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About the schematic. What is the fat switch doing? Is it switching between 2 capacitors? I can't make out what it includes/isolates when selected.

NippleWrestler wrote: ↑Sun Jan 31, 2021 5:23 pm About the schematic. What is the fat switch doing? Is it switching between 2 capacitors? I can't make out what it includes/isolates when selected.

Yeah thats a good question. When S2=S3 its the High pass filter formed between the C2 and R5//Grid of 12AU7A

When S2=S1 an additional HPF is switched in. The impedance of C12//R3 changes from ~1k @ 50Hz to ~460R @ 3kHz, forming the voltage divider with R4. This has the effect of attenuating more of the lower frequencies, so this position sounds 'brighter'. There are simpler/better ways to do this... I've since learned ... but it works and sounds good.

Cdog wrote: ↑Sun Jan 31, 2021 6:33 pm

NippleWrestler wrote: ↑Sun Jan 31, 2021 5:23 pm About the schematic. What is the fat switch doing? Is it switching between 2 capacitors? I can't make out what it includes/isolates when selected.

Yeah thats a good question. When S2=S3 its the High pass filter formed between the C2 and R5//Grid of 12AU7A

When S2=S1 an additional HPF is switched in. The impedance of C12//R3 changes from ~1k @ 50Hz to ~460R @ 3kHz, forming the voltage divider with R4. This has the effect of attenuating more of the lower frequencies, so this position sounds 'brighter'. There are simpler/better ways to do this... I've since learned ... but it works and sounds good.

Yeah you could remove the switch, keep C2 where it is, then have an on/on switch to select between the 1m to GND and whatever other resistor value you wanted to GND to get another cut off frequency. 27n/1m = 6hz so it's not really affecting the audible spectrum from what I can see, I'm not sure what to factor in for the tube if anything though. A 27n/100k would cut off at 59hz which would remove flub I guess?

NippleWrestler wrote: ↑Sun Jan 31, 2021 7:18 pm

Cdog wrote: ↑Sun Jan 31, 2021 6:33 pm

NippleWrestler wrote: ↑Sun Jan 31, 2021 5:23 pm About the schematic. What is the fat switch doing? Is it switching between 2 capacitors? I can't make out what it includes/isolates when selected.

Yeah thats a good question. When S2=S3 its the High pass filter formed between the C2 and R5//Grid of 12AU7A

When S2=S1 an additional HPF is switched in. The impedance of C12//R3 changes from ~1k @ 50Hz to ~460R @ 3kHz, forming the voltage divider with R4. This has the effect of attenuating more of the lower frequencies, so this position sounds 'brighter'. There are simpler/better ways to do this... I've since learned ... but it works and sounds good.

Yeah you could remove the switch, keep C2 where it is, then have an on/on switch to select between the 1m to GND and whatever other resistor value you wanted to GND to get another cut off frequency. 27n/1m = 6hz so it's not really affecting the audible spectrum from what I can see, I'm not sure what to factor in for the tube if anything though. A 27n/100k would cut off at 59hz which would remove flub I guess?

Yes that's right there are other ways to do it. The 1M resistor is //with grid of the 12AU7A, so it's effectively a much lower resistance, to hard to simply say from a datasheet as it's run on a starved plate. The input filters were auditioned on a breadboard during the design process, proof of the pudding is always in the listenin

Presumably the 3m3/3m3 network at each opamp is a voltage divider to make a +6v input for pins 3 and 5 of the 072, and 12v going to pin 8? All the power lines are called VA but I'm wondering if a net called VA (at +12v) and another net called VREF for the +6v is the same thing.

Is the gain control working as a master volume control also (kinda)? I'm wondering about putting a voltage divider pot as a volume control after the 220uf (220uf in series with lug 3, lug 2 to speaker out, lug 1 to GND). Looks like any pot value isn't going to shave off any Hz since the 220uf is such a beast.

NippleWrestler wrote: ↑Sat Jan 30, 2021 3:22 pm Marshall Dsl1?

Interesting, thanks. A bit pricy and too dirty for my taste.

NippleWrestler wrote: ↑Sat Jan 30, 2021 3:22 pm Marshall Dsl1?

I try to avoid Marshalls, Fenders and Gibsons because I believe they are ripping as off..

