Guitar Gear Forum

Project completed! Now it's time for











All pictures on http://www.ampspecs.com

Congrats!!! That's a find looking amp!!!!

awesome job man. looks incredible

@am_i_evil:
I know this a bit of an old thread but I though I would chime in.

I've built several SLO clones. You're biasing way too cold. Your test points are for two tubes so if you're running 6l6gc's then you should set the bias to 70ma per test point (i.e. you want each tube to draw 35ma so since the test points test two tubes you need to set it to 70ma)
If you're running the stock 5881's then bias at 50ma per test point.



(B)-----------(G) ----------(B) <Test points
70ma______ 0_________70ma

Crazynutz, thank you for info!

I haven't been on this forum for a while. From last time I fine tune my SLO, so now everything is ok , except week ago my normal channel died, but i think there was some bad connection to preamp tube, now it works again, bias is set normaly, and I also made few cosmetics adjustments.

Hi

I need some help with my clone... :? I'm struggling with this hum/buzz for a while now... I tried to fix it, but I think I make it worst...

Because I tried a lot of different stuff, there become some collateral damage...(tube socket broke...), and wiring is awful, but when I find the issue I will rewire it.

video buzz/hum
http://vid203.photobucket.com/albums/aa196/kusar/WP_20150516_001.mp4

Current status: laud hum on buzz?

- Hum changing tone if I turn the knobs on the tone stack (bass/middle/treble...)
- Hum is present on the all channels, but it becomes quieter on crunch/clean channel


info on wiring
- I use Center Tap from transformer instead of two 100Ohm resistors.
- Effect loop jack isolated from chassis,
- Outputs isolated from chassis
- channels jack isolated from chassis, if connect to chassis the db102 is fried..
-

I grounded all wires from transformer on one point on the chassis. I tried different one but there is no difference.


pictures

It's your effects loop isolated? It doesn't look like it on the pics.

It should be grounded at the send point on the pcb.

Actually I just read the loop is fine.

Ungrounded the switching ct and then ground the foot switch to the chassis.

The ct is why the db101 is burning up

sure is pretty, but it ever came across my bench id spend 5 minutes admiring it, and then want to punch you for using the same color wiring everywhere

am_i_evil wrote:

I would use a separate loop for the preamp tubes. Split into two separate chains before the 6.3V heaters hit the first power amp tube. Routing underneath the preamp board at the P/I might induce some hum.

am_i_evil wrote:

The transformer primaries are tied to the heater wires which can produce some hum. I would run them so they are flat on the chassis all the way to the power tube anodes.

Also this may not be the issue, but I would pick a choke with end bells instead of an open choke..

Thanks,

I cut and isolate CT(3A). I also add two 100Ohm resistors back. Situation is still the same, noise is still present.

I'm not sure about the PT wiring. I connected both black wires(400m and 7,5A) to the same ground point on the chassis?

am_i_evil wrote:Thanks,

I cut and isolate CT(3A). I also add two 100Ohm resistors back. Situation is still the same, noise is still present.

I'm not sure about the PT wiring. I connected both black wires(400m and 7,5A) to the same ground point on the chassis?

In the SLO there are two main ground points (excluding IEC Earth)

Use a bolt near the PSU PCB as you already have connect the following here
Ground from PSU PCB
Ground from Preamp PCB
Power valve grounds (Pin1)
Output jacks (isolate using washers or plastic jacks)
PT Centre taps (You can unground the 7.5A filament CT as you are using a faux CT with the 2x 100r resistors that should join with the power valve ground bus

All pot casings should be grounded to the chassis

then do the following if you have them
Slave out Jack & pot grounded to chassis
Effects loop jacks isolated from the chassis grounded at the send side on the preamp PCB
Input jack should be isolated from the chassis and grounded on the ground bus for the pots
Foot switch jack should be grounded to the chassis
make sure all switches have continuity to ground.

With the above arrangement even with the open choke (all my builds have them) your build should be virtually silent.

You can also try elevating the heater supply if you think it's heater noise.

Hi,

I made everything what toe knee wrote, and I have to say it is better. The biggest difference was when I connect footswitch to chassis. There is still some noise present, but now at least it is playable

I will also try to use CT(3A) from PT instead faux ct with 2x100 Ohm restistor.

The next step would be to twist heater wires...


Thanks for help!

You should be fine with the parallel runs between the sockets but definitely twist going up to the power valves and between the pre and power.

I'm glad you are making progress

Hello,

I compared CT(3A) from PT vs faux ct with 2x100 Ohm resistors. And 2x 100 Ohm option is a little bit quieter. I also twist wires to preamp tubes, and I also think there is some progress here. I also try to change 1 tube on each position, but there was no success, amp has more noise with new tube...

