Hi there,
I have just finished my C'tone build and it is working pretty good. Sound is coming along as I am burning in and tweaking my trimmers.
My main concern is voltages with the Hammond 290DEX (for UK).
On V4 and 5 I am getting 470-474V with TAD 6L6 WGC and V1-1 is a bit high at 207V with an old Telefunken. I have tried some different V1 and V2 tubes but it seems about the same.
V3 is a Sovtek LPS balanced up at around 298V.
I have attached the layout showing where I was told to look at dropping the voltage to V1. I have tried some different values but I can only get the voltage up not down.
This is only my second build so I am no expert. I really would like to get the V1 down to 195-200V as this would be a good starting point for tone tweaking.
Nobody said this was gonna be easy.....
Thanks
Rog
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I have attached the layout showing where I was told to look at dropping the voltage to V1. I have tried some different values but I can only get the voltage up not down.
I don't think that I qualify as an experienced builder having done only two D style amps so far.
Anyway....which values did you try? Increasing the 3k3 dropping resistor should help but it will also drop voltages at V2 and V3.
Still you might try something in the range of 6k...
If you want to keep voltages at V3 you may increase the 22k dropping resistor (which will lower V1 and V2) or the 2k2 close to the green circle on the right (which will only affect V1).
Edit: Alternatively, you could try to reduce the 220k in the right green circle to 150k. This will, however, also affect V2 and V3.
Why a 220K to ground to simulate the FET? The baseline value to start from is 150K. Not that there is a right or worng, but in real Dumbles, 150K would be more like it.
Also, I noted a bunch of tweaks that deviate from HRM101. I'd suggest using the ampgarage schematic. Then tweak from there. What you have is just not going to sound as good as the tried and proven recipes.
Markus, thanks so much for your help. I targeted the 22K as I had a 5K knocking about, this gave me 27K in series. I also wanted, as per your advice, to just reduce V1 and 2.
I also swapped some tubes around.
So
V1 - 1 - 195V Old Brimar Ecc83
V2 -1 - 206V Old Telefunken ECC83
V3 - 296/ 295V New Sovtek LPS
As far as I can tell, this is spot on. I reset my HRM trimmers and getting a nice full tone even at lower volumes, single notes sustaining and blooming into feedback on a Strat.
V4 and V5 are 473V with the TAD 6L6 still and 37.5-38 mV bias. Does this sound OK? Certainly so far I am pleased, but I understand that plenty of burn in is required.
Anyway, I am also busy building my head cab today as I am off work, cut all the 18mm ply to size and will do the fingerjoints tomorrow. I am not really looking forward to Tolexing but like everything I will give it a go!
dogears wrote:Why a 220K to ground to simulate the FET? The baseline value to start from is 150K. Not that there is a right or worng, but in real Dumbles, 150K would be more like it.
Also, I noted a bunch of tweaks that deviate from HRM101. I'd suggest using the ampgarage schematic. Then tweak from there. What you have is just not going to sound as good as the tried and proven recipes.
Ive got to thank you for pointing that out, I checked it over and forgot (noob speak for being a total ****) to run the 220K to ground, hence no FET simulation. Once it is grounded (more ) I will try a 150K as per the 101.
I will tweak following your advice from 101... thanks guys. I am so embarassed now. Right, black wire to ground and try again...
Right - grounded the 220K. I will leave this for now as I only have a 1/2w 150K.
Voltage dropped down a lot so took out the additional 5K and put back both Telefunkens.
Back to a 193 at V1 and 204 at V2.
This seems more like it, phew and thanks to you both for your help.
Just gonna wait till the neighbours and their kid are out tomorrow then CRANK IT just a little. Put a touch of reverb in the loop, which will have to do until I get the Dlator built.
dogears wrote:Why a 220K to ground to simulate the FET? The baseline value to start from is 150K. Not that there is a right or worng, but in real Dumbles, 150K would be more like it.
Also, I noted a bunch of tweaks that deviate from HRM101. I'd suggest using the ampgarage schematic. Then tweak from there. What you have is just not going to sound as good as the tried and proven recipes.
Is the (3.3k; 22k; 2.2k; 220k) PS dropping string combination (used on the Ceriatone HRM and OTS) a match to any Dumble model? It doesn't appear to me to match the 101 or 124 schematics.
The voltages that my HRM had, using this combo, were way too high. After adjusting them, the sound was substantially better IMHO.
This may be bad advice as I'm just a novice, but I replaced the first three dropping string resistors with appropriately high powered pots. Then I tweeked the pots to get the best sound/feel without deviating too far from proven voltages. After that I replaced the pots with resistors to match the values that I settled on. Sometimes stupidity is the mother of invention. Other times it's just stupid. Not sure where I landed on this scale, but my sound/feel got closer to target.
scotto wrote:This may be bad advice as I'm just a novice, but I replaced the first three dropping string resistors with appropriately high powered pots. Then I tweeked the pots to get the best sound/feel without deviating too far from proven voltages. After that I replaced the pots with resistors to match the values that I settled on. Sometimes stupidity is the mother of invention. Other times it's just stupid. Not sure where I landed on this scale, but my sound/feel got closer to target.
I also wanted to try this but never did because I was too lazy
Which values did you finally end up with?
Just measured:
6.7, 18.5 and 6.2
This yields some pretty low voltages vs.typical, but they seem to work pretty well for me. I have V1=180, V2=192, V3=269. I don't recommend trying my values as your taste, tube type and playing style will likely point towards different targets. This gives a more compressed sound than typical and that seems to work well with my arguably poor right hand technique. Higher voltages had more ping but were less forgiving. Tweeking to your sweet spot is the trick. I still have much to learn in playing and tweeking!
