Tweaking Advice Hoffman Blues Jr Conversion

[Tbone55]

Hi All,

I've been playing around with my recently converted Blues Jr and would like to get some advice. The amp has a Celestion Vintage G30 in it and it feels like I don't have enough high end in it. Don't get me wrong, the amp sounds amazing, clear sound, very touch responsive and can be loud if you want it to. I have the meat control almost dimed to remove more bass, treble at around 9, bass at 4 and mids at 6-7. I was hoping that those of you who have done this conversion could provide me with your advice. There's one other thing I changed in the amp. I used the output transformer for a Reverb Deluxe rather than the one it came with. I believe this has more to do with the loudness of the amp but since I'm new to amp circuitry and how it works I might be wrong. Also, has anyone added a presence control to this amp?

Thanks in advance.

[shooter]

this is the schematic I glanced at;
https://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

2 quick n easy trys
C1 take it to 2.2uf - 10uf
if that gets you "in the right direction", try the same with C4

[Tbone55]

this is the schematic I glanced at;
https://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf

2 quick n easy trys
C1 take it to 2.2uf - 10uf
if that gets you "in the right direction", try the same with C4

Thanks kindly. Would you recommend starting with the lowest value first or the higher value or something in between?

[sluckey]

Also, has anyone added a presence control to this amp?

The "Meat" control, AKA Resonance, is very similar to a presence control. They both operate in the NFB loop. Probably have to trade one for the other.

Start with the 2.2µF and don't look back.

[Tbone55]

Also, has anyone added a presence control to this amp?

The "Meat" control, AKA Resonance, is very similar to a presence control. They both operate in the NFB loop. Probably have to trade one for the other.

Start with the 2.2µF and don't look back.

Thanks kindly. That's where I'll start.

[Tbone55]

I haven't been able to change the capacitor yet but was looking at the original schematic for the Blues Jr and comparing it to the Hoffman schematic. The original Fender schematic has a 22uf in the C1 position and the Hoffman schematic has a 47uf cap in the C1 position. It was suggested to go with a 2.2uf cap. I just want to verify that this is correct as I was going to go with a 22uf cap but came back to check this post before I did. Lower value caps let more of the higher frequencies through and higher value caps reduce higher frequencies. Have I got this right? 

Thanks.

[shooter]

2.2uf

a lot of us have found the 22 or 25uf in V1 lets in to much bass, causing a "muddied" sound.  by dropping down you get a tighter, cleaner tone, unless you're going for that fully distort, can't play a guitar, but I'm LOUD sound 

[Colas LeGrippa]

Put a 500pF accross the vol pot ( in and out  legs). Too trebly ? Put a 250.

[Tbone55]

Thanks for the input. I'd like to understand how putting the cap across the volume pot helps. I know I've used a cap and resistor across some of my guitars volume pot to prevent the volume from killing some of the highs when you roll the volume down. Is this a similar idea? For guitars it's called a treble bleed circuit.

Cheers!

[tubenit]

how putting the cap across the volume pot helps

The cap allows certain frequencies to bypass resistance.   Let's say you have a volume pot where the resistance from the wiper (middle lug) to ground is 250k & the resistance going to the wiper is 750k.  A cap from the non ground lug to the wiper allows certain frequencies to bypass that 750k resistance.  This tends to be helpful when the volume is not turned up real high.  The more the volume is turned up, the less resistance to the wiper.

On some amps, one might see a 220k resistor bypassed by a 500p cap going into V2-7 grid (between a volume pot and the V2-7 grid) .  This bypass cap is allowing certain frequencies to bypass the 220k of resistance.  Same principle as on the volume pot.

Having explained that, go with the 2.2uf cathode cap idea.  IF that allows too much treble then try 5uf on V1-3 cathode.

With respect, Tubenit

[Tbone55]

Thanks Kindly for that explanation. I'll start with the 2.2uf cap first on V1 and go from there. The second cap you mentioned that would go to the cathode of V2 would be an additional frequency filter if the amp still has too much treble then. This cap is C8 on th3 schematic, .0022uf. Is there a capacitor value to frequency chart that shows what frequency range a capacitor value will allow to pass?

Thanks Again.  (

[sluckey]

This cap is C8 on th3 schematic, .0022uf. Is there a capacitor value to frequency chart that shows what frequency range a capacitor value will allow to pass?

It's not that simple. You could make a chart for C8 in that particular circuit, but that chart would not be applicable to any other circuit. A general rule that applies to caps is use big caps to pass low frequencies and use small caps to pass high frequencies. So get a bucketful of caps and experiment. If you need a deeper understanding you will want to read some basic AC theory.

[st]

Is there a capacitor value to frequency chart that shows what frequency range a capacitor value will allow to pass?

Not exactly the graphs you're after, but the following calcultors might help you.
https://www.ampbooks.com/mobile/amplifier-calculators/coupling-capacitor/
https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/

[Tbone55]

This cap is C8 on th3 schematic, .0022uf. Is there a capacitor value to frequency chart that shows what frequency range a capacitor value will allow to pass?

It's not that simple. You could make a chart for C8 in that particular circuit, but that chart would not be applicable to any other circuit. A general rule that applies to caps is use big caps to pass low frequencies and use small caps to pass high frequencies. So get a bucketful of caps and experiment. If you need a deeper understanding you will want to read some basic AC theory.

You're right. I've been reading through some material that's making it perfectly clear. Part of it is having to know the impedance of the circuit that the cap is going to and that's not that simple. Guess I will have to get a bucket of caps after all. 

[Tbone55]

Is there a capacitor value to frequency chart that shows what frequency range a capacitor value will allow to pass?

Not exactly the graphs you're after, but the following calcultors might help you.
https://www.ampbooks.com/mobile/amplifier-calculators/coupling-capacitor/
https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/

Thanks for the links!