hi there..
i want to share my latest project with you..
it´s a two independent channel tube preamp. The OD channel it´s a dual rectifier preamp, with a switch between the bypass caps and ground for two states of gain...
The clean channel is gain stage 1 bypassed to gain stage 4, and both bypass caps not connected to ground..the clean channel gain voicing is made at the gain pot..point to point to suit taste...
use a dpdt switch to change channel and disconnect ground from bypass caps..
the tonestack board is pretty standard, choose your preferred values there
The power section is based on real mctube idea....two transformers (one 120-12 and 6-120 in america.. i use 220-12/12-220 in Chile)..
a separate box contains the transformers and the rectifying board...the filtering and regulation board goes inside the main box...power is transmitted trough a 3 wire power cable (340VDC, 17VDC, and ground)
Missing the 5th stage? well.. it´s a MOSFET BUFFER!!!!!! hehehe...well, if RG sez that they are good..who am i to disagree???
I did the layout and boards by hand, with a graphic editing SW...so if you see an error please point it out!!!
I´m currently building it and will post the results as soon it works...
the layouts:
(http://diynoise.googlepages.com/layouts.gif)
the boards:
(http://diynoise.googlepages.com/PCBs.gif)
Any questions and observations are welcome!!!
Looks like you've put alot of work into this project - can't wait to see the finished article.
Got a schematic?
8)
That looks great.
A high voltage tube project is a wonderful thing to share.
I like the separate boards.
If I where to build it I think I would go with a large power transformer and use the MAINs AC.
What the advantage of the back to back transformers over using MAINs AC?
I've looked at the Real McTube before but can't see the advantage now. I'll have another peek.
A schematic would really help us check your layout.
Another question...
Are you planning on soldering the tube pins directly to the PCB?
What are the large yellowish rectangles on the main board?
Is this going to be in a "pedal" chassis?
Thanks for sharing.
Quote from: Pushtone on November 09, 2007, 05:27:14 PM
If I where to build it I think I would go with a large power transformer and use the MAINs AC.
What the advantage of the back to back transformers over using MAINs AC?
I've looked at the Real McTube before but can't see the advantage now. I'll have another peek.
The back-to-back transformers isolate the tube HT supply from the mains power supply. Simply rectifying the mains AC is an incredibly dangerous thing to do!
For sure, nobody should to rectify mains (mains in my area are only specified to have spikes less than 2000 VAC ! Hopefully, they are brief !).
The advantage of two transformers back-to-back is that they are cheap (re-cycled?), not expensive amp transformers (eg Hammonds). Of course, if someone builds cheap low-current, high voltage transformers, they would be great for such a project. How much is the transformer in the Epi Junior, I wonder ?
cheers
Looks good Daniel. I would make the traces a bit larger though if you can. Either that or use heavy copper for PCB. 2 oz or more.
Yes, the back to back transformer thing is cheap and also that you can get 12v from the first transformer and 100+ ish volts from the second, clever!
ALthough Weber and Hoffman have inexpensive transformers for pre amps...
John
Quote from: Pushtone on November 09, 2007, 05:27:14 PM
That looks great.
A high voltage tube project is a wonderful thing to share.
I like the separate boards.
If I where to build it I think I would go with a large power transformer and use the MAINs AC.
What the advantage of the back to back transformers over using MAINs AC?
I've looked at the Real McTube before but can't see the advantage now. I'll have another peek.
A schematic would really help us check your layout.
Another question...
Are you planning on soldering the tube pins directly to the PCB?
What are the large yellowish rectangles on the main board?
Is this going to be in a "pedal" chassis?
Thanks for sharing.
Looks like the big yellow things are relays..................
Aharon
Whithout schematic, it's difficult to find mistakes on yours PCBs
sorry for the lack of an schematic..i did it with livewire but when i was finishing an error ocurred and the file got corrupted..damn!!
Yes, the yellow things are relays..5 volts that´s why there´s a voltage divider on the power board (the two unmarked resistors)
since we have 220Volts main here, a back to back pair of 12v transformers will give me around 320 volts DC rectified.. not bad..
yes it will be a pedal..
no, i wont solder the tube pins..i will use sockets..
i noticed some traces were thin..but i will use solder to make them thicker where high voltage pass...maybe in a new version i´ll make them thicker..
i´m gonna make the schematic, so i´ll post it when it´s ready..
i´m so proud of this, i hope it works..
i finished the power supply part..i got 290 volts DC will this voiltage be enough?? the rectifier preamp sez 340 volts..so..do i have to change some parts????
the power supply:
(http://diynoise.googlepages.com/PS.gif)
the preamp:
(http://diynoise.googlepages.com/schem.gif)
imho the switching is pretty clever.....
any comment is VERY appreciated!!
Looks like a nice project so far! :icon_cool:
one thing i left out.. sorry.. the mosfet can be a IRF822 or alike...
I did the layout by hand following my instincts..
Can someone help me by detecting risks of oscilations, noise??
i mean, are the B+, signal and ground traces placed correctly so the build won´t have any layout-related issues?
Have you add mods on the original rectifier schematic?
hmm only the switching part is a mod..
also..the mosfet buffer instead of a triode buffer, and the tonestack is scaled down by 10 (like dr boogie´s) to lower output impedance..
i´m thinking about lowering the first coupling cap, too.. but all the rest of the parts are the same..
C14 is not on the original schematics
There is a 5nF caps but to ground probably next to tube for decoupling supply
i´ve found two versions of that cap (both of them 5nF..i´ll use 2.2nF) one goes from B+ to ground, and other from B+ to plate in parellel with the resistor.. i was confused so i studied what are they for and other preamp schems, and decided that the correct position was in parallel with the resistor...as low pass filter avoiding oscilations..
Look at this recent schematic I've found:
http://www.neufgiga.com/index.php?m=c9ae77e8&a=7d397569&share=LNK8998473c92cb4c44d
hey that´s great.. but looks asa newer version...fets instead of LDR´s for some switching...
and yes, there´s no cap on the third stage
In my version I have used 4.7nF cap to ground but I have had squealing on this stage.
For canceling it, I have had a 10pF ceramic cap between plate and grid of this stage
you could tried that 4.7nF in parallel w/the plate resistor, maybe that would stopped the oscilations..
That will reduce highs and mids on this stage
maybe thát´s the point?
