My preamp (Rotel RC-991) has started to fail recently; a quick look inside told me all I needed to know. Leaking capacitors and a failing pot/opamp (left channel significantly lower - deoxit was no help). I thought to myself I'll order replacements and fix it. Then I thought, perhaps a new one. Then: perhaps I'll build it myself... I'm currently building my first DAC/DAP so perhaps this is a great goal! Bonus, I can make them look the same.
I wasn't expecting the world I just put myself into, actives, passives, attenuators, relay-switched resistors, rotary encoders, tubes, opamps... well it's been quite a learning curve.
Not sure if I was ready to actually build the thing, I started looking for prebuilt boards. I came across Twisted Pear and am considering the Joshua Tree attenuator as well as the Retro RIIA stage for my turntable. Then I realized these are likely to have very different outputs so I'm now considering the Neurochrome Universal Buffer after the attenuator. On top of this, I'll need an input selector as well. My DAC will have balanced and unbalanced outputs and the turntable is unbalanced only.
So, here's the question. Does any of this even make sense? Am I tackling this the right way, or should I be looking to build something myself instead?
At least for now, the preamp will be paired with two Rotel RB-980BX power amplifiers in bridged mono, my custom DAP and a Project Debut Carbon TT.
Thanks, and apologies for the totally newbie questions!
I wasn't expecting the world I just put myself into, actives, passives, attenuators, relay-switched resistors, rotary encoders, tubes, opamps... well it's been quite a learning curve.
Not sure if I was ready to actually build the thing, I started looking for prebuilt boards. I came across Twisted Pear and am considering the Joshua Tree attenuator as well as the Retro RIIA stage for my turntable. Then I realized these are likely to have very different outputs so I'm now considering the Neurochrome Universal Buffer after the attenuator. On top of this, I'll need an input selector as well. My DAC will have balanced and unbalanced outputs and the turntable is unbalanced only.
So, here's the question. Does any of this even make sense? Am I tackling this the right way, or should I be looking to build something myself instead?
At least for now, the preamp will be paired with two Rotel RB-980BX power amplifiers in bridged mono, my custom DAP and a Project Debut Carbon TT.
Thanks, and apologies for the totally newbie questions!
You have two choices
1. Define your requirements and pick kits that allow that
2. Be kid in a sweet shop and build a whole load of them.
You are currently on 2. If you want to stay there fine, but if insanity is looming you may want to jump 🙂. There are many fine preamp designs out there from simple to complex. Something for everyone once you know what you want.
1. Define your requirements and pick kits that allow that
2. Be kid in a sweet shop and build a whole load of them.
You are currently on 2. If you want to stay there fine, but if insanity is looming you may want to jump 🙂. There are many fine preamp designs out there from simple to complex. Something for everyone once you know what you want.
Insanity is always looming, but that's almost nothing to do with this 😀
You're absolutely right, I am a kid in a candy store, I guess it's a big new store and I'm trying to take it all in!
So, what do I need? I guess I'm after:
Hopefully that's a largely complete list of requirements! I can't say "money is no object" but I certainly don't mind spending some money if the components are worth it. My budget is around, say $500.
You're absolutely right, I am a kid in a candy store, I guess it's a big new store and I'm trying to take it all in!
So, what do I need? I guess I'm after:
- At least one balanced (XLR) input, multiple unbalanced inputs
- Both balanced and unbalanced outputs
- Volume control (a remote control is not required)
- A phono stage
- Something I can build myself. I have years of electronics experience and many years ago was an electrician, but am somewhat of a novice when it comes to EE and audio. I'm always happy to learn something new!
- A design I can put into my own chassis
Hopefully that's a largely complete list of requirements! I can't say "money is no object" but I certainly don't mind spending some money if the components are worth it. My budget is around, say $500.
That makes sense as a set of requirements. I'll put in my recommendations when I get time later, meanwhile sure someone will chip in 🙂
You can avoid the whole input selection thing by building a mixer. Everything on at once! Just turn on the input source to activate. Level already set!
Low noise op amps avoid the hiss that was inevitable from mixing in the 60's when preamps with a big selector knob were king.
