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Vintage threads from the first ten years

Re: Replacement Speaker for Peavey Classic 30

2/25/1998 8:38 PM
Steve Ahola	Re: Replacement Speaker for Peavey Classic 30 Doc: >>>In the next week, I plan to have my C-30 taken apart for Steve's tone stack mods.<<< You may want to hold off on those mods as I should be posting "Advanced Mods for the Classic 30" on my web site in the next few days. (The text portion is almost done, but I haven't drawn up the pictorials yet.) I may post just the text portion later tonight since I'm sure that you don't need pictures to follow the mods which include: - add-on relay board so that boost circuit can be turned on and off with the footswitch - the boost circuit relay also toggles the value of the bass cap between .022uf in the boosted mode and .055uf in the unboosted mode for smoother OD sounds and a fuller Normal tone. (I also added a "trick" on-on-on DPDT mini-toggle switch to force the value to either .022uf or .055uf regardless of the state of the boost relay.) - Center-off DPDT mini-toggle switches to select the value of the cathode resistor bypass cap for V1A (22uf-0uf-0.68uf) and V2B (22uf-0uf-1.0uf). With these switches you can get quite a few different sounds from the Classic 30. - Full-sized toggle switch to select between the stock .001uf coupling cap from V2A and a .01uf cap for a stronger and fuller OD signal. - And coming soon... a Torres style dual stage master volume control between the split phase driver and the output tubes. As for the different responses from the two speaker taps, I noticed that when I reinstalled the stock speaker. The great sounds and response I was getting with a Celestion Silver Series 60 disappeared! Plugging the stock speaker into the 8 ohm tap restored most of the tone and response, which struck me as a bit unusual since it usually doesn't make THAT much of a difference with other amps. The 8 ohm tap has a "live wire" response for leads that the 16 ohm tap just doesn't have. Steve Ahola

2/25/1998 8:38 PM

Steve Ahola

Re: Replacement Speaker for Peavey Classic 30

Doc:

>>>In the next week, I plan to have my C-30
taken apart for Steve's tone stack mods.<<<

You may want to hold off on those mods as I should be posting "Advanced Mods for the Classic 30" on my web site in the next few days. (The text portion is almost done, but I haven't drawn up the pictorials yet.) I may post just the text portion later tonight since I'm sure that you don't need pictures to follow the mods which include:
- add-on relay board so that boost circuit can be turned on and off with the footswitch
- the boost circuit relay also toggles the value of the bass cap between .022uf in the boosted mode and .055uf in the unboosted mode for smoother OD sounds and a fuller Normal tone. (I also added a "trick" on-on-on DPDT mini-toggle switch to force the value to either .022uf or .055uf regardless of the state of the boost relay.)
- Center-off DPDT mini-toggle switches to select the value of the cathode resistor bypass cap for V1A (22uf-0uf-0.68uf) and V2B (22uf-0uf-1.0uf). With these switches you can get quite a few different sounds from the Classic 30.
- Full-sized toggle switch to select between the stock .001uf coupling cap from V2A and a .01uf cap for a stronger and fuller OD signal.
- And coming soon... a Torres style dual stage master volume control between the split phase driver and the output tubes.

As for the different responses from the two speaker taps, I noticed that when I reinstalled the stock speaker. The great sounds and response I was getting with a Celestion Silver Series 60 disappeared! Plugging the stock speaker into the 8 ohm tap restored most of the tone and response, which struck me as a bit unusual since it usually doesn't make THAT much of a difference with other amps. The 8 ohm tap has a "live wire" response for leads that the 16 ohm tap just doesn't have.