Try it and you will see that you will have a sound whith bass only .
IMO it's awful.
THE BOGNER ECSTASY OD channel has a 1nF cap on that point...
i wouldn´t say that´s an ugly sounding amp ...
anyway, if i don´t like it.. i´ll put it out...
Putting a .0047 uf cap across a plate resistor will only cut out some very high frequencies.
Mesa, Soldano, bogner etc etc all do this. Mainly this is for citting out the fizzy distortion and possible oscillations.
Maybe a 4uf cap is what you are thinking stephanovitch?
John
Relays are very nice for switching, but often they need special measures to get rid of the spikes and pops they produce. Taking a look at your schem:
I wouldn't leave the cathode caps floating when they're OFF. It will cause a huge POP when you connect the - terminal to gnd, especially at higher gain settings. It's better to put there a 100k to ground and use a switch to short it.
One good rule when using relays in the signal path is not to believe in the caps quality and their leakage current parameter. I'd put the pull down resistors after C5, C7 and before the tone stacks. They will keep the relay terminals at ground.
I'd recommend a use of separate grounds for signal and switching. Looking at your layout: A relative high current spike from 5V relay will travel close to the ground of the first input grid and cathode resistor. Isolate the relay grounds and let them meet the common ground at the power supply.
Another options:
- use a P-FET or N-FET (you'll need a negative voltage to cut it off) or Opto-FET (H11Fx) to switch the cathode caps,
- use LDRs to switch between Gain pots. LDRs do not produce spikes and the closer you are to the input, the more sensitive the circuit is.
- use some tricks to slow down the relay switching voltage: example at Geofex (http://www.geofex.com/Article_Folders/pffootsw.pdf), more examples at Tom's page (http://www.mif.pg.gda.pl/homepages/tom/misc.htm#Pops) (the page is in polish, but the schematics are easy to understand)
- use some other tricks like a cutting out the spikes by muting the output for a short period of time, during the switching moment. Take a look at the engl and trace elliot bonneville schematics, these amps are full of relays.
Hope that helps.
There are some nice mods for "rectified" preamp on the Tom's homepage, just take a look at the schematics over there. It's really a mine of ideas :)
Piotr
Hi electron..thanks for your observations!!!
i did noticed the problem with the bypass cap switching, so i already added 100k resistors to avoid popping..i saw that on the original boogie sschems..
i did isolate the relays ground.. cut the traces and wired them to the switch and from the switch to power supply ground..
the ldr´s and fets switching ideas are great (and used on the originals) but if i do that, i have to redo the hole thing..and..lets say i´m not in the mood ;D..
i don´s have easy acces to vtl´s optos here in chile, only some cheap ldrs..i´m not shure if they will do the work correctly, so i didnt take that chance and used relays for switching..
i plan to add leak resistors when i test the preamp running..only if the switches pops..just adding some resistors here and there maybe will do the job..
no one noticed..that the tube pins are backwards!!!???
damn!!all over again!! damn!!
im doing the pcb again with all your suggestions (well the ones i liked)..so..
Any idea how to take the relays out of the board without damaging it? i´ll have to recycle the parts for the new board...
Use a desolder pump.
Which pins of yours tubes have you supply for heater?
For 12V supply, pin 9 of 12AX7 is the mid point of filaments.
You must supply pin 4 and 5 (two filaments in serial)
Use a TO220 package for the 12V regualtor with heatsink.
In 12V supply heater of a 12AX7 use 300mV.
Your regulator will dissipate 2X 0.3A X (17V- 12V)= 3W
Quote from: stephanovitch on November 19, 2007, 01:28:33 PM
Use a desolder pump.
Which pins of yours tubes have you supply for heater?
For 12V supply, pin 9 of 12AX7 is the mid point of filaments.
You must supply pin 4 and 5 (two filaments in serial)
Use a TO220 package for the 12V regualtor with heatsink.
In 12V supply heater of a 12AX7 use 300mV.
Your regulator will dissipate 2X 0.3A X (17V- 12V)= 3W
yes i got it all wrong..my first layout was a complete disaster...i put the heaters in parallel with 12 volts.. and pin 9 to ground.. so.. WRONG!!.. i put the pins mirrored on the PCB so .. WRONG!!!..
i shared the ground with relays..WRONG!!
the deenergized state of the relay was the clean channel... WRONG!!!
at least the PS is working.. i used the TO220 regulators, a 7812 and a 7805..planning to put the heatsink soon..
Don't worry, the next pcb will be better :)
i wired the heaters like this:
12v--->tube 1 pin 4
pin 9 no connection
tube 1 pin 5---> tube 2 pin 4
tube 2 pin 5 ---> ground
is that OK???
Quote from: dschwartz on November 20, 2007, 08:06:45 AM
12v--->tube 1 pin 4
pin 9 no connection
tube 1 pin 5---> tube 2 pin 4
tube 2 pin 5 ---> ground
is that OK???
No, now you have four heaters in series supplied with 12V.
Put 12V between 4 and 5 pin of each tube, leave all the 9s.
that would be:
12V--> tube 1 pin 5 ---> tube 2 pin 5
ground -->tube 1 pin 4 ---> tube 2 pin 4
i can´t believe i´m so confused with something so simple.....
one schem says more than 100 words:
http://s236.photobucket.com/albums/ff176/314_tr/?action=view¤t=heat.gif
Tap F------F------F------F
I I I I
Tap L------L------L-------L
The tube filaments are paralleled between the heater taps voltage, or this is the way I've always seen it done.
The two wires ~tightly twisted together between all connection points to reduce noise.
yes peter, that´s the traditional way when you have 6.3V AC..
i´m using 12VDC regulated.. so it´s not necessary to twist the wires..
It looks it's not much of an issue if you leave them untwisted even for AC, take SLO amp for instance, they use two parallel buses for heaters.
Best,
Bane
yeah.. twisting heater wires always sounded kind of "suspicious" to me...maybe it helps..but must be marginal....
anyway, i twist wires on my builds just because it looks cleaner..
Agree, it does look cleaner. It's important not to have signal wires near AC heater wires, but twisted or not apparently doesn't change much.
the new PCB for the main board..
I hope this time someone find any errors! :icon_rolleyes:
(http://diynoise.googlepages.com/version2.gif)
note: the relays must be connected in parallel, a single 5 v supply for both and ground to the switch.
