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Carvin PB15 preamp
- Thread starter fruitlabor
- Start date
Hi, yes I have one, had it for years but didn't use it much. Just never sounded that great to me (more in a minute). Here's a link to the Carvin Museum site about it:
[Invalid or Expired Link Removed]
Was also basically the same preamp in all the Carvin Pro Bass amps in the early 1990's (PB300, 500) but without the graphic EQ.
Doesn't seem to get too much love or don't think many folks have one.
About a year ago I happened across a review by someone who did some measurements and dissected it and found one particular thing that was interesting.
[Invalid or Expired Link Removed]
Carvin has what it calls a "mudcutter" circuit (it's in the manual should be a PDF somewhere on the web that has the schematic as well) which is really a 600Hz fixed, non-defeatable
notch filter after the first stage of the preamp. So no matter what you do, it will always have a scooped sound (mudcutter?). He defeated it by soldering a jumper wire on the PCB.
I got mine cheap ($95 IIRC) so I said what the heck, I tried it. Holy crap, the sound opened up after I did that and actually sounded pretty darn good (also been playing around with it and a Carvin DCM1500 into a nEARful cabinet). I decided to put a little toggle switch on the front panel instead of a permanent jumper. I also changed out a few of the op amps (the originals are the cheapest you can find, basically dual 741's which are considered junk by today's standards, but hey they work), with TL072's which while not state of the art (they are used in the Eden WT series amps) are a big improvement of the originals in terms of getting rid of some of the noise. Out of the box this preamp can be kind of hissy with the treble boosted.
I would say, as the reviewer stated, if you can do a bit of soldering and MAYBE if you want to get the noise down by replacing some op amps (they are cheap and just plug in, no soldering for those), then it's worth a shot if you can get it really cheap (less than $100). Otherwise I'd pass on it.
[Invalid or Expired Link Removed]
Was also basically the same preamp in all the Carvin Pro Bass amps in the early 1990's (PB300, 500) but without the graphic EQ.
Doesn't seem to get too much love or don't think many folks have one.
About a year ago I happened across a review by someone who did some measurements and dissected it and found one particular thing that was interesting.
[Invalid or Expired Link Removed]
Carvin has what it calls a "mudcutter" circuit (it's in the manual should be a PDF somewhere on the web that has the schematic as well) which is really a 600Hz fixed, non-defeatable
notch filter after the first stage of the preamp. So no matter what you do, it will always have a scooped sound (mudcutter?). He defeated it by soldering a jumper wire on the PCB. I got mine cheap ($95 IIRC) so I said what the heck, I tried it. Holy crap, the sound opened up after I did that and actually sounded pretty darn good (also been playing around with it and a Carvin DCM1500 into a nEARful cabinet). I decided to put a little toggle switch on the front panel instead of a permanent jumper. I also changed out a few of the op amps (the originals are the cheapest you can find, basically dual 741's which are considered junk by today's standards, but hey they work), with TL072's which while not state of the art (they are used in the Eden WT series amps) are a big improvement of the originals in terms of getting rid of some of the noise. Out of the box this preamp can be kind of hissy with the treble boosted.
I would say, as the reviewer stated, if you can do a bit of soldering and MAYBE if you want to get the noise down by replacing some op amps (they are cheap and just plug in, no soldering for those), then it's worth a shot if you can get it really cheap (less than $100). Otherwise I'd pass on it.
Hi, yes I have one, had it for years but didn't use it much. Just never sounded that great to me (more in a minute). Here's a link to the Carvin Museum site about it:
[Invalid or Expired Link Removed]
Was also basically the same preamp in all the Carvin Pro Bass amps in the early 1990's (PB300, 500) but without the graphic EQ.
Doesn't seem to get too much love or don't think many folks have one.
About a year ago I happened across a review by someone who did some measurements and dissected it and found one particular thing that was interesting.
[Invalid or Expired Link Removed]
Carvin has what it calls a "mudcutter" circuit (it's in the manual should be a PDF somewhere on the web that has the schematic as well) which is really a 600Hz fixed, non-defeatable
I got mine cheap ($95 IIRC) so I said what the heck, I tried it. Holy crap, the sound opened up after I did that and actually sounded pretty darn good (also been playing around with it and a Carvin DCM1500 into a nEARful cabinet). I decided to put a little toggle switch on the front panel instead of a permanent jumper. I also changed out a few of the op amps (the originals are the cheapest you can find, basically dual 741's which are considered junk by today's standards, but hey they work), with TL072's which while not state of the art (they are used in the Eden WT series amps) are a big improvement of the originals in terms of getting rid of some of the noise. Out of the box this preamp can be kind of hissy with the treble boosted.