Steve Ahola

2/26/1998 6:25 AM
Doc	Steve: Did you get the best sound from the 8-ohm celestion on the 8-ohm tap or the 16? When you reconnected the stock 16-ohm speaker, it sounded better than the stock setup by connecting it to the 8-ohm tap? BTW, thanks for the description of the switchable mods. I can surely hold off until your instructions are completed. Doc

2/27/1998 1:02 AM
Steve A.	Doc: I tested both speaker taps with the stock 16 ohm Peavy speaker, the 8 ohm Celestion and the 16 ohm load from a Classic 50-410- in all cases the 8 ohm tap sounded much more alive- the response was much faster and the notes would sustain longer. At least that is my subjective opinion when playing through either tap. The only instance I could think of in which the 16 ohm tap would be preferable might be playing mellow Kenny Burrell-type jazz guitar where you'd want a muffled tone. Incidentally, with the Classic 50-410, there was hardly any difference noted between its two taps. The circuits are practically identical except for the presence control (on the FB loop) and the Boost circuit. Even with identical mods on both amps, I haven't been able to get the same "live wire" response out of the 50-410 so I think it has to do with the feedback loop. Or it could be that the 50-410 has a "real" output transformer while the one on the Classic 30 looks like something out of a transistor radio! Steve Ahola

2/27/1998 1:02 AM

Steve A.

Doc:

I tested both speaker taps with the stock 16 ohm Peavy speaker, the 8 ohm Celestion and the 16 ohm load from a Classic 50-410- in all cases the 8 ohm tap sounded much more alive- the response was much faster and the notes would sustain longer. At least that is my subjective opinion when playing through either tap. The only instance I could think of in which the 16 ohm tap would be preferable might be playing mellow Kenny Burrell-type jazz guitar where you'd want a muffled tone.

Incidentally, with the Classic 50-410, there was hardly any difference noted between its two taps. The circuits are practically identical except for the presence control (on the FB loop) and the Boost circuit. Even with identical mods on both amps, I haven't been able to get the same "live wire" response out of the 50-410 so I think it has to do with the feedback loop. Or it could be that the 50-410 has a "real" output transformer while the one on the Classic 30 looks like something out of a transistor radio!

Steve Ahola

2/27/1998 2:55 AM
Bruce	That is a good example of what I was talking about. The 8 ohm tap DOES have less AC voltage developed across it then the 16 does so the 8 sounds like you have less negative feedback . So a more open sound because it is not holding the amp back a much. You have effectivly cut the FB loop voltage way down just as if you put more resistance in the feedback loop. Bruce

2/27/1998 8:33 AM
Doc	But the FB loop is permanently connected to the 8-ohm tap on this amp. So, wouldn't the feedback voltage be the same no matter which speaker was connected, or whatever tap it was connected to? Doc

2/27/1998 9:44 AM
Bruce	Well, good question. God knows I have been wrong half the time in any assumption I come up with! But here are my thoughts Doc. And I am open to any comments of course. You know this already....... The signal voltage we are dealing with is an AC one subject to the true total " impedances" of the circuit as if you were to Thevinize (sp?) the whole thing . The OT secondary is tapped so when you use those taps, isn't it like a few inductors in series? Wouldn't the impedances be different if the inductances were different. Relative to th ecommon gnd, we could measure the inductance at different spots along the windings that were terminated in a tap of some kind. I would guess so, other wise there would be no imedance ratio and no such thing as 4 ohm 8 ohm and 16 ohm tap. I was thinking that if you connected an LCR lump (the speaker) in parallel to one of those taps to ground then that section would have some different Zed at a finite frequency because you shunted the section to the common gnd Picture it like a swamping resistor across a tank circuit to lower the Q. Now this is LOOSE here...... : ) Given: Some test freq with X voltage through the OT If the sum of the voltages measured across the taps equal the total secondary voltage, then connecting the FB send line to different OT taps would change the basic negative FB voltage and also, would not paralleling a different load ( shunting with the different speaker) also effect the AC voltage at the FB connection point because the OT secondary circuit is acting like an impedance divider with one of the sections variable with different speaker loads. I mean by the laws of distributed addition? And that OT secondary tap to the speaker load is also now in parallel to gnd with the total FB resistance connected at some point PI/ driver or cathode resistor in a preamp tube (or wherever)...but the rest of the secondary inductance is in series between the two.. Like PI network with the one of the legs being the OT tap shunted by the LCR of the speaker and the other leg being the voltage divider circuit of the FB loop to the preamp. Boy this gets complicated. Another kind of impedance divider. So what I thought was happening is that the FB voltage has to change also when the OT secondaries are terminated in a mismatch of the taps because the voltage is distributed differently now and what ever is left over is the FB voltage at that point.. Somewhere along the line I came up with that idea that the AC feedback voltage is going all over the place when we juggle the speaker loads around with mismatches. What do you think? Misinformed mumbo jumbo! Start over? Bruce