Changes:
- Corrected the tubes orientation.. (plz check if it´s right!)
- Corrected heater wiring.
- Added 100kR to bypass caps for popless switching
- relays isolated from circuit.
- Distortion channel when deenergized position
- some parts moved around..
- Bigger space for 400v caps
greetings to all!!!
Try to enlarge copper connection of the heater supply (4mm )
The 6V supply for the relays and LED won't work. It will produce 6V as long as you have no load on it, but look at it this way - you're trying to power relays and LEDs through a 100k current limiting resistor...
I'd avoid the active regulator for the heaters. According to Kevin O'Connor, DC-heaters in general will usually create more problems than it could solve, in particular with active regulation. A simple RC-filter should work well enough. A more efficient way to eliminate heater hum is to reference the heaters to a standoff voltage of e.g. 70-80V. You can derive this voltage from the main preamp voltage using a voltage divider and a filter cap. (I haven't tried DC heaters myself though, but Kevin is usually right about these things...)
DC heater work very well but it's right that regulation is not necessary.
In my tube preamp I have only use single power diode and a RC filter and I have no noise.
What software do you use, its beautiful!!
Robert
i changed the 6V divider for a 7805.. the voltage with 100k ohm would drop too much.. i am learning soooo much doing this thing!!!!
as i already did the supply board, i think i wont change it if it´s not necesary..if heater hum appears, i´ll take out the regulation for heaters and use an rc filter (although its already filtered by two 2200 uF caps) as you said..
i did the layout with a lot of patience with firewoks...draw each part and made a "library" ..with some testing i got the right sizes...
then followed the schematics done with livewire (I dont trust pcb wizard) and draw the lines and dots of the PCB..
i know is more work than using eagle.. but i just don´t find eagle very comfortable and intuitive..and i like freedom i have for drawing the pcb´s..
FIY fireworks is an image editor from adobe, intended for web designing use..
i powered the board last night..it didn´t blow up!!!!
and the heaters worked OK..lighten up right away.
same for relays, they worked fine...
I changed the coupling caps for 200v rating.. since the power supply gives around 260 voltage, i think drain resistors will drop it below 200V.. they fitted much better on the pcb...
i saw a schematic where they put a 22uF cap across de relay coil..parallel to the diode..what is that for? slower action? smother contact??
i just have to do the wiring and test the monster!!!!
(..plz god..make it work!!)
Quote from: dschwartz on November 21, 2007, 07:37:16 AM
i saw a schematic where they put a 22uF cap across de relay coil..parallel to the diode..what is that for? slower action? smother contact??
There's also a resistor with value equal to the relays coil in series, and the relay is powered with 2 x higher voltage. Yes, this slows down the switching action and reduces the spikes.
Quote
I changed the coupling caps for 200v rating.. since the power supply gives around 260 voltage, i think drain resistors will drop it below 200V.. they fitted much better on the pcb...
I wouldn'd do that. Think about what is happening when you turn on the power. Since you are not using a stand-by switch, for some time the caps are overvoltaged. It may not damage the caps at first time but it is not good for them, in time they can deteriorate and even blow out! Besides, the el-caps shouldn't work very close to their maximum ratings.
For more safety add a 470k 1W resistor across C3 in the power supply. It will discharge the caps when you turn the power off.
Very nice looking pcb layout!
Hey Dan,
This looks very good indeed! I'll check everything when I get home from work, and contact you by messenger!
Keep up the good work!
Kind regards, Jake
Quote from: dschwartz on November 21, 2007, 07:37:16 AM
I changed the coupling caps for 200v rating.. since the power supply gives around 260 voltage, i think drain resistors will drop it below 200V.. they fitted much better on the pcb...
Just remember that the coupling caps need to handle the anode voltage + the signal voltage (e.g. 200V at the anode + 60V signal peak). To be safe, it's best to make sure they can withstand the full voltage of the preamp.
It will be very interesting to follow this project. Getting the power supply working is a good start.
Daniel, you can add a 1V zener or a diode on the ground pin of the 5V regulator to have a voltage near to 6V for the relays.
Hi rafa!!
well the relays are rated for 5 volts so 6 volts are not needed (DS2Y - 5DC)
i´ll be posting the progress as i go.. i´m so close!!!
i´m planning to start it up before friday so stay tuned!!!!!
last night took some pics..enjoy!
(http://diynoise.googlepages.com/TP_2.jpg)
(http://diynoise.googlepages.com/TP_1.jpg)
(http://diynoise.googlepages.com/TP3.jpg)
God! Now that looks nasty!
Awsome work dude, nice little hours spent on there.
Gotta give it a try sometime. ;)
Frequin' B-Dazz-Mahn !
That looks like some fine work D !
thanks guys!!!
i´ve put a lot of work on this...mi future wife it´s kind of mad hahaha
I´m building this thing for a customer so it HAS to be great..it´s my first tube preamp, well the first good one , i hope(real mctube didnt float my boat).. and well..i like my pedals to be pretty..
i´ve never design a pcb before, and learned so much these days, heaters, voltage ratings, voltage dropping, how much a PS cap discharge shock hurts ( :o), how relays works, and since i´ve not finished yet, i feel that´s going to be ALOT MORE learning when i get this thing going!!!!
so thank you all!!!
I took another look at the schematic (the first one you posted, don't know what you've changed since then). Some more notes:
The first three gain stages share the same power supply node. This could be very bad in a high-gain circuit, and could lead to oscillation and "motorboating". The best solution would be to add another RC node on the power supply for the first (and most sensitive) gain stage. Another solution would be to move the third gain stage to the "B" node. Adding more filter nodes seems like a good idea though, considering that a typical high-gain amp will have about 5 nodes including a choke.
Some of the frequency shaping is odd. For instance, the 220p cap across the 50k Clean volume pot will only affect frequencies above 14kHz, so it will let through noise but do nothing with guitar frequencies. The 1n cap across the 1M Dist gain pot seems very big (470p/1M in a Plexi bright channel is considered extremely bright). The 2.2n cap across the 680k resistor before the Dist pot essentially takes the resistor out of the circuit, since everything above about 100Hz will pass through the cap.
The 3M3/50k voltage divider on the clean channel takes the signal down 36dB even at full clean volume. Are you sure you want to attenuate this much?
