- Feb 12, 2006
- 61,075
- 5
- 221,153
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Scopes aren't a great tool for investigating radiated emissions (without additional accessories)
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Mods to my Ampeg SVP-PRO!
- Thread starter jazzbass_5
- Start date
For unregulated supplies you may reduce ripple a little bit with highish C but there is no way to totally eliminate ripple. Its also doubtfull that you'd actually notice "audible" reduction if there was already some audible Harmonics "noise" that was caused by the rectifier.
Rail supply charging C's are not directly meant to eliminte all kinds of "noise". If proper designed then the capacity of the C is sufficiant enough to charge and discharge electrical energy in demand of the schematic max. power consumption.
Increasing the capacity of the rail supplies also means decreasing current charging total angle so the current charging/discharging peak numbers along the C's will dramatically increase. Make sure your bigger C's are capable to handle this plus of peak current save over time.
Personally I'm an advocate of proper designed capacity rather than highish oversized numbers cause there is only little benefit (if any) along with highish C numbers but lots of drawbacks
I meant to use the scope to measure hash noise on the output of the switching supplies, and to measure possible noise induced into the audio signal chain.
I felt this would be more beneficial in evaluating if the switching supplies offer any benefit or drawbacks vs. using the original three terminal regulators.
To the OP:
I admire your perseverance and willingness to learn.
Also admire how you continue on with YOUR project even if it's not technically headed in the best direction based on standard engineering practices.
You move forward with a smile on your face in spite of people telling you about these shortcomings.
There was an Everett Hull quote in an early catalog (too lazy to grab it) that warns about turning up an Ampeg amp too "loud as it was wrong and obnoxious. It just isn't musical", or something along those lines.
Obviously the Stones thought otherwise.
Bottom line; who knows?
If you make the specs worse during your mods, and, you like it better, then it is better.
For me, a stock SVP-CL with a big iron power amp is just right!
I admire your perseverance and willingness to learn.
Also admire how you continue on with YOUR project even if it's not technically headed in the best direction based on standard engineering practices.
You move forward with a smile on your face in spite of people telling you about these shortcomings.
There was an Everett Hull quote in an early catalog (too lazy to grab it) that warns about turning up an Ampeg amp too "loud as it was wrong and obnoxious. It just isn't musical", or something along those lines.
Obviously the Stones thought otherwise.
Bottom line; who knows?
If you make the specs worse during your mods, and, you like it better, then it is better.
For me, a stock SVP-CL with a big iron power amp is just right!
To the OP:
I admire your perseverance and willingness to learn.
Also admire how you continue on with YOUR project even if it's not technically headed in the best direction based on standard engineering practices.
You move forward with a smile on your face in spite of people telling you about these shortcomings.
There was an Everett Hull quote in an early catalog (too lazy to grab it) that warns about turning up an Ampeg amp too "loud as it was wrong and obnoxious. It just isn't musical", or something along those lines.
Obviously the Stones thought otherwise.
Bottom line; who knows?
If you make the specs worse during your mods, and, you like it better, then it is better.
For me, a stock SVP-CL with a big iron power amp is just right!
I admire your perseverance and willingness to learn.
Also admire how you continue on with YOUR project even if it's not technically headed in the best direction based on standard engineering practices.
You move forward with a smile on your face in spite of people telling you about these shortcomings.
There was an Everett Hull quote in an early catalog (too lazy to grab it) that warns about turning up an Ampeg amp too "loud as it was wrong and obnoxious. It just isn't musical", or something along those lines.
Obviously the Stones thought otherwise.
Bottom line; who knows?
If you make the specs worse during your mods, and, you like it better, then it is better.
For me, a stock SVP-CL with a big iron power amp is just right!
Well said and thank you.
As I've said, I'm just a mid level tech in electronics with my associates degree. I have years of experience as a lead technician and liaison between the test/repair department and engineering of a small electronics company that produced test equipment and standards for high voltage electronics. (Ive since changed jobs and for the last 17 years I've been an appliance repairman.) I understand power supplies pretty well, from small DC rails to +- 20kv, AC to DC, DC to DC switching supplies and flyback circuits, but I'm still dangerous.
The TBers here that are giving me advice are well above my level of expertise and I appreciate their advice. Hence the reason I switched from discreet voltage regulators to the SMPS. even with that they bring up excellent points.
Bottom line? It isn't going to stop me from having fun with my equipment, sure, I may destroy a 350-400 Ampeg preamp. Or not.
