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Author Topic: CR112 guy here...again  (Read 886 times)

Jopyeweed

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CR112 guy here...again
« on: February 21, 2021, 12:27:33 PM »
Hey everyone,
 I found a review online for my old Crate CR 112 that suggested upgrading the power amp transistors from TIP110/TIP115 to  nte2343/nte2344 and the preamp opamps to OPA 2134.  No other instructions beyond that. It looks like the nte2343/nte2344 combo is just a little more robust overall, and 80 watts vs 50 with the TIP's. Would these NTE's work as a drop in replacement in this circuit and if so what/ if any improvement would they really offer? I'm assuming it wouldn't really be much louder? (The watts vs db's ratio)

The main problem I'm having is what I believe is harmonic distortion coming from the boosting circuit in the feedback loop of the 2nd half of the 4558 opamp. Ear stabbing sound pressure harshness unless the mids and bright switch are off.
It actually sounds like piercing, whistling overtones. What I dont know is if the harshness is coming from the boosting within the opamp itself, or if the boosting from the op amp is hitting the transistors too hard downstream in the power amp causing harmonic distortion there. Hence maybe beefier transistors would help? Anyone have any ideas?

I've already had some good suggestions for mods to the first op amp loop in this circuit from forum members in the past, and after tinkering alot with the preamp circuit in a simulator, and learning to use a simulator in general, I have some plans for that section.  Many thanks for the help in the past. I'm using this amp circuit to learn about electronics. Thinking about this amp gives my mind something to do other than be anxious.   :-\  Of course, a hemp cone speaker might be all I really need, but then what would I learn?  ;) Schematic is in the manual attached.



nosaj

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Re: CR112 guy here...again
« Reply #1 on: February 21, 2021, 01:42:46 PM »
You might learn that a speaker can make or break how an amplifier sounds.

Think of it like this ..Say your car is riding a little rough  do you look at redesigning the suspension when all that is really needed is a set of tires?

nosaj

Jopyeweed

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Re: CR112 guy here...again
« Reply #2 on: February 21, 2021, 02:36:45 PM »
You might learn that a speaker can make or break how an amplifier sounds.

Think of it like this ..Say your car is riding a little rough  do you look at redesigning the suspension when all that is really needed is a set of tires?

nosaj
Thanks Nosaj,
I have tried an eminence swamp thang and the gold label eminence fender special design that I think they used to put in the hot rod deluxes. I was dead set on trying the cannabis rex next but am now leaning toward the Eminence Guit-Fiddle as it has a hemp cone but also reduced/flat mids in the 800hz -2k frequencies where the harshness seems to live. Maybe that'll be the one. Fingers crossed!

nosaj

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Re: CR112 guy here...again
« Reply #3 on: February 21, 2021, 03:28:28 PM »
i would also check out these guys
https://wgsusa.com/

nosaj

Enzo

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Re: CR112 guy here...again
« Reply #4 on: February 21, 2021, 07:44:53 PM »
What do you think these changes will do?  The original 50 watt part is plenty capable, the amp doesn't produce near that much.  Installing heavier duty parts will not increase the power output in the slightest.  Power comes from the power supply, not the output transistors.  Their 60v ratings are plenty for the 41v supply, of which neither part ever sees more than about 35v on peaks.  These amps are not known as transistor killers, so adding overkill ratings won't really improve reliability.

It won't be ANY louder, the parts ratings only tell you the maximum they can survive, not what will come out from them.  And as to preamp hitting downstream too hard, the signal is limited by the power supply.  The preamp runs on a single 24v rail, which the op amp has to center in so 12v either way from rest.  Minus a volt or so for limits and the signal cannot peak over about 11v.  NO stress on teh power amp.

To answer your question, yes the NTE guys will drop in place, though I consider it a waste of time.


I will say the power amp could be where your distortion lies, but not from being hit too hard.  You might have crossover distortion, and that is a matter of bias adjustment.  Yours is not adjustable other than by changing circuit part values around Q4.

phatt

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Re: CR112 guy here...again
« Reply #5 on: February 21, 2021, 08:33:05 PM »
As like any audio circuit, SS or Glass *Swapping actives is a mugs game*.
The issue is in the **Passives as they define the parameters of the actives.**

C15 is going to make it extremely bright ,,and then the bright switch C11 on top it will certainly annoy the poor Dog.
C3 and C8 can be much bigger to help but I believe I've suggested all this before. 8|
So until you change some or all of those it will remain ear shattering.
Phil.