EDIT: Another thing - how is the grounding layout? Tube stuff is very sensitive about grounding and it's important to isolate high-current ground returns from sensitive signal grounds. For your preamp, the main retifier ground, heater rectifier ground, heater regulator grounds and the relay ground are high current and should not mix with signal grounds. Try to use some kind of "star" grounding scheme. Getting the grounding right is critical in order to reduce hum in a tube circuit.
Quote from: bancika on November 20, 2007, 03:18:39 PM
Agree, it does look cleaner. It's important not to have signal wires near AC heater wires, but twisted or not apparently doesn't change much.
Twisting AC wires helps to cancel out the magnetic field generated, but it works just as well to have the wires paralell and close together (e.g. like in a piece of lamp cord). The Soldano heater busses work because of the 90 degree angle to all crossing signal wires.
Quote from: d95err on November 22, 2007, 03:38:54 AM
I took another look at the schematic (the first one you posted, don't know what you've changed since then). Some more notes:
The first three gain stages share the same power supply node. This could be very bad in a high-gain circuit, and could lead to oscillation and "motorboating". The best solution would be to add another RC node on the power supply for the first (and most sensitive) gain stage. Another solution would be to move the third gain stage to the "B" node. Adding more filter nodes seems like a good idea though, considering that a typical high-gain amp will have about 5 nodes including a choke.
Hmm.. another RC node will not fit in the box.. maybe i can redistribute the B+ supply.. since i have 2 RC nodes, could be 1 for stage one, and the other for the rest of the stages?
Some of the frequency shaping is odd. For instance, the 220p cap across the 50k Clean volume pot will only affect frequencies above 14kHz, so it will let through noise but do nothing with guitar frequencies. The 1n cap across the 1M Dist gain pot seems very big (470p/1M in a Plexi bright channel is considered extremely bright). The 2.2n cap across the 680k resistor before the Dist pot essentially takes the resistor out of the circuit, since everything above about 100Hz will pass through the cap.
Actually, clean volume is 500K now.. 50k is too low.. i want the clean channel to be very bright..will 680pF be better for this job?..anyway, i did not put those caps on the layout cause i want to test different values.. The 2.2n/680k is just like mesa preamps..Eh! and i changed the first coupling cap for 3.3nF (2KV) to clear the bass content...i went too far?..
The 3M3/50k voltage divider on the clean channel takes the signal down 36dB even at full clean volume. Are you sure you want to attenuate this much?
Ehmm nopes :icon_lol: ... i didnt put that part on the layout either, cause i wasnt sure.. wich value do you recomment to get a bright clean, but not that attenuated?
EDIT: Another thing - how is the grounding layout? Tube stuff is very sensitive about grounding and it's important to isolate high-current ground returns from sensitive signal grounds. For your preamp, the main retifier ground, heater rectifier ground, heater regulator grounds and the relay ground are high current and should not mix with signal grounds. Try to use some kind of "star" grounding scheme. Getting the grounding right is critical in order to reduce hum in a tube circuit.
Hmm i tried to do the best with that.. i couldt separate heater and b+ grounds because of the way i did the box (separated transformers).. so.. i only could have 3 wires going to the enclosure..The filtering/regulation is done inside the main box and have only one ground output..
so i did this:
- led´s and relays ground goes directly to the PS ground
- B+, signal, and heaters share the same ground at the PCB. i think the PCB has plenty of ground and not looping..star ground? i dont know..you tell me....
- signal ground of wiring and jacks goes to chassis ground
thats it...Great Observations by the way
On second thoughts, I may have gotten some of the frequency response calculations wrong, so don't put to much faith in them. Comparing to existing values of well-known circuits should work well. As for the cap and resistor values , just experiment! It's not likely that you'll get the perfect sound the first time around anyway. Try to get something working as soon as possible and then tweak to perfection.
About the filtering, I saw that the Soldano Supercharger GTO used only 2 filter nodes, so I guess you should be allright with three. Try moving the third gain stage to the "B" node if you can. I think oscillations and motorboating will be more likely if you have two gain stages with the same phase on the same node, since there is a risk of positive feedback leaking through the power supply.
Keep going! I'm looking forward to hearing the results! If my posts were any help I'll take all the credit... ;D
yes, mi plan is to make it work, and make a lot of tweaking after..something like design "as it goes" (sorry for my english, i tend to make up words and phrases sometimes)
i´m having a big PITA with the wiring now..it´s a LOT, even though i made a PCB for the tonestacks, i have to use really long cables (wich i hate) coz i put the input too far from the bypass switch..and it´s starting to look scary now..if i pull up the lit, i can see a lot of cables..and there only for leds and switching..
BTW, for signal, i am using shielded cable...
debbuging and tweaking is going to be a real painstaking, horrible experience!!!!! :icon_frown:
THE MOTHER &%&$$ IS ALIVE!!!!!!
i finished the wiring, checked connections and plug this thing on!!!!
first a pic:
(http://diynoise.googlepages.com/TP_3.jpg)
well..i didnt posted a clip cause now starts the debbuging phase!!!! i sounds like crap!!!!! hahaha
first of all...it have a huge low freq hum, like a muffled hum...maybe that´s motor boating?
its a hum that affects the signal..making it sound fuzzy and octave-ish.
i have other bugs on the tonestacks..the pcbs were wrong, so bass and presence controls work backwards..but i expected those kind of errors.. and a pot seems faulty..affecting the overall response of the tonestack..
the clean gain pot works weird. (i havent put a cap there yet) about 10 o clock the sounds abruptly changes, loosing a lot of bass content..
it´s a mean clean channel!!! it gets to heavy overdrive.. but not a nice one yet..
the sound is fizzy and somewhat gated.. i think the loud hum produces interference distorting the wave in an ugly way, i hope that the sound improves a lot if i put a filter to stage 1 B+, and separate it from the other b+ (2nd and 3rd stages)..
i didnt noticed normal noises.. no hiss at all..and no typical magnetic hum...
the switching didnt pop at all, too. those are the good things..
so i hope with your help i can make this beast sound good!!
greeting for everybody!!!!
dschwartz, can you take a full picture of the enclosure?
Could you post the latest version of the schematic and PCB layouts? It would make it easier to discuss the voicing and problems.