I would say, as the reviewer stated, if you can do a bit of soldering and MAYBE if you want to get the noise down by replacing some op amps (they are cheap and just plug in, no soldering for those), then it's worth a shot if you can get it really cheap (less than $100). Otherwise I'd pass on it.
Thanks. Ebay has one for $150. But this sounds like it's not worth the money or upgrades.
Saw that one. Was curious to see if it would go or not. Was relisted. Some folks might like it (fenderslaper did), but I thought it was much improved after I did the mods (before that it was collecting dust). Up to you, but I would look around a bit more. Actually some reasonable newer stuff around others have been discussing here. Also, depends on what your budget is.
Hi, yes I have one, had it for years but didn't use it much. Just never sounded that great to me (more in a minute). Here's a link to the Carvin Museum site about it:
[Invalid or Expired Link Removed]
Was also basically the same preamp in all the Carvin Pro Bass amps in the early 1990's (PB300, 500) but without the graphic EQ.
Doesn't seem to get too much love or don't think many folks have one.
About a year ago I happened across a review by someone who did some measurements and dissected it and found one particular thing that was interesting.
[Invalid or Expired Link Removed]
Carvin has what it calls a "mudcutter" circuit (it's in the manual should be a PDF somewhere on the web that has the schematic as well) which is really a 600Hz fixed, non-defeatable
I got mine cheap ($95 IIRC) so I said what the heck, I tried it. Holy crap, the sound opened up after I did that and actually sounded pretty darn good (also been playing around with it and a Carvin DCM1500 into a nEARful cabinet). I decided to put a little toggle switch on the front panel instead of a permanent jumper. I also changed out a few of the op amps (the originals are the cheapest you can find, basically dual 741's which are considered junk by today's standards, but hey they work), with TL072's which while not state of the art (they are used in the Eden WT series amps) are a big improvement of the originals in terms of getting rid of some of the noise. Out of the box this preamp can be kind of hissy with the treble boosted.
I would say, as the reviewer stated, if you can do a bit of soldering and MAYBE if you want to get the noise down by replacing some op amps (they are cheap and just plug in, no soldering for those), then it's worth a shot if you can get it really cheap (less than $100). Otherwise I'd pass on it.
I know this is an old thread but if anyone has any information on the mods to this pre-amp I would love to see them. I have been playing on mine for over a decade and it is time.
Hi Mike. Just saw this. I can fill you in later today about what I did. Getting ready to head to the gym now. The main thing was addressing the built-in scoop which is actually quite simple.
I just saw this. too. Would you (or anyone else) know if Carvin used that 600 Hz notch filter on the B1500?
I don't think so. I'm looking at the B1500 schematic on the Carvin archive site:
Bass Amplifier Schematics
No sign of anything that looks like a permanent notch filter. Looks like it's on the older Pro Bass models and the Redline models, although the Redline and some of the Pro Bass models (Pro Bass 100, 200 and Pro Bass II from what I can see) have a mid-shift version of the notch filter, just letting you select the frequency but not completely bypass it. These look as though they could be easily modded as well. I have a few photos showing the mod I'll upload later. I also swapped out some of the op-amps to reduce the noise.
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Thank you for that. The B1500 (with a DBX compressor unit) has become my go-to rig for medium-sized venues.
Ok, as promised here are the details. Here is the schematic portion showing the modification for bypassing the notch filter. You just have to jumper capacitor C6 as shown with the red jumper. The notch filter is comprised of C6,C7, R6, and R7.
You can see C6 on top of the PC board here circled in red:
The easiest way to bypass it is on the bottom of the board. The bottom plate comes off easily since the PC board is held on by all the pots. Here is where you add the jumper. Note that I added a switch so I can run it bypassed or in-circuit as originally. Kind of like a "slap switch".
If you want to improve noise performance you can replace opamps A1, A2, A3, and A4 which are the most critical for noise performance, circled in red with TL072's. They are much better noise-wise than the 4558's that are in there which are just dual 741's and they are maybe $0.50 a piece.
If you have any questions, let me know. Of course there are much better preamps out there, but this mod significantly improves the PB15 IMHO.
You can see C6 on top of the PC board here circled in red:
The easiest way to bypass it is on the bottom of the board. The bottom plate comes off easily since the PC board is held on by all the pots. Here is where you add the jumper. Note that I added a switch so I can run it bypassed or in-circuit as originally. Kind of like a "slap switch".
If you want to improve noise performance you can replace opamps A1, A2, A3, and A4 which are the most critical for noise performance, circled in red with TL072's. They are much better noise-wise than the 4558's that are in there which are just dual 741's and they are maybe $0.50 a piece.
