Volume difference between channel 1 and channel 2

[halfmassive]

I just built an amp that is basically a 2 channel matchless spitfire with the standard spitfire power amp section and 12ax7 preamp on channel 1 with an ef86 preamp in channel 2. The 2nd channel (ef86) sounds awesome but the first channel (the 12ax7 spitfire) is lacking in volume. It still gets loud but its not nearly as punchy or bright as the other spitfires I’ve built. I need to turn the volume up half way before I get any gig worth volume on my other amps this size it get really loud at about 10 o'clock on the vol pot.

The only difference is this is a two channel version and my other 2 spitfires were single channels.



All voltages on the preamp tubes seem to check out just fine and my power voltages also seem good. The only thing different here is I have both preamps going to the same filter cap (like on an 18watt). Could the shared preamp filter cap cause this volume difference?



Any ideas on what may be causing the lack of volume?

[Structo]

It would help if you could post the schematic and or layout you used.

Plus, clear photos of the interior of the amp can help as well.

[halfmassive]

Here is the layout I used. I basically cobbled it together from the spitfire layout and added the ef86 channel from the dc30. I believe I am using the opposing pi inputs for each channel but I'm not really sure this the first time I've not used a "stock" layout.

I am aware of the ef86 gain difference and I wouldn't call the volume difference on the spitfire channel night and day from my other spitfire but it's lacking in comparison.

I can add pics of the amp later on but don't have any at the moment

Thanks very much for your help yet again!

[matt h]

(deleted)

[halfmassive]

Thanks very much. What you describe sounds about right from what I am hearing.

Sorry for my ignorance, but if I were to go the route of reducing the dropping resistor, you are referring to the 22k resistor on the preamp filter cap correct? How low would I want to go here? I guess I would start with something around 10k or so? Also for the “second resistor on the feed to the plate resistor for the ef86. Essentially running a split-load-plate on the ef86.” How would I do this? Right now I have a 330k plate resistor going to pin 6, how would I split this? I’m not super familiar with the ef86.

Would I avoid some of these changes if I just added another 22uf filter cap and ran it directly to the spit channel, instead of the shared cap? I noticed in the dc30 this is how it's run.

Again I really appreciate your help and sorry for my lack of knowledge on some of this stuff.

[matt h]

(deleted)

[halfmassive]

Thank very much Matt. I appreciate your extensive help. I'm going to try some of these out and report back with my findings.
Thanks again

[halfmassive]

I just added a filter cap to the spitfire stage which brought the voltage up to the preamp which brought the amp back to life. Its still not as tough sounding as my other spitfire but its much closer. Although I did use a 16 uf instead of a 22 uf since it was all I had on hand at the moment. I plan on putting a 22uf in place of the 16 uf when I get one and playing around with the phase inverter and some of the other tips you gave me just to tweak the sound a bit, but overall I'm pleased with the amp.

Thanks again your information really helped.