OK, maybe dumb question, but since I've not encountered this issue in my other builds (dozen or so), I'll ask. I've just finished a fendery amp w/ reverb, and it has a lot of what I'd call hash noise. Even with the volume all the way down. It's not 60 Hz or 120 Hz, but a whooshy hashy sound. It's different than high-gain tube hiss, and this is not a high gain amp.
What are the usual suspects? Are they:
1. bad tubes
2. wonky solder joints
3. wonky resistors
I use PRP 1 watts on all the plates, have for a while now, never a problem with them. The only CC is the 3M3 reverb resistor.
Ideas? Suggestions? Stupidly obvious things I missed?
Cure for hash?
Moderators: pompeiisneaks, Colossal
Cure for hash?
Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
Re: Cure for hash?
Can you post a sound clip?
Re: Cure for hash?
Paul,
That's a good idea. I'm heading out of town in today, but I'll do it next week, if I don't get it fixed.
I've just been too busy to mess with it this week. I do, however, suspect either the plate resistor on V3b, because switching from a 12AX7 to a 12AT7 makes the noise worse. Since the AT is lower mu but much higher plate current, I suspect the plate resistor. I hope to yank it out next week.
Do you agree with that logic? I just don't have any experience with bad/noisy plate resistors.
That's a good idea. I'm heading out of town in today, but I'll do it next week, if I don't get it fixed.
I've just been too busy to mess with it this week. I do, however, suspect either the plate resistor on V3b, because switching from a 12AX7 to a 12AT7 makes the noise worse. Since the AT is lower mu but much higher plate current, I suspect the plate resistor. I hope to yank it out next week.
Do you agree with that logic? I just don't have any experience with bad/noisy plate resistors.
Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
-
David Root
- Posts: 3540
- Joined: Fri Aug 04, 2006 3:00 pm
- Location: Chilliwack BC
PRP plate resistor
You never know, but I'd be surprised if a PRP resistor went bad. I've been using them for 3 years, zero problems.
I did fry a pair of 100 ohm 1W PRPs balancing the end of a heater chain by grounding the PT centertap driving a 4-diode full bridge rectifier, duh! Put >3A thru 'em because the mains fuse blew right after they flamed out.
I did fry a pair of 100 ohm 1W PRPs balancing the end of a heater chain by grounding the PT centertap driving a 4-diode full bridge rectifier, duh! Put >3A thru 'em because the mains fuse blew right after they flamed out.
Re: Cure for hash?
I've been meaning to post this, but y'all know how it is...
Fixed it a week or so ago. It was a wierd thing, cuz the amp sounded real mellow, but was full o' tube hiss. Turns out the mellowness was a wonky connection at the volume pot dumping signal to ground. When I found and fixed that, the amp was a raging beast! Whoa, Nelly! That, in turn, revealed the source of the hiss--the first two gain stages were running a bit too hot for the common good. So I re-did them to semi Dumble values, and now the machine is mighty fine, mighty fine. Those PRPs on the plates even give up a wee tiny bit of chirp.
I'm gonna take the amp to our recording session on Monday, so maybe I'll have a clip for y'all. I need to re-cut the guitar part from our new instrumental tune "Twilight Conversation."
In other news, the radio show Car Talk played our song "Cadillac Girl" on the air today. Now if only all those loyal Car Talk listeners ran to their iTunes and downloaded our song.....I've got two college funds to fatten up!
Here's a pic of it (the Longneck) and the newest Roadhouse. I'm going to the Premier Guitar Mag festival at the Dulles Expo center in November, so these are two of the three I've got ready to sell.
Yeah, yeah, y'all want some gut shots. I'll do that next time I pull the chassis on the Longneck. Might not need to do the Roadhouse.
Fixed it a week or so ago. It was a wierd thing, cuz the amp sounded real mellow, but was full o' tube hiss. Turns out the mellowness was a wonky connection at the volume pot dumping signal to ground. When I found and fixed that, the amp was a raging beast! Whoa, Nelly! That, in turn, revealed the source of the hiss--the first two gain stages were running a bit too hot for the common good. So I re-did them to semi Dumble values, and now the machine is mighty fine, mighty fine. Those PRPs on the plates even give up a wee tiny bit of chirp.
I'm gonna take the amp to our recording session on Monday, so maybe I'll have a clip for y'all. I need to re-cut the guitar part from our new instrumental tune "Twilight Conversation."
In other news, the radio show Car Talk played our song "Cadillac Girl" on the air today. Now if only all those loyal Car Talk listeners ran to their iTunes and downloaded our song.....I've got two college funds to fatten up!
Here's a pic of it (the Longneck) and the newest Roadhouse. I'm going to the Premier Guitar Mag festival at the Dulles Expo center in November, so these are two of the three I've got ready to sell.
Yeah, yeah, y'all want some gut shots. I'll do that next time I pull the chassis on the Longneck. Might not need to do the Roadhouse.
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Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
Re: Cure for hash?
Nice builds! Amp porn is always welcome! 