Everything to gain... or not.
As with all things valve audio, the theory gets you so far, then the tweaking takes over. ;-)
I've been messing with the values of the anode resistors on the ECC82, and the cathode resistor on the triode-strapped EF86H. Mainly just to see what effect the changes would have on the tone and "responsiveness" of the amp with my own selection of bass guitars.
I also tried various cathode bypass capacitors on the EF86H, but found I prefer the tone with this valve's cathode left unbypassed. Less gain on that stage because of the omission, but not really a hassle because the pre-amp is feeding 340 watts RMS of power amps. More than enough to upset the neighbours.
This morning I was looking through my collection of valves and found an old Mullard ECC83. Given that it's pin-compatible with the ECC82, I threw it in there just to have a listen. And that's when I knew I'd found the sound I was looking for!
The gain was a bit fierce until I swapped out the 220K resistors I'd been using on the anodes of the two stages of ECC82. Dropping them to 120K, then increasing the value of the cathode resistor on the EF86H tamed the levels really nicely. It's clean and warm with the initial gain control set to anything up to the halfway point. Beyond that and it starts to overdrive quite nicely, should I ever need a rich, distorted bass sound.
There are still a couple of further tweaks I want to do. According to Watford Electronics, the Russian-made Svetlana EF86H sonically superior to the Electro-Harmonix bottle I'm currently using, so one of those is on my shopping list. They also offer their own brand, specially treated ECC83 that is supposed to be the dog's bollocks, so I'll be throwing one of those in the shopping cart too.
The cabinet this thing is built into is a toy box/jewellery box that I got cheap from Amazon and cut extra holes in to mount the controls and the mains socket. To finish that off I want to get a couple of spring-loaded catches to keep the lid closed, and make some sort of grille so I can cut a vent in the top above the valves to keep temperatures reasonable when it's in use.
Could this be the start of a new range of DD amps, aimed specifically at bass players?
Watch this space.
The current circuit diagram is here if you fancy having a go at building your own. remember all the warnings! Building valve amps is DANGEROUS! Please be careful. If you are not confident around high voltages, then don't attempt to build one of these without putting in some time learning what's involved. I cannot be held responsible for you become a Darwin Award candidate.
I've been messing with the values of the anode resistors on the ECC82, and the cathode resistor on the triode-strapped EF86H. Mainly just to see what effect the changes would have on the tone and "responsiveness" of the amp with my own selection of bass guitars.
I also tried various cathode bypass capacitors on the EF86H, but found I prefer the tone with this valve's cathode left unbypassed. Less gain on that stage because of the omission, but not really a hassle because the pre-amp is feeding 340 watts RMS of power amps. More than enough to upset the neighbours.
This morning I was looking through my collection of valves and found an old Mullard ECC83. Given that it's pin-compatible with the ECC82, I threw it in there just to have a listen. And that's when I knew I'd found the sound I was looking for!
The gain was a bit fierce until I swapped out the 220K resistors I'd been using on the anodes of the two stages of ECC82. Dropping them to 120K, then increasing the value of the cathode resistor on the EF86H tamed the levels really nicely. It's clean and warm with the initial gain control set to anything up to the halfway point. Beyond that and it starts to overdrive quite nicely, should I ever need a rich, distorted bass sound.
There are still a couple of further tweaks I want to do. According to Watford Electronics, the Russian-made Svetlana EF86H sonically superior to the Electro-Harmonix bottle I'm currently using, so one of those is on my shopping list. They also offer their own brand, specially treated ECC83 that is supposed to be the dog's bollocks, so I'll be throwing one of those in the shopping cart too.
The cabinet this thing is built into is a toy box/jewellery box that I got cheap from Amazon and cut extra holes in to mount the controls and the mains socket. To finish that off I want to get a couple of spring-loaded catches to keep the lid closed, and make some sort of grille so I can cut a vent in the top above the valves to keep temperatures reasonable when it's in use.
Could this be the start of a new range of DD amps, aimed specifically at bass players?
Watch this space.
The current circuit diagram is here if you fancy having a go at building your own. remember all the warnings! Building valve amps is DANGEROUS! Please be careful. If you are not confident around high voltages, then don't attempt to build one of these without putting in some time learning what's involved. I cannot be held responsible for you become a Darwin Award candidate.
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