rich64 6/29/2018 12:51 PM
More Headroom For A Blues Deluxe Reissue
I have this BDRI on the bench that now sounds great with one glaring exception: regardless of the bias setting I can't get much headroom out of it. It has ample output though. I even swapped V1's 12AX7 for a 12AT7. This gave me a little more headroom but not enough. My client is a pedalboard user and therefore counts on it. I also tried a known good speaker only to find that the stock one is fine. Any ideas folks?
 
g1 6/29/2018 12:59 PM
Loud but distorted? Check both plate resistors on the PI tube, it's not an uncommon fault with these that one of those resistors goes open.
 
rich64 6/29/2018 1:46 PM
Hey g1, Thanks for the hip tip! Before I pulled the tube board I checked the voltage at the PI plates and came up with 200 to 215 volts. The schemo says to expect around 4 volts! I suppose I'll pull the tube board now to check the plate load resistors. Thank you!
 
Dave H 6/29/2018 2:45 PM
Quote Originally Posted by rich64 View Post
I can't get much headroom out of it. It has ample output though.
If the PI plate resistors are OK check to see if it will do ample output both clean and distorted even if you have to set the controls to '1' for ample clean output.
I notice from the schematic that the vol and drive controls are set up as variable resistors rather than potentiometers, this spoils the gradual taper and makes them come up too quickly. It's just the way it's designed.

[ATTACH=CONFIG]49546[/ATTACH]
 
Enzo 6/29/2018 5:59 PM
Easy way yo check the resistors without finding them on the board: measure voltage on pins 1 and 6 of the phase splitter. If a plate resistor is open, the B+ will be missing from that pin.
 
J M Fahey 6/29/2018 6:41 PM
Quote Originally Posted by rich64 View Post
I can't get much headroom out of it. It has ample output though.
Those are contradicting statements so "to put some numbers into it":

1) please inject 100mV 1kHz into it, set Master Volume to 10, all tone controls (including Presence if present) to 7 , slooowly rise volume while scoping output, stop when you start seeing clipping: what power do you measure?

2) what number is volume set to when it starts clipping?

3) exactly why does your customer complain of lack of headroom? meaning amp starts distorting in an ugly way.
With the flat amp setting I suggested above: at what volume setting does amp start to sound ugly?

a) same as before
b) at a higher volume
c) at a much lower volume setting. In all cases post "the number" at which the knob is pointing.

I even swapped V1's 12AX7 for a 12AT7. This gave me a little more headroom but not enough. My client is a pedalboard user and therefore counts on it. I also tried a known good speaker only to find that the stock one is fine. Any ideas folks?
Yes, the "pedalboard user" bit is a red flag.
Doubly so if coupled to a Blues Deluxe thingie.

4) That amp is officially pushing 40W through a standard 12" speaker ... which means itīs probably 35W clean ... tops.

A perfect combination if you plug your guitar straight into it, you have up to 35W clean which is enough on a mid/small Club setting, and full blast probably does not go beyond 45/50W no matter what, enough to be comfortably heard but killing nobody, drowning nobody, killer creamy power tube distortion.

Now you add a digital simulator ahead of it, which has tons of new sounds , and itīs like fitting 10 pounds of sh*t in a 2 pound bag ..... it wonīt fit, period.

Please do the tests I suggested above, it *might* have a Technical problem after all, which should be solved, but my firm hunch is that the pedalboard output is smashing that preamp input big time, and to boot injecting sounds the amp and speaker combination are not designed to handle.

Not that anything is "broken" , far from it, simply (way) mismatched.

Your Customer needs a loud clean amp for his pedalboard, anything "100/120W" class, SS, 2 x 12" ... tons of amps matching that, from Peavey, Crate, even Fender itself.

