18watt Clone Lite IIb volume slope is a little too aggressive early on.

[Woodrow F Call]

Update: loose ground at volume pot fixed the issue.


Original post below:


I have a amp I built from a Brownnote Kit years ago (Lite IIb).  When using the volume knob on the amp, it goes from nothing to lots of volume very quick.  Is there a good way to maybe adjust it?

I'm also looking for a suggestion to bring the overall volume down a little.  I pretty much just play local jams and don't get to take this out much because it's pretty loud. 

I'm running a 1X12 with a G12H30 in it.  I was thinking about a Warehouse ET65 or Green Beret..... but the ratings look similar.... but the speaker magnets are a bit smaller and more inline with a Greenback which is about 3dB less sensitivity.    Got some ideas?  It doesn't have to be to much quieter.  I take a Custom Deluxe Reverb or a Blues Junior to the jams mostly and those work fine.... The CDR has some mid magnet Celestion in it from the factory. 

Thanks!   

[stratomaster]

Your best bet is to make sure you're using a 10% taper log pot for the volume control.

If you're using a linear or 30%(J) taper then the behavior will be as you described.

Alternative options, if you never run the volume full up, add a 100k resistor to the outer lug.  This will limit the output of the pot to about 85% of its current max volume and smear the response over the full rotation. Or fit a post phase inverter master volume control to knock down the volume once you've dialed in your desired gain.

[Latole]

A 10% taper log pot, means you get 10% output with with 50% rotation.

First, did you use A pot ,not B pot ? Look , you may use a B pot

[shooter]

for testing, put a 12AU7A in V1. 
... move you in the right direction?

[Latole]

for testing, put a 12AU7A in V1. 
... move you in the right direction?

I don't think this will change the operation of the potentiometer in any acceptable way.

[ac427v]

The schematic you included has great Tweaker Info. Which values have you used for each item that affects gain?

[shooter]

sometimes "pot operation" is a layman's way of describing TOO MUCH GAIN...bonus, no soldering required for testing.

[Latole]

sometimes "pot operation" is a layman's way of describing TOO MUCH GAIN...bonus, no soldering required for testing.

"  ...When using the volume knob on the amp, it goes from nothing to lots of volume very quick".

To me it si not a mater of gain.

[Woodrow F Call]

The pots are A470K Alpha pots. 

It's not the gain, it's volume.... kinda hard to go from near nothing to Too Loud.  I can barely crack the knob and it's too loud.... where I can run my DR up to about 4 on the volume for the same jam and not be too loud.

Tweaker.... honestly, I built this a long time ago.  I don't remember.

I don't have a 12AU7A..... maybe I should get one for future testing.

[Latole]

Check for a bad ground for volume pot ; bad solder, bad wiring.......

[Wonder2121]

Answers in the schematic you posted - Tweekers guide at the bottom...To lower gain you need to lower V1 RK....120k try 46k...If it was me I would split that plate load resistors to 82k/18k...Just google Split Load Plate Resistors and thank me later!

[pdf64]

 
 ...
It's not the gain, it's volume.... kinda hard to go from near nothing to Too Loud.   ..,

Gain is what makes volume loud 

[Latole]

 
 ...
It's not the gain, it's volume.... kinda hard to go from near nothing to Too Loud.   ..,

Gain is what makes volume loud 

Less gain doesn't mean that the volume potentiometer doesn't reach its maximum from the beginning.

I'll try a 1M pot.
Looking to many schematics Fender , Traynor and many more , they all use 1 meg volume pot

[stratomaster]

A change in pot value will affect both the insertion loss (could be louder overall with a higher value pot) AND, more importantly, the frequency response due to the capacitors that precede and follow the pot.  It's not a transparent change.  You'd have to scale the caps accordingly to keep the same general frequency response.

[pdf64]

...
Less gain doesn't mean that the volume potentiometer doesn't reach its maximum from the beginning.

Of course it does!
For a given input signal (eg Woodrow F Call strumming his guitar), reducing gain reduces signal level.
Reducing signal level will reduce how loud his amp gets when set to a volume of eg 4.

I'll try a 1M pot.

What's your rationale behind that suggestion?

The amp's volume control sets the gain of the amp.

[Latole]

I'll try a 1M pot.

What's your rationale behind that suggestion?


Don't you read my previous answer #12. ?

[SEL49]

I'll try a 1M pot.
Looking to many schematics Fender , Traynor and many more , they all use 1 meg volume pot

This amp is based on a Marshall 1974 18 watt amp that uses 500K-A volume pots. I have built the Marshall 1974 as well as the Lite IIB. The 500K-A pot works very well in both amps. I suspect the op may be using a linear pot.

