Taming amp gain in single channel deluxe reverb build

[bepone]

there is a good way to test the amp how good is , lift tone controls up from the gnd, and see how good amp behaves in higher gain, must be excelent..otherwise there are problems in the amp stages (lead dress probably)

[imo1]

Out of curiosity, what does the amp sound like with the master on 10? Mine sounds terrible. Regardless of whether i implement this or not, I would like to have a somewhat usable amp through the volume sweep.

I mostly played the amp with the MV on 10, but the volume pot was down below 5. I only play at home. I cranked it wide open a couple times in the shop just to see how loud it would get. Wide open added a little hair to the sound but nothing I would say sounded terrible. I ran 6L6s for a while but eventually switched back to 6V6s. I used MM iron and a reissue Jensen P12N speaker.

There's more info, including how I dealt with the extra gain, on my website. The 100K MV was my final fix for the extra gain due to the missing tremolo intensity pot in my amp. Works fine.

Sounds like you may have other issues. I'd sub in a proper OT for starters.

Yeah. I'm thinking the OT is not going to cut it. It is the endbell style, so there is a big hole in the chassis. I'm gonna try to see if I can find an OT with a similar size and mounting style so I don't have a giant hole in the chassis.

I was able to get my AC signals pretty close by subbing in a pot where I had the 330k. Right about 190k was the spot. I need to play it and see what it sounds like next

[imo1]

there is a good way to test the amp how good is , lift tone controls up from the gnd, and see how good amp behaves in higher gain, must be excelent..otherwise there are problems in the amp stages (lead dress probably)

I don't think there are any issues with lead dress. Its a clean build with good seperation from grid/power/etc. There is simply too much gain, and possibly an OT that can't handle it as well.

[bepone]

I don't think there are any issues with lead dress. Its a clean build with good seperation from grid/power/etc. There is simply too much gain, and possibly an OT that can't handle it as well.

i didnt see anything, you are mentioned not ok sound on high volume, falling apart is not good sign.. we can only imagine.. you didnt provide any picture or sound example, described amp with wrong terminology.. only telepathy metods we need to use here until something changes.
too much gain (?) is low gain amp means some error.

[imo1]

With the pot at 190k, the voltages fell much closer in line with Rob's expected voltages. I went out to the studio, plugged it into a nice 8 ohm speaker and the amp sounded amazing!
I was able to use the volume knob all the way to the top of its range, and at the top it had that warm, loose feel of a deluxe run up!

I'm still curious as to why the 47k and 330k to ground weren't enough to tame the input to the PI, but the amp sounds great and I actually really like the Hammond OT. It saturates in a really cool way. I think the amp has a little less power than a deluxe but for my kids use this will probably be good. I am still stunned by how quiet guitarists have to play these days.

I spent the majority of the day making a jig for finger joints and then remaking the final board over and over. I finally have a box. Gonna have to use some putty where the dado blade blew out some wood, but it will be nice and sturdy.

Thanks yall. I really appreciate the help. I have learned a ton on this forum and everyone is very generous with their time and knowledge.

Ian

[cdemike]

Glad the amp is working how you wanted it to! Also really cool to hear the OT worked out -- the concept kind of reminds me of JTM45 OTs with high Z ratios.

I'm still curious as to why the 47k and 330k to ground weren't enough to tame the input to the PI

The 47k and 330k to ground aren't truly in parallel because of the 220k resistor between them. So the 47k goes to ground immediately after the 100nF coupling cap, then the 220k and 330k form a voltage divider. If the order were switched where the 220k resistor were before the 47k or after the 330k, then you'd have parallel paths to ground, but adjusting the 330k to 190k didn't so much create a parallel path to ground as much as adjusting the ratios in the voltage divider. Strictly speaking, in other words, if there's some interruption of current from one path and another (the 220k resistor in this case), it's not a parallel pathway.

[imo1]

Glad the amp is working how you wanted it to! Also really cool to hear the OT worked out -- the concept kind of reminds me of JTM45 OTs with high Z ratios.

I'm still curious as to why the 47k and 330k to ground weren't enough to tame the input to the PI

The 47k and 330k to ground aren't truly in parallel because of the 220k resistor between them. So the 47k goes to ground immediately after the 100nF coupling cap, then the 220k and 330k form a voltage divider. If the order were switched where the 220k resistor were before the 47k or after the 330k, then you'd have parallel paths to ground, but adjusting the 330k to 190k didn't so much create a parallel path to ground as much as adjusting the ratios in the voltage divider. Strictly speaking, in other words, if there's some interruption of current from one path and another (the 220k resistor in this case), it's not a parallel pathway.

I didn't know that with the JTM45, but that is my favorite of the Marshall amps, and that makes sense.

Thank you for your explanation. Its a bit confusing to me with how the resistance is affected my various components. Ive done a ton of reading, but don't really have an engineer brain.
So the 47k would then be a voltage divider with the plate resistance(tube and resistor)?

I think this amp will serve his purposes well!

[pdf64]

... So the 47k would then be a voltage divider with the plate resistance(tube and resistor)?

That's exactly it!
The Thevenin equivalent circuit for the triode stage is a voltage source (zero impedance) in series with about a 40k resistance (anode load resistor // valve's internal anode resistance).
So the 47k load (pretend trem intensity pot) almost halves the voltage output of that stage.

[didit]

Hello again --

Hello --

Wondering what type of tube is presently installed in the PI position? Either V4 or V6 depending on reference schematic.