EDIT: What frequency is the hum? Can you tell if it's 50/60Hz (grounding problem or heater hum) or 100/120Hz (rectifier noise)?
the pcb posted above is the latest version..
the power supply is the same, but replaced the voltage divider resistors for a 7805...
the hum sounds like 50hz..feels like low freq oscilation to me as it distorts the signal..or probably is hum+oscilation...
tonight i´ll try to post some inside shots, and a clip..
It sounds like a grounding issue. The first thing I'd try would be to get rid of the heater rectification and run regular AC heaters. That would at least eliminate a possible error source. The second thing would be to get better filtering for the preamp gain stages. If that doesn't work, you may have to redesign the grounding scheme completely.
Since you're using a separate box for the power supply, a complete star ground may be impossible. One thing you could do though, is to move the last two filter caps to the effect board. Try to make sure the grounds of each gain stage goes directly to the negative pole of the corresponding filter cap using as short path as possible.
If you want to keep the DC heaters, it will be very important to separate the heater grond from signal ground. One thing you could do (also with AC heaters) is to use twisted wires for the heaters that are raised above the PCB, connecting directly to the tube socket heater pins.
And a question: How is the chassis connected to the PCB grounds? One single point? Multiple places? Are you using isolated jacks?
Hi D95! your'e really helping me out here..i´ll give you full credit when this thing gets done..
First of all i am redesigning the power supply..please look at this schem:
(http://diynoise.googlepages.com/PS_version2.gif)
it has a lot of improvements over the current power supply:
- Groun loop elimination trick (some people has told me that actually works)
- Separated B+ for stages 1, 2 and 3, 4 and 5.
- Separated ground for B+ and heaters (is that separated?)
it looks nicer too hahaha!!!
well D95.. for grounding the chassis i soldered a wire between ground of output jack and master volume´s pot back cover..
since jacks are isolated from chassis i grounded all jacks directly to power supply at a single point..
Gain, tonestacks, and bypass caps switches use this ground...
pcb ground directly to power supply. too
all signal wires were shielded at one side (from the pcb side) except for the output jack that feeds ground to the chassis
did i mess it up?
and is my new power supply ok?
Hi, first of all, you're doing all the hard work, so you take the credit! I'm not a tube expert by any means, I've just built one tube amp (but I've spent far too many hours on tube web forums...) ;)
It's a lot of fun to assit you though!
The schematic doesn't really tell if B+ and heater grounds are separated (a schematic wire is not the same as a physical wire), it depends on how you layout the PCB trace. If you want to make the separation really clear, you can use different symbols for heater ground and signal ground.
I'm a bit sceptical about the ground loop prevention circuit. As drawn in your schematic it isolates the rectifier ground from signal ground and heater ground, which I think may be a bad idea and could cause even more problems. I think it's better to try to get the basics right first, before experimenting with this kind of solution. You could try this later, but it should be between chassis ground and the whole circuit ground (signal, heaters, relays). That would help eliminate ground loop between your pedal and other devices it is connected to (e.g. an amp), but it won't fix the problems within the pedal. Hmm... it could perhaps be used to separate heater/relay ground and signal ground. Still, I'd try to keep things simple to begin with. The same goes for the 7812 regulator - I'd replace it with a suitable resistor for now and if things work OK, you could add it back later. You could still kee the same PCB layout for the regulator.
I recommend moving the first filter cap for each rectifier in the power supply box. The rectifier grounds are the most noisy and biggest potential problems. The first filter cap should be as close as possible (physically) to the rectifier. I.e. ideally, the ground end of the rectifier should be soldered directly connected to the negative side of the filter cap and the positive side directly to the positive side of the cap. That reduces the dirty ground currents through the power cable, and also makes the high voltage and heater voltages less noisy.
The heater currents are still a problem. Make sure they are separated from signal ground on the PCB and meet as close as possible to the jack for the power cable. If you could switch to 12V relays, they could use the same power supply as the heaters. That way, you could move the whole heater regulation in the power supply box and have only a well filtered 12V instead of the very noisy 17V in the power cable.
If it's possible, try to keep the gain stage grounds separate too. The grounds of each stage should meet at the negative leg of the corresponding filter cap. From there you can put a PCB trace to the common signal ground. By one stage, I mean from the cathode of a triode to every ground that follows until the grid of the next triode. So, don't take the grounds for volume and tonestacks to the shared ground, take them back to the filter cap ground of their corresponding B+ node.
Some of these tips may be overkill. I haven't built a tube pedal myself. I'm just telling you things I've tried in my tube amp (or should have tried), and stuff I've read about in books or on the web. It's a lot easier to do this stuff in a point-to-point built amp, because it's easier to move things around and add wires here and there. With a PCB I guess you need to plan ahead more...
BTW, please call me Erik! (d95err just happened to one of my first computer usernames 12 years ago...) ;)
i'm getting frustrated here...
took me all day to:
- Put a ground lift on the power supply...
- separated ground traces for heaters, relays and B+ at the power supply
- separated heaters ground from signal ground at the main board
- separated b+ for the first triode
- added a 47uF cap next to HV rectifier
- replaced the 12V reg for a 4ohm resistor (GAVE ME 12.4 VOLTS W/HEATERS ON)
- Changed coupling caps for 630V rating caps
- Added a 47uF filter for relays 5V
- Added a 10nF fiter cap for B+
and the big hum is still there!!! and hiss made appereance....
when i switched the ground lift at the supply (choosing the rectifier´s ground) this thing squealed like a pig
NOticed that even with gain at 0 there was the loud hum (cleaner, but loud..)
i think the ratio of noise is 1:1..
im losing my nerve here!!!!!
Cut the wire of the actual 12 V supply
Try in first to supply the heater circuit with a 12V battery (car).
It's an easy mods to identify if your noise come from heater circuit.
Tube stuff can be tricky, especially high-gain...
I noticed one thing about your switching system. The input to the high gain stages (second and third) is not grounded when switched out. The unconnected input will work as an antennae and pickup lots of noise. Although the output of those stages is not connected to anything when switched out, there is a lot of amplified noise in there and that could affect other parts of the circuit through crosstalk between traces or leakage through the power supply. This is probably not the main problem, but it could make things worse.
Try to disconnect as much of the circuit as possible to find the problems. Temporarily hardwire the whole thing for clean channel only. Remove the relays, MOSFET source follower, tonestacks and DC heaters. Cut power to the high-gain channel stages. Once you get that working, try adding features one by one.