Even a humble FM212 will work better ***in that duty*** than a barely 40W Tweed amp.
 
glebert 6/29/2018 10:16 PM
Maybe try an AT7 in the PI position as well? I found my Hot Rod Deluxe to break up too early, I can't remember if I did V1 and the PI or just V1. In doing research on it everyone basically says "this ain't a clean amp, it is going to break up." It was very sensitive to dynamics, which most distortion is but for whatever reason the Deluxe seemed moreso.
 
rich64 6/29/2018 10:32 PM
Thank you sooo much for all of your posts! I now have a battle plan for my early morning bench time. Have a great weekend everyone. Rich
 
Chuck H 6/29/2018 11:07 PM
I oppose all attempts to mitigate gain in search of more headroom. Headroom is a badly misused term WRT guitar amps. Headroom would be how much clean power the amp can make with a given input signal. The knob setting IS ENTIRELY ARBITRARY!!!!!!!!! Trying to get the right amount of gain at a given stock knob setting by using lower gain tubes changes everything else about the amp and is how people with limited knowledge of the real issue tend to approach it. Don't be THAT guy.

It's really all about what the amp will make in watts relative to input. You test for that. If the amp is performing, and I'll bet it is if it's adjusted correctly and not broken, then YOU DO NOT HAVE A HEADROOM PROBLEM!!!!!!!!!!

If the above checks out and the amp is making adequate clean watts then what you really want is a different gain adjustment ratio to "look" more intuitive on the volume knob setting. This is absolutely not the same thing as headroom.

Perhaps look into a replacement volume pot that offers a smaller/slower taper.
 
glebert 6/30/2018 12:36 AM
Quote Originally Posted by Chuck H View Post
I oppose all attempts to mitigate gain in search of more headroom. Headroom is a badly misused term WRT guitar amps. Headroom would be how much clean power the amp can make with a given input signal. The knob setting IS ENTIRELY ARBITRARY!!!!!!!!! Trying to get the right amount of gain at a given stock knob setting by using lower gain tubes changes everything else about the amp and is how people with limited knowledge of the real issue tend to approach it. Don't be THAT guy.
I'm going to respectfully disagree with this. If you think of a Vin vs. Vout plot the slope is the gain, right? At some point the gain tops out as you max out the Vout. Higher gain means a steeper slope. It also means for a dynamic signal it is harder to keep the signal from getting up to the point of clipping. Reducing the gain reduces the slope which slows the approach to clipping. On my HR Deluxe I found if you played a note or chord with increasing intensity it would be clean, clean, clean, clean, totally distorted. So if you were playing a chord the first note might be distorted and the rest of them clean, or in a solo the notes would bounce from clean to dirty. I found reducing the gain helped smooth these issues out. YMMV
 
Steve A. 6/30/2018 5:56 AM
Quote Originally Posted by Dave H View Post
If the PI plate resistors are OK check to see if it will do ample output both clean and distorted even if you have to set the controls to '1' for ample clean output.
I notice from the schematic that the vol and drive controls are set up as variable resistors rather than potentiometers, this spoils the gradual taper and makes them come up too quickly. It's just the way it's designed.

[ATTACH=CONFIG]49546[/ATTACH]
I guess it was the Hot Rod amps that reconfigured one or both of these controls as 3 terminal potentiometers... So Fender has not changed the BD circuit since 2004? I don't keep up with stuff like that...

I have no idea what the PCB looks like but in my FrankenAmp experiments I have reconfigured pots and tube input grids since they are so easy to trace. Not that I am suggesting it here for a customer's amp...

As for replacing V1 with a 12AT7, I always try a 12AY7, 5751, 12AZ7 or even a 12AU7 first since the bias (or whatever!) is basically the same as a 12AX7, right?

"Pedal pushers" might try plugging into the power amp input...

Steve A.

EDIT Has the bias voltage/current been checked?
 
