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Re: Replacement Speaker for Peavey Classic 30

3/2/1998 2:23 PM
Bruce	Re: Replacement Speaker for Peavey Classic 30 OK! I really tried every combination I could think of that mixed the output Zed with the speaker's Zed and how the different feedback taps sounded with mismatched outputs. The best sounding feedback loop for me was a 100K pot to the 4 ohm tap with the 8 ohm secondary output connected to an 8 ohm speaker load. Maybe that means, I just like the sound of less feedback! Close to what you are finding? By the way I have some of the custom Torres caps too but I don't notice enough diference as you did to warrant the extra expense. But I also am not so hung up on the 250pF-.022uF-.022uF ..and .01 or .022 coupling cap combination everyone else seems to be. HA! I know you arent; either!! But we like to experiment. I mix that stuff up regularly to get a tone that turns me on. I wonder if you tried checking the measured uF of the Torres caps versus what they are supposed to be. My 715P Orange Drops are all VERY accurate according to my cap meter. Also Dan once told me that he likes that, 2 x .033uF and a 330pF trebl;e cap sound. It sounded real good in a BF Pro I hot rodded too. But that amp sounded even better to me with the 2 x .022. and 250pF cap... AFTER I dumped the OT and used a BF Super OT. The Super OT was about 30% biiger and the Pro amp sounded about 30% bigger!! This turned into a great Fender amp on steroids. I'd do that mod again in a minute if I had one. Bruce

3/2/1998 2:23 PM

Bruce

Re: Replacement Speaker for Peavey Classic 30

OK!

I really tried every combination I could think of that mixed the output Zed with the speaker's Zed and how the different feedback taps sounded with mismatched outputs.
The best sounding feedback loop for me was a 100K pot to the 4 ohm tap with the 8 ohm secondary output connected to an 8 ohm speaker load.
Maybe that means, I just like the sound of less feedback!
Close to what you are finding?

By the way I have some of the custom Torres caps too but I don't notice enough diference as you did to warrant the extra expense.
But I also am not so hung up on the 250pF-.022uF-.022uF ..and .01 or .022 coupling cap combination everyone else seems to be.
HA! I know you arent; either!! But we like to experiment.
I mix that stuff up regularly to get a tone that turns me on.
I wonder if you tried checking the measured uF of the Torres caps versus what they are supposed to be.
My 715P Orange Drops are all VERY accurate according to my cap meter.
Also Dan once told me that he likes that, 2 x .033uF and a 330pF trebl;e cap sound.
It sounded real good in a BF Pro I hot rodded too.
But that amp sounded even better to me with the
2 x .022. and 250pF cap... AFTER I dumped the OT and used a BF Super OT. The Super OT was about 30% biiger and the Pro amp sounded about 30% bigger!!
This turned into a great Fender amp on steroids.
I'd do that mod again in a minute if I had one.

Bruce

3/3/1998 2:31 AM
Steve A.	Bruce: I put a 1 meg pot in series with that 100k resistor in the FB loop and it really opens up the amp using either speaker tap, making it louder and more responsive. My "hunch" on the stock setup was just that when the 8 ohm speaker tap is being used, it "robs" enough of the signal from the OT being sent back through the feedback loop to liven up the sound. Steve Ahola

3/4/1998 1:06 AM
Bruce	Steve: I think like any impedance... the voltage will rise with a higher Zed. When you tap the OT for a feedback loop at the 16ohm position, the voltage should be higher then at the 4 or 8 and then the FB loop will have more effect in clamping or dampening the amp down. If you move the FB loop over to the 8 ohm tap, the impedance is less. At that point, relative to ground, the voltage should be less ( just as if you put more resistance in theloop with that pot) and the FB loop will haev less effect on the amp and it should sound a little more open and loose. Or less dampened. With the 1M pot you have just about removed all the FB voltage and the amp shoud be running wide open. I use a 100K to 250K pot in my FB loops but I hold the loop up by a 1K to 2K5 resistor so I can never run the pot so far as to have no resitance in the loop. What I have been doing is fixing the resistor on the board and connecting the FB voltage from the pot to it before it is connected back to the PI/driver tube. In other words, if the pot is turned to them zero resistance spot, there is still the value of the fixed resistor in the loop to limit the voltage but more importantly to keep the secondary from being shunted to ground at a resistance less then the speaker. That , of course depnds on what the grounded grid cap is terminated in with a PP longtail pair PI/driver. There is no magic value ( fender uses a ratio of about 8:1 ... I picked the 1K to 2K5 because I like the way it cleans up the amp with the pot set to about 10K but still is warm sounding. When the FB control is set for min FB, it is wide open anyhow. Confusing huh? Bruce

3/4/1998 1:06 AM

Bruce

Steve:
I think like any impedance... the voltage will rise with a higher Zed.
When you tap the OT for a feedback loop at the 16ohm position, the voltage should be higher then at the 4 or 8 and then the FB loop will have more effect in clamping or dampening the amp down.
If you move the FB loop over to the 8 ohm tap, the impedance is less. At that point, relative to ground, the voltage should be less ( just as if you put more resistance in theloop with that pot) and the FB loop will haev less effect on the amp and it should sound a little more open and loose. Or less dampened.
With the 1M pot you have just about removed all the FB voltage and the amp shoud be running wide open.
I use a 100K to 250K pot in my FB loops but I hold the loop up by a 1K to 2K5 resistor so I can never run the
pot so far as to have no resitance in the loop.
What I have been doing is fixing the resistor on the board and connecting the FB voltage from the pot to it before it is connected back to the PI/driver tube.
In other words, if the pot is turned to them zero resistance spot, there is still the value of the fixed resistor in the loop to limit the voltage but more importantly to keep the secondary from being shunted to ground at a resistance less then the speaker.
That , of course depnds on what the grounded grid cap is terminated in with a PP longtail pair PI/driver.
There is no magic value ( fender uses a ratio of about 8:1 ... I picked the 1K to 2K5 because I like the way it cleans up the amp with the pot set to about 10K but still is warm sounding. When the FB control is set for min FB, it is wide open anyhow.
Confusing huh?

