Good on YOU!!!! WELL DONE!! looks awesome, & me, as someone put above, I just don't have the elec. know how!!!
Tell us how it sounds too!!
Rod.
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My DIY SVT bass amp
- Thread starter okabass
- Start date
Good on YOU!!!! WELL DONE!! looks awesome, & me, as someone put above, I just don't have the elec. know how!!! Tell us how it sounds too!!
Rod.
Hi,
That looks like a very well built project, congratulations!
Perhaps you ought to make a web page about it, sharing your experience with the world? That'd be cool.
By the way, Finland is a beautiful place!
That looks like a very well built project, congratulations!
Perhaps you ought to make a web page about it, sharing your experience with the world? That'd be cool.
By the way, Finland is a beautiful place!
hope you are still tracking this thread... I am about to attempt the same build using the stock Ampeg pre-amp but Kevin O'connors 'simplified' SVT Power amp with the schmitt splitter as shown in TUT3. the problem is that the Kevin's power amp/spliiter has less gain and he recommends that the 6C4 cathode follower at the last stage of the stock pre-amp design should most likely be a gain stage. I noticed you dont list 6C4 in your spec what did you use ?
dan
dan
The SVT-VR is a good guide as to what to do. I haven't seen the KO'C book but I can tell you that in the SVT-VR they used a 12AU7 for the cathode follower. The gain is less than, but close to unity. The signal is fed to the power amp which puts a 12AX7 gain stage following the CF.
Pre-amp CF output:
SVT-VR power amp gain stage:
Pre-amp CF output:
SVT-VR power amp gain stage:
Yeah thats basically the same circuit as the 6C4 stage. on the earlier versions of SVT
just trying to figure out if it has enough gain to adequately drive Kevins splitter design here:
V2 here is 12AX7 and Voltage at Vp2 is approx 400v
Also I'm only building channel 1 and dont plan on building in pre-amp out and power amp in connections... so do I need this CF stage at all ? Was also considering replacing that stage with a 12AU7 or 12DW7 or 12AX7 but using first triode for as gain stage and the second as a CF (like the first tube of the input to the pre-amp)
just trying to figure out if it has enough gain to adequately drive Kevins splitter design here:
V2 here is 12AX7 and Voltage at Vp2 is approx 400v
Also I'm only building channel 1 and dont plan on building in pre-amp out and power amp in connections... so do I need this CF stage at all ? Was also considering replacing that stage with a 12AU7 or 12DW7 or 12AX7 but using first triode for as gain stage and the second as a CF (like the first tube of the input to the pre-amp)
The only way that you'll know if the CF that he is recommending is going to sound good is to try it. What you use will affect your tone. I assume that he has tried it and feels that this works well in his circuit.
As you alluded to, in the case of the SVT, after the pre there is a pre-amp out jack, the CF ensures that the impedance of the pre-out will drive whatever it is connected to. But the CF also follows the tone stages and helps drive the signal that was reduced by the tone stage. Some amps have a CF in this position, some don't. Whether or not you have a CF depends on what the output impedance is of the tone stage. It is common to have a gain stage following the tone stage to make up for insertion loss.
You can certainly go from a tone stage directly into a PI without a gain stage or a CF. A lot of amps do this. Check out some of the Fender schematics (vibroverb, dual showman, baseman) to see what they do. There is no CF but they have a gain stage before the long tailed pair phase inverter.
You want a PI that is going to have a good bass response. Some PI designs are better suited for guitar. Finding the right one is half the battle. You might find it interesting to look at some of the McIntosh designs like the MC60. They are available Invalid Link Removed. They have a driver before the PI.
As you alluded to, in the case of the SVT, after the pre there is a pre-amp out jack, the CF ensures that the impedance of the pre-out will drive whatever it is connected to. But the CF also follows the tone stages and helps drive the signal that was reduced by the tone stage. Some amps have a CF in this position, some don't. Whether or not you have a CF depends on what the output impedance is of the tone stage. It is common to have a gain stage following the tone stage to make up for insertion loss.
You can certainly go from a tone stage directly into a PI without a gain stage or a CF. A lot of amps do this. Check out some of the Fender schematics (vibroverb, dual showman, baseman) to see what they do. There is no CF but they have a gain stage before the long tailed pair phase inverter.
You want a PI that is going to have a good bass response. Some PI designs are better suited for guitar. Finding the right one is half the battle. You might find it interesting to look at some of the McIntosh designs like the MC60. They are available Invalid Link Removed. They have a driver before the PI.
I have most of Kevin's books, a guitar player friend gave them to me. Let's just say I was disappointed. I also had the misfortune of having to work on one of his builds. It took a while to get it to where I would allow a friend to use it. 
