LDR300x.V3 Preamp Tour

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tortugaranger

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Re: LDR300x.V3 Preamp Tour
« Reply #80 on: 21 Dec 2020, 09:48 pm »

Interesting update on the LDR3000x.V3 Active version

https://www.audiocircle.com/index.php?topic=168215.msg1836816#msg1836816

jriggy

Re: LDR300x.V3 Preamp Tour
« Reply #81 on: 29 Dec 2020, 06:19 pm »
Hey guys,

The preamp did not get rerouted, landed here yesterday, and I turned it around to Michigan via USPS today, with a prepaid label from Morten.

Was a bummer having it here and sending it off right away. Really wish I could participate.

Have fun

Jason

tortugaranger

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Re: LDR300x.V3 Preamp Tour
« Reply #82 on: 5 Jan 2021, 06:50 pm »
Hi All,

The tour preamp has suffered some damage due to having been shipped multiple times where the shaking/vibration has broken loose one of the CuTf coupling caps. This doesn't surprise me given that those caps are about as big and heavy as a roll of quarters and we do not have provisions for strapping down these caps in the current board design.

The good news is Bob2 has agreed to put on his repairman hat and have at it. However, rather than simply reattaching the CuTf VCap I've instructed Bob2 to remove them both altogether. Instead we are converting the active gain/buffer board over to direct coupled output.

Some background. The SSPB.V2 gain/buffer board is a second gen design where we changed to a split voltage power supply (+/- 12V), added an input stage (op amp), and added the ability to adjust the bias current of the JFET output buffer using trim pots (the 2 blue cubes with a screw on top). The split voltage PS together with the adjustable output bias current was intended to allow for the elimination of the output coupling caps (AC coupling) and thus run DC coupled instead. This follows the philosophy of "the best coupling cap is no coupling cap". DC coupling works well provided the DC offset can be kept to a minimum - typically 50 millivolt or less - ideally zero MV.

The SSPB.V2 provided for the use of coupling caps as an initial default. Meanwhile we've had some time to explore running the board without the caps while monitoring the behavior of the DC offset. What we've determined is that once adjusted to near zero DC offset, the offset remains very stable and typically can be held under +/- 5 MV which is more than acceptable. Also, there's no power-on or power-off bump or pop because the SSPB.V2 board has its own muting relay with a delayed unmute when power is first applied. And when power is dropped, the muting relay shunts all output to ground.

Once Bob2 has made the modifications including adjusting the JFET bias current to yield ~0 DC offset, he'll keep the unit for up to a week of listening and then it's back on the road again to the next person but with a direct coupled output.

uncola

Re: LDR300x.V3 Preamp Tour
« Reply #83 on: 5 Jan 2021, 10:43 pm »
Not to mention direct coupled is cheaper because it doesn't need those fancy capacitors!

tortugaranger

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Re: LDR300x.V3 Preamp Tour
« Reply #84 on: 6 Jan 2021, 12:25 am »
Not to mention direct coupled is cheaper because it doesn't need those fancy capacitors!


Indeed!

LarryD56

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Re: LDR300x.V3 Preamp Tour
« Reply #85 on: 6 Jan 2021, 01:02 am »
    When I was preparing the preamp's box to be shipped out the cardboard was already getting rather loose, so I removed all the loose tape and tightly re-taped the entire box. It was looking a bit beat up when I got it. Glad the preamp's case didn't get damaged. Looks like FedEx charged me an additional $5 for their botched re-routing to Bob2. I will be speaking with their billing dept. this week about a refund.  I usually don't have any problems with them.

   Yeah, I'd prefer a stable direct coupled design. Now I'm even more interested in the preamp. Wanting to hear what Bob2 thinks of the LDR300x.V3 after he fixes it.

  Larry D.

tortugaranger

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Re: LDR300x.V3 Preamp Tour
« Reply #86 on: 7 Jan 2021, 06:43 pm »

Success! Bob made the modifications removing the VCaps, installing direct links, and adjusting the DC offset to ~zero.  Says it's sounding great. Looking forward to reading his review.