Steve A. 6/30/2018 6:12 AM
Quote Originally Posted by Chuck H View Post
I oppose all attempts to mitigate gain in search of more headroom. Headroom is a badly misused term WRT guitar amps. Headroom would be how much clean power the amp can make with a given input signal. The knob setting IS ENTIRELY ARBITRARY!!!!!!!!! Trying to get the right amount of gain at a given stock knob setting by using lower gain tubes changes everything else about the amp and is how people with limited knowledge of the real issue tend to approach it. Don't be THAT guy.
I agree with what you said about the knob setting being arbitrary BUT too many modern amps have way too much gain for me so I will try replacing V1 and/or V2 with lower gain members if the 12A_7 family.

Headroom, shredroom... all I care about is TONE. And if a simple tube roll doesn't solve the amp problem then back to GC it goes...

Steve A.
 
J M Fahey 6/30/2018 6:17 AM
Perhaps look into a replacement volume pot that offers a smaller/slower taper.
Which is a Psychological or at best, Ergonomic solution: " aaaahhhhh!!!! before I could not rise it above 3, now I can rise it to SEVEN!!!!!!! .... I am HAPPY!!!!" while actual power out, and more important, SPL, is **exactly** the same as before.

**REAL** headroom means: "I can play clean by a drummer and be heard, no crunch unless I want to"

Which in practical terms means 30W into a very efficient speaker (Marshall 4 x 12" or 2 of the best Celestions such as in a VOX AC30) or 50W into a normal-good speaker (your average Eminence) or if using SS, 80W into a good Celestion (think Valvestate 80 and such) or 100W into cheapish but still usable speakers (FM212 and most Peavey/Crate/Laney 2 x 12" combos)

Many will rise a hand and say: "hey!! I play very comfortably with 22W 2 x 6V6 1x12" Eminence, never needed more" .... typically such players are 50ish, give/take 10 years, play in a similar age group, usually play "da Blooz" or older style RocknīRoll , have milder drummers, Clubs do not let them play too loud anyway, but most important, always play around the "sweet spot" which means they are already crunching , meaning they are *always* putting out maximum power output (by definition ), and just go somewhat above or below that "sweet spot" by guitar volume adjustment or even finger pressure.
Never *really* clean, at most "Fender clean" which is not the same, just scope it.

Now you plug a Computer into it with 256 sounds, modes, presets, and it simply canīt cope with the clean ones, and will smooth the dirty onbes.

Just try to use some Doom or Death Metal preset
Or any crystal clean one above garage band levels.
 
Dave H 6/30/2018 6:30 AM
Quote Originally Posted by Chuck H View Post
If the above checks out and the amp is making adequate clean watts then what you really want is a different gain adjustment ratio to "look" more intuitive on the volume knob setting. This is absolutely not the same thing as headroom.

Perhaps look into a replacement volume pot that offers a smaller/slower taper.
The term 'Headroom' should be banned. Guitarists and engineers will never agree on what it really means.

II don't think replacing the vol pot will make much difference because it's used as a rheostat not a potentiometer. I think the vol pot is 15% now, even a 10% log pot will only attenuate 12dB (x4) at half rotation not 20dB (x10) as you would expect. The Drive control is the same.
 
Chuck H 6/30/2018 7:08 AM
Quote Originally Posted by Steve A. View Post
I agree with what you said about the knob setting being arbitrary BUT too many modern amps have way too much gain for me so I will try replacing V1 and/or V2 with lower gain members if the 12A_7 family.

Headroom, shredroom... all I care about is TONE. And if a simple tube roll doesn't solve the amp problem then back to GC it goes...

Steve A.
Absolutely! By all means, if it pleases you to have less gain then you can try lowering gain with lower gain tubes

I still oppose doing it in search of more headroom. Assuming one likes everything else about the amp. You can quickly end up in that pickle where "Hey! Now I have the gain I want at five but the amp doesn't rock at ten anymore "
 
Chuck H 6/30/2018 7:35 AM
I looked into it a little... I can't find significantly detailed specs on the original pot. I did discover that the pot "kit" (available at a popular on line parts vendor) is different for the Blues Deluxe and the Blues Deluxe Reissue.?. They are still bracketed pots. I'm sure the geometry for bracket fit is critical or one has those cumbersome staggered pins. I see this as small consequence. If ONE pot on the board isn't bracketed I don't expect the structural stability would be significantly compromised. I've done this sort of mod many times when I couldn't get an exact replacement pot for such a bracketed pot. It's a little bit of a retrofit, but not usually difficult.