I believe there is still too much noise for this amp... I think we solve ground issues, and this one I think it is a hiss... It is constant sssss in amp... if I turn volume up it gets louder and if I turn it down the amp is quiet. Hiss also increases with gain control, so I think the problem is in the preamp and not in the power amp. Any idea what do do? I also read, that hiss can be caused because "bad or to week" resistors which are connected to the first pin of the each preamp tube.

Hello,

This is current state of the amp. Is this to much noise for slo, or this is normal?

http://vid203.photobucket.com/albums/aa ... 02_003.mp4

I watched your video. Seems like normal hiss, but its 100% relative to actually playing volume. Basically noise floor vs signal amplitude. At low gain settings there can be some hiss when cranking the master, and it will only seem loud until you actually strike a chord. But with High Gain, its much more difficult to mitigate. Sometimes getting a super low noise input resistor and plate resistors can help reduce that hiss. I don't think this recording does justice to the actual sound.

I never liked the SLO grounding scheme, but I guess it works since many SLOs are very quiet.

The noise I can hear in your video clip is either resistor or tube noise. The most susceptible resistors are the input grids, cathodes, and plates. Then any large resistor early in the preamp.

Did you use decent metal film resistors at the input of the amp? I would use CF60's or even RN65's at the input. The CF60's have a 500V tolerance so they can be used everywhere. Metal oxide can be better than carbon, but cheaper ones tend to be as worse as carbon. Also, the input grid resistor in the SLO can be reduced to like 10k, which can have a profound effect on the noise heard at high gains. Also the P/I stages 1M resistors should be metal film.

A peavey style noise gate might help

http://smg.photobucket.com/user/Cool_Da ... 7345b3.jpg

[quote="Zozobra"]A peavey style noise gate might help

http://s81.photobucket.com/user/merlinb ... h.jpg.html
http://www.ax84.com/bbs/dm.php?thread=377070

Hello,

I was so unhappy with my amp that I decided to start build from beginning. Reason for that is because debugging and modifying caused such a mess in my amp that i couldn't watch it...

And after I finish it once again, I believe it sounds better than before, but there is some new issue, I think it is hum. I tried to play it but it is so annoying that is not playable...

- I carefully read all instruction on this forum about ground loops and try to avoid them...
- All input jack are isolated from chassis
- I tried to make build clean as possible
- I also add choke on the outside of the chassis
- I change resistors on preamp tubes to metal film 2w resistors to avoid hiss
- Neutral green is grounded at chassis by itself
- heater CT (2 100 ohm resistors) grounded at power board.
- Power board, OT, CT(400m) are grounded together at pt lug.
- I cut all wires from PT that I don't need.
- I make all connection wires short as possible
- I also change the preamp tubes.

I really don't know what else to do..., but overall ...It sounds good,if only I could make it quitter...

Video:
https://youtu.be/oftI3Bt4vk8

Update:

- I connected two 100 ohms resistors to different pt lug, it doesn't make any difference, so I put it back to power board.

I connected output jack directly to chassis and cut wire to pt lug(I think there is a little difference, but it is worst) so I isolated it from chassis and connect back to pt lug.

- I connected footswitch jack directly to chassis without isolation and this "brum" dissapears, but now is doing SSsssSSSSssss. Before I've done this it was "broum" on all channels and it was unacceptable. Now clean is ok, crunch is a little bit worst and overdrive is not ok. This ssSSSSss increases with gain and volume.

Any idea what else to do?

I know you're in the middle of troubleshooting, but just wanted to stop in and say the amp looks awesome! I may have to do one of these. I had an SLO with all the factory mods on it years ago. It was a great amp, but ended up sticking with an early '82 JCM 800 w/6550's and boosting the front end with a Tube Screamer. That said, I'd really like to try one of these out again as it's been years but they've gotten so expensive.

Hello
I apologise for late reply! I found the issue in my amp and fix it I mounted footswitch jack directly to chassis, and hum almost disappeared, after that I add chassis into the head isolated with aluminium. The amp is now really quiet, more quiet than my EVH 50W head.

I also made two modifications:
- fotswitchable solo boost
one alpha 250k "solo volume" pot and relay, which switches from master volume to solo volume. (it works great, without any pops, and the tone stays is the same)

- Footswitchable fx-loop
I add one relay which disconnect fx-loop.

I also extended footswitch, now it has three switches (channel/solo/fx-loop), and is connected to 9V(this is for relays).

I will also make video and share it with you guys!

Thank for all the help!

Uros