Ampeg SVP-Pro Schematic Tutorial

[Jerrold Tiers]

V4 should indeed be a 12AU7.

If you have a surface mount version of an SVP-PRO, you have the only one I have ever heard of!

[B-string]

Meet a Surface Mount board (SMT) http://www.parts-express.com/pe/show...number=320-329

From your pic above you have hole through boards. While they maybe plate through they are still WAY easier to service than SMT

[Count Bassie]

I put an EHX 12AU7 into spot #4, and moved the one that was in #4- also a 12AU7 (ECC 83 I think) into #5. Sounds more under control, cleaner and manageable than before. Still noisy though, and I think that's because of the ribbon cable laying over that little transformer coil.

[hodgy]

Originally Posted by Count Bassie

I put an EHX 12AU7 into spot #4, and moved the one that was in #4- also a 12AU7 (ECC 83 I think) into #5. Sounds more under control, cleaner and manageable than before. Still noisy though, and I think that's because of the ribbon cable laying over that little transformer coil.

An ECC 83 would be a 12AX7.

[Jerrold Tiers]

Originally Posted by B-string

Meet a Surface Mount board (SMT) http://www.parts-express.com/pe/show...number=320-329

From your pic above you have hole through boards. While they maybe plate through they are still WAY easier to service than SMT

I am fairly familiar with SMT (!), and reasonably routinely modify prototypes, etc. It does get hairy to replace a 44 or 64 pin TQFP package processor, but not impossible, even without the best SMT rework stuff. In some ways SMT is EASIER to work on, it can be heck to get a tight lead out of a plated through hole, especially on a board with a lot of copper area.......

But............. Did you mean to say that you had an SMT SVP-PRO? Or were you just contrasting the ease of repair of SMT with thru-hole?

[bgavin]

I incorrectly used the term SMT when actually meaning "not socketed" for the ICs.

[Count Bassie]

Originally Posted by hodgy

An ECC 83 would be a 12AX7.

I think I mis-typed that- it was late... anyway it sounds like I said. There was a 12AX7 in #4- so that's fixed now.

[B-string]

Originally Posted by Jerrold Tiers

I am fairly familiar with SMT (!), and reasonably routinely modify prototypes, etc. It does get hairy to replace a 44 or 64 pin TQFP package processor, but not impossible, even without the best SMT rework stuff. In some ways SMT is EASIER to work on, it can be heck to get a tight lead out of a plated through hole, especially on a board with a lot of copper area.......

But............. Did you mean to say that you had an SMT SVP-PRO? Or were you just contrasting the ease of repair of SMT with thru-hole?

I was contrasting the lay-person trying to do repairs with a pencil soldering iron on a plate through and attempting repair with same iron on a SMT board.

[bgavin]

Back on track, I got curious about the frequency response and set up the SVP-Pro with my RTA.

Link to Straight Up

The Straight Up chart is with all controls at 12:00, Graphic EQ not engaged, no buttons engaged.
These are active controls, so the 12:00 position is unity gain, i.e. no change.

The RTA was calibrated to Flat with a standard guitar cable as a reference point.
The Straight Up response is +/- 1dB from 23 Hz to about 12 KHz. Very usable for those wanting a visual Flat setting.

Link to Max Drive

The Maximum Drive is quite strong in its effect.
The Yellow chart is an attempt to use the dial controls to get close to Flat.
The Blue chart is overlaid, with the Drive at maximum as the only change.

Link to Flat GEQ Chart

This chart shows the combination of controls and Graphic EQ to dial in ruler flat response.
All Dial controls at 12:00 straight up.

Link to GEQ Sliders for Flat

The sliders image is a photo of the GEQ sliders settings used to get a Flat response with the dial controls at 12:00.

Link to Max Mids 1..5

The Dial controls all have significant impact on the response curve, both Boost and Cut.
The Max Mids chart shows all controls at 12:00, except Mid=Maximum.
The chart shows positions 1 through 5, left through right.
The center frequency increases as the position number increase.

After an hour of testing, the free standing unit cover temps measured 40C / 104F over the tube section.
Ambient is 73F. This rig does not appear to run overly hot.
The main transformer has proximity to the top cover, so some 60 Hz hum is audible due to physical buzzing. No big deal.