Best .. Ian

Ian! My dear old friend Ian McClagan would say "Us Ian's gotta stick together!" so passing that down the line in his honor.

I have 2 old stock At7's I was using in the PI. I ordered all new JJ's for the build, but am 1 short, so had to dig into my tube boxes. I am going to try the JJ in the PI position

I'll stick with you for a few more observations.

Seems that closing one more potential blind alley. Sometimes people will swap in 12AX7 or other similar with awkward results.

That leads to sharing expectations with you and others that your AO35 transformer is at least part of observed misbehaviour. A semi-radical though often recommended upgrade for a DR output transformer is Hammond's 1620. It fits a nominal 6k6 impedance but is comparatively beefy with hi-fi level performance including bottom end. Might also obscure most if not all your gapping chassis gap.

I anticipate simple affirmation, but for completeness asking what you've used for a choke and what DC voltage is present at B+3 power node?

Will suggest if you have the AO35 chassis and all transformers that you pull all that back together, building something it suites it better such as Zaire's Carmen Ghia.

Best .. Ian

[lonote]

So Just to clarify where you ended up, using 190K in place of the 330K on your original schematic addressed the issue?

[imo1]

Hello again --

Hello --

Wondering what type of tube is presently installed in the PI position? Either V4 or V6 depending on reference schematic.

Best .. Ian

Ian! My dear old friend Ian McClagan would say "Us Ian's gotta stick together!" so passing that down the line in his honor.

I have 2 old stock At7's I was using in the PI. I ordered all new JJ's for the build, but am 1 short, so had to dig into my tube boxes. I am going to try the JJ in the PI position

I'll stick with you for a few more observations.

Seems that closing one more potential blind alley. Sometimes people will swap in 12AX7 or other similar with awkward results.

That leads to sharing expectations with you and others that your AO35 transformer is at least part of observed misbehaviour. A semi-radical though often recommended upgrade for a DR output transformer is Hammond's 1620. It fits a nominal 6k6 impedance but is comparatively beefy with hi-fi level performance including bottom end. Might also obscure most if not all your gapping chassis gap.

I anticipate simple affirmation, but for completeness asking what you've used for a choke and what DC voltage is present at B+3 power node?

Will suggest if you have the AO35 chassis and all transformers that you pull all that back together, building something it suites it better such as Zaire's Carmen Ghia.

Best .. Ian

I actually built this in a chassis to fit an old supro I had laying around. Ive built a couple of AC15 style amps in the old reverb chassis, but I think the deluxe is a much more utilitarian amp.

I used a hammond 194BA for the choke. PI voltages were around 290 and 280(from memory)

Interesting on the OT. I will look at the physical dimensions and see how close a fit they are for mounting. I am getting pretty busy with touring season ramping up so trying to button up the amp building part for now. I have the cab built and just need to tolex and figure out some practical stuff there.

[imo1]

So Just to clarify where you ended up, using 190K in place of the 330K on your original schematic addressed the issue?

I haven't actually put a 190k in yet, but that is the value that gets my build right in the lane of where the voltages should be. It also maximizes the design to my ears. I messed around with 150k ish and higher. The 150k knocked the gain down considerable and the 250k ish was making the final 25% unusable

[imo1]

Hello again --

Hello --

Wondering what type of tube is presently installed in the PI position? Either V4 or V6 depending on reference schematic.

Best .. Ian

Ian! My dear old friend Ian McClagan would say "Us Ian's gotta stick together!" so passing that down the line in his honor.

I have 2 old stock At7's I was using in the PI. I ordered all new JJ's for the build, but am 1 short, so had to dig into my tube boxes. I am going to try the JJ in the PI position

I'll stick with you for a few more observations.

Seems that closing one more potential blind alley. Sometimes people will swap in 12AX7 or other similar with awkward results.

That leads to sharing expectations with you and others that your AO35 transformer is at least part of observed misbehaviour. A semi-radical though often recommended upgrade for a DR output transformer is Hammond's 1620. It fits a nominal 6k6 impedance but is comparatively beefy with hi-fi level performance including bottom end. Might also obscure most if not all your gapping chassis gap.

I anticipate simple affirmation, but for completeness asking what you've used for a choke and what DC voltage is present at B+3 power node?

Will suggest if you have the AO35 chassis and all transformers that you pull all that back together, building something it suites it better such as Zaire's Carmen Ghia.

Best .. Ian

Well, I bit. The transformer actually is off on all the holes by about a 1/4” so I’m probably gonna have to move it over to make it work, but when I started reading about it, it sounded like it would be more utilitarian for my kid. If it were mine I would just keep it as is..

Anyway. Thanks for the tip

[didit]

Hello Ian —

Well, I bit. The transformer actually is off on all the holes by about a 1/4” so I’m probably gonna have to move it over to make it work, but when I started reading about it, it sounded like it would be more utilitarian for my kid. If it were mine I would just keep it as is..

Anyway. Thanks for the tip

Unfortunate holes don’t properly align. Will be curious to know how this ultimately turns out.

Also curious what you’re illustrating with the word “utilitarian”; and of course then versus what might qualify as particularly worthwhile that hasn’t utility.

Best .. Ian

[imo1]

My point with that is that if I was building it for myself, having quite a bit of recording experience, I would keep it “as is” and use it in the studio, where I am often looking for unusual and unique sounds. For my kid, who will have one amp for all his use, I want the widest usage and most practical application. At this point in history, for the type of player he is growing into, that is the deluxe reverb