I looked into the Bourns pots but found the Mouser search engine limited for narrowing to PC mount, 15mm, 10% audio. I do like the bourns pots though and I know they offer 10% pots. Worth more research. Mesa also sells pots for their amps and most are 15mm and have their actual taper % indicated. This has been convenient for me at times and is also worth checking out.

You just need to know the value and stock taper of the volume pot that's in there. Then you can look for a fit-able replacement with a smaller taper.
 
Chuck H 6/30/2018 7:55 AM
I looked into it a little more, and...

The schematic shows the clean channel volume pot is a 250k 15% taper wired as a damn variable resistor. Not much to be done there Changing to a 10% would make a small difference, but the real issue is that the volume control isn't wired as a voltage divider. Attempting to change that would interfere with the other channel topologies.

Mesa offers a 250k 5% taper with solder lugs. A 5% taper should make a notable difference.

https://store.mesaboogie.com/product...dio-taper.html

You'd need to panel mount it and solder it to leads from the board where the original pot was. I've done this before with no trouble.
 
Leo_Gnardo 6/30/2018 8:17 AM
Quote Originally Posted by Chuck H View Post
The schematic shows the clean channel volume pot is a 250k 15% taper wired as a damn variable resistor. Not much to be done there
Though the volume pot itself isn't a voltage divider in this circuit, the pot - wired as a rheostat (variable resistor) - in series with the fixed resistor "above" it does make a voltage divider. A couple more field solutions: you could solder a resistor across the pot which limits the maximum volume available with the control at 10, and decreases the volume proportionately so the user can dial up the control further eliminating the complaint "it's already too loud by the time I have it dialed up to one & a half." Downside, tone won't be quite as bright. Which would be perceived as a good thing to most users of these amps.

Another, the series resistor "above" the pot can be increased, same results, perhaps the tone will be a little brighter.

The no fuss no muss solution of using lower gain V1 tube should not be ignored. Recently a customer responded to subbing in a 12AY7 here joyously "this is just what I've been looking for! Why don't they do this at the Fender factory?" Well, they did, 1959 on back. I'd recommend trying that first, before swapping pots & resistors, what a tedious job that is.
 
rich64 6/30/2018 8:49 AM
JMF, Rather than flog my client over his choice of amp/rig as a service man I'm going to do my best to give him what he wants. My headroom/output statement refers to the fact that regardless of bias setting the thing will get plenty loud (a technical term for customer pleasing) and clean-ish. There still is a little "fizziness" in there. Take me to task if you must for my lack of specificity regarding "numbers" but for 35 years I've pleased my clients and been able to communicate clearly with fellow techs. That said I DO appreciate you taking a few minutes to address my post. A Blues Deluxe is not my choice of amp either. However I could use it at one of my gigs along with my pedalboard and do just fine. Have a blessed day, 64
 
rich64 6/30/2018 9:25 AM
Hello Chuck H, Your statement "If the amp is performing, and I'll bet it is if it's adjusted correctly and not broken, then YOU DO NOT HAVE A HEADROOM PROBLEM!!!!!!!!!!!!" is rather astute if not self evident. Like most folks that participate in these forums I'm well versed in gain structure within an amp and the signal chain external to it. I guess that I am making this reply to thank you for your one sentence suggestion at the end of three paragraphs of scolding. Funny how much consternation the word "headroom" and the assumption that I am "THAT guy" that doesn't understand its meaning caused. 64
 
glebert 6/30/2018 9:29 AM
Rich64, wanted to go back to the original post and get a clarification. You say it lacks headroom but has ample output power. As others have said, headroom means different things to different people. Juan's definition works for him but is not how I use the term. When you say "ample power" does that mean measured with a scope or meter, or actual loudness? As I said earlier, I found my HR Deluxe to break up to easily based on dynamics, if you would hit a note with increasing intensity it would be clean, clean, clean, clean, totally distorted, but just momentarily before it cleaned up as it decayed. A chord seemed like the first note would be distorted and clean up halfway through, or vice versa. I found tube rolling to help with the gain/slope sort of problem that I was getting dynanically, but it did not make the amp any louder.