RIAA is the one thing that you can't get in a commercial mixer. There are one or two, low quality, olson and Herald RA-88a. They have a lot of room in them to put other circuits, especially after you pull out the hummy 34 VCT transformer and AC power switch. 7 really nice 40 k pots. I paid $15 for mine, I've seen the olson on ebay for 30. Nice stainless steel panel, steel box to keep the AM CB and police band radio out.
Course if you like building a chassis, have at it.
My upgrade cost was $25, for all new 33078 op amps to replace the hissy 4558, a race car transformer and RF and surge suppression power supply. Differential out would run the cost a little higher, XLR in would too. I added a PS bypass cap & 6 feedback resistor bypass caps to kill 1 mhz oscillation of the faster 33078's.
Actually you can do everything you listed with a PV8 mixer, except the RIAA part. If you can work surface mount parts you could probably cram one in on one of the stereo channels in (5-6, 7-8), but there is not a lot of room in there. Also has tone controls and effect loop sockets.
No room for tubes in either box except 7812. I think tubes are overrated for hifi anyway. My modded RA-88a sounds as good as my tube PAS2 preamp, uses 1/20 the wattage, and doesn't require switching the source and changing the volume every time I change sources. RA-88a also will drive 4 m of RCA cable to power amp instead of the 2 m limit of the PAS2.
Low noise op amps avoid the hiss that was inevitable from mixing in the 60's when preamps with a big selector knob were king.
RIAA is the one thing that you can't get in a commercial mixer. There are one or two, low quality, olson and Herald RA-88a. They have a lot of room in them to put other circuits, especially after you pull out the hummy 34 VCT transformer and AC power switch. 7 really nice 40 k pots. I paid $15 for mine, I've seen the olson on ebay for 30. Nice stainless steel panel, steel box to keep the AM CB and police band radio out.
Course if you like building a chassis, have at it.
My upgrade cost was $25, for all new 33078 op amps to replace the hissy 4558, a race car transformer and RF and surge suppression power supply. Differential out would run the cost a little higher, XLR in would too. I added a PS bypass cap & 6 feedback resistor bypass caps to kill 1 mhz oscillation of the faster 33078's.
Actually you can do everything you listed with a PV8 mixer, except the RIAA part. If you can work surface mount parts you could probably cram one in on one of the stereo channels in (5-6, 7-8), but there is not a lot of room in there. Also has tone controls and effect loop sockets.
No room for tubes in either box except 7812. I think tubes are overrated for hifi anyway. My modded RA-88a sounds as good as my tube PAS2 preamp, uses 1/20 the wattage, and doesn't require switching the source and changing the volume every time I change sources. RA-88a also will drive 4 m of RCA cable to power amp instead of the 2 m limit of the PAS2.
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OK have a little time. Starting with the phono stage. I happen to have a couple of the twisted pair retro boards and they are very nice, BUT it's a balanced phono stage and you have stated your TT is unbalanced (nothing a cable change wont fix mind, and you appear to be very good with wire!). Not to worry many other options that are single ended. BTW MM or MC?
Once the Phono stage is decided we can work out if you need gain in the line stage. Your Rotel uses single ended connections so the gain required for that is one data point for gain and just need to confirm what the balanced output would plug into.
If you make things modular you can get things working and always upgrade as you fancy. a volume pot and rotary selector are a great way to go initially and then fancy stepped relay attenuators and input boards can follow.
TomChr's universal buffer has amazing performance but it's something you package rather than build. If this isn't an issue then it sorts out the line stage and outputs in one.
Once the Phono stage is decided we can work out if you need gain in the line stage. Your Rotel uses single ended connections so the gain required for that is one data point for gain and just need to confirm what the balanced output would plug into.
If you make things modular you can get things working and always upgrade as you fancy. a volume pot and rotary selector are a great way to go initially and then fancy stepped relay attenuators and input boards can follow.
TomChr's universal buffer has amazing performance but it's something you package rather than build. If this isn't an issue then it sorts out the line stage and outputs in one.
Thanks!
@indianajo, I'm looking to build something myself really but thanks for the suggestion!
