Princeton Reverb clone advice

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foreverstrung
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Princeton Reverb clone advice

Post by foreverstrung »

I'm going to build a Princeton Reverb clone. I was hoping you guys might have some input on this. I'm wanting to get the right OT and PT. I'd also like to maybe use a 12"speaker instead of a 10". IDK if I can go maybe 15w instead of 10 or 12w as a clone might be,
I picked up one of these PCB boards
https://www.aaelectronicspcb.com/produc ... verb-style
Anyways, I was hoping you might have some thoughts.
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Re: Princeton Reverb clone advice

Post by Bieworm »

PT hammond 291AEX
OT hammond 1760E

Those are what I use

If you put in a 12” speaker you will have to lower the value of the cathode bypass cap on V1A to 4.7uf. I highly recommend the Celestion cream Alnico. It sounds amazing in a PR. Expensive but worth it imho
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Re: Princeton Reverb clone advice

Post by foreverstrung »

What about Reverb choke? Mercury Magnetics?
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Re: Princeton Reverb clone advice

Post by Bieworm »

Also hammond. 1750A
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Re: Princeton Reverb clone advice

Post by KagliostroAmpwww »

I think Mercury Magnetics products are overestimated

I don't say they aren't of good quality but if you go for other Brands you can save money and be satisfied by the product you get, there are may good quality Brand that are less expensive

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Re: Princeton Reverb clone advice

Post by foreverstrung »

I pulled up the BOM for this build today. Any particular thoughts or beliefs about caps n resistors? Any to avoid? Any preferred?
Thx
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Re: Princeton Reverb clone advice

Post by KagliostroAmpwww »

I prefer to use 2W Metal Film resistors (they are less noisy than CC resistors, also the high W is a reason to be less noisy) and, yes, one other advantage is they aren't small, you can see them well and they looks nice in turret or eyelet board, more than the small 1/2W - 1W resistors

if you want to exagerate there are the RN65 resistors but not strictly necessary

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Re: Princeton Reverb clone advice

Post by JMPGuitars »

1W CMF metal film resistors are my favorite for general resistors. Pay attention to voltage requirements too though. The 1W CMF is usually good to 500V.
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Re: Princeton Reverb clone advice

Post by foreverstrung »

If you put in a 12” speaker you will have to lower the value of the cathode bypass cap on V1A to 4.7uf. I highly recommend the Celestion cream Alnico. It sounds amazing in a PR. Expensive but worth it imho
Is this a coupling cap this 4.7 uF I assume or would an electrolytic cap work as I have a couple of these in stock.
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Re: Princeton Reverb clone advice

Post by KagliostroAmpwww »

V1a bypass is the cathode cap

Despite the fact that new wave guy prefer to use non e-caps in that position you can surely use an e-cap there

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Re: Princeton Reverb clone advice

Post by Bieworm »

It’s more obvious to use electrolytic caps for cathode bypass. They require a lower voltage rating and that reduces the physical dimension. Non polarised caps are usually higher voltage rating and thus a lot larger in size. I thought the 25uf of a standard Princeton V1a cathode makes it too bass heavy, so I settled for 4.7uf after some experimenting.
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Re: Princeton Reverb clone advice

Post by KagliostroAmpwww »

If I can suggest

Use a 4.7k pot connected as rehostat in series with the 25uf cap, then you can adjust the bypass at taste

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Re: Princeton Reverb clone advice

Post by Bieworm »

KagliostroAmpwww wrote:
Mon 06/26/23 3:32 pm
If I can suggest

Use a 4.7k pot connected as rehostat in series with the 25uf cap, then you can adjust the bypass at taste

K
That’s a good idea too ofcourse
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Re: Princeton Reverb clone advice

Post by foreverstrung »

Use a 4.7k pot connected as rehostat in series with the 25uf cap, then you can adjust the bypass at taste
Can I get a sketch of how this would go together? How this might look on your board.
Thx
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Re: Princeton Reverb clone advice

Post by KagliostroAmpwww »

This is one way
Cathode Bypass Capacitor Control.jpg
other people do it this way
Cathode Bypass Capacitor Control 02_Pagina_1.jpg
K
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Re: Princeton Reverb clone advice