If louder is what is needed no one has mentioned a speaker swap, I don't know how efficient the BD stock speaker is vs. something aftemarket.
 
Chuck H 6/30/2018 9:39 AM
None of it was directly related to you as a tech. It's just become such frustrating internet jargon that the number on the volume knob = loudness. So when an amp breaks up at three or four some players think the amp would be louder if it didn't break up until eight.?.

It's also become a common fix for these issues to use a lower gain tube. That would change the gain structure of all the channels (for better or worse). If that's the goal, fine, otherwise the issue needs to be handled at the circuit.

So none of of my previous posts should have been viewed as judgement toward you personally. Just me trying to fight the hoards of misinformation that you were bound to intercept. Remember, we do not know what you do or don't know and there are plenty of techs out there that don't know much. You might have been one for all the information we have.

But taking it personally is cool too. Maybe swap that second cup in the morning for decaf.?.
 
Jazz P Bass 6/30/2018 9:55 AM
"There still is a little "fizziness" in there."

???????

At what output wattage?

From glebert's post:
" if you would hit a note with increasing intensity it would be clean, clean, clean, clean, totally distorted, but just momentarily before it cleaned up as it decayed. A chord seemed like the first note would be distorted and clean up halfway through, or vice versa."

That is to be expected at or near the maximum clean output of the amp.
Over the edge is over the edge.

On most newer Fender amps, that is '4' on the volume knob. (depending on guitar input amplitude)
 
Chuck H 6/30/2018 10:41 AM
Quote Originally Posted by Jazz P Bass View Post
On most newer Fender amps, that is '4' on the volume knob. (depending on guitar input amplitude)
Right! With any humbucker hotter than a PAF you get down to a setting of 2.5 to 3.

And yes, there are little warbles and voltage spikes in the signal of a vibrating string through a pickup. Especially with humbuckers. These can make an amp seem to crackle annoyingly right at the line between true clean and clipping because these spikes can be generously over what's necessary to clip the amp where the rest of the signal stays below the threshold. The phenomenon is most common when higher bass levels are dialed in.
 
J M Fahey 6/30/2018 7:21 PM
Quote Originally Posted by rich64 View Post
JMF, Rather than flog my client over his choice of amp/rig
"flog"??????
In a Musician/Tech relationship he is asking you about a technical problem,you provide the correct answer , which in this case is : "that amp does not provide much headroom to begin with"
as a service man I'm going to do my best to give him what he wants.
which is? .......

My headroom/output statement refers to the fact that regardless of bias setting the thing will get plenty loud (a technical term for customer pleasing) and clean-ish. There still is a little "fizziness" in there.
Ok.
It is caused either by crossover distortion, which can be solved by proper biasing, or lack of clean power, which can not. (since biasing wonīt add a single watt to current power out)

Take me to task if you must for my lack of specificity regarding "numbers" but for 35 years I've pleased my clients and been able to communicate clearly with fellow techs.
That presumed clear communication starts with a conflicting statement in the very first question.
I suggest "troubleshooting" which includes a couple tests and measuring, without that itīs not much of tech talk.
That said I DO appreciate you taking a few minutes to address my post.
Youīre welcome.
A Blues Deluxe is not my choice of amp either. However I could use it at one of my gigs along with my pedalboard and do just fine.
Cool.
Can your customer do the same, with his pedalboard and at his gigs?

As a side note:
There still is a little "fizziness" in there.
may also mean there is some oscillation or instability present .... but I donīt dare tell you to scope it.
 