Hi All,

The tour preamp has suffered some damage due to having been shipped multiple times where the shaking/vibration has broken loose one of the CuTf coupling caps. This doesn't surprise me given that those caps are about as big and heavy as a roll of quarters and we do not have provisions for strapping down these caps in the current board design.

The good news is Bob2 has agreed to put on his repairman hat and have at it. However, rather than simply reattaching the CuTf VCap I've instructed Bob2 to remove them both altogether. Instead we are converting the active gain/buffer board over to direct coupled output.

Some background. The SSPB.V2 gain/buffer board is a second gen design where we changed to a split voltage power supply (+/- 12V), added an input stage (op amp), and added the ability to adjust the bias current of the JFET output buffer using trim pots (the 2 blue cubes with a screw on top). The split voltage PS together with the adjustable output bias current was intended to allow for the elimination of the output coupling caps (AC coupling) and thus run DC coupled instead. This follows the philosophy of "the best coupling cap is no coupling cap". DC coupling works well provided the DC offset can be kept to a minimum - typically 50 millivolt or less - ideally zero MV.

The SSPB.V2 provided for the use of coupling caps as an initial default. Meanwhile we've had some time to explore running the board without the caps while monitoring the behavior of the DC offset. What we've determined is that once adjusted to near zero DC offset, the offset remains very stable and typically can be held under +/- 5 MV which is more than acceptable. Also, there's no power-on or power-off bump or pop because the SSPB.V2 board has its own muting relay with a delayed unmute when power is first applied. And when power is dropped, the muting relay shunts all output to ground.

Once Bob2 has made the modifications including adjusting the JFET bias current to yield ~0 DC offset, he'll keep the unit for up to a week of listening and then it's back on the road again to the next person but with a direct coupled output.

tortugaranger

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Re: LDR300x.V3 Preamp Tour
« Reply #87 on: 13 Jan 2021, 02:15 pm »
Hi All,
A quick update on the tour. Had the typical holiday slow down but we are moving forward now.
sruffle is up next.

1) uncola - HI
2) MttBsh - WA
3) Delta77 - CA
4) Emiel - AZ
5) LarryD56 - ID
6) Bob2 - MI

7) sruffle - NJ (up next)
8') krustykat - NC
9) GentleBender - FL
10) Mollydog

Standby List
1) ** open **

Bob2

Re: LDR300x.V3 Preamp Tour
« Reply #88 on: 14 Jan 2021, 04:44 pm »
The 300 preamp has been here and is on it's way to the next person.

Let me preface this post. I'm not an Audiophile. I'm an enthusiast so no Fancy Pants verbiage, plots or charts.

I use a tone control tube preamp to drive my amp. When Morten started collecting names to try his LDR300x.V3 I thought it was a good time to see how a SS preamp would handle my Stratos Extreme. I signed up and away we go!

Morten has explained what happened with the preamp so no need to get into that.

With the 300 working again I hooked it up for my first listening session. I use a PC that plays music ripped to a hard drive. The PC utilizes an Asus Essence STX II sound card to send the analog signal.
I also use an Azur 851N streaming from various sources.

I spent about 7 hours over two evenings going through a collection of music.
Sound was different than my preamp of course but very good never the less.
I did find that bass was less than I am accustomed to. Mids were a bit more present.
Sound stage was wide and reasonably deep. The 300 presented itself very well.

I planned to listen to vinyl for the next session. That unfortunately did not happen.
I started the session with Brubeck's Take Five Lp cued up. As soon as the needle starting sending a signal the preamp froze. The volume control as well as the remote became unresponsive then the preamp shut down.
I checked to make sure everything was connected properly and tried the album again. Same thing.
I tried with my second tt only to have the same results.

Contacted Morten and he offered up a couple of suggestions for me to try. Sadly those did not rectify the issue.
After some e-mails and phone conversation with Morten there was not much that could be done. The 300 is working in active and passive modes when connected to my PC and the Azur.

I went back through this thread but didn't see any that stated they had listened to vinyl.
So I'm not sure if the stated issue was there prior to the vcap ricocheting around the enclosure.

