Cathode bypass cap and freq roll off

[xcortes]

Wow, you're selling the 19s ! 

I use smaller pf caps in all my horn amps. Will remove the bypass cathode caps and see what happens.

[xcortes]

The sound is much better without the bypass caps. BUT I get a slight high frequency buzz. I can hear it through the mid horns and tweeters so it's not specific to one amp. Still the "removing a veil" cliché applies. Any idea as why removing the caps causes this?

[johnsonad]

Nice! I'm glad it did something for you! I will try it again but I'm in no hurry. 

Yes they are going. I can't get new speakers if they are always in the background

[BNAL]

Aaron,

I can't believe you're parting with the 19s. From the very limited listing I had they sounded great and dialed in. They imaged feat and had that wonderful texture of live music. The 755s must sound wonderful.

By the way I have been working my way through all the albums.

Brad

[xcortes]

I put them back in because of the noise but the sound isn't half as good as without.

[johnsonad]

@Brad, you will have to come down and listen to the 755's. They are not the 19's but still sound great and are easier to PCS with

@Xavier, could it be PS noise you are hearing? Hopefully PJ will chime in. Mine are essentially Paramounts but the layout is much different and I have zero noise when removing the bypass cap.

[xcortes]

Mine are 2a3 Paramounts. Took them off again. Nice! Yes hopefully PJ can comment because the noise is too intrusive (on 110dB horns). Same on both channels.

[Paul Joppa]

The unbypassed cathode resistor raises the effective plate impedance of the tube - quite a lot in the case of the direct-coupled amps because that cathode resistor is much larger. That means the power supply noise isolation provided by the plate choke is greatly reduced. A much better power supply filter would be the only good answer - CLC instead of CRC, bigger caps, etc...  Ultimately, a shunt regulated supply?  :^)

[johnsonad]

Xavier, I'm not sure how much current that design draws but the Paramount stock plate choke makes an excellent PS choke in CLC (I use two per channel). With your top mounted OPT there should be plenty of room for one under the hood of a stock chassis plate.

[xcortes]

Thanks. I already have a clc ps. I asked my friend Jorge who has my sr45s with horns to try and report.

[johnsonad]

Are you using the Triad choke in your PS? If so, the BH choke has more Henries and better filtering.

[xcortes]

Mq bcp  something

[2wo]

I run my SR-45 without a cathode cap and didn't notice an increase in noise. My speakers are only ~95db though...John 

[johnsonad]

That may be my situation too John. Xavier's horns are much more sensitive. Have you tried it on the WE's?

[xcortes]

My speakers are 110dB efficient. With 93/95 db speakers it wouldn't be an issue. And according to PJ the problem exacerbates with dc amps which neither John's nor Aaron's are.

I need those new SR45s!