Space Heater - simple tube preamp

[MichaelW]

Yes. The mullard is a new issue version and sounds great. I did have an order with a NOS tube seller that went south fast and took me weeks to get my $ back. After that I decided to stick with new issue tubes from legitimate vendors that have been around for years.

The old RCAs are Truly amazing but finding a “real” one for a reasonable price is next to impossible. And the difference is very incremental for what the cost is. I have a real RCA 7025 in my West amp from the 70’s and have pulled it and tried it in other amps and it makes anything it is in sound like perfection to my ears. But I have bought a couple “used” RCA 7025s and none of them have the same sound. I do notice that these TAD tubes, first time I’ve ever tried them, are very clean low noise but do seem to have a low end boost in their sound which is cool but seems strange because no other tube I’ve ever played does that. It also just might be the extra headroom from being lower gain tubes causing the boosted low end, I haven’t tried any other branded at7 or au7s. With that said though I’ve decided to run with the TAD at7 as the gain stage in my 1st Black eye build.

The bummer… is now I have all these tube I’m going to have to build more tube pedals… hehe.

One thing I love about Amperex preamp tubes is that they are "lush" sounding, very 3D. It's not always appropriate but I love it in my Revv D2.
I did find some used Amperex 12AU7's but they're not cheap. I think I'll live with the JJ in here for a while before dropping any more $$.

 

[vigilante398]

oh the horrors....reading what SH is doing with variuos tubes might change from connecting it to a 10 watt board to the 60 to have retro bass amp moments

I'm currently working on a partscaster P-bass with a built-in Space Heater for the onboard preamp. It's a neat circuit, especially for how simple it is.

 

[andare]

I'm currently working on a partscaster P-bass with a built-in Space Heater for the onboard preamp. It's a neat circuit, especially for how simple it is.

I will forgive an active P bass only because it has a tube in it and you made the circuit. Otherwise...sacrilege!
At least make sure it's sunburst with a tort pickguard and put Labella flats on it or the bass gods will smite thee.

 

[Deperduci]

then I won't be showing you my purple P with white guard black DR's and purp davies knobs

getting a SH in to a p-bass would almost make it a hollowbody hogging out that much wood....

 

[MichaelW]

I'm currently working on a partscaster P-bass with a built-in Space Heater for the onboard preamp. It's a neat circuit, especially for how simple it is.

A tube IN the bass?? I gotta see that......!

I noticed running the SH as the last pedal in my chain AFTER my modulation loop (which is a dedicated buffered loop) gives me some slight bit of whining noise. (Noticeable with the headphones on) Which is strange because the buffer loop pedal is true bypass output, only the internal loop is buffered.

Anyway, running it as the last pedal before the loop solves that, so that's where the pedal is staying for now. Hard to quantify what it actually does to the signal. I can "warm it up" a bit before it hits my digital interface by bringing up the gain a skootch on the SH. Or leave it around 9 O'clock for a very transparent signal conditioner. VERY COOL!

Now what would be totally awesome would be a more full fledged Space Heater tube preamp with more EQ control.
@vigilante398 I think you're working on some more comprehensive tube based DI?

 

[vigilante398]

I will forgive an active P bass only because it has a tube in it and you made the circuit. Otherwise...sacrilege!
At least make sure it's sunburst with a tort pickguard and put Labella flats on it or the bass gods will smite thee.

I mean it's going to have a bypass switch so passive is an option but it's going to be black with a black pickguard. It will have LaBella tapewounds though, so I've got that going. Never cared much for bursts or tort, but I love my carrots.

A tube IN the bass?? I gotta see that......!

I noticed running the SH as the last pedal in my chain AFTER my modulation loop (which is a dedicated buffered loop) gives me some slight bit of whining noise. (Noticeable with the headphones on) Which is strange because the buffer loop pedal is true bypass output, only the internal loop is buffered.

Anyway, running it as the last pedal before the loop solves that, so that's where the pedal is staying for now. Hard to quantify what it actually does to the signal. I can "warm it up" a bit before it hits my digital interface by bringing up the gain a skootch on the SH. Or leave it around 9 O'clock for a very transparent signal conditioner. VERY COOL!

Now what would be totally awesome would be a more full fledged Space Heater tube preamp with more EQ control.
@vigilante398 I think you're working on some more comprehensive tube based DI?

If you're looking for a Space Heater with an EQ, you're looking for Underground Accelerator, which does not have a DIY project as it has 5 pots and wouldn't be able to mount the same way I did this and the Black Eye.

I am working on a more feature-packed version of a D.I., and I have a tentative schematic of it drawn up, but I'm not happy enough with it to actually spin a prototype yet.

