Smitty wrote:The wiring on the switches looks very clean Aaron. Looks like you spent a lot of time...
What type of resistors are those? Xicon 1W CF??
Looks like Xicon 1w CF to me.
Thanks!
Is there a consensus regarding which current-production carbon-film resistor is a suitable substitute for the Sprague Q-Lines in non-plate/non-cathode positions? Do the Xicon 1W CF sound close?
Progress report..... Up and running! Still have to build the FET circuit so voltages are a little higher, but everything is sounding sweet. Haven't had a chance to really turn it up cause of late nights.
Really like the tone shaping of the filters, worth the effort.
Changed some values in the voltage rail to get closer to the voltages on the schematic. The transformer in the schematic shows 565vac where mine is 660vac, so my 6l6's are running a bit higher. But the rest of the voltages are pretty close to the rest of the schematic (biased to suit though).
Sorry Martin, I still haven't tried to bypass the inductor yet, spent the night getting the voltages right. Will get there soon though.
Aaron
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Aaron, what about the 100k resistor between the 0.01u and the inductor shown in the hand-drawn schematic? It does not appear in the re-drawn version by 10thtx. Did you include that in your build?
Do you use AC filaments throughout the amp? I suggest watching you don't place audio signal wires in top of the filament wires. Looks like you may have done that in the reverb area? You mentioned the reverb hums?
martin manning wrote:Aaron, what about the 100k resistor between the 0.01u and the inductor shown in the hand-drawn schematic? It does not appear in the re-drawn version by 10thtx. Did you include that in your build?
Hi Martin, yes I have the 100k in series. I found this regarding the filter too.
glasman wrote:I had some time this morning and breadboarded the SSS Filter stack. The only liberty I took was to use a 1M pot in lieu of the switched resistor array. The results were interesting. I measured the frequency response of the filter using an Ono Sokki CF-5220 FFT Analyzer. Swept from 1 to 20000 Hz.
Observations :
1. The frequency response does not change at all for inductors from .5H to 1H.
2. You get EXACTLY the same response if you substitute the inductor with a piece of wire.
Conclusion : Inductor is not required. Look at the XL of the inductor it is extremely low at the frequencies we are working with and has no effect.
Here are the response charts I measured for the various switched cap values. All measurements were taken with the pot set to simulate Position 4.
bruce egnater wrote:Do you use AC filaments throughout the amp? I suggest watching you don't place audio signal wires in top of the filament wires. Looks like you may have done that in the reverb area? You mentioned the reverb hums?
Hi Bruce, I changed the wires from the tank to sheilded and it made a big difference but still slightly there. I ran those heater wires along the chassis cause I figured standing them up might put them to close to the boards.
You can't hear it with a band, but in a quiet studio there's a slight hum.
Actually, I was referring to the heater wires at the sockets. Don't lay the grid wires on top of them. Also the placement of the pan is a big deal. Be sure the output end of the pan is as far away from the power transformer as possible.
Aaron wrote:
Hi Martin, yes I have the 100k in series. I found this regarding the filter too...
Thanks Aaron, I found Gary's post and Bode plots too. I can reproduce those results with SPICE, confirming that the inductor has no effect. (Edit: after I put the 100k resistor in!)
Last edited by martin manning on Mon Jul 14, 2014 4:24 pm, edited 1 time in total.
Wired up my first FET circuit!!!! All I had was a MPF102, so have used that to test it until my NTE452's arrive.
I think I'll change the capacitors throughout as well. In my Pentode build I used yellow tubulars and the amp sounded a bit dark, so for this amp I used 715/6 orange drops and this amp is a bit too bright for my taste. I've ordered some 6PS orange drops, so maybe a mixture of both?
I've been reading threads on different capacitors and their effect on the tone. Anyone used a combination of different capacitors? Eg, 716's for PI and 6PS's for tonestack or vice versa.