Another thing - make sure you try different preamp tubes. You could have had bad luck and ended up with a microphonic or damaged tube.
Keep working! I'm sure you'll get it working eventually!
hmm... that battery idea seems good...
but i dont have one.. maybe if i use a separated 12 v adapter?
should i change the hole PCB???
anybody sees any suspicious traces or something....
Are you still using the same PCBs that you posted, or have you made any changes?
yes i´m using the same pcb's.. but cut some ground traces...
by the way i missed grounding the chassis..and that lowered the hum a lot!!!..but it´s still there..it let´s you play, but annoying anyway..
i´ll try to put the 12v regulator again....and maybe redo all the pcb..makinmg one big board including the power filters next toi the cathodes..and appliyng all i´ve learn thanks to you all!!!
more news...
i did these things:
- put back the 7812, with a diode for 12,6V
- star grounded to the chassis the b+ ground, main board ground, AC Main ground, heater filters ground.
- Added a 100 Ohm 2W resistor in series with the heaters ground (the ground going to the main board, i read somewhere that that will bias the heater ground more positive, reducing noise, although i have a DC regulated supply, i think that it works, or doesnt hurt at least)
- Isolated jacks from chassis
- Wired input jack ground to the board input ground, output and tonestacks to the board output ground
results:
- Goodbye oscilations!!!!
- less louder hum and cleaner..BUT..the hum wasn´t affected by the gain or volume settings, at min or max vol/gain, the hum was there.. my instinct (and empiric knowledge) tells me that it means that i still have a ground loop at the output wiring, somewhere between the master volume and the out jack (i have a passive fx loop between both)..
so i have the SOB against the wall!!!!! i know where yua´re you bastard!!!
are my thoughts OK?
by the way.. it´s starting to sound REALLY good
Quote from: dschwartz on November 28, 2007, 07:45:27 AM
more news...
i did these things:
- put back the 7812, with a diode for 12,6V
- star grounded to the chassis the b+ ground, main board ground, AC Main ground, heater filters ground.
- Added a 100 Ohm 2W resistor in series with the heaters ground (the ground going to the main board, i read somewhere that that will bias the heater ground more positive, reducing noise, although i have a DC regulated supply, i think that it works, or doesnt hurt at least)
- Isolated jacks from chassis
- Wired input jack ground to the board input ground, output and tonestacks to the board output ground
results:
- Goodbye oscilations!!!!
- less louder hum and cleaner..BUT..the hum wasn´t affected by the gain or volume settings, at min or max vol/gain, the hum was there.. my instinct (and empiric knowledge) tells me that it means that i still have a ground loop at the output wiring, somewhere between the master volume and the out jack (i have a passive fx loop between both)..
so i have the SOB against the wall!!!!! i know where yua´re you bastard!!!
are my thoughts OK?
by the way.. it´s starting to sound REALLY good
Another thing you may want to try is unscrew the transformers, and physically move them around to see if the PT is causing you troubles. It's better (from a safety POV) to fire up the pre, listen, shut it off, discharge the caps, move the PT's, and repeat. While I'm thinking about safety, what I do when I'm working on an amp is keep one hand tucked away in my back pocket, or into the waistband of my pants. This greatly reduces the chances of me being grounded with my left hand, touching B+ with my right hand, and having the current travel through my heart. It takes longer to get the work done, but being dead REALLY pushes back the time of completion.
Also, I'm assuming you poked around in there with a chopstick to make sure your lead dress is up to par ? If not, you could try moving some wires around and see if it produces an audible difference one way or the other.
the PT is outside the box..in other enclosure.. y moved it around, and did´nt change at all..it´s shielded.. so, no hum from that...
moved the wires inside the box, too.. no change.. except for one that was "sensitive" to the touch,,
i´ll redo the wiring anyway..
} so.. i´ll keep you all informed..
well.. i don´t know if anyone still cares.. but
this thing is noiseless now!!!!!!
i rewired the output section, bypassed a master volume pot and the passive fx loop, just to hear what happened with a properly grounded output..
and this thing is quiet as a dead mouse!!!!!!! really really good!!!
i think is due to the different angles i attacked the problem. (heaters regulation, filtering and ground reference, B+ filtering, star grounding, shielding wires, perpendicular wiring, jack isolation, chassis shielding, etc..)
one more thing..it had a strage ugly clipping..allways present...i reversed the mosfet and voilá!!! really great smooth clipping!!! that´s odd cause i originally put the mosfet according to the datasheet pinout...well.. i think, if it sounds better, then is correct...
Now i know that the hum was not coming from the main board or input signal cables, the layout is OK..i have to redo now the master volume and fx loop section, but with proper grounding and shielding..
The next step is tweaking the tone..change some caps here and there..
One question though: i used the scaled down tonestack version from gaussmarkov´s dr boogey (all resistors 10 times lower, all caps 10 times higher) in order to get better output impedance..but my bass tone control is not quite effective..i mean, it doesnt change anything at all.. remember i have a mosfet buffer, probably with a lower output impedance than a tube...is that OK?
The sound has a nice low end whoomp, so it´s not a lack of bass content..i think the freqs affected by the control were shifted down.. any suggestions?
MAN I´VE LEARN A LOT!!!!!!!!!!!!! THANKS TO ALL YOU GUYS!!!! REALLY!!!
Quote from: dschwartz on November 29, 2007, 08:14:03 AM
well.. i don´t know if anyone still cares.. but
this thing is noiseless now!!!!!!
Awesome! I've been following this thread since it was posted. Keep it up man!
i too have been following this thread. ordering the parts to build my own very soon.
Cant remember now if it's been said, but what power transformer are you using, and is your preamp voltage way lower than mesa's for any particular reason? (theirs are run around 400v)
Reason I ask, is that weber makes a 260Vsec/100ma, 6.3V/3a transformer for $15 that could possibly do the trick as long as 330-350v is ok (or better? closer to original?) for running the preamp...
i´m running it from a back to back pair of transformers.. ordinary ones...
220-12 to a 9-220.. that gives me around 320V of b+ ....is enough...
Quote from: dschwartz on November 20, 2007, 09:31:18 AM
yes peter, that´s the traditional way when you have 6.3V AC..
i´m using 12VDC regulated.. so it´s not necessary to twist the wires..
