I just built an HDAM (V1.3) "preamplifier" I bought off Ebay. I knew it would sound good and I figured, why the heck not?
Check this thing out, and yes, it does sound really good.
Yes, it is just simply sitting on top of the inner surface in an aluminum chassis box that I grounded. It is not screwed in, just sitting there.
What did I change from the kit as I built it? I threw out the resistors, 5% carbon film things and used mostly Dale RN55 resistors that I matched by hand. Then I matched the supplied transistors and stuck them together with heat shrink and some thermal grease. The supplied capacitors, 10 pF and 100 pF were replaced with Polystyrene types the ones supplied were ceramic axial ones.
The unit was on for maybe 10 minutes or less when I took the measurements. The only adjustment is for zero DC offset, which was done. It seems to be happy sitting around 1/2 a mV on each channel.
I'm feeding it +/- 20 VDC from an HP 6237B power supply 'cause I didn't have a transformer handy.
Here is the unit I bought on Ebay: NEW Marantz HDAM Circuit Preamp Kit Class A Output with 3-Bit Input Select | eBay It is item # 183526337118.
This kit sat here for months before I decided to build it today. I think there are still a couple left. The schematic is too blurry to make out any detail, but it is there.
-Chris
Check this thing out, and yes, it does sound really good.
Yes, it is just simply sitting on top of the inner surface in an aluminum chassis box that I grounded. It is not screwed in, just sitting there.
What did I change from the kit as I built it? I threw out the resistors, 5% carbon film things and used mostly Dale RN55 resistors that I matched by hand. Then I matched the supplied transistors and stuck them together with heat shrink and some thermal grease. The supplied capacitors, 10 pF and 100 pF were replaced with Polystyrene types the ones supplied were ceramic axial ones.
The unit was on for maybe 10 minutes or less when I took the measurements. The only adjustment is for zero DC offset, which was done. It seems to be happy sitting around 1/2 a mV on each channel.
I'm feeding it +/- 20 VDC from an HP 6237B power supply 'cause I didn't have a transformer handy.
Here is the unit I bought on Ebay: NEW Marantz HDAM Circuit Preamp Kit Class A Output with 3-Bit Input Select | eBay It is item # 183526337118.
This kit sat here for months before I decided to build it today. I think there are still a couple left. The schematic is too blurry to make out any detail, but it is there.
-Chris
Attachments
Hi Chris,
Did the kit come with the Alps pot and elecaudio type rca jacks?
Looks like a bump at 60Hz, any audible background hum?
With your part replacements this is a neat quicky project
Cheers,
Vunce
Hi Vunce,
No, the volume control and RCA connectors are sourced separately. I had the volume control already and bought the RCA connectors elsewhere. The kit would have been much more expensive if they were included. Keep in mind this isn't an Op Amp with volume control kit. We're talking individual transistors here. The kit is a lot more involved than just an Op Amp.
I have zero connection with the seller here. I bought it months ago and put it together today. The performance was so good I decided to post about it.
That 60 Hz peak is at -120 dB! You can't hear it, and the board isn't in a case either. Most preamps measure a 60 Hz component at -100 dB to - 80 dB. The bench speakers I am using are 98 dB/watt (Klipsch THX 6000) and are very good. I can hear everything clearly.
-Chris
No, the volume control and RCA connectors are sourced separately. I had the volume control already and bought the RCA connectors elsewhere. The kit would have been much more expensive if they were included. Keep in mind this isn't an Op Amp with volume control kit. We're talking individual transistors here. The kit is a lot more involved than just an Op Amp.
I have zero connection with the seller here. I bought it months ago and put it together today. The performance was so good I decided to post about it.
That 60 Hz peak is at -120 dB! You can't hear it, and the board isn't in a case either. Most preamps measure a 60 Hz component at -100 dB to - 80 dB. The bench speakers I am using are 98 dB/watt (Klipsch THX 6000) and are very good. I can hear everything clearly.
-Chris
For the price of the kit I didn’t think they were included. But I saw them in the listing pictures and on your built board, so I just wanted to confirm that. I did read in the fine print after I had posted that question that the parts were not included. That is not a dealbreaker at all! Discrete circuit with onboard switching makes this kit very attractive, and your measurements are piece of mind that this is not just another “junk eBay” kit. Thanks for posting this.
Last edited:
Hi Dave,
Nope, all I have is this from their site. I'm afraid it isn't very clear and I made my decision to buy it on that vague schematic and PCB pictures.
There are many different circuits called "HDAM" with Marantz. Most are based on some form of diamond buffer. Diamond buffers are most famous as audio buffers, like the old BUF03, BUF634 and LME49600 to name a few. Many of the DSL buffers are also partly a diamond buffer.
Diamond buffers are fascinating in that they cancel out non-linearity of the transistors while also being extremely fast. As an output stage they are inherently low distortion. Look at the Nakamichi 620 and Marantz 170DC, 300DC power amplifiers. There are more examples out there.
For the money, I don't think you can beat this unit, and that is including throwing out all the resistors and the four ceramic capacitors. It seems to be a good PCB with a standard 317 / 337 type regulator pair. We can discuss what to change further if you want, but the performance is extremely high. It's still on my bench because I love listening to it - but I have to get back to work at some point soon.
-Chris
Nope, all I have is this from their site. I'm afraid it isn't very clear and I made my decision to buy it on that vague schematic and PCB pictures.