I heed their words check what they say and as you've said, if this are working and it sounds good, it's a win for me!
It's also got me thinking about other mods, including lowering the output of my bass, it's too damn hot.
Anyway, off to work and good morning to all!
I'm kind of like Tim The Tool man around our house but my girlfriend uses the term overclocking "are you overclocking that?"
Longtime 1995 black face SVP Pro user here, but no electronic-guy.
I put a rca 7025 in my svp pro (v1) and it got a bit less noisy.
I tried about 20 different tubes but the hiss remains. Since the last years I run an 12AU7/ECC82 in V5, less power - but also less hiss or I use the effects send-out into the power amp with no hiss (but also no master-knob(like an svt-IIp)).
Did that SMPS take the hissing away?
I put a rca 7025 in my svp pro (v1) and it got a bit less noisy.
I tried about 20 different tubes but the hiss remains. Since the last years I run an 12AU7/ECC82 in V5, less power - but also less hiss or I use the effects send-out into the power amp with no hiss (but also no master-knob(like an svt-IIp)).
Did that SMPS take the hissing away?
I can't say I'd be much of a help there my black face is dead quiet, I had a gray face that was very noisy this one is one of the exceptions.
Edit:
That being said, my grey face had more of a 60Hz buzz to it and I couldn't get rid of it no matter what I did.
My blackface prior to my mods (and now) has a very sensitive input and even with the pad on I can never really get it above 9 o'clock before it starts to "grind" or distort more than my taste and of course when I do I get some preamp noise that I would expect.
I usually leave it at 9 o'clock and use the "drive" knob to get the grinding ampeg sound I like. Even then, my master knob is never much above 9 o'clock either and I use a bridged DPC 1400 into 8 ohms right now for power.
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That and the fact that there wasn't enough headroom to drive the higher voltage regulators is the reason I went with the SMPS.
Seen here.
Also, I did some study of the circuit design for the SVT II PRO which is what the SVP-PRO'S circuit is supposed to be copied from. It's pretty much the same and runs +-15VDC supplies. There really isn't much difference component wise.
- Feb 12, 2006
- 61,075
- 5
- 221,153
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
An SMPS will have no improvement on his, and could make things a lot noisier in fact.
Some circuit designs are simply noisier than others. Sometimes you can improve things by reducing the master volume a bit and increasing the input volume (if your amp is so equipped.
With that being said, there really doesn't seem to be anymore audible noise then prior stock form coming from my unit with the new supplies. That doesn't mean that there's no high frequency noise riding on the signal.
- Feb 12, 2006
- 61,075
- 5
- 221,153
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Maybe not, in your case, but sum/difference products and RF can cause all kinds of inconsistent, unpredictable noises. Some audible and some not. Those not audible tend to annoy the FCC worse.
⠀
Mine hisses from firing up. No matter if an instrument/cable is plugged in or if the gain and master knobs are at "0" or "11".
It's a permanent hiss/buzz.
The '78 SVT is quiet (besides the cooling fan).
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Correct.
As you just now run 12V regulators versus 8V for the graphic EQ section the headroom is improved by about 3.5dB which (honestly speaking) isn't a ton of improvement. I don't think a tiny plus of +3.5dB could ever be sufficiant improvement just to fix "issues" if there really had been (complained) issues with "weak" headroom for the graphic EQ section.
So here you are what the schematic tells about headrom.
As I told already earlier tube stage V4B acts as buffer that drives both the graphic EQ input as well as the (active) midrange EQ section. If gain structure for the tube preamp signal level was set "correctly" with the gain pot for best SNR number all along the tube signal path then the V4b buffer outputs about 16V(peak) which is quite a lot. Then followed by a resistive voltage devider that does a signal reduction down to 0.4Vrms respectively 0.56Vpeak as (nominal) input level for the graphic EQ section.
For a "flat" setting of the graphic EQ the available headroom with 8V regulators predicts about +23dB versus about +27dB of headroom for 12V rail supply regulators.
Either way even the "smallish" 8V regulators provide pretty much headroom just to fully crank one or two sliders of the graphic EQ without clipping. Of course it was possible to crank the total graphic EQ section into clipping if all sliders was cranked and even the EQ level slider adjusted to "full" level. However even for 15V regulators as is for the svt II pro can't protect from clipping if everything was cranked all the way up.
May be some folks may have experienced some audible difference of the svp pro versus svt II pro preamp section IF the level controls are cranked. But hey, there was still the possibility for proper adjustment of signal levels just to avoid unwanted clipping at the graphic EQ section.