Bruce

2/28/1998 3:47 AM
Steve A.	Bruce: So a more open sound because it is not holding the amp back as much. You have effectivly cut the FB loop voltage way down just as if you put more resistance in the feedback loop. So to open up the response of the amp, I could try increasing the resistance within the feedback loop- from the 8 ohm tap the FB signal goes through an RC network (220k/.0047uf) to R57 (100k) to the weird cathode circuit. Rather than alter the tuned RC network or mess with the cathode circuit of V3A, it seems like R57 would be the logical part to play around with. With the C30 using a pcb, I could pull R57, solder 2 leads to its pads and then run those 2 leads in series through an 100k resistor to an offboard pot wired as a variable resistor for an add-on Presence (Brilliance?) control? With the VR set to 0 ohms, you'd get the stock sound and as you open up the control, you could dial in some more open sounds... Definitely worth trying out- I suppose I could try a 100k (1 meg?) linear pot for starters and if there was a point that the amp became unstable I could replace the pot with a smaller value. I'll post my results here. Steve Ahola

2/28/1998 3:47 AM

Steve A.

Bruce:

    So a more open sound because it is not
holding the amp back as much. You have
effectivly cut the FB loop voltage way down
just as if you put more resistance in
the feedback loop.

    So to open up the response of the amp, I could try increasing the resistance within the feedback loop- from the 8 ohm tap the FB signal goes through an RC network (220k/.0047uf) to R57 (100k) to the weird cathode circuit. Rather than alter the tuned RC network or mess with the cathode circuit of V3A, it seems like R57 would be the logical part to play around with. With the C30 using a pcb, I could pull R57, solder 2 leads to its pads and then run those 2 leads in series through an 100k resistor to an offboard pot wired as a variable resistor for an add-on Presence (Brilliance?) control? With the VR set to 0 ohms, you'd get the stock sound and as you open up the control, you could dial in some more open sounds...
    Definitely worth trying out- I suppose I could try a 100k (1 meg?) linear pot for starters and if there was a point that the amp became unstable I could replace the pot with a smaller value. I'll post my results here.

Steve Ahola

3/4/1998 6:46 AM
Stephen	Steve... I only picked up the end of this thread. First question would be...Are you moving the feedback resistor between the 8 and 16 taps, along with the various speakers? That could account for the different kind of sound Another possibility that occurs to me....I wonder if the extra winding for 16 ohms on that little OT is an overwind, on the outside of the other windings....poorer coupling...higher leakage inductance, some HF loss...and what it would do to speaker/output tube interaction is anyone's guess. I did a bit of govt-funded research into tube amp OT's. Amongst the things I discovered, were that making a great-sounding OT is usually less straightforward than you might expect...and that a section of secondary winding right on the outside of the pile often has noticeably poorer coupling than a similar section buried anywhere inside the pile. (FWIW, the best thing to put on the outside seems to be one primary B+ end, which is also conveniently close to AC ground and zero signal anyway. - Stephen.

3/4/1998 6:46 AM

Stephen

Steve...
I only picked up the end of this thread.
First question would be...Are you moving the feedback resistor between the 8 and 16 taps, along with the various speakers? That could account for the different kind of sound
Another possibility that occurs to me....I wonder if the extra winding for 16 ohms on that little OT is an overwind, on the outside of the other windings....poorer coupling...higher leakage inductance, some HF loss...and what it would do to speaker/output tube interaction is anyone's guess. I did a bit of govt-funded research into tube amp OT's. Amongst the things I discovered, were that making a great-sounding OT is usually less straightforward than you might expect...and that a section of secondary winding right on the outside of the pile often has noticeably poorer coupling than a similar section buried anywhere inside the pile. (FWIW, the best thing to put on the outside seems to be one primary B+ end, which is also conveniently close to AC ground and zero signal anyway.
- Stephen.

3/7/1998 1:49 AM
Steve A.	Stephen: Are you moving the feedback resistor between the 8 and 16 taps? No, I've left the FB loop connected to the 8 ohm tap and just hooked up the various speakers to either jack. Incidentally, in looking over the schematic for the Classic 50, it appears that the FB loop is connected to the 16 ohm tap (which is the one used for the 4 10" speakers I have). I haven't been able to get the very open response out of the C50-410 that I have gotten from my C30 and it may have to do with differences between the FB loops, and the Presence control on the Classic 50... Steve Ahola

3/7/1998 1:49 AM

Steve A.

Stephen:

Are you moving the feedback resistor between the 8 and 16 taps?

No, I've left the FB loop connected to the 8 ohm tap and just hooked up the various speakers to either jack.

Incidentally, in looking over the schematic for the Classic 50, it appears that the FB loop is connected to the 16 ohm tap (which is the one used for the 4 10" speakers I have). I haven't been able to get the very open response out of the C50-410 that I have gotten from my C30 and it may have to do with differences between the FB loops, and the Presence control on the Classic 50...

Steve Ahola

3/7/1998 2:21 AM
stephen	haven't... very open response out of the C50-410 that I have gotten from my C30...differences..FB loops, Hmm....Now I'm curious.... Steve, do you have both schems on your site? - Stephen

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