2/27/1998 9:44 AM

Bruce

Well, good question.
God knows I have been wrong half the time in any assumption I come up with!

But here are my thoughts Doc. And I am open to any comments of course.
You know this already.......
The signal voltage we are dealing with is an AC one subject to the true total " impedances" of the circuit as
if you were to Thevinize (sp?) the whole thing .
The OT secondary is tapped so when you use those taps, isn't it like a few inductors in series?
Wouldn't the impedances be different if the inductances were different.
Relative to th ecommon gnd, we could measure the inductance at different spots along the windings that were terminated in a tap of some kind.
I would guess so, other wise there would be no imedance ratio and no such thing as 4 ohm 8 ohm and 16 ohm tap.
I was thinking that if you connected an LCR lump
(the speaker) in parallel to one of those taps to ground then that section would have some different Zed at a finite frequency because you shunted the section to the common gnd Picture it like a swamping resistor across a tank circuit to lower the Q.
Now this is LOOSE here...... : )
Given: Some test freq with X voltage through the OT
If the sum of the voltages measured across the taps equal the total secondary voltage, then connecting the FB send line to different OT taps would change the basic negative FB voltage and also, would not paralleling a different load ( shunting with the different speaker) also effect the AC voltage at the FB connection point because the OT secondary circuit is acting like an impedance divider with one of the sections variable with different speaker loads.
I mean by the laws of distributed addition?
And that OT secondary tap to the speaker load is also now in parallel to gnd with the total FB resistance connected at some point PI/ driver or cathode resistor in a preamp tube (or wherever)...but the rest of the secondary inductance is in series between the two.. Like PI network with the one of the legs being the OT tap shunted by the LCR of the speaker and the other leg being the voltage divider circuit of the FB loop to the preamp. Boy this gets complicated.
Another kind of impedance divider.

So what I thought was happening is that the FB voltage has to change also when the OT secondaries are terminated in a mismatch of the taps because the voltage is distributed differently now and what ever is left over is the FB voltage at that point..

Somewhere along the line I came up with that idea that the AC feedback voltage is going all over the place when we juggle the speaker loads around with mismatches.
What do you think? Misinformed mumbo jumbo!

Start over?

Bruce

3/2/1998 12:40 AM
Steve A.	Bruce: Somewhere along the line I came up with that idea that the AC feedback voltage is going all over the place when we juggle the speaker loads around with mismatches. What do you think? Misinformed mumbo jumbo! I just wanted to reiterate the observation that the best sounds I get are with the 8 ohm Celestion plugged into the 8 ohm tap so I don't think mismatched impedances are the issue here. I'll let you know how the pot on the FB loop works out. Steve Ahola

3/2/1998 12:40 AM

Steve A.

Bruce:

Somewhere along the line I came up with that idea that the AC feedback
voltage is going all over the place when we juggle the speaker loads around with mismatches.
What do you think? Misinformed mumbo
jumbo!

I just wanted to reiterate the observation that the best sounds I get are with the 8 ohm Celestion plugged into the 8 ohm tap so I don't think mismatched impedances are the issue here. I'll let you know how the pot on the FB loop works out.

Steve Ahola

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