Enzo 6/30/2018 7:29 PM
Hi rich, welcome to the forum.

Just an observation: when you have only three posts on the forum, we cannot assume very much about your experience, skill level, troubleshooting ability, or much else. So it is not obvious to us that you would have considered or tried anything in particular.
 
rich64 7/1/2018 6:47 AM
Hey there Enzo, Thanks for the kind greeting. As well as your observation. In no situation that I am new to do I expect automatic credibility. I need to remind myself of this here. I find the notion of being able to speak with a large community of fellow techs valuable and fun. While I know that any group will contain some with strong opinions I suppose I wasn't prepared to be scolded or shouted down. I am of the mind that even if I were a newbie encouragement would be preferred to all caps yelling. All of that said I value the experience and yes, the opinions of the forum members. I hope that I can be of value in this forum as well.64
 
J M Fahey 7/1/2018 11:41 AM
Quote Originally Posted by rich64 View Post
I wasn't prepared to be scolded or shouted down.
No need to, because you werenīt ... ever.
Not in this thread at least.
I am of the mind that even if I were a newbie encouragement would be preferred to all caps yelling.
Where?
All of that said I value the experience and yes, the opinions of the forum members.
Thanks.

In my particular case please reread post#5:

a) I treated you as a full equal *Tech* .... and to be able to offer solid suggestions, instead of ... um ... "opinion" which is what you find by the truckload in all other Forums (My Les Paul, Harmony Central, The Marshall Forum, etc.) I suggested instead you grab your multimeter, inject some signal, >>measure<< and if possible >scope< the amp.
"What Techs do".

Do you think I would have suggested doing so to a regular Musician? Or a noob?
I treated you as a full equal *Tech* , asked you to do exactly what I would have done if I had that amp on my bench. What else?

b) Meters show numbers on their screens, I asked you to post them here.
Depending on results might suggest other tests, what to adjust or replace, etc.

c) shouldnīt need to remind it, but please notice suggestions start with the word: >>please<<

I hope that I can be of value in this forum as well. 64
Oh, no doubt about that

PS: one last suggestion: please sign full "rich64" .... we have another "64" member who is very active and helpful and it might be confusing: PDF64
Thanks.
 
glebert 7/1/2018 11:48 AM
I thought this thread turned toward condescension pretty quickly. But hey, when people ask for free advice (myself included) sometimes you get some attitude include at no charge.
 
Chuck H 7/1/2018 12:50 PM
Quote Originally Posted by glebert View Post
I thought this thread turned toward condescension pretty quickly. But hey, when people ask for free advice (myself included) sometimes you get some attitude include at no charge.
And just what does that mean coming from you?



 
Enzo 7/1/2018 1:43 PM
Ohhh, how about we just go back to amplifiers?
 
Malcolm Irving 7/1/2018 2:04 PM
Probably not relevant to the original posted question in this thread, but I've found that many guitarists are perfectly happy to get distortion at lower sound levels by setting the 'vol.' or 'gain' high with the 'master' low. However, when they want clean high sound levels, they seem reluctant to put the 'master' at max and control the level with the pre-amp control.

The definition of 'headroom' that I like is: the input signal swing (in volts) that a stage or series of stages can tolerate before the output gets clipped. (Strictly speaking the positive-going headroom and negative-going headroom can be different.)

The average guitarist's concept of 'headroom' is therefore not far off the mark, but the problem is that the maximum headroom of the entire amp (assuming it is properly designed) is limited only by the output stage and can't be increased by changing pre-amp tubes.
 
Malcolm Irving 7/1/2018 2:11 PM
Quote Originally Posted by Malcolm Irving View Post
... However, when they want clean high sound levels, they seem reluctant to put the 'master' at max and control the level with the pre-amp control.
One reason for this could be, for some high gain amps, when you try this you are limited between about '0' and '1' out of '10' on the pre-amp control, which makes setting the level difficult or impossible. - So in this case a lower gain tube in V1 might be good.