Cdog wrote: ↑Sat Jan 30, 2021 3:46 pm

Well... if you want build one, this is a little project I designed a few moons ago, runs off 12VDC. Lots of verified builders from around the globe. Build doc link on youtube page.

This is really nice.. I forgot that once I was planning to build a 5w and I bought a board, then I became lazy and I bought an amp than someone else built. But this might be easy enough for a beginner in soldering. How much cost, roughly? Do you use an overdrive pedal on this video?

robthemac wrote: ↑Sat Jan 30, 2021 5:41 pm I loved my Marshall DSL-1R.

I have heard good things about Wangs 1W head, provided you have a good relationship with your insurers.

Yep, I had a Wang and it was great. I stupidly sold it because I bought the 5w. Also because I read these safety issues and got afraid that my home will go on fire..

MikeC wrote: ↑Sun Jan 31, 2021 4:01 pm

chrisz wrote: ↑Sat Jan 30, 2021 2:59 pm I'm looking for a 1W tube amp for home, bedroom volume use.
Anyone knows if there is something out there in the market?
I have a 5w using it at low wattage mode all the time and I feel its a bit same.

How about this?
1W Amp.jpg

Wow, this looks more than 1w.. Thanks, I guess DIY its a really nice option, I just need a bit patience and time.

NippleWrestler wrote: ↑Sun Jan 31, 2021 7:59 pm Presumably the 3m3/3m3 network at each opamp is a voltage divider to make a +6v input for pins 3 and 5 of the 072, and 12v going to pin 8? All the power lines are called VA but I'm wondering if a net called VA (at +12v) and another net called VREF for the +6v is the same thing.

Yes thats the bias network. VA is 12V.

Is the gain control working as a master volume control also (kinda)? I'm wondering about putting a voltage divider pot as a volume control after the 220uf (220uf in series with lug 3, lug 2 to speaker out, lug 1 to GND). Looks like any pot value isn't going to shave off any Hz since the 220uf is such a beast.

Yes. The ''gain' of the circuit is fixed. That 'gain' knob technically is a master volume, that basically slams the input of the LM386. Most of the overdrive will happen in the Poweramp. Have a look at the datasheet for the LM386

chrisz wrote: ↑Sun Jan 31, 2021 9:43 pm

Cdog wrote: ↑Sat Jan 30, 2021 3:46 pm

Well... if you want build one, this is a little project I designed a few moons ago, runs off 12VDC. Lots of verified builders from around the globe. Build doc link on youtube page.

This is really nice.. I forgot that once I was planning to build a 5w and I bought a board, then I became lazy and I bought an amp than someone else built. But this might be easy enough for a beginner in soldering. How much cost, roughly? Do you use an overdrive pedal on this video?

Thanks. As far as tube amp builds go its very simple and cheap. However, it might not be the best project for a complete beginner, really depends on you. The tube might be the most expensive part... Theres a parts list on the build doc, you could price it up. There was a klone overdrive and a rangemaster booster pedal used in the vid

I'm currently building that Rob Rubinette 1/3W tube amp, I have some 12AU7s for 1W, but need to order a 12BH7 for the 3W output.
Havent finished it yet though so not sure how it will sound.

chrisz wrote: ↑Sat Jan 30, 2021 2:59 pm I'm looking for a 1W tube amp for home, bedroom volume use.
Anyone knows if there is something out there in the market?
I have a 5w using it at low wattage mode all the time and I feel its a bit same.

"I feel it's a bit same"? .. what does this mean

Personally I would just get some kind of Boss Katana for anything at all "home use" ... nothing will sound better at low volumes

willow13 wrote: ↑Mon Feb 01, 2021 3:59 pm

chrisz wrote: ↑Sat Jan 30, 2021 2:59 pm I'm looking for a 1W tube amp for home, bedroom volume use.
Anyone knows if there is something out there in the market?
I have a 5w using it at low wattage mode all the time and I feel its a bit same.

"I feel it's a bit same"? .. what does this mean

Personally I would just get some kind of Boss Katana for anything at all "home use" ... nothing will sound better at low volumes

I have a Marshall Class 5 and I’m doing a trick to play it in low volume, plugging (halfway) the speaker into the headphones input, not sure if this is alright for the amp. Also I have a relatively big amp on my sofa..
This amp is good to just crank it up properly (impossible in the apartment). He is doing good just one thing (or two).
Yes, I see these Katanas are very popular.