[Latole]

[ I suspect the op may be using a linear pot.

That is why I ask to check yesterday if it is a A or B .

Woodrow F Call said it is . 

[pdf64]

Don't you read my previous answer #12. ?

Indeed but I was hoping for an electrical reason why a 1M log pot would work better than a 500k log pot in resolving Woodrow's issue?

As evidence of the contrary, and backing up the point of reply 14, see the table at the top of p2 https://frank.pocnet.net/sheets/093/1/12AX7.pdf
It should be apparent that as Rs (eg the volume control track resistance) is increased, the gain and maximum output voltage of the preceding stage increase.
Hence increasing the volume control to 1M will tend to exacerbate the issue.

[Latole]

Don't you read my previous answer #12. ?

Indeed but I was hoping for an electrical reason why a 1M log pot would work better than a 500k log pot in resolving Woodrow's issue?

You are right.
My reason it is we is that we have no other solution.

Or the author has made mistakes that he doesn't see.

[Woodrow F Call]

[ I suspect the op may be using a linear pot.

That is why I ask to check yesterday if it is a A or B .

Woodrow F Call said it is . 

Previously, I said A pots.

[danhei]

Previously, I said A pots.

Have you measured the taper of your volume pot out of circuit?

[Latole]

Previously, I said A pots.

How do you know it is a A. ?

You understand that this would be the only possibility for your problem.
 OR.
2- Wiring error.

I just repaired a Trinity amp, a 5e3 kit that had a problem similar to yours : Wiring errors
_______________

A short Google search and I am unable to find 470 K A Alpha pots from reliable suppliers. They're all 500k .

 " Questionable” supplier sites; E-bay, Aliexpress..ans other , offer 470k. Are they bad copies?

Where did you buy it?

[Woodrow F Call]

Previously, I said A pots.

How do you know it is a A. ?

You understand that this would be the only possibility for your problem.
 OR.
2- Wiring error.

I just repaired a Trinity amp, a 5e3 kit that had a problem similar to yours : Wiring errors
_______________

A short Google search and I am unable to find 470 K A Alpha pots from reliable suppliers. They're all 500k .

 " Questionable” supplier sites; E-bay, Aliexpress..ans other , offer 470k. Are they bad copies?

Where did you buy it?

The pot is stamped (ink actually) "A470K" it was part of a kit I built years ago. Haven't tested out of circui t.

Will check wiring, but I'm sure it's ok. Might just replace the pot (if I'm going to pull them to check).

Might try a less efficient speaker after that.

Amp seems to work fine otherwise..... Just not enough taper to the volume.

[acheld]

Did you try Shooter's suggestion of using a lower mu tube in V1?   Even a 5751 or 12AY7 will tell you something.

Simple to do, and may (or may not . . .) do what you want.  Worth a try.

[Latole]

[
The pot is stamped (ink actually) "A470K" it was part of a kit I built years ago. Haven't tested out of circui t.

Will check wiring, but I'm sure it's ok. Might just replace the pot (if I'm going to pull them to check).

Might try a less efficient speaker after that.

Amp seems to work fine otherwise..... Just not enough taper to the volume.

Thank for the answer ;

Testing a pot ; just disconnect center tab wire and use ohmeter.

[danhei]

My guess, assuming the pot is log, there’s a short between the wiper and the top lug of the volume pot.

[Latole]

My guess, assuming the pot is log, there’s a short between the wiper and the top lug of the volume pot.

A log pot ( A ) is the best choice for volume.

The short !  ; That is the way it should work
I see no issue

[danhei]

A log pot ( A ) is the best choice for volume.

The short !  ; That is the way it should work
I see no issue

Of course a log pot is the best choice for a volume control.


However, if the circuit was wired with an inadvertent short between the wiper and the top of the pot it would act as a variable resistor, rather than a voltage divider. And, at "minimum"on the pot the wiper/top would be grounded, with no signal output to the phase inverter. And at all other settings there would be no attenuation of the signal at all beyond the load the resistance places on the preceding gain stage.


But this is all speculative, with no pictures of the amp.

[Woodrow F Call]

Did you try Shooter's suggestion of using a lower mu tube in V1?   Even a 5751 or 12AY7 will tell you something.

Simple to do, and may (or may not . . .) do what you want.  Worth a try.

I don't have one to try.  I might order one next parts order though.

[Woodrow F Call]

A log pot ( A ) is the best choice for volume.

The short !  ; That is the way it should work
I see no issue

Of course a log pot is the best choice for a volume control.