Post by foreverstrung »

I'm not able to copy n paste those drawings, but the 2nd one, what is the "L" refer to in the Gain 2.5K resistor? In the drawing it has, 2.5K-L. I don't understand this. I am kind of new to this, but I do relatively understand this cathode bypass as it's laid out here with this one exception.
Also, I liked the idea of a 4.7k pot in series with a 25uF cap. I thought that sounded interesting to be able to adjust the tone with a 12" speaker being used. That's kind of what I was hoping to see a drawing of
Thx. I can use all the help I can get. Very grateful
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Re: Princeton Reverb clone advice

Post by KagliostroAmpwww »

2.5K-L means 2.5Kohm - Linear

A stay for Audio

L stay for Linear

---

As english isn't my language I don't understand well you

Did you understand the 4.7k pot in series with the bypass cap use or you have problems ?

In the first image I posted a 1uF cap is shown, but you must read it as a 25uF cap

Have you doubts or all is clear ?

----
I'm not able to copy n paste those drawings
And .... which problem came from that ?

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Re: Princeton Reverb clone advice

Post by Bieworm »

IMHO it’s still better to set the cathode bypass cap fixed at a value that suits you the best. If you want more flexibility you could add an extra parallel cap that is activated through a switch. If you do the variable thing with a resistor in series, you’ll be messing with the bias because that series cap/resistor will be paralleled with the bias resistor. What I suggest is a fat switch by adding a noticeable extra value capacitor in parallel that will only be active with the switch.
A mini toggle switch is easier to implement on the control plate than adding an extra pot. Plus in reality you won't need more than 2 settings anyway.

You can take it even a little bit further and add a DPDT switch. One side switches the extra cathode bypass cap and the other side can be used to lower or raise the next coupling cap value, so you can switch between a flubby F*nder bass and tighter British preamp.

here's an example how the fat switch on the Superlite TMB works:
fat switch.png
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Re: Princeton Reverb clone advice

Post by foreverstrung »

2.5K-L means 2.5Kohm - Linear

A stay for Audio

L stay for Linear

---

As english isn't my language I don't understand well you

Did you understand the 4.7k pot in series with the bypass cap use or you have problems ?

In the first image I posted a 1uF cap is shown, but you must read it as a 25uF cap

Have you doubts or all is clear ?
Yes. Thank you. Very helpful and I do understand better now.
IMHO it’s still better to set the cathode bypass cap fixed at a value that suits you the best. If you want more flexibility you could add an extra parallel cap that is activated through a switch. If you do the variable thing with a resistor in series, you’ll be messing with the bias because that series cap/resistor will be paralleled with the bias resistor. What I suggest is a fat switch by adding a noticeable extra value capacitor in parallel that will only be active with the switch.
A mini toggle switch is easier to implement on the control plate than adding an extra pot. Plus in reality you won't need more than 2 settings anyway.

You can take it even a little bit further and add a DPDT switch. One side switches the extra cathode bypass cap and the other side can be used to lower or raise the next coupling cap value, so you can switch between a flubby F*nder bass and tighter British preamp.

here's an example how the fat switch on the Superlite TMB works:
Good stuff. Thx. I think I'm going to go with the fixed cathode bypass to taste. I'll play with that first.
It's nice to have options tho and a toggle switch changing up tone might not be a bad addition down the road.
Thx again.
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Re: Princeton Reverb clone advice

Post by foreverstrung »

This guy in the UK that i've purchased this PCB board and drawings has different transformers. He's got a 125P1B PT and a 125A10B OT and a 125A20B RT. I've got a all Hammonds, 291AEX PT and 1760E OT and a 1750A RT........Do you guys think I can use what I've got for this layout or am I going to have to go a different way?
I'm attaching the drawings
LAYOUT_princeton_reverb.pdf
SCHEMATIC_princeton_reverb.pdf
He's also modified the original PR and has no cap can.....I'd appreciate your thoughts on all of this. I'm just getting started, but I've got a lot of time and money into the components to this layout here.
Thx
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