God's sake!!!! (is this correct?) Daniel, do not blasfem!
Ampere's law tell us about how magnetic flux and current are related, and that's the first principle U must use coaxial cables on videocable TV or AC or DC (yeeeeeeeeeeeeeah! AC/DC!) filaments! And experts always say "just twist the, doesn't matter..."
So why, in the name of God, I have to spend 4 months of my life studying Physics nº2 at the university (well, they were 8, I have to do the course twice...) learning about these?????????????????????????????????????????????????????????????????????????????????????????????
Va en castellano:
Para què carajo estudio para poder ser (lo serè?) ingeniero electronico, cuando una de las materias me explica sobre los flujos magenticos y su relacion con las corrientes por el mismno conductor que genera ese flujo magenetico, para que alguien diga "enrollalos, nad mas"????? El cable mallado aka coaxil/coaxial se creo para eso! Asi no tenes señal saliendo o entrando al cable (bueno, si la malla fuera completamente sin huecos...)
A proposito, Daniel, tu laburo es del carajo!!!!! Muuuuuuy bueno, y me quedo corto! Pero fijate, que los PCB de las paginas mencionadas no son comercializables (invente una palabra?)
a qué PCB´s te refieres??
..
okay, i.m not an electronic´s engineer, so dont get so mad man!!! ..i twisted the wires anyway!!!
slideman, you need a variable magnetic field to have electromagnetic induction, if you use DC on the heathers they shouldn´t induce noise on the signal unless you have a mecanical vibration of the wires.
I did that class two times too :icon_evil:= tambien di ese maldito ramo 2 veces...
saludos
Seems like you made it work after all! I admire your persistence and patience. good work! Now you can get down to the fun part - fine tuning and tweaking. I hope we'll get to hear some clips of it... :)
yeah thaks!!
i´ll be posting some clips this weekend.. as soon as i tweak the sound as i like..
Quote from: 12afael on November 29, 2007, 02:02:54 PM
slideman, you need a variable magnetic field to have electromagnetic induction, if you use DC on the heathers they shouldn´t induce noise on the signal unless you have a mecanical vibration of the wires.
I did that class two times too :icon_evil:= tambien di ese maldito ramo 2 veces...
saludos
yes, you're right, a time dependent magnetic field (function of t...). Anyway, I always use shielded cable!
I have to add something...
i left out all the bypass caps ground lifting for less gain ideas..it was screaming GROUND LOOPS!!!!!!!!! and the sound was not very nice either because of the wider band of amplification and harsher clipping.. instead, for a hi/lo gain switch, i placed a switchable resistor to ground parallel to the OD gain pot..it works much better and quieter.. and its so simple...
Quote from: dschwartz on November 29, 2007, 02:30:52 PM
yeah thaks!!
i´ll be posting some clips this weekend.. as soon as i tweak the sound as i like..
Can't wait to hear them. Awesome project. Kudos to your hard work. :)
OK.. is showtime!!!!!!!!
i finally recorded some demos...
the preamp is going directly to the sound card, through my korg ax1000 amp sim (not so good) no added effects..
now..the goods:
- clean channel..tweaking from clean clean to mean crunch:
http://diynoise.googlepages.com/clean2.mp3 (http://diynoise.googlepages.com/clean2.mp3)
- high gain channel..tweaking from lower gains to higher ..
http://diynoise.googlepages.com/gain.mp3 (http://diynoise.googlepages.com/gain.mp3)
Notice the super low noise!!! thanks guys!!!
especially to richon and d95err...
some pics:
front:
(http://diynoise.googlepages.com/front.jpg)
back:
(http://diynoise.googlepages.com/back.jpg)
point to point tonestack (what a mess!!!):
(http://diynoise.googlepages.com/tonestack.jpg)
main board an PS:
(http://diynoise.googlepages.com/power_main.jpg)
guts:
(http://diynoise.googlepages.com/tripas1.jpg)
Wow! glad it is working great !
Both sides too !
the Soundclips brightened up my day !
Thanks
IN-CRED-IBLE!
Man that thing sounds good! Really really nice clips!
(and nice chops too!)
It sounds great - well done!
Fantastic man ! :icon_smile:
Thanks for your replies!!..
anyway, did you noticed a bit of excess of bass content on the high gain clipping?..at max gain sounds a little fuzzy i think....
This thing rocks !!
What tubes did you use ?
Oh yes, Is your schematic up to date now ?
Alf
no.. i have not updated the schem.. as soon as i have the time i will
Congratulation!!!
Your sound is over great!
Try to put transfo inside the same box now.
I don't think that you will have noise induction.
the next oine will have the trafo´s inside..it will be a rack mounted preamp..
today i´ll lower the coupling cap to about 2.2nF.. for the high gain channel
Have you try to remove the 5nf cap on plate resistor?
yes i did that, also, the first coupling cap is 5.8nF, second 39nF and third 33nF
i lowered the 2,2nF cap in parallel with the 680K resistor before gain pot, for a 1nF..no change..so i´m thinking of putting a 2.2nF (or 3.3nF) alone as a second coupling cap for the high gain channel.. i need just a bit less bass content to clear off mushy distortion on lower strings
FYI, i changed the 39nF coupling cap for a 5.8nF and the things cleared up nicely..
some new demos, with some value tweaking and changing a crappy EH tube:
Clean-clean
http://diynoise.googlepages.com/cleaner.mp3 (http://diynoise.googlepages.com/cleaner.mp3)
clean mid gain:
http://diynoise.googlepages.com/clean_med_gain.mp3 (http://diynoise.googlepages.com/clean_med_gain.mp3)
clean top gain:
http://diynoise.googlepages.com/clean_max_gain.mp3 (http://diynoise.googlepages.com/clean_max_gain.mp3)
high gain channel-mid gain (marshall style)
http://diynoise.googlepages.com/marshall_gain.mp3 (http://diynoise.googlepages.com/marshall_gain.mp3)
very high gain
http://diynoise.googlepages.com/Veryhighgaion.mp3 (http://diynoise.googlepages.com/Veryhighgaion.mp3)
all recorded directly to the pc trough my korg ax3000g cab sim (vintage 4x12)
Wow
What's the latest scoop on this project?
