Is there a vintage style Ampeg SVT preamp clone?

The ampeg svp-cl IS the preamp of a 70's svtm. I own a vintage svt and have the schematics for it as well as the svpcl. They are 98 percent the same. My 3rd svpcl should arrive tomorow and ill run it into the old svt's power section just to see how close. I need to not sell this one. It takes me awhile to learn my lesson sometimes

 

Like everybody has said in a mountain of threads, most of the grit and overdrive comes from the poweramp. Ive run other preamps onto the power section and many sound just as good or better than the svt's actual preamp.

 

As I said, I have the schematics and can read them. It's 98% the same, right down to the component values. Into a solidstate poweramp it wont sound exactly like an all tube svt, but it's as close to a clean svt as you will get. Turn the master volume all the way up and use the gain as your volume and you will be using it just like you would have to with a real svt. Having the master volume is a nice option though.

 

The SVP is the same as the CL's preamp but it's really quite different from the 70s ones, schematically speaking. I'm not sure where you got the impression that they're 98% the same. The front end of the SVP is a 12AX7 gain stage directly driving the ultra-hi/lo circuit. The front end of an old SVT is the high gain side of a 12DW7 driving the low gain side as a cathode follower, which then drives the ultra switches. I can't say what the sonic differences are as I've never directly compared them but there's enough difference in the circuits to potentially make a lot of difference.

 

The 12dw7 tubes are each, 1 half a 21ax7 and 1 half a 12au7, so ampeg used two ax7's and two au7's to build the circuit. I've gone point to point through the circuit and except for adding two more mid frequencies and two more low cut options, it is the same preamp. Take the time to dig through it if you can and you will see. Thats the SVP-CL. The SVP-PRO is a different story. The SVT-CL head is different as well. The pro series does some different things in general that mess things up. So, the SVP-CL IS the old preamp, just without the tube poweramp. I'll compare the two tomorow.

 

Hmm, maybe I'm looking at the wrong schematic for the SVP-CL, then. Just checked and it does say SVP-CL on it but there's no 12AU7s in sight. It's exactly the same as the SVT CL's. Must be mislabeled if you've been inside and traced the circuit. Clearly can't replicate the original without using either actual DWs or their equivalent in AXs and AUs.

 

Trust me on this. or, talk to an ampeg engineer. Or, look up one of the many threads where we have went through it already.

 

Jerrold Tiers has said many times that the SVP-CL is the same preamp as the ones in vintage SVT's.

 

Just got up and feeling grumpy. But, nobody does searches on here anymore. There is so much information about so much on here, it is truly insane.

 

I have a schematic labeled SVP-CL, which as it turns out is incorrect. Even so, I'm not sure I really needed to do a search in order to vett that schematic before posting. If that offends your TB sensibilities I can't help that and I'm not liable to do anything about it. Seriously, I posted something that turned out to be wrong and subsequently admitted that it was incorrect and you're cheesed off because I didn't do a search? Tough crowd.

Edit: And speaking of grumpy....

 

There are two preamps, the SVP-CL and SVP-Pro, it's possible one was labeled for the other in the version you have as the CL uses 2 12AX7s and 2 12AU7s while the Pro uses 4 12AX7s and one 12AU7 and you said your schem doesn't have the 12AU7 listed.

 

The svt IIP comes very close to the 70's preamp section.
The main difference are the different tubes.
The 70's svt pre runs with 12dw7 whereas the svtIIp runs with 12AX7.

Several years ago I modified my 70's svt pre into something like a clone of the svt-IIp.
Since that time my 70's svt runs with 12ax7 instead of 12dw7.

The mod may be done in both directions.
It is possible to convert the svt-IIp into a 70's clone with 12dw7, and it is also possible to convert the 70's svt into 12ax7 version.

There is one thing that can't be addressed with a seperate preamp. A seperate preamp has got an independent net transformer. The anode voltage in these preamps stays constant whereas the anode voltage in an all tube head will be impacted by the power amp section.

Every custum amp designer knows about that. A seperate tube preamp and tube power amp sounds different to an all tube head (only one net transformer) even if the schematic were just the same.

 

Preface: I may or may not know what I'm talking about, but..

For the cheaper options, there are some pedals that are supposed to give close to that svt tube saturation. Catalinbread sft being one and the JHS pandamonium (also has a cool gated fuzz channel)

I'm actually trying to get one of the JHS pedals.. An sft as a backup.

 

This is key!

 

You're not a club member (that I know of) so you can't speak about being grumpy!

 

If you can't find those the tech 21 vt rack sounds good. Tried it for a dirty pre in my clean/dirty rack set up and I just don't like the svt distorted tone, but aside from my personal dislike its a rock solid preamp

 

I Like the old SVTIIP best, it's a bit better signal to noise than the later SVP Pre and as I run a clean dirty two amp rig I need the pre amp cleanish, the pedal in circuit along with with one tube amps pre amp gets me my dirt.