I did spend a couple of hours listening in passive mode. I feel that active mode is a bit better.
If you are looking for a preamp on a budget it is worth checking it out.

I want to thank Morten for giving us an opportunity to try it out. I have to say that Morten is a brave man for turning me lose making repairs.
Also thanks to Audio Circle for creating a great forum that makes this possible.

Equipment used:
Speakers, Focal Aria 948
Digital Sources, PC, Azur 851N
Analog Sources, Specific Dynamics tt, Sony 3000tt
Phono preamps, Goldnote PH-10, Creek OBH-15 mk2
Amplification, Odyssey Stratos Extreme
Interconnects, Wireworld



tortugaranger

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Re: LDR300x.V3 Preamp Tour
« Reply #89 on: 14 Jan 2021, 06:42 pm »
I want to thank Bob for participating and especially for his help in converting the preamp over to active direct coupled.

Bob encountered a problem when he connected his phono preamp(s) to the LDR300x. When he dropped the needle on his turntable the LDR300x would either freeze or shut down. We've not had reports of anything similar ever happening to any of our earlier preamps so this is new. I told Bob I didn't have a simple fix from afar. We were able to determine that this has nothing to do with the active part of the LDR300x - it also happened when running passive with the active gain/buffer board literally removed from the unit. While I don't have a specific explanation it's highly likely that the phono preamp linestage signal ground is inducing sufficient ground current to cause the power internal to the LDR300x to fluctuate and trip the microcontroller. We will be looking into this here at our shop with our phono rig which we usually don't use during development or commissioning.

The 300 preamp has been here and is on it's way to the next person.

Let me preface this post. I'm not an Audiophile. I'm an enthusiast so no Fancy Pants verbiage, plots or charts.

I use a tone control tube preamp to drive my amp. When Morten started collecting names to try his LDR300x.V3 I thought it was a good time to see how a SS preamp would handle my Stratos Extreme. I signed up and away we go!

Morten has explained what happened with the preamp so no need to get into that.

With the 300 working again I hooked it up for my first listening session. I use a PC that plays music ripped to a hard drive. The PC utilizes an Asus Essence STX II sound card to send the analog signal.
I also use an Azur 851N streaming from various sources.

I spent about 7 hours over two evenings going through a collection of music.
Sound was different than my preamp of course but very good never the less.
I did find that bass was less than I am accustomed to. Mids were a bit more present.
Sound stage was wide and reasonably deep. The 300 presented itself very well.

I planned to listen to vinyl for the next session. That unfortunately did not happen.
I started the session with Brubeck's Take Five Lp cued up. As soon as the needle starting sending a signal the preamp froze. The volume control as well as the remote became unresponsive then the preamp shut down.
I checked to make sure everything was connected properly and tried the album again. Same thing.
I tried with my second tt only to have the same results.

Contacted Morten and he offered up a couple of suggestions for me to try. Sadly those did not rectify the issue.
After some e-mails and phone conversation with Morten there was not much that could be done. The 300 is working in active and passive modes when connected to my PC and the Azur.

I went back through this thread but didn't see any that stated they had listened to vinyl.
So I'm not sure if the stated issue was there prior to the vcap ricocheting around the enclosure.

I did spend a couple of hours listening in passive mode. I feel that active mode is a bit better.
If you are looking for a preamp on a budget it is worth checking it out.

I want to thank Morten for giving us an opportunity to try it out. I have to say that Morten is a brave man for turning me lose making repairs.
Also thanks to Audio Circle for creating a great forum that makes this possible.

Equipment used:
Speakers, Focal Aria 948
Digital Sources, PC, Azur 851N
Analog Sources, Specific Dynamics tt, Sony 3000tt
Phono preamps, Goldnote PH-10, Creek OBH-15 mk2
Amplification, Odyssey Stratos Extreme
Interconnects, Wireworld



sruffle

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Re: LDR300x.V3 Preamp Tour
« Reply #90 on: 16 Jan 2021, 10:22 pm »
Hello all.  I had a pleasant surprise today when the pre-amp arrived earlier than expected.  I will be setting it up this weekend and will give a report within the next week.