QuoteMissing the 5th stage? well.. it´s a MOSFET BUFFER!!!!!! hehehe...well, if RG sez that they are good..who am i to disagree???
Can somebody please point me to RG's thread/article, where I could read more about using MOSFET BUFFER instead real tube stage? Thanks!
here it is:
http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm (http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm)
i am building the rack version right now..still in process
now thats a true tube pre amp!!!!
this is what im looking for! im waiting for the updated schem... please work on the schem... ;D
So how is the rack version coming along? is it going to be a single rack space?
What VA value did you use for the transformers?
Love the project, btw ;D
well, here are 2 pícs of the (unfinished still) enclosure..
http://dsmnoisemaker.blogspot.com/2008/01/double-shot-iila-versin-rack.html (http://dsmnoisemaker.blogspot.com/2008/01/double-shot-iila-versin-rack.html)
the rack is made wth U shaped 50mm x 25mm aluminum profiles (those used for window making), so the rack is 1.3U or so ;D
i had troubles with the power supply and the mosfet follower impedance (check some of my last threads), so i ended up using 3 transformers,
- 12V 1A only for heaters and relays
- 12V 500mA coupled with 9V 300mA for B+
and changed the 100k source resistor for the buffer for a 33k...
now how it sounds??
SUPERB!!!!!!!
the clean is pretty sparkly and percusive, not very compressed until some light saturation, some friends told me that sounds pretty much like a blackface...for my taste, is nothing to throw fireworks, but it was the best i could get with my "easy cheap clean channel" method
The distortion channel is heaven for me, goes from "tube screamer pushed pre" sounds to full metal scooped kick ass bottom end..i´m so proud of the results..really happy...i hope the owner make justice with his playing (i think he plays punk rock :icon_cry:)
just amazing!
esta muy bien la version de rack, se ve que tienes un buen acabado, muy profesional. saludos desde Peru.
It looks beautiful, and I'm sure it sounds as good ;D
I'm in the process of thinking up a 1u rack bass pre-amp, and I'm liking your powersupply 8). The only thing I'm not liking is 3 xformers, so I'll see if I could do it with 2 back to back.
Keep up the good work!
OMG what an amazing build!!! COndrads man
Do you have a final PCB layout?
Thanks to all for your kind words..
well i don´t have a final PCB, and i think it will never be, cause i like to tweak the values a lot until i get the sound i like, sometimes that means changing pot values, cap values and resistors..but in this file:
http://diynoise.googlepages.com/double_shot2.rar (http://diynoise.googlepages.com/double_shot2.rar)
i have the latest version of the basic PCB and schems, that will get you on the ballpark..it includes:
- Gain stages PCB: this pcb contains the gain stages and mosfet follower..the output goes to the switching and tonestack (TS) PCB..
- Tonestack PCB: contains the TS for both channels, a relay switch for the boost, and other for the FX loop. Also the 2nd relay of the channel switching ( the 1st one is on the gain stages PCB)
- Signal schematic
- power supply schematic
BE WARNED that the values on the schem may not match the values on the PCB, i´m kind of lazy and i don´t have time to update all the changes on all the files, specially if i make changes on the physical board a lot. i socket a lot of comnpoinents to tune to taste and use trims for critical resistors..
You MUST understand what´s going on to build this, this is not a "read and build" preamp..it´s a "read, understand, build, debug, tweak and enjoy" kind of thing..
i would be glad if someone builds it...
Quote from: Rmanen on February 14, 2008, 04:55:22 PM
It looks beautiful, and I'm sure it sounds as good ;D
I'm in the process of thinking up a 1u rack bass pre-amp, and I'm liking your powersupply 8). The only thing I'm not liking is 3 xformers, so I'll see if I could do it with 2 back to back.
Keep up the good work!
my first version had a back to back 1A 12V and 9V 500mA, i used a 7812 for heaters in series with a 7805 for relays...using the 2 regulators in series helped a lot controlling the current load to the xfomers..and got good results..
on the actual version i used 12V relays but i wired them in parallel with the heaters, son the loading was HUGE...
i reccomend the 5V/ 2 regs way (as shown in the schems)
great!!! congrats
te envidio sanamente, algun dia construire el mio :icon_biggrin:
Great to follow along here Dscwartz !
I've been reading and listening to clips since you started, and noting all the little and big mistakes [er...learning experiences] you've overcome...thank YOU for overcoming them and sharing your experiences in such great detail, and with all the soundclips !
All your work and diligence and persistance and sticktuitiveness have rewarded you with a fine tube preamp, and us with excellent tutorials on building approaches.
Tones are super, look is stellar...excellent task management !
Quote from: petemoore on February 15, 2008, 08:51:47 AM
Great to follow along here Dscwartz !
I've been reading and listening to clips since you started, and noting all the little and big mistakes [er...learning experiences] you've overcome...thank YOU for overcoming them and sharing your experiences in such great detail, and with all the soundclips !
All your work and diligence and persistance and sticktuitiveness have rewarded you with a fine tube preamp, and us with excellent tutorials on building approaches.
Tones are super, look is stellar...excellent task management !
:icon_redface: :icon_redface:
i´m touched..coming from you means a lot to me...
I think that with a good brain, information, good parts and the support of this forum and people like you, anyone can build really good devices..
But is PASSION that makes one to try to go further, and makes the difference between really good, and excellence...
This passion makes me want to share the joy that learning gives me, and hope that someone, far, far away from me, feels the same way i do when discovers something new (at least for him), and find that truly magical feeling when starts to design and comes alive like a living been..
I don´t build to play my stuff..i do it for the satisfaction of it, and the face of a happy customer that goes home with a really special piece of gear.. one of my children goes away..some of them stay at home..
Forging ahead, and dropping a line !
This kind of comradery is what makes this site work great for all of us.
at last...
a sound clip...
this is the double shot II high gain channel..
enjoy!:
http://diynoise.googlepages.com/ds2.mp3 (http://diynoise.googlepages.com/ds2.mp3)
no one listened to it?
Yupp...sounds like wah on there...
nopes, theres no wah there.. maybe the paf pro that gives that "whawhy" tone
That's a nice sounding tone. Kind of has an off-axis mic effect. Great work !
well, hearing it again, it definetly doesn´t make justice to the real thing, it sounds like crap compared to the tight, punchy sound it has live.....i´m gonna try direct through a cab sim...