Please Recommend a Preamp!

[Davec113]

I need a preamp for my Simple SE amp I built about 5 years ago. I built it with a 12bh7a driver tube because I had an active preamp, an Anthem Pre1 with the outboard PS. The Anthem was a good preamp but has too much gain, 28 dB... I think ~12 dB gain would be more suitable. The Anthem just had a tube go out and it resulted in the power supply overheating and burning. I switched it off before there was flame, but there was a smell of burning electronics in the air. I may try to fix it but I don't have schematics and would like a pre with more suitable gain anyway.

The Simple SE drives a pair of Omega XRS 4.5" single driver speakers in triode mode with no feedback.

I only require a linestage, no phono.

My level of experience is moderate... I have a ME degree and a basic knowledge of circuits. I have a lot of experience wiring homes and cars, and I found the Simple SE project very easy. I am looking for another fairly easy project, although I'd be ok with either pcb or point to point wiring. I can follow a schematic but I am not interested in making my own, so I'd like a kit or a finished project to follow. I am mainly doing the DIY thing to save money, not because I love doing the work... it's the results I'm after. And saving money.

So far I'm considering the SAS 7A preamp kit. This kit has an assembled PCB that needs to be wired into a chassis, so it is super-easy. I don't know anything about the actual circuit, just going off of recommendations and reviews...

SAS Audio Labs: 7A tube preamplifier kit

I have also seen the Bottlehead Foreplay, Aikido and Grounded Grid preamp kits.... I have not heard any of them and am not sure which of these (SAS included) would be the superior option.

I'd also be open to any other recommendations as well. Thanks!

 

[popilin]

Hi Davec113
If you have stomach, here are some suggestions

http://www.diyaudio.com/forums/tubes-valves/207544-ecc82-12au7-line-preamp.html

If you do not like the high voltage, you can use more civilized voltages, at a cost of increased distortion.

Skip the discussions, there are some interesting circuits IMHO, including other valves.Judge for yourself.

Best regards
Johann

 

[SY]

Do you actually need ANY gain? Most modern sources will output 2VRMS or more, which is more than enough for most power amps. Either a simple 10k volume control or (if you have long leads) a volume control followed by a unity gain buffer may work and be higher performance than any preamp.

 

[Davec113]

Do you actually need ANY gain? Most modern sources will output 2VRMS or more, which is more than enough for most power amps. Either a simple 10k volume control or (if you have long leads) a volume control followed by a unity gain buffer may work and be higher performance than any preamp.

I have tried my Simple SE with only volume control and some line sources do need more gain.

 

[KatieandDad]

Why not just attenuate the gain of your existing pre-amp.

You dont necessarily need to play around with the feedback loop to adjust the gain, just use a preset pot to adjust the output, or input.

 

[Davec113]

Why not just attenuate the gain of your existing pre-amp.

You dont necessarily need to play around with the feedback loop to adjust the gain, just use a preset pot to adjust the output, or input.

My existing preamp just lost a tube (maybe), and the PS started burning... I have no schematics for this amp and can't find them. The unit does have a series resistor on a switch to reduce gain, but it doesn't perform as well in the lower gain mode.

Without a schematic I am unable to diagnose the issue and do not have the experience to attempt a repair without it. So, I am left with paying someone to diagnose/repair the preamp and I am not sure I want to invest money in an old preamp that I cannot obtain schematics for... IMO the money is best spent on a new preamp that has a more suitable amount of gain.

 

[Simon B]

... I have no schematics for this amp

[Help Needed] Anthem pre line schematic

I suppose you'd have to join to get help, but just so you know you can probably get one if you want to.

 

[tinitus]

. I built it with a 12bh7a driver tube because I had an active preamp

why not change to the 'original' tube, 12AT7, and get back the lost gain ?

 

[Davec113]

[Help Needed] Anthem pre line schematic

I suppose you'd have to join to get help, but just so you know you can probably get one if you want to.

I actually saw that, but it is the wrong model. My preamp has a phono section and an outboard power supply. It seems schematics are around for the newer models but I can't find one for the Pre1 (no L).

I just emailed partsconnexion to see if they have the correct schematics.

 

[Davec113]

why not change to the 'original' tube, 12AT7, and get back the lost gain ?

I would still need a passive preamp, which I suppose would be a pretty easy project vs a tube preamp.... this is possible but I'm not sure the 12at7 will sound as good as the 12bh7a, although with the CCS loading it may make less of a difference than the specs suggest. I would only need to change out one resistor per channel on the pcb to run a 12at7, which isn't that big of a deal....

Do you think going with the 12at7 + passive preamp is a better solution than an active pre with ~12 dB gain?

 

[tinitus]

Do you think going with the 12at7 + passive preamp is a better solution than an active pre with ~12 dB gain?

just guessing
but I think you might loose more quality by adding preamp, than you would going from 12BH7 to 12AT7
depends on several other aspects

 

[tinitus]

but hey, no harm in trying this neat chip attenuator, its cheap

http://electronics.dantimax.dk/Kits/Selectors_-_attenuators/index.html

edit, can't make the link direct to it....clik on Chip Vol1

 

[Davec113]

but hey, no harm in trying this neat chip attenuator, its cheap

Dantimax (elektronik) - Selectors_-_attenuators

edit, can't make the link direct to it....clik on Chip Vol1

Wait a minute, isn't this the tube forum?

 

[tinitus]

ok, then make it a tube attenuator

 

[Simon B]

ok, then make it a tube attenuator

That's a nice idea tinitus - is there any particular topology that you'd favour? Perhaps a directly heated monode - ?

 

[tinitus]

i better bail out here

 

[vinylkid58]

I built it with a 12bh7a driver tube because I had an active preamp, an Anthem Pre1 with the outboard PS. The Anthem was a good preamp but has too much gain, 28 dB... I think ~12 dB gain would be more suitable.

Another option would be to gut the Pre1 enclosure to experiment with different attenuator/linestage/buffer options.

jeff

 

[Davec113]

OK, Partsconnexion sent me the schematics and gave me a few things to look into.

Unfortunately, it looks like the power transformer was overheated and the coatings melted a little bit. It's not obvious at 1st glance, but there was melted epoxy or whatever they use to coat the trafo near the heads of the bolts that hold the trafo together.

I am thinking this is a loss, not sure if its worth looking into a new PT... The sticker on the PT says "ATC-FROST", which looks like it was sold to another company in 2001. The PT is soldered to the power supply PCB so if I do replace it, it is unlikely I will find a PT that would be a direct replacement.

 

[Davec113]

PCX got back to me already on the trafo. They can fix it for $400 using 2 other trafos in place of the original, which includes 3 hrs labor, so I assume they can sell me the parts for around $250... or they will buy it from me in it's current condition for $275, they pick up the UPS bill for shipping to Canada.

I am thinking of selling it and putting the $275 into another preamp...

I heard back from SAS audio and the 7A can be configured for ~15 dB gain:

http://www.sasaudiolabs.com/pream7a.htm

And a fellow diyaudio member offered this for $250, but it has only 2 inputs so I'd need to add a 3rd set, which may or may not be a big deal... depends if there is space to add them in the chassis which is awfully small.

12AU7 Preamplifier | Tube | AudiogoN

 

[vinylkid58]

so I assume they can sell me the parts for around $250...

That sounds like a lot for 2 small transformers. Did they give you the specs for the original?

jeff