I'll also add a switchable boogie 1st stage, as well as another modest gain stage, or this fake PI I've read about at the end of the chain, and cathode bias.
This is probably a disaster waiting to happen but I'm gonna build a board anyway
SE Boogxpress
Moderators: pompeiisneaks, Colossal
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Smokebreak
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SE Boogxpress
I drilled out a cute lil 12x8 chassis over the holiday and wired up power, not really knowing where I was gonna go with it. I've been wanting to build a MKI as well as a mini-express, so I had the idea to mash em up a bit. The preamps are similar, with the tone stack being the big difference, in my mind, along with attenuation, or lack thereofit, oh yea and much different couplers. Well at least the cathode values are similar haha.
I'll also add a switchable boogie 1st stage, as well as another modest gain stage, or this fake PI I've read about at the end of the chain, and cathode bias.
This is probably a disaster waiting to happen but I'm gonna build a board anyway
I'll also add a switchable boogie 1st stage, as well as another modest gain stage, or this fake PI I've read about at the end of the chain, and cathode bias.
This is probably a disaster waiting to happen but I'm gonna build a board anyway
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Re: SE Boogxpress
Man, if that ain't a build junkie talking, I don't what is!
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Smokebreak
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Re: SE Boogxpress
Guilty 
here's my board
here's my boardYou do not have the required permissions to view the files attached to this post.
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Smokebreak
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Re: SE Boogxpress
I wanted to share this schematic and get some feedback on some improvements that could be made, as it's a neat little amp that's been a fun project. This amp has seen a lot of changes over the past week, but this is basically where she sits now.
It's a SE 6V6, and I tried to incorporate an Express circuit with a MKI circuit.
So in "normal" operation, the preamp is close to AB763/MKI, 3 stages. Still in normal mode, with SW1 pulled, it shorts the Fender 3M3//10p network, and adds a parallel resistor to the 220K grid leak, putting it at express specs. I haven't put the 2nd stage cathode on a switch to get to 2.7K express values yet.
SW2 gets me 10K, 5K, 1.8K cathodes
Then there's an extra gain stage in front, ala MKI, but switchable via Jose type switching. I should put that bottom leg of the 470K divider on the unused lug of the corresponding(unlabeled) switch, so it floats when in normal mode, otherwise it acts as a grid leak. It's not a huge drop in signal, though. Switch in that stage and the express SW1, and it gets wild!
In normal mode the cleans are great, and with the 10K on the 3rd stage, it stays clean all day long, and switched 1.8K gets a great Stonesy thing cranked.
Here's my beef #1 : When I introduce the extra gain stage, it sounds good, not great, and I get some slight fizz that seems to be around 7Khz. Not that good highmid sizzle, but an annoying undertone that seems "separate" from the rest of the distortion. That's why I've been messing around with the conjunctive filters. That kills it, but blankets the amp.
Beef #2: when in normal operation, and I pull the express SW1, I get some slight flarty flub notes here and there, but only when the 3rd stage Rk is 10K(express value). When I go to 1.8K there, it clears up. However, I can then introduce the extra stage(did I say wild!), and I don't have the flartyflub issue, regardless of stage 3 Rk or the gobs of gain. Wild mode is where the conjunctive filter gives the amp the super-smooth singing quality, but again with the blanket.
CFilter aside, I'm looking for some suggestions to help with these issues. I've since taken off the Ck on V4 and V1 is now 2K7/.68 . That helped. Also tried some small caps across plate resistors with no help. I dropped couplers too and that didn't do much for the fizzle.
Edit: I originally had an extra modest gain stage right before the 6V6 since there is no PI, but it was way too much. I believe it was 47K plate 22K cathode
Here's some pro:roll: clips I did the other day to demonstrate the nice cleans, and some of the harshness when pushed. No good example of the flartyflub as I just heard it yesterday , and I hadn't put in the Cfilter yet.
I haven't messed with the dropping string in days, but I'm thinking that changing voltages may help, as you can see the fluctuation I get on the plates of V4 with the Rk change. Maybe larger grid stoppers?
https://soundcloud.com/jeremyslemenda/boogxpress
It's a SE 6V6, and I tried to incorporate an Express circuit with a MKI circuit.