However, if the circuit was wired with an inadvertent short between the wiper and the top of the pot it would act as a variable resistor, rather than a voltage divider. And, at "minimum"on the pot the wiper/top would be grounded, with no signal output to the phase inverter. And at all other settings there would be no attenuation of the signal at all beyond the load the resistance places on the preceding gain stage.


But this is all speculative, with no pictures of the amp.

I'll post pictures in a bit. I should have thought to do that earlier. 

[stratomaster]

Did you try Shooter's suggestion of using a lower mu tube in V1?   Even a 5751 or 12AY7 will tell you something.

Simple to do, and may (or may not . . .) do what you want.  Worth a try.

I don't have one to try.  I might order one next parts order though.

I've never understood this advice on a builders' forum.  Just add a 33k resistor between the plate lug on the tube socket and the existing wire.  You now have a signal reduction of about 25%, close to a 5751.  There's a modest gain increase through the triode, but the signal level will be attenuated. No need to buy a tube and will tell you the same information--at least for testing and troubleshooting purposes.  You can tweak the values to your liking later.

[shooter]

I've never understood this advice on a builders' forum.

most tube builders have spares laying around for TESTING, no solder required.  once you decide ya/no, then you break out the solder, re-bias, re-work....


once you're seasoned builder, you'll have a scope to actually make informed decisions, no shotgunsing required, no 27 reply's guessing in the dark.

[pdf64]

With all the talk of swappjng in different valve types, and the widespread misapprehension thatstage gain directly follows the 'typical conditions' mu, it seems appropriate to remind people of a more realistic analysis https://www.thegearpage.net/board/index.php?threads/updated-tube-comparison-table.2279173/

[shooter]

I suggest it as a "quick n dirty" for testing, once you decide yep, that's the ticket, as mentioned, it's re-bias/re-work for the new tube.  the 1st column says it all gain 100 vs gain 14 (ball-park given a different tube setup)
and as mentioned it's just to easy, no soldering, scopes... simply using ears to determine "direction" from here.


when you're a salaried employee, finding/resolving problems "fast" gets you out before all the traffic   

[scstill]

I built a similar amp recently and also had a way too loud syndrome.
Tamed by running a 12AU7 in the PI position.
Still loud but in a very good way.
https://el34world.com/Forum/index.php?topic=32389.msg359822#msg359822

Some good 12AU7s on ebay they seem to be quite common in vintage organ amps.
https://www.ebay.com/itm/404723013034?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=pfld36tht_y&sssrc=2047675&ssuid=AKdBLREQQeC&widget_ver=artemis&media=COPY

[Woodrow F Call]

Hey I found the issue!  So I was looking at the volume pot wiring as suggested. The wiring was correct, but I found that the chassis to volume pot ground was loose.  I tightened it up and I can now get pretty quiet with the knob.


Thank you for pointing me in the correct direction.  I'm still going to buy/try some other preamp tubes as I'm starting to get interested in trying stuff out. 

[Latole]

Hey I found the issue!  So I was looking at the volume pot wiring as suggested. The wiring was correct, but I found that the chassis to volume pot ground was loose.  I tightened it up and I can now get pretty quiet with the knob.


Thank you for pointing me in the correct direction.  I'm still going to buy/try some other preamp tubes as I'm starting to get interested in trying stuff out.

Answer #7...... 4 days ago 

[pdf64]

I don't understand how that symptom was resolved by that fix, ie a bad ground would have made a mute setting of the volume control impossible / intermittent 

[Latole]

I don't understand how that symptom was resolved by that fix, ie a bad ground would have made a mute setting of the volume control impossible / intermittent 

IMO By having a resistive reference with the ground, the potentiometer being “floating”, the volume control could be quickly set to a high level.

And without having the amp in front of you, it's very difficult to get all the information you need for a repair.

[pdf64]

... without having the amp in front of you, it's very difficult to get all the information you need for a repair.

[Woodrow F Call]

Hey I found the issue!  So I was looking at the volume pot wiring as suggested. The wiring was correct, but I found that the chassis to volume pot ground was loose.  I tightened it up and I can now get pretty quiet with the knob.


Thank you for pointing me in the correct direction.  I'm still going to buy/try some other preamp tubes as I'm starting to get interested in trying stuff out.

Answer #7...... 4 days ago 

Yeah, I just didn't have it apart to look at till I got a chance to look at it.

I also fixed some loose rectifier pins, that were causing some static.

[Woodrow F Call]

I don't understand how that symptom was resolved by that fix, ie a bad ground would have made a mute setting of the volume control impossible / intermittent 

I think it was more of the quality of the ground being compromised.