I am stumped . A new dumbleator build is not giving me any gain. When I plug it in with the send and return turned all the way up there is very little sound and it is slightly distorted (mostly clean). I have build another dumblator and it works fine but it is currently out of the house so I cannot compare the multimeter readings. Here they are on a 12at7:
1 300
2 20.7
3 35
6 146
7 1.3mv
8 2.18
The pic is below. I would love any suggestions on where to go next for trouble shooting. My build is a little odd because I rushed it a little. Thanks for you time TJ
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The pic is below. I would love any suggestions on where to go next for trouble shooting. My build is a little odd because I rushed it a little. Thanks for you time TJ
Your problem is on the 1.3mv on pin 7. That voltage should be far higher,
Also, the 12AT7. Unless you tweaked the coupling caps and plate/cathode resistor, I'd use a 12AX7. The circuit is far from optimized for the gain and lower plate resistance of the 12AT7.
tonejunkie wrote:I am stumped . A new dumbleator build is not giving me any gain. When I plug it in with the send and return turned all the way up there is very little sound and it is slightly distorted (mostly clean). I have build another dumblator and it works fine but it is currently out of the house so I cannot compare the multimeter readings. Here they are on a 12at7:
1 300
2 20.7
3 35
6 146
7 1.3mv
8 2.18
The pic is below. I would love any suggestions on where to go next for trouble shooting. My build is a little odd because I rushed it a little. Thanks for you time TJ
It should be trivial to isolate the problem to either the cathode follower or the return stage. Plug the PREAMP send from your amp into the input of the D-lator and then take the FX out of the D-lator and plug it back into the POWER AMP IN in your amp. Dime the SEND control and you should have close to unity gain. If not, the problem is in the gain stage.
If the problem is in the return stage, you can plug your guitar into the FX return in the D-lator and take the OUT from the D-lator into the POWER AMP IN of the amp. You should get a really loud sound (like the amp itself) like that when the stage is operating properly.
On the 12AX77 VS 12AT7 thing, well... it's certainly not going to make or break the thing.
If you want to use a 12AT7, I'd consider upping the .1 cap on the plate to a .22, also up the bypass cap. 12AT7 tubes have much less bass than 12AX7 when swapped into the same circuit (unless you adjust things)
You may also want to remove the feedback loop as there is much less gain to begin with.
Tweaking the string to get the "correct" voltages on both triodes is another important thing to do.
Aside from that, I agree with Gil. Whichever floats your boat.
I'll just stick with using the ax7 as I trouble shoot. I have my signal probe on this thing and with the signal going in the fx return jack I get a clean signal although attenuated after the parrallel 220k, 500pf at the grid. Then after the tube at the plate my signal is slightly distorted and very very weak. I removed the .22uf cap to see if removing the feedback loop would give me more gain and it does not. I'm probobly going about this all wrong but I'm trying my best .
tonejunkie wrote:TimS whats the comment about aim mean?
Sorry, it's a just a bad play on words. Troubleshooting in the way you meant it is a single word; my failed attempt at a joke involved taking "trouble shooting a Dumbleator" to mean that you had difficulty hitting a Dumbleator with a projectile propelled from a firearm.
I'll get some better pics up tomorrow. I redone the whole thing trying to find the culprit. No luck . Just the same weak slightly distorted tone. I don't get it? Maybee I'm reading something wrong. I have built 6 amps, 2 dumblators, and many many pedals and never have I had this sort of problem. Just venting. TJ
P.S. TimS I like the comment now that I get it. I may have to do some trouble shooting Sunday if I don't figure this thing out!
Last edited by tonejunkie on Sat Oct 13, 2007 1:38 am, edited 1 time in total.
In frustration I rebuilt the circuit. I did replace the ck and measured the rest of the components. I still have the same problem. Here are a couple of pics.
What's the best way to get pics that are not blurry. I am using what I thought was a decent camera and all the pics I took suck. I will try again tomorrow.
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. A new dumbleator build is not giving me any gain. When I plug it in with the send and return turned all the way up there is very little sound and it is slightly distorted (mostly clean). I have build another dumblator and it works fine but it is currently out of the house so I cannot compare the multimeter readings. Here they are on a 12at7:
. I am going to get my probe out and try and see where the signal drops off.
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. Just the same weak slightly distorted tone. I don't get it? Maybee I'm reading something wrong. I have built 6 amps, 2 dumblators, and many many pedals and never have I had this sort of problem. Just venting. TJ