So in "normal" operation, the preamp is close to AB763/MKI, 3 stages. Still in normal mode, with SW1 pulled, it shorts the Fender 3M3//10p network, and adds a parallel resistor to the 220K grid leak, putting it at express specs. I haven't put the 2nd stage cathode on a switch to get to 2.7K express values yet.
SW2 gets me 10K, 5K, 1.8K cathodes
Then there's an extra gain stage in front, ala MKI, but switchable via Jose type switching. I should put that bottom leg of the 470K divider on the unused lug of the corresponding(unlabeled) switch, so it floats when in normal mode, otherwise it acts as a grid leak. It's not a huge drop in signal, though. Switch in that stage and the express SW1, and it gets wild!
In normal mode the cleans are great, and with the 10K on the 3rd stage, it stays clean all day long, and switched 1.8K gets a great Stonesy thing cranked.
Here's my beef #1 : When I introduce the extra gain stage, it sounds good, not great, and I get some slight fizz that seems to be around 7Khz. Not that good highmid sizzle, but an annoying undertone that seems "separate" from the rest of the distortion. That's why I've been messing around with the conjunctive filters. That kills it, but blankets the amp.
Beef #2: when in normal operation, and I pull the express SW1, I get some slight flarty flub notes here and there, but only when the 3rd stage Rk is 10K(express value). When I go to 1.8K there, it clears up. However, I can then introduce the extra stage(did I say wild!), and I don't have the flartyflub issue, regardless of stage 3 Rk or the gobs of gain. Wild mode is where the conjunctive filter gives the amp the super-smooth singing quality, but again with the blanket.
CFilter aside, I'm looking for some suggestions to help with these issues. I've since taken off the Ck on V4 and V1 is now 2K7/.68 . That helped. Also tried some small caps across plate resistors with no help. I dropped couplers too and that didn't do much for the fizzle.
Edit: I originally had an extra modest gain stage right before the 6V6 since there is no PI, but it was way too much. I believe it was 47K plate 22K cathode
Here's some pro:roll: clips I did the other day to demonstrate the nice cleans, and some of the harshness when pushed. No good example of the flartyflub as I just heard it yesterday , and I hadn't put in the Cfilter yet.
I haven't messed with the dropping string in days, but I'm thinking that changing voltages may help, as you can see the fluctuation I get on the plates of V4 with the Rk change. Maybe larger grid stoppers?
https://soundcloud.com/jeremyslemenda/boogxpress
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Re: SE Boogxpress
I have zero experience with SE amps but yours sounds great if that is the question.
Often times an amp is compared to a Push Pull amp.
From the recording your's sounds really good, so very good for a recording amp.
Often times an amp is compared to a Push Pull amp.
From the recording your's sounds really good, so very good for a recording amp.
Tom
Don't let that smoke out!
Don't let that smoke out!
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Smokebreak
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Re: SE Boogxpress
Thanks, Structo. I dig the cleans but the little fizzle in overdrive is buggin me. I think it's more apparent sitting next to the speaker, for some reason. Perhaps this one's fate is indeed a recording amp. I'm definitely comparing it to PP, which I know I shouldn't.. I just changed it over to cathode follower, and the fizzle is still there, but disappears in the mega-gain. I'm gonna change it back and keep stabbin at it.Structo wrote:I have zero experience with SE amps but yours sounds great if that is the question.
Often times an amp is compared to a Push Pull amp.
From the recording your's sounds really good, so very good for a recording amp.
Re: SE Boogxpress
(deleted)
Last edited by matt h on Fri Mar 27, 2015 2:34 am, edited 1 time in total.
Re: SE Boogxpress
Grid stopper on stage 1?
Lower the 5n there for cc to stage 2?
Maybe it can help.
Lower the 5n there for cc to stage 2?
Maybe it can help.
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Smokebreak
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Re: SE Boogxpress
Thanks Matt and Surfsup. Great suggestions!
Caps on the Rp didn't have much audible affect(killing fizz or audible high end) except on the 4th stage. I ended with 600p there. I *think* I can still hear a little fizz on frequencies passed, but it's a big improvement. Of course I lost a little high end, but a bright cap either on the MV or the gain pot puts it back in. I'm thinking it'll work better on the MV if I've killed the fizz right before it, but I'm still experimenting with values. It'll be a small pf.