Honestly speaking some folks (sometimes) may think they can't get sufficiant signal level IF a level pot was not cranked all the way up. Let me tell it this way, even the best experienced design enginners can't fully prevent from nasty artefacts which are (sometimes) caused by wrong understanding or abuse respectively faulty preamp adjustments.
So sometimes a distinct schemtaic design may be "blamed" as poorly designed while actually the schamtic was designed with lots of care but pretty much "abused" by the user due to some lack of (technical) understanding.
Sometimes users complain buzz issues with the svp pro preamp. This buzz issues may happen if the Master pot was set to all the way up position and total volume adjusted with the gain pot. In this case the SNR number becomes much decreased which then may make some buzz audible caused by the DC filament supply for V1.
The issue can be easily fixed by proper level adjustment with the gain pot and total volume adjustement with the master pot.
Unfortunatelly some players prefer it the "old school" way just to get an "old school" sound with "old school" handling of the preamp.
Another possibility to fix the issue was to mod the V1 filament, in particular that means swapping the DC supply for AC filament supply as is for tubes V2..V5. The drawback would be the following: the tube that does cause the most amount of hum within a set of four tubes could no more be "extracted" by just place it at V1 with "independent" DC filament supply.
As I don't handle my svp pro the "old school" way I don't suffer on buzz issues like some "old school" folks might complain. So at least to me there was no need to "fix" a problem that is only caused along with some unhappy "gain level" adjustment
The issue can be easily fixed by proper level adjustment with the gain pot and total volume adjustement with the master pot.
Unfortunatelly some players prefer it the "old school" way just to get an "old school" sound with "old school" handling of the preamp.
Another possibility to fix the issue was to mod the V1 filament, in particular that means swapping the DC supply for AC filament supply as is for tubes V2..V5. The drawback would be the following: the tube that does cause the most amount of hum within a set of four tubes could no more be "extracted" by just place it at V1 with "independent" DC filament supply.
As I don't handle my svp pro the "old school" way I don't suffer on buzz issues like some "old school" folks might complain. So at least to me there was no need to "fix" a problem that is only caused along with some unhappy "gain level" adjustment
This not audible could also be
Again, there isn't a lot of difference. Maybe it's in my head.. I had no idea what changing the rails would do if anything, Bottom line is (still) I did it because I could.. wanted to see what would happen, Instead of asking first and getting all these answers and never even trying. It was fun, it's working and it's mine..
I'm confused about all the, what I can only interpret as, negatively persuasive comments leading me to believe maybe I shouldn't have done what I did, leave it alone, you're probably only going to make it worse, the engineers know what they're doing. Not one positive comment about how I did it, the Ingenuity behind using the (floating) 12 volt switch mode power supplies, fitting them in and making a +- 12VDC system. The fact that now the power transformer driving the HV and filiment voltage, (same transformer) has less work to do and less chance of overheating like my first SVP-PRO. (Btw, it was an open winding in the HV secondary, not the thermal fuse in my previous SVP-PRO transformer), no comments about the addition of a cooling fan.. all good. I hope someone sees this and maybe takes it a step further uses my silly ideas for something they're building. Saves some cash using thrift store wall warts as power supply or puts a fan in a project and uses the same idea behind what I did with my fan and a phone charger SMPS.
It's working folks, it's not noisey, I haven't opened any time space rifts yet powering it up and I have backup units that I use to play out with too.
If you're a proponent of leaving things stock and are upset that I violated this piece of equipment than I am truly sorry. I still have the components to return this to its stock original form if I don't end up destroying it,
Anyway.. back to work.
The load imposed on the power transformer by the 8 volt rails probably didn't even amount to 80ma, almost nothing.
Not to take anything away from your abilities in electronics, but the reality is, tying two separate supplies to a common ground to create a split supply is 1st year electronics.
I've modified gear in the past, but before doing so, I ask myself these questions:
What specific problem(s) is this modification resolving; is there a clear benefit?
Is there any life safety issues to a user or technician that may arise from my proposed modification?
Is there any negative effects due to my modification; is it creating another problem?
What is the long term reliability of my modification?
From an educational standpoint, I'm not sure tinkering with things blindly offer much in the way of learning. The net is full of instances of people doing so, for no definite reason. For those wishing to learn, theory would be the first thing to tackle, and then start building and experimenting on your own circuits.
The mute itself works, bu No difference if I push the mute knob or not.
Another idea was to took the grounding/earthing(ground loop) away (unsave).
Hiss/buzz remains.