Jopyeweed

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Re: CR112 guy here...again
« Reply #6 on: February 21, 2021, 11:05:46 PM »
What do you think these changes will do?  The original 50 watt part is plenty capable, the amp doesn't produce near that much.  Installing heavier duty parts will not increase the power output in the slightest.  Power comes from the power supply, not the output transistors.  Their 60v ratings are plenty for the 41v supply, of which neither part ever sees more than about 35v on peaks.  These amps are not known as transistor killers, so adding overkill ratings won't really improve reliability.

It won't be ANY louder, the parts ratings only tell you the maximum they can survive, not what will come out from them.  And as to preamp hitting downstream too hard, the signal is limited by the power supply.  The preamp runs on a single 24v rail, which the op amp has to center in so 12v either way from rest.  Minus a volt or so for limits and the signal cannot peak over about 11v.  NO stress on teh power amp.

To answer your question, yes the NTE guys will drop in place, though I consider it a waste of time.


I will say the power amp could be where your distortion lies, but not from being hit too hard.  You might have crossover distortion, and that is a matter of bias adjustment.  Yours is not adjustable other than by changing circuit part values around Q4.
Thank you Enzo. It was just a theory. I'll leave all that stuff alone.

Jopyeweed

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Re: CR112 guy here...again
« Reply #7 on: February 21, 2021, 11:11:39 PM »
As like any audio circuit, SS or Glass *Swapping actives is a mugs game*.
The issue is in the **Passives as they define the parameters of the actives.**

C15 is going to make it extremely bright ,,and then the bright switch C11 on top it will certainly annoy the poor Dog.
C3 and C8 can be much bigger to help but I believe I've suggested all this before. 8|
So until you change some or all of those it will remain ear shattering.
Phil.
Thanks Phil, I'm guessing you meant C13, the treble cap, rather than c15? The treble cap is the one I've never adjusted so far in my simulations.  :duh Thank you for the direction.

phatt

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Re: CR112 guy here...again
« Reply #8 on: February 22, 2021, 12:39:19 AM »
Opps,,  :-[ Sorry I meant C4 which is .15 (150nF) This is just above the gain pot.
Then bass is wiped again at C11 .1 (100nF)

Small values there will wipe off a ton of Bass.

All 4 positions that I've noted need to be larger so rather than remove existing parts which might damage the PCB you can simply tack larger values on the track side of the PCB to test the outcome.
Maybe change one at a time so you know just where you are winning or losing mojo.

So that is C3,C4,C8,C11 can be larger.
C3 and C8 can be as large as 1nF.
As for C4 it's a tough one to guess as 470nF there might make the OD way too loud when S1 is closed. so suck it and see what happens.

As for C11 you may find that raising the value of R11 might help to wipe off extreme treble. Maybe try 4k7 or 10k.  you will have to lift at least one end of that resistor.

Just search for opamp design principles,  in this configuration the combination of R3 and R4 sets the gain and the value of C4 determines the bass roll off which of course raises the treble response of the circuit.
Same goes for the second stage;
This time R8, R10 and C10 set the gain and R11, C11 are switched which gives the treble boost.

If I remember,, in clean mode the first stage is lifted from ground Via S1 and that is likely not a very good idea,, others here might know more about that but to me it looks like it could be unstable. :-\
Phil.
« Last Edit: February 22, 2021, 12:40:48 AM by phatt »

Jopyeweed

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Re: CR112 guy here...again
« Reply #9 on: February 23, 2021, 10:00:45 PM »
Opps,,  :-[ Sorry I meant C4 which is .15 (150nF) This is just above the gain pot.
Then bass is wiped again at C11 .1 (100nF)

Small values there will wipe off a ton of Bass.

All 4 positions that I've noted need to be larger so rather than remove existing parts which might damage the PCB you can simply tack larger values on the track side of the PCB to test the outcome.
Maybe change one at a time so you know just where you are winning or losing mojo.

So that is C3,C4,C8,C11 can be larger.
C3 and C8 can be as large as 1nF.
As for C4 it's a tough one to guess as 470nF there might make the OD way too loud when S1 is closed. so suck it and see what happens.

As for C11 you may find that raising the value of R11 might help to wipe off extreme treble. Maybe try 4k7 or 10k.  you will have to lift at least one end of that resistor.

Just search for opamp design principles,  in this configuration the combination of R3 and R4 sets the gain and the value of C4 determines the bass roll off which of course raises the treble response of the circuit.
Same goes for the second stage;
This time R8, R10 and C10 set the gain and R11, C11 are switched which gives the treble boost.

If I remember,, in clean mode the first stage is lifted from ground Via S1 and that is likely not a very good idea,, others here might know more about that but to me it looks like it could be unstable. :-\
Phil.


Thanks Phil,

I'll experiment with adjusting those caps in the simulator. I use a mobile app called Circuit Safari. Then in a couple weeks I'm going to have some free time to tinker with the amp. Many thanks for your time and the detailed direction.