If you have any questions, let me know. Of course there are much better preamps out there, but this mod significantly improves the PB15 IMHO.
Thanks! I really appreciate this! Maybe this old amp will get a new spot on my gigging rig.
Hey gerryjazzman...I too have a PB15 Carvin stack, (1x18 bottom 4x10 top FET1000 amp). I did the cap mod with toggle per your instructions and WOW!, what a difference. It was always hard to get the mids to punch through without either sacrificing or over emphasizing one or the other end of the frequency spectrum. Pretty much had to always run the BASS knob at zero. I can actually utilize the BASS knob now. At one point I had even added an ALEMBIC SF-2 SUPERFILTER to try to rectify the sound issue but that seemed to compound the sound problem. Maybe now I can put it back in the rack and see what kind of ear damage I can inflict on the family, ha ha. I'm psyched to swap out the OP-AMPS and see what that does. Thanks so much for sharing that info. I hope others can find some new love for their PB15's that are still out there. I know these are old posts so I hope you're able to get this at some point. Cheers and keep on rockin'.
Wow, so glad this information was helpful! I'm surprised that Carvin made this design decision. I always hated that amp manufacturers feel the need to bake in certain voicings. Give me the EQ control and I'll dial it in myself. Enjoy!
I had a 200 watt Carvin PB-200 12" combo with a mid contour switch that toggled between two cut frequencies but couldn't be defeated. I could dial some mids back in with the graphic/semi-parametric EQ but definitely not the same. Frustrating as the cabinet sounded very good with heads including Mesa-Boogie Bass 400, GK 400RB and Eden WT-400.
Interesting! I have a Pro Bass 200-15 on the way. Supposed to be delivered tomorrow, actually.
My main amp for years has been an R600 that has the same "Pre-Shape" buttons but it has a more comprehensive EQ section after. I feel like I can dial in a reasonably flat, transparent midrange on that amp but I also use a couple preamp pedals for getting different, basic tones.
Hopefully the PB-200 gets close enough to what I'm used to. I only bought it since it was super cheap, has familiar controls and it weighs less than half what my current amp weighs.
My main amp for years has been an R600 that has the same "Pre-Shape" buttons but it has a more comprehensive EQ section after. I feel like I can dial in a reasonably flat, transparent midrange on that amp but I also use a couple preamp pedals for getting different, basic tones.
Hopefully the PB-200 gets close enough to what I'm used to. I only bought it since it was super cheap, has familiar controls and it weighs less than half what my current amp weighs.
Bonjour et merci pour cette info, j'ai réalisé la modification C6 : c'est juste fantastique !!!
Je ne reconnais plus l'ampli.
Ça sonne vintage à souhait, Jazz Bass ou Precision Bass, c'est génial, rondeur, puissance, du grain, aucune agressivité, bref c'est ce qu'il lui manquait.
J'ai installé un mini switch : Scoop/Vintage ,,,,, tout est OK.
Merci encore.
Maintenant je vais me renseigner pour les petits "amplis opérationnels", ça améliore aussi cet ampli en termes de bruits.
Je ne reconnais plus l'ampli.
Ça sonne vintage à souhait, Jazz Bass ou Precision Bass, c'est génial, rondeur, puissance, du grain, aucune agressivité, bref c'est ce qu'il lui manquait.
J'ai installé un mini switch : Scoop/Vintage ,,,,, tout est OK.
Merci encore.
Maintenant je vais me renseigner pour les petits "amplis opérationnels", ça améliore aussi cet ampli en termes de bruits.
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Ouah! Treize ans et ce fil porte encore ses fruits ! Je suis ravi que ça ait marché pour toi Jean Marc. Ça a l'air génial ! Profitez de votre ampli.
Heyyyy, oui ça a très bien marché, un ami bassiste a joué cet ampli, verdict : très bon ampli désormais.... mais le son d'origine,,,, c'était vraiment ça ????? 
, il manque quand même l'essentiel !
Sinon, une petite précision : mon PB300 est une 1ere génération, c'est-à-dire pas de tweeter (tant mieux), pas de poignées (j'en ai installé), pas d'évent donc il n'est pas bass reflex,,,,, je vais lui percer 2 ouvertures ouvertures de 8cm de diamètre : bonne idée ou pas ?
courage !
, il manque quand même l'essentiel !Sinon, une petite précision : mon PB300 est une 1ere génération, c'est-à-dire pas de tweeter (tant mieux), pas de poignées (j'en ai installé), pas d'évent donc il n'est pas bass reflex,,,,, je vais lui percer 2 ouvertures ouvertures de 8cm de diamètre : bonne idée ou pas ?
courage !