[fdeck]

Originally Posted by B-string

Meet a Surface Mount board (SMT) http://www.parts-express.com/pe/show...number=320-329

From your pic above you have hole through boards. While they maybe plate through they are still WAY easier to service than SMT

Totally off topic, but I bought a couple of those boards from Parts Express. They're great.

[B-string]

Yeah....darn candy store always reaching into the wallet

[Jerrold Tiers]

Originally Posted by B-string

I was contrasting the lay-person trying to do repairs with a pencil soldering iron on a plate through and attempting repair with same iron on a SMT board.

Musta mixed B-string up with bgavin..... I think I blamed one of you for the other's post.... oopsie....

Anyhow, funny you should mention that, as for quite a while my favorite SMT repair iron was a Weller with a 3/32 flat tip..... pretty big as SMT irons go.

Now I still use the Weller, but usually with a finer tip. Work with less SMT power stuff now, the IGBTs are up to the size of a paperback book, and you need a torque wrench for them, not a soldering iron.....

OK, thread derail over......

[cableguy]

I finally had a new connector soldered in my board. Instead of replacing it with the same ribbon type of connector I went with a solder type. I soldered the connection this time to eliminate any intermitant connection problems like before. No I realize the unit may have the wrong tube in slot #3. Here's what it had when I got it.

1)Groove Tubes GT12AX7R (ECC83/7025)
2)12AX7WA (Made in Russia)
3)7025/12AU7WA Made in Rusia Sovtek
4)12AU7A/ECC82EH Electro Harmonix Made in Russia 04 03
5)Groove Tubes GT12AX7R (ECC83/7025)

I have two new tubes on the way to do some testing.

[B-string]

Slot 3 makes no sense? A 7025 and 12AU7WA are different tubes. One is a Dual Hi-mu triode and the other a Dual Med-Mu triode?

[Count Bassie]

Originally Posted by cableguy

I finally had a new connector soldered in my board. Instead of replacing it with the same ribbon type of connector I went with a solder type. I soldered the connection this time to eliminate any intermitant connection problems like before. No I realize the unit may have the wrong tube in slot #3. Here's what it had when I got it.

1)Groove Tubes GT12AX7R (ECC83/7025)
2)12AX7WA (Made in Russia)
3)7025/12AU7WA Made in Rusia Sovtek
4)12AU7A/ECC82EH Electro Harmonix Made in Russia 04 03
5)Groove Tubes GT12AX7R (ECC83/7025)

I have two new tubes on the way to do some testing.

Maybe I missed it, but what year is your SVP Pro? I have a '96 and it gets pretty noisy when I start to work the Master Volume up. I have a ribbon cable that I think might be part of why it's such a noisy pre, and I'm interested in what happens with yours.

[cableguy]

Originally Posted by B-string

Slot 3 makes no sense? A 7025 and 12AU7WA are different tubes. One is a Dual Hi-mu triode and the other a Dual Med-Mu triode?

maybe I wrote it down wrong. I'll take it apart later to check.

[cableguy]

Originally Posted by B-string

Slot 3 makes no sense? A 7025 and 12AU7WA are different tubes. One is a Dual Hi-mu triode and the other a Dual Med-Mu triode?

Yep,

I wrote it down wrong. It was a 12A7WA in slot 3, my bad. I have 2 new Tung-Sol 12AX7 tubes coming in a week to play around with. I probably order another 12AU7WA to switch that out as well. Should be able to eliminate any bad tubes from the pre and give it a full work-out for a while.

[cableguy]

So since I have my SVP-Pro put back together I have a static/popping sound coming out when I play. The harder or lower I play the more static. The pre's quiet when not playing. It's a very loud sound, almost as loud as the notes. I put my new tubes in slot 1&2 and no change. I switched out tubes 3&5 with the tubes I pulled out since I figured these were still good and no change. I don't have a tube to replace slot #4 but I have the drive turned down all the way since that is what this tube controls. Anybody have any ideas? I'll pick up a tube for slot 4 tomorrow, just don't like replacing a tube if that's not the problem.

[cableguy]

I also noticed that the tubes in slot 1 & 2 don't seem to glow as much as the others. I don't know if this is because they are new, just how the design is, or it signals some sort of voltage issue with those slots.

[JGR]

It's just the construction of the tube.