I have most of Kevin's books, a guitar player friend gave them to me. Let's just say I was disappointed. I also had the misfortune of having to work on one of his builds. It took a while to get it to where I would allow a friend to use it.
Maybe you should write your own books.
This is my second build using Kevin's design for inspiration and some of his design tips.
(I built a 100watt B15 using lots of guidance from his books)
but i haven't built an exact KOC design yet. I'm looking at building his 'simplified' SVT from TUT3 but his pre-amp seems way to simple to even call it "SVT-like". His simplified power amp design using 6 6550s is pretty straightforward and I like the individual bias controls but the splitter on that design has fewer gain stages than the original. I traded a few emails with him and he indicated that if I go foward with my plan to use the stock SVT-pre-amp design I'd probably want the last stage of the pre-amp to be a gain stage instead of the spec'ed CF. Haven't decide whether to leave it as is (go stock) and see if i have enough gain or build in a gain stage from step 1.
Also not going with KOCs all Hammond transformer design for PSU. His design requires 3 transformers (2PT 1 FL)for PSU instead of the standard 2 required for SVT (1PT 1FL)
But I don't have anything bad to say about the TUT series as they inspired me to do my first build which my son has been gigging with for 2 years.
(I built a 100watt B15 using lots of guidance from his books)
but i haven't built an exact KOC design yet. I'm looking at building his 'simplified' SVT from TUT3 but his pre-amp seems way to simple to even call it "SVT-like". His simplified power amp design using 6 6550s is pretty straightforward and I like the individual bias controls but the splitter on that design has fewer gain stages than the original. I traded a few emails with him and he indicated that if I go foward with my plan to use the stock SVT-pre-amp design I'd probably want the last stage of the pre-amp to be a gain stage instead of the spec'ed CF. Haven't decide whether to leave it as is (go stock) and see if i have enough gain or build in a gain stage from step 1.
Also not going with KOCs all Hammond transformer design for PSU. His design requires 3 transformers (2PT 1 FL)for PSU instead of the standard 2 required for SVT (1PT 1FL)
But I don't have anything bad to say about the TUT series as they inspired me to do my first build which my son has been gigging with for 2 years.
I like having a balance pot like they do on the SVT to balance the positive and negative amplitude of the phase inverter output. No PI is perfect. I might go for a bias adjustment for each tube. They have some gain after the phase inverter in the SVT to provide more signal going into the power tubes. It seems to work well.
I guess you have to consider how clean you want the power amp. Hi-fi clean or a bit gritty.
I guess you have to consider how clean you want the power amp. Hi-fi clean or a bit gritty.
Yeah that balance control seemed interesting but I figured with the indidiual bias contraols I should be able to dial-in the same effect. it's that gain stage to the grids that is the missing section in KOCs design that why i'm looking at boosting the last stage of the stock pre-amp. Although if I can work out how to unwind the original power amp design to enable individual bias adjust I could stay with the original splitter.
Re thinking my plan to use stock PSU and go with KOC design. KOC PSU uses a Hammond 717 for Va(6550 plates - 710volts) and Hammond 272DX for Vs (6550 screens - 410volts).
Stock PSU only has 350V screen supply.
KOC specs 1K-5W screen resistors and no plate resistors.
I just need to adjust the PSU so the Vpreamp voltage is 300vdc not 400.
Stock PSU only has 350V screen supply.
KOC specs 1K-5W screen resistors and no plate resistors.
I just need to adjust the PSU so the Vpreamp voltage is 300vdc not 400.
Here's what I got so far.. stock single channel pre-amp except the last stage has an added gain stage.
KOC splitter, Power and Hammond Iron.
https://www.dropbox.com/s/1pxlf6dqtxhu8qe/DV300-V1.pdf
KOC splitter, Power and Hammond Iron.
https://www.dropbox.com/s/1pxlf6dqtxhu8qe/DV300-V1.pdf
If I may ask, is there a reason you chose 12DW7s? Are they in plentiful supply? Why not use 12AX7 and 12AU7 (I think that's what a 12DW7 is)?
Also, would a tube bass amp benefit from a DC filament supply for hum reduction?
12DW7's are in plentiful supply both new and NOS, although I'm still looking for a new one that's worth a crap. All I see are these JJ's...cheap enough you can afford to replace them regularly I guess, and to be fair they sound good enough, but they're built terribly and don't last long. All mine failed within the first year.
Perhaps, but I have already built a 100w bass amp and I have found that the filament hum is easily controlled with a hum balance pot and the place you need the absolute cleanest DC (besides the B+ is the Bias supply.