There are many different circuits called "HDAM" with Marantz. Most are based on some form of diamond buffer. Diamond buffers are most famous as audio buffers, like the old BUF03, BUF634 and LME49600 to name a few. Many of the DSL buffers are also partly a diamond buffer.
Diamond buffers are fascinating in that they cancel out non-linearity of the transistors while also being extremely fast. As an output stage they are inherently low distortion. Look at the Nakamichi 620 and Marantz 170DC, 300DC power amplifiers. There are more examples out there.
For the money, I don't think you can beat this unit, and that is including throwing out all the resistors and the four ceramic capacitors. It seems to be a good PCB with a standard 317 / 337 type regulator pair. We can discuss what to change further if you want, but the performance is extremely high. It's still on my bench because I love listening to it - but I have to get back to work at some point soon.
-Chris
Attachments
OK, OK, I bit!!
The Canada site is out. I found this on the US eBay site:
NEW Marantz HDAM Circuit Preamp Kit Class A Output with 3-Bit Input Select | eBay
Anyone need a preamp???
The Canada site is out. I found this on the US eBay site:
NEW Marantz HDAM Circuit Preamp Kit Class A Output with 3-Bit Input Select | eBay
Anyone need a preamp???
Hi Billy,
Excellent! I'm glad you found one. Can you ask for the schematic for it? I asked when I bought one but didn't get one yet.
Too bad they don't ship to Canada! Darn. I think I know some friends who would like one of these. We should discuss building them better, and additional things they really should have to be a finished preamp.
-Chris
Excellent! I'm glad you found one. Can you ask for the schematic for it? I asked when I bought one but didn't get one yet.
Too bad they don't ship to Canada! Darn. I think I know some friends who would like one of these. We should discuss building them better, and additional things they really should have to be a finished preamp.
-Chris
Hi Chris,
Well, I ended up purchasing this kit. I’m always a bit skeptical about buying transistors on these types of marketplaces. But, your posted measurements are very good, so I’m hoping they are real.
Other than the slight modifications you did to this preamp, would you change anything else?
The sellers posted schematic stinks! Blurry and doesn’t include the psu section.
Enjoy it a bit longer before clearing your bench
-Vunce
Wow Fellas! They are moving like hot potato’s! I bought mine last night, the seller had a couple left now out of stock. I believe there’s four left from another US seller.
Well, I ended up purchasing this kit. I’m always a bit skeptical about buying transistors on these types of marketplaces. But, your posted measurements are very good, so I’m hoping they are real.
Other than the slight modifications you did to this preamp, would you change anything else?
The sellers posted schematic stinks! Blurry and doesn’t include the psu section.
Enjoy it a bit longer before clearing your bench
-Vunce
Wow Fellas! They are moving like hot potato’s! I bought mine last night, the seller had a couple left now out of stock. I believe there’s four left from another US seller.
Last edited:
Hi Vunce,
Well, I would start by throwing out the resistors and ordering Dale RN55 1% metal film resistors. There are a pair each of 10 pF and 100 pF capacitors. Throw those out and use polystyrene, or NP0 ceramic disc capacitors instead. I used everything else as shipped.
Additionally, I would match a set of BC550 and BC560 to replace the bipolar ones. They also used some ZTX transistors for outputs. I would try to find something in a larger package. The old MPSU series would have been perfect, and they also discontinued the series transistors. I haven't looked for anything else that might work yet. I would have redesigned the PCB to use transistor with a TO-126 case for the outputs.
Otherwise the regulators run cool, but I want to check the voltages again. Something seemed off and I was waiting for the schematic to save some time.
There should be capacitors in series with the outputs, and a muting relay would be nice to have. Power should come from a 33 VCT or 36 VCT transformer. The circuit draws about 100 mA, but there will be housekeeping circuitry added. I'm buying a 1 ampere, 33 VCT transformer for it, Digikey # HM4397-ND. The heavier transformer will have a lower flux density and should be quieter.
Let's bounce idea around for this animal.
-Chris
Well, I would start by throwing out the resistors and ordering Dale RN55 1% metal film resistors. There are a pair each of 10 pF and 100 pF capacitors. Throw those out and use polystyrene, or NP0 ceramic disc capacitors instead. I used everything else as shipped.
Additionally, I would match a set of BC550 and BC560 to replace the bipolar ones. They also used some ZTX transistors for outputs. I would try to find something in a larger package. The old MPSU series would have been perfect, and they also discontinued the series transistors. I haven't looked for anything else that might work yet. I would have redesigned the PCB to use transistor with a TO-126 case for the outputs.
Otherwise the regulators run cool, but I want to check the voltages again. Something seemed off and I was waiting for the schematic to save some time.
There should be capacitors in series with the outputs, and a muting relay would be nice to have. Power should come from a 33 VCT or 36 VCT transformer. The circuit draws about 100 mA, but there will be housekeeping circuitry added. I'm buying a 1 ampere, 33 VCT transformer for it, Digikey # HM4397-ND. The heavier transformer will have a lower flux density and should be quieter.
Let's bounce idea around for this animal.
-Chris
Heck yeah, pretty psyched actually. Just finished the ACP+ pre/hpa. Man does that sound great. Genuine matched J74s too.
This was just too nice to pass up, nice, quiet, good sounding, 3 inputs, cheap. I'll find a place for it!
