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Mods to my Ampeg SVP-PRO!

#22
@byacey and @agedhorse
I heeded your advice about sagging transformer voltages and bypassed the problem completely.
I added 2, 12V 1.5A SMPS and removed the LVPS section of the preamp all together. Pictures below. (Yes it's working :) )
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#23
IMO, you now have a solution looking for a problem.

Did you ever explore how signal levels throughout the amp compare to the rail voltages? You might find that the engineers behind the product actually understood what they were doing. Just a thought.
 
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#24
agedhorse said:
IMO, you now have a solution looking for a problem.

Did you ever explore how signal levels throughout the amp compare to the rail voltages? You might find that the engineers behind the product actually understood what they were doing. Just a thought.
Click to expand...

No my friend I did not and I'm sure if I reach out to the engineers involved I might not get much in return, I am sure the engineer's involve knew exactly what they're doing (don't they always) But with that being said, and please don't take this wrong because I know as an electronics tech with limited engineering experience and technician level experience only that I'm sure I can be wrong.
That being said. I've upped the rails on the preamp giving the unit more dynamic range and headroom. I've been practicing, playing (burning the unit in) all morning using the preamp without any issues and because it's mine and I spent the money to buy it I'm okay if it fails and or dies completely. There does seen to be more adjustability in the EQ section. Bottom line is... I changed things in MY preamp, and it's working, it hasn't failed... lol, it seems to sound better, but that only to my ears.. and that's okay, isnt that what matters? I'm not worried about resale value. It was a project I had the extra parts and I had fun doing it and it's still working, it's also something that has been mentioned by others here on TB that could have been improved on, so I did, hehe. (I'm not the type of person to just leave things alone ;) ). This isn't a big FU to the engineers that developed this preamp, I respect them immensely, I couldn't have done it. But I think I made an improvement and it seems to be working and if I have more problems or the preamp fails I would not be embarrassed post that and that I screwed up.
 
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#25
Regarding headroom and rail voltages in general, in pro audio and recording, in addition to many of the new modeling or DSP based amps, the ADC/DAC's operate on either +5V or +3.3V and have no problem with dynamic range. They are simply scaled in and out.
 
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#27
I'm not sure that you've improved anything. Switch mode supplies generate more noise, electromagnetic radiation, and high frequency noise on the rails. I'd be willing to bet your noise floor has increased significantly.

However, if you're happy with what you have, the details really don't matter.
 
#28
byacey said:
Switch mode supplies generate more noise, electromagnetic radiation, and high frequency noise on the rails. I'd be willing to bet your noise floor has increased significantly.
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I wondered about that but more over I wondered about running the line voltage across the back like that and near that side of the preamp causing 60Hz hum. I know the SMPS switch at a high frequency (usually above hearing). I Don't hear any new noise and this particular preamp was void of the horrible noise that most SVP-PROs have. I know, I had a grey face that was noisey. It SEEMS to have a different sound and adjustability but again, I never could hear a huge difference when rolling tubes either, even V1. So, it's more of an experiment, I'm also thinking about installing ic sockets and swapping out the TLO72 op amps in the front end of the preamp for maybe some OP27 op amps. Most of this stuff I have laying around (like the SMPS, I got them for a buck a piece at a thrift store, they're wall adaptors taken apart)
It's just something I'm doing for fun, I have an SVPCL and a Sansamp RBI I use and my newest toy the Quilter Bass Block 800. So if I break anything I'll still be in business.
It's getting close to upgrading my computer again soon too, I always over clock the crap outta them when I'm done with the build too.. HA!
 
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#29
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#31
JimmyM said:
I'm completely clueless about what you did, bro :D
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Lol, all good, Ive got the real engineers up in arms. I'm an associate's level electronics tech and all that means is I know enough to get myself in trouble and these guys are pointing out those realities and possibilities, and I just can't leave well enough alone.
 
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#33
jazzbass_5 said:
Side note: this preamp is supposed to be touted as the same preamp section of one of the SVTs, not sure which one and from that I'm seeing they all had +-15V rails for their op amps.
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Even so, that's a 6dB difference that can be scaled out exactly by a suitable gain structure choice.

Beware when rolling op amps that there are doecsvthat may look better on paper yet perform worse (sometimes far worse) in circuit.
 
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#34
It's always fun to experiment and learn.

If you would have used an ultra quiet AC fan such as an Orion OA825AP-11-3TB, you could have run it off the line voltage (Invalid Link Removed).

Interesting to note that the first transistorized SVT was the SBT, which came out in 1969. They took the topology of the tube based SVT and repackaged it with transistors. The design used +24V in the power supply. Interesting that they chose to use BC169B transistors throughout which are sought after for effect pedals today.

http://el34world.com/charts/Schematics/files/ampeg/Ampeg_ABTpreamp.pdf
 
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#35
beans-on-toast said:
It's always fun to experiment and learn.

If you would have used an ultra quiet AC fan such as an Orion OA825AP-11-3TB, you could have run it off the line voltage (Invalid Link Removed).

Interesting to note that the first transistorized SVT was the SBT, which came out in 1969. They took the topology of the tube based SVT and repackaged it with transistors. The design used +24V in the power supply. Interesting that they chose to use BC169B transistors throughout which are sought after for effect pedals today.

http://el34world.com/charts/Schematics/files/ampeg/Ampeg_ABTpreamp.pdf
Click to expand...

The fan is running on its own tiny SMPS, 5.3VDC 650ma that I've tucked down in the right rear corner The fan itself is from a Whirlpool refrigerator (DC PMW evap fan), an ultra quiet fan that I've collected quite a few of during repairs. It's running a lot slower than its designed speed and is moving air through the chassis so it's doing its job well.
 
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#37
jazzbass_5 said:
The fan is running on its own tiny SMPS, 5.3VDC 650ma that I've tucked down in the right rear corner The fan itself is from a Whirlpool refrigerator (DC PMW evap fan), an ultra quiet fan that I've collected quite a few of during repairs. It's running a lot slower than its designed speed and is moving air through the chassis so it's doing its job well.
Click to expand...

Always good if you can use what you have on hand.
 
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#38
beans-on-toast said:
Always good if you can ise what you have on hand.
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Always had to build my own power supplies. But, I've learned if you go to the local good will or thrift store, pick up the wall warts for a buck (especially the light ones, they're the transformer less units) you've got yourself a sweet little SMPS, they're floating supplies so I took 2, 12VDC supplies and made them +-12vdc by tying together a negative and a positive of each and grounding that connection. No more building power supplies!
 
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#40
jazzbass_5 said:
Always had to build my own power supplies. But, I've learned if you go to the local good will or thrift store, pick up the wall warts for a buck (especially the light ones, they're the transformer less units) you've got yourself a sweet little SMPS, they're floating supplies so I took 2, 12VDC supplies and made them +-12vdc by tying together a negative and a positive of each and grounding that connection. No more building power supplies!
Click to expand...
I think you'll also find the original linear power supply regulators more reliable long term than the re-purposed wall wart switchers.
 

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