groovtubin wrote:Ben, can ya post a clip w/SANTANA gain? I`d love to hear the amp sorta gained up w/those drivers!! Thanks, jimoldmacman wrote:Yup.
ODS 75W!
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groovtubin
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Re: ODS 75W!
Last edited by groovtubin on Tue Apr 25, 2006 7:07 pm, edited 1 time in total.
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ElectronAvalanche
- Posts: 376
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Re: ODS 75W!
Here is a very rough schematic of my approach.
I have some slight problems:
1. Fixed the Reverb (loose wire on the return), but it is too much Reverb for my taste.
2. When I bias the KT88 hotter, there is some distorted sound even with the MV all the way down or the PI input cap grounded.
Ben: how much filtering do you have on the Main B+ Filter?
Electron!
I have some slight problems:
1. Fixed the Reverb (loose wire on the return), but it is too much Reverb for my taste.
2. When I bias the KT88 hotter, there is some distorted sound even with the MV all the way down or the PI input cap grounded.
Ben: how much filtering do you have on the Main B+ Filter?
Electron!
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Re: ODS 75W!
2x100uF/350V in series with 270K bleeder resistor across each (total of 50uF).
40uF on the screens.
40uF on the screens.
Re: ODS 75W!
I'm having the same issue. The reverb return knob on almost 0 produces as much reverb as I can stand, on 3 it's Dick Dale on 4 it's drenched. I've already lowered the return amps plate load and cathode resistors to 22k/820.ElectronAvalanche wrote:Here is a very rough schematic of my approach.
I have some slight problems:
1. Fixed the Reverb (loose wire on the return), but it is too much Reverb for my taste.
How hot is "hotter". Maybe yopu're pushing too far into class B.2. When I bias the KT88 hotter, there is some distorted sound even with the MV all the way down or the PI input cap grounded.
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ElectronAvalanche
- Posts: 376
- Joined: Mon Feb 06, 2006 9:17 pm
Re: ODS 75W!
Hi Bob,
concerning the Reverb:
I think the problem is the Recovery stages. Too much gain there. I even had the Reverb section feedback when the pot was dialed up.
In my amp, the two recovery stages share one 820 Ohm/10uF cathode resistor. From the top of my head, I am using a 5751. Maybe a 12AT7 would be better?
Attenuating the signal might help. Maybe using LNFB on the second stage? grid -> 10M - 01. uF-> anode.
Biasing hot means 37 mA per Tube @520V Anode voltage.
I will have to look into this today after work. It did not do this when the Reverb did not work. At least I do not remember....
Electron
concerning the Reverb:
I think the problem is the Recovery stages. Too much gain there. I even had the Reverb section feedback when the pot was dialed up.
In my amp, the two recovery stages share one 820 Ohm/10uF cathode resistor. From the top of my head, I am using a 5751. Maybe a 12AT7 would be better?
Attenuating the signal might help. Maybe using LNFB on the second stage? grid -> 10M - 01. uF-> anode.
Biasing hot means 37 mA per Tube @520V Anode voltage.
I will have to look into this today after work. It did not do this when the Reverb did not work. At least I do not remember....
Electron
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glasman
- Posts: 1446
- Joined: Wed Jan 19, 2005 10:37 pm
- Location: Afton, MN (St Croix River Valley)
- Contact:
Re: ODS 75W!
I saw the comments on too much reverb. Have you tried adding a Dwell resistor to the input of the reverb driver. Normally the input is a 500pf to the grid with a 1M to ground. If you split the 1M into parts (ie 470K and 470K) and feed the grid with 1/2 the signal it can help a lot. especially with Long Decay tanks.
The older fender external reverb tanks used a pot at that location to control how much signal you applied to the tank. Here is a schematic of the idea.
Gary
The older fender external reverb tanks used a pot at that location to control how much signal you applied to the tank. Here is a schematic of the idea.
Gary
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification
www.glaswerks.com
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification
www.glaswerks.com
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ElectronAvalanche
- Posts: 376
- Joined: Mon Feb 06, 2006 9:17 pm
Re: ODS 75W!
Hi there,
a couple of fixes:
The squeal was due to not shielding the wire coming from the channel select relay going to the FX-Loop jacks. In this amp I thought I was clever and put the FX-Loop before the Master (no Dumbleator FX-loop merely Preamp out and Power amp in).
Due to the tight space in my amp, the aforementioned wire runs close to the input grid resistors of the first tube (CL1). I need to change that wire to a shielded one. Maybe I should go back to the Dumble way and put the Preamp out after the MV?
The distortion sound I heard was due to the Reverb driver tube. Pulling that one got rid of the distorted sound (which was there even with no Tank attached).
I have the Reverb transformer output grounded to the chassis, might have to change that as well.
I will definitely have to reduce the signal into the Reverb driver. Garys hint is more than correct.
I am a bit torn concerning the Reverb. I really do not like the spring Reverb. It is fine for Fender amps, but I like a digital Reverb more on high gain amps. Maybe I will pull the Reverb ckt out again. Don´t´know yet.
Grounding is another issue:
I have the FX-loop grounded on the Reverb return filter ground. Maybe I have to change that. Another thing is the ground of the Post PI CF (33ks) which should probably go directly to the corresponding filter cap. For now they are grounded on the preamp board bus ground.
BTW: the 4M7 is only there to get rid of the pop when switching the Mid Boost. I forgot that and before soldering it in, I played with or without the resistor and apart from the pop there is NO difference.
Concerning the EQ discussion of another thread:
The Dumble EQ is very different from what one is used to from Fender amps or other amps (Marshall, Soldano).
It will not behave like a Fender one, you have to use the Mid pot a bit higher to get good bass on a Strat.
Cheers for now,
Electron
a couple of fixes:
The squeal was due to not shielding the wire coming from the channel select relay going to the FX-Loop jacks. In this amp I thought I was clever and put the FX-Loop before the Master (no Dumbleator FX-loop merely Preamp out and Power amp in).
Due to the tight space in my amp, the aforementioned wire runs close to the input grid resistors of the first tube (CL1). I need to change that wire to a shielded one. Maybe I should go back to the Dumble way and put the Preamp out after the MV?
The distortion sound I heard was due to the Reverb driver tube. Pulling that one got rid of the distorted sound (which was there even with no Tank attached).
I have the Reverb transformer output grounded to the chassis, might have to change that as well.
I will definitely have to reduce the signal into the Reverb driver. Garys hint is more than correct.
I am a bit torn concerning the Reverb. I really do not like the spring Reverb. It is fine for Fender amps, but I like a digital Reverb more on high gain amps. Maybe I will pull the Reverb ckt out again. Don´t´know yet.
Grounding is another issue:
I have the FX-loop grounded on the Reverb return filter ground. Maybe I have to change that. Another thing is the ground of the Post PI CF (33ks) which should probably go directly to the corresponding filter cap. For now they are grounded on the preamp board bus ground.
BTW: the 4M7 is only there to get rid of the pop when switching the Mid Boost. I forgot that and before soldering it in, I played with or without the resistor and apart from the pop there is NO difference.
Concerning the EQ discussion of another thread:
The Dumble EQ is very different from what one is used to from Fender amps or other amps (Marshall, Soldano).
It will not behave like a Fender one, you have to use the Mid pot a bit higher to get good bass on a Strat.
Cheers for now,
Electron