high/low voltage HT... 27v or 12v...the supply to the tubes stays at 12v.
How does it sound... I will post clips later... Sounds sweet! I can't stop playing and turning knobs. The K281 sounds wonderful through a 12" Celestion Green Back... I then tried going straight from the preamp out into the effects return of my Axl Akita... Wow again... This allows the new preamp to control the power amp of the Akita... Man this kicked some but... The Akita always sounded great but the new pre sends it to another level. My friend Justin brought over 3 guitars: Fender USA Strat, John Mayer Stray, Les Paul Studio. He also tried my strat with active EMGs. Every instrument sounded very different and unique... Coolness. That is the best my strat has ever sounded. Period. Justin was completely amazed at the clean tone... It is thick.. Lots of bottom end but nowhere near mushy or flabby... Very tight. He played it clean through my strat on the 12v mode for 1 1/2 hours straight. I think he left at about 1:00 or so... Still talking about it... He definitely wants one. We also ran the pre directly into the line in on his Peavy Classic 30 head. We dimmed all the controls on the clean channel and let her rip... Awesome! We are gonna record some clips on Thursday. I didn't realize how versatile this preamp would be.
My face now hurts from smiling too much!

[jcgss77]

My face now hurts from smiling too much!

That is the beauty of being a builder. You always can cook up something new, and all your buddies start making bids and offers of trades for what they would have to remove an arm to finance from a brand name...great way to score new gear!

[dorrisant]

Sorry I haven't posted clips yet... My buddy Justin has been sick and we've all been kinda busy... Will get them up soon... When Justin brings the good mics over.