For bias, I've gone all the way up to 575R, so my screens are under 1W now. This change helped the fizzies greatly as well, in addition to making for a more pleasing overall tone.
Also, for express mode, Instead of the short across the 3M3/10p, I went with 220K, which is still a great boost, but much smoother.
Surfsup , than 5n is actually a poorly written 15n on my part, but it got me thinking so I went all the way down to 1n and high gain mode is tight! Along with 1st stage 2.7k/.68 it's a 80's metal amp now, if it needs to be
I'm still hesitant about the stage 1 grid stop because of the sensitivity, but I'll experiment with them, as I just got my first radio station tonight, too.
Now I'm really kicking myself for not getting the ESE OT!! I've actually got one in another amp but I've gotta stop cannibalizing my own crap.
Matt, can you explain the two statements below? What could you predict, with the biasing of the stages? I'm assuming lack of any hot biasing...?
I'm generally confused by the second statement concerning peak to peak at the grid?
Thanks for cluing me in to the local FB for SE power tubes. I'd never even seen a discussion about that. I just now "got it" so I'll give it a shot.
Caps on the Rp didn't have much audible affect(killing fizz or audible high end) except on the 4th stage. I ended with 600p there. I *think* I can still hear a little fizz on frequencies passed, but it's a big improvement. Of course I lost a little high end, but a bright cap either on the MV or the gain pot puts it back in. I'm thinking it'll work better on the MV if I've killed the fizz right before it, but I'm still experimenting with values. It'll be a small pf.
For bias, I've gone all the way up to 575R, so my screens are under 1W now. This change helped the fizzies greatly as well, in addition to making for a more pleasing overall tone.
Also, for express mode, Instead of the short across the 3M3/10p, I went with 220K, which is still a great boost, but much smoother.
Surfsup , than 5n is actually a poorly written 15n on my part, but it got me thinking so I went all the way down to 1n and high gain mode is tight! Along with 1st stage 2.7k/.68 it's a 80's metal amp now, if it needs to be
I'm still hesitant about the stage 1 grid stop because of the sensitivity, but I'll experiment with them, as I just got my first radio station tonight, too.
Now I'm really kicking myself for not getting the ESE OT!! I've actually got one in another amp but I've gotta stop cannibalizing my own crap.
Matt, can you explain the two statements below? What could you predict, with the biasing of the stages? I'm assuming lack of any hot biasing...?
I'm generally confused by the second statement concerning peak to peak at the grid?
Thanks for cluing me in to the local FB for SE power tubes. I'd never even seen a discussion about that. I just now "got it" so I'll give it a shot.
matt h wrote:
well, there are lotsa center and/or cold biased preamp stages...
also, that 6v6 is probably getting overloaded pretty quickly. A 6v6 at those voltages caves in completely at what, 20Vpp signalwise? Use your bias voltage as a quick check for that.
.
Re: SE Boogxpress
(deleted)
Last edited by matt h on Fri Mar 27, 2015 2:33 am, edited 1 time in total.
Re: SE Boogxpress
"15n on my part"
yowza...glad you changed that. I figured there was too much bass.
the first stage GS might stop some parasitic oscillation that is developing through the amp into audible at the end. Use a 22k to a 47k - will not attenuate any frequencies you will hear - not even close. Use a 1W metal film right on the socket.
what matt is saying is all your stages are "positioned" the same (i.e. 100k plate resistor with the same Rk I believe - from memory didn't look at your schemo this AM). I noticed the same but figured you wanted it that way and I didn't look at the tube graph to see what was going on (I don't have that stuff committed to memory)
The use of stage positioning is to warm up or cool down the tone. You can set them alternating, you can use a higher current tube later in the string like an AU, etc...
yowza...glad you changed that. I figured there was too much bass.
the first stage GS might stop some parasitic oscillation that is developing through the amp into audible at the end. Use a 22k to a 47k - will not attenuate any frequencies you will hear - not even close. Use a 1W metal film right on the socket.
what matt is saying is all your stages are "positioned" the same (i.e. 100k plate resistor with the same Rk I believe - from memory didn't look at your schemo this AM). I noticed the same but figured you wanted it that way and I didn't look at the tube graph to see what was going on (I don't have that stuff committed to memory)
The use of stage positioning is to warm up or cool down the tone. You can set them alternating, you can use a higher current tube later in the string like an AU, etc...