@billshurv, I had noticed that the TP RIAA was balanced. I'm considering converting my turntable, but perhaps it would be better to start simple and go with something single ended. I can always upgrade later, I guess. Any suggestions? I currently have an Ortofon 2M blue fitted, so I'm MM.
The current power amps are single ended, but long term I'll probably look to replace them with something I'll build myself. But that has to come after the pre since that's the more urgent need!
I'm not too worried about using a prebuilt component like the universal buffer. It will help the build initially, and keeping modular would mean that I can change things out as I want to - keeping the initial cost low and project simple and upgrading it / making it more fancy over time!
I really appreciate the input
@indianajo, I'm looking to build something myself really but thanks for the suggestion!
@billshurv, I had noticed that the TP RIAA was balanced. I'm considering converting my turntable, but perhaps it would be better to start simple and go with something single ended. I can always upgrade later, I guess. Any suggestions? I currently have an Ortofon 2M blue fitted, so I'm MM.
The current power amps are single ended, but long term I'll probably look to replace them with something I'll build myself. But that has to come after the pre since that's the more urgent need!
I'm not too worried about using a prebuilt component like the universal buffer. It will help the build initially, and keeping modular would mean that I can change things out as I want to - keeping the initial cost low and project simple and upgrading it / making it more fancy over time!
I really appreciate the input
OK, so I've been doing some research and I now probably have enough knowledge to be dangerous. Let's find out.
I want to create a preamp that offers at least one balanced channel end-to-end (for my DAC). But I need to be able to support single-ended connections in (for other devices) and out (because my current power amps are single ended).
So my new plan is to build my own input switching board using relays. It will essentially turn every single-ended input into a balanced one using something like an AD8476 and OP1177 per channel to convert to balanced (well, differential). The board will offer a single internal balanced connection for an RIAA stage. I'll probably use a single-ended RIAA stage with one of the Universal Buffers to provide a phono stage then look to upgrade this later.
The balanced inputs will then go through an input selector and a volume control (which will probably be a pot to begin with, but then I'll look at a relay board later).
Finally, I'll use the NeoChrome Universal Buffer at the output to provide options for both single-ended and balanced outputs.
Does that sound like a sane plan? I need to build the schematic and PCBs for the input selector / converter board but I don't want to go down that path if this plan is plain insanity!
I want to create a preamp that offers at least one balanced channel end-to-end (for my DAC). But I need to be able to support single-ended connections in (for other devices) and out (because my current power amps are single ended).
So my new plan is to build my own input switching board using relays. It will essentially turn every single-ended input into a balanced one using something like an AD8476 and OP1177 per channel to convert to balanced (well, differential). The board will offer a single internal balanced connection for an RIAA stage. I'll probably use a single-ended RIAA stage with one of the Universal Buffers to provide a phono stage then look to upgrade this later.
The balanced inputs will then go through an input selector and a volume control (which will probably be a pot to begin with, but then I'll look at a relay board later).
Finally, I'll use the NeoChrome Universal Buffer at the output to provide options for both single-ended and balanced outputs.
Does that sound like a sane plan? I need to build the schematic and PCBs for the input selector / converter board but I don't want to go down that path if this plan is plain insanity!
Why not make all inputs balanced? Connecting an unbalanced source to a balanced input is straightforward.
Thanks! Great idea, that way I don't have to deal with any conversion inside the box.
I've started down the path of designing my own input switch board for four balanced inputs. Three will be on the rear of the unit with one internal for the RIAA board (to be decided). I plan to pair this with a volume control board.
However, there's one thing I can't find a definitive answer on: do I need to switch only the +/- of the balanced connections and connect the grounds together with a bus, or should I be looking at switching the grounds as well?
Before you ask, I'm building my own because I want to pair it with a microcontroller on a separate board, so I can do some other stuff, like a small display, etc.
I've started down the path of designing my own input switch board for four balanced inputs. Three will be on the rear of the unit with one internal for the RIAA board (to be decided). I plan to pair this with a volume control board.
However, there's one thing I can't find a definitive answer on: do I need to switch only the +/- of the balanced connections and connect the grounds together with a bus, or should I be looking at switching the grounds as well?
Before you ask, I'm building my own because I want to pair it with a microcontroller on a separate board, so I can do some other stuff, like a small display, etc.