 

[vigilante398]

Oh and here are some progress pics of the Space Heater bass. I'm using a 9.6V RC car battery pack, which according to my math should last about 8 hours on a charge. Still waiting on the stuff I need to finish it up, but should be in the next week or so. It's more or less just a gimmick, but it's a pretty neat gimmick.

 

[Mentaltossflycoon]

Oh and here are some progress pics of the Space Heater bass. I'm using a 9.6V RC car battery pack, which according to my math should last about 8 hours on a charge. Still waiting on the stuff I need to finish it up, but should be in the next week or so. It's more or less just a gimmick, but it's a pretty neat gimmick.

View attachment 31801

View attachment 31802

If this is sacrilege, I don't want to be pious.

 

[Smrtokvitek]

Hi @vigilante398, I was looking at the layout you are using and I have a question about generally avoiding the feedback and oscillations in the tube circuits. Have you encountered this problem when designing your preamps? I have built a circuit similar to the Space Heater and have to be very careful where to put the input jack with respect to the components on the PCB. Making it really difficult to fit it into the 1590BB2 box. Is this the reason you use this type of PCB mounting ("standing" instead of a "flat" as usual in guitar effects)?

 

[fig]

Tube	Gain	Acceptable Substitutes
12AX7	100		5751	12AT7	12AY7
5751	70	12AX7		12AT7	12AY7
12AT7	60		5751		12AY7
12AY7	45		5751	12AT7		12AV7
12AV7	41				12AY7		12AU7
12AU7	19

I’ll leave this..not meant as a bible, just a limited snapshot reference.

 

[vigilante398]

Hi @vigilante398, I was looking at the layout you are using and I have a question about generally avoiding the feedback and oscillations in the tube circuits. Have you encountered this problem when designing your preamps? I have built a circuit similar to the Space Heater and have to be very careful where to put the input jack with respect to the components on the PCB. Making it really difficult to fit it into the 1590BB2 box. Is this the reason you use this type of PCB mounting ("standing" instead of a "flat" as usual in guitar effects)?

I have absolutely encountered these issues with high gain circuits (if you look around at the thread on the Black Eye you'll see the ongoing discussion), but lower gain circuits like Space Heater I haven't had any issues with, it doesn't seem very sensitive to layout. The vertical "standing" mounting method was actually done to make this easier to build for DIYers, I don't typically do that on my personal builds. This mounting eliminates the need for a right-angle mounted daughter board for the tube, which was the goal.

 

[Mike McLane]

I've seen references to the Space Heater "buffer board". Nathan has mentioned that he hasn't had issues with impedance or signal levels coming of his pedals into downstream devices. What does this refer to?

 

[MichaelW]

I've seen references to the Space Heater "buffer board". Nathan has mentioned that he hasn't had issues with impedance or signal levels coming of his pedals into downstream devices. What does this refer to?

I think it's a "conflation" between the BE issues and the SH. I don't know of anyone that's got any issues with their SH build squealing.

edit: I may be guilty of said conflation....

 

[vigilante398]

I've seen references to the Space Heater "buffer board". Nathan has mentioned that he hasn't had issues with impedance or signal levels coming of his pedals into downstream devices. What does this refer to?

That's an issue with Black Eye, not Space Heater. Space Heater is a low gain design and does not having any issues requiring a buffer up front.

 

[Mike McLane]

Is Space Heater designed to yield a FLAT response curve so it renders a "faithful" signal of what's coming into it?

 

[Caldo71]

I was used to being able to poke my fingers inside pedals when they were powered up and handle unboxed PCBs that are powered up.

Hey @vigilante398 question: does “the danger go away” with poking around high voltage tube circuits the moment one unplugs the power supply? Or are dangerous voltages still sometimes retained for a period of time within capacitors or anything like that?

 

[vigilante398]

Hey @vigilante398 question: does “the danger go away” with poking around high voltage tube circuits the moment one unplugs the power supply? Or are dangerous voltages still sometimes retained for a period of time within capacitors or anything like that?

Capacitors in this one (and everything I design) drain more or less immediately, the board is safe to handle within seconds of power being removed.

 

[Caldo71]

Capacitors in this one (and everything I design) drain more or less immediately, the board is safe to handle within seconds of power being removed.

Rad thank you!!!

 

[Mentaltossflycoon]

I'm glad you asked this, I was assuming the zaps lingered for longer.

 

[vigilante398]

I'm glad you asked this, I was assuming the zaps lingered for longer.

And there is of course nothing wrong with waiting longer to be safe, as most amps still don't have automatic discharging built in and will hang on to high voltage long after power has been removed. I like the idea of automatically discharging the caps as I've been "bitten" way too many times even when an amp I was working on was powered off.

One of these days when I'm bored I'll plug a pedal into the oscilloscope so I can measure exactly how long it takes for the caps to discharge down to safe (<2V or so) levels, but a quick test with a stopwatch was difficult as it's right around one or two seconds.