That is perfectly fine. Nothing wrong with that in my view.
Here is more on the adapter...
Attachments
I’ve tried a few opamps; Burson V4 and V5, dual opa627, a few NE5532. Both Burson opamps is introducing quite a bit of hum. The NE5532 and opa627 are completely silent.
I went ahead and ordered a couple of Core type 30vct transformers so I will put that 36vct back in the parts box and hopefully avoid any regulators frying of caps exploding down the road (if it did happen would not be the first time for me 🙂
I also found the gain excessive but now for source I am using a WIIM streamer and those all have adjustable line level output in steps of .200,.500,1, and 2 volts RMS. So I set it at .200 mv and volume through the passive preamp on the input is much more controllable.
I guess I will document here my attempt to re-purpose the DH-101 units for housing these clones (unless anyone has objection since it is not much electronics info but could be a bit wordy and numerous pics)
The plan is to complete the two PASS AmpCamp unbuilt kits I have here and use one of the these clone preamps for control.
By the way, anyone have experience with that combination: C-3850 clone to PASS AmpCamp v1.8 monoblocks?
The amps will be driving a pair of Ref3A DeCapo I speakers which are fairly sensitive, impedance benign, and sound glorious to my ears...
I also found the gain excessive but now for source I am using a WIIM streamer and those all have adjustable line level output in steps of .200,.500,1, and 2 volts RMS. So I set it at .200 mv and volume through the passive preamp on the input is much more controllable.
I guess I will document here my attempt to re-purpose the DH-101 units for housing these clones (unless anyone has objection since it is not much electronics info but could be a bit wordy and numerous pics)
The plan is to complete the two PASS AmpCamp unbuilt kits I have here and use one of the these clone preamps for control.
By the way, anyone have experience with that combination: C-3850 clone to PASS AmpCamp v1.8 monoblocks?
The amps will be driving a pair of Ref3A DeCapo I speakers which are fairly sensitive, impedance benign, and sound glorious to my ears...
I need a little clarification. According to Michael Beeny's mods, feedback resistor R29 and R46 (green) sets the gain, but isn't it R3 and R6 (blue) that dose it?
On my firs boar I've only changed R29 and R46 to 560 and C1 and C2 is set to 27p.
On my firs boar I've only changed R29 and R46 to 560 and C1 and C2 is set to 27p.
R29 and R46 (in the schematic above; there are different versions) set the gain. The resistors connect directly to the 100uF cap and then to the inverting input of the op amp. Increasing the resistor will increase the global negative feedback, and reduce gain.
The blue resistors are on the output pin of the op amp, which suppress oscillations.
The blue resistors are on the output pin of the op amp, which suppress oscillations.
🙏 Is it beneficial to increase R3 and R6 as well, to 560 like the schematic shows or other value? And would a better quality resistor make any improvement?
Different op amps might need a higher op amp output resistor. The LME49720, for example, has higher slew rate and greater potential for oscillation. When I ask ChatGPT, it says:
"The LME49720 op amp is typically used with an output resistor in the range of 100 to 1,000 ohms. The specific value depends on the intended application and the desired load driving capabilities. For many general-purpose applications, a 100-ohm to 220-ohm resistor is commonly used.
This output resistor helps with stability and prevents oscillations when driving capacitive loads. However, for high-performance audio applications, you may not use an output resistor at all if you're driving low-impedance loads (like headphones or line-level inputs), as the LME49720 is designed to drive low impedance directly without issue.
It’s also important to consider any specific requirements like load impedance or the need for filtering, which could influence the choice of resistor."
"The LME49720 op amp is typically used with an output resistor in the range of 100 to 1,000 ohms. The specific value depends on the intended application and the desired load driving capabilities. For many general-purpose applications, a 100-ohm to 220-ohm resistor is commonly used.
This output resistor helps with stability and prevents oscillations when driving capacitive loads. However, for high-performance audio applications, you may not use an output resistor at all if you're driving low-impedance loads (like headphones or line-level inputs), as the LME49720 is designed to drive low impedance directly without issue.
It’s also important to consider any specific requirements like load impedance or the need for filtering, which could influence the choice of resistor."
Here's one of the DH-101s that I will be attempting to repurpose as a clone preamp. I already rebuilt the power supply and the RCA jack strips, but of course the power supply will have to go.
The pots will have to go also, I guess I will cover the tone control holes and labels on the faceplate with some type of plate or cover; would be unsightly to leave them empty.
It will be great if the input switching works out, The switches are in great condition so I can think of no reason it should not.
After the power supply upgrade the 101 sounded OK, but I had no success trying to find replacements for the bass and treble pots, and they short in use and send significant DC to the outputs. And I read their impedance is used elsewhere in the circuit so bypass is not simple.
I bought the 101s quite cheaply years ago on the Bay, but with the vintage fad now the prices for these units there have skyrocketed.
I am a self-taught amateur so any hints will be much appreciated. The Accuphase clone will be a huge improvement.
This should fly?
The pots will have to go also, I guess I will cover the tone control holes and labels on the faceplate with some type of plate or cover; would be unsightly to leave them empty.
It will be great if the input switching works out, The switches are in great condition so I can think of no reason it should not.
After the power supply upgrade the 101 sounded OK, but I had no success trying to find replacements for the bass and treble pots, and they short in use and send significant DC to the outputs. And I read their impedance is used elsewhere in the circuit so bypass is not simple.
I bought the 101s quite cheaply years ago on the Bay, but with the vintage fad now the prices for these units there have skyrocketed.
I am a self-taught amateur so any hints will be much appreciated. The Accuphase clone will be a huge improvement.
This should fly?
I would leave the pots in place so that you can use the original knobs. Keep the original look. I can't tell what type of shafts they are.
Try to mount the MOFI PCB as close to the back panel RCA jacks as possible, so the leads are short. If you have a volume control to the front panel, it is best to have the pot mounted very close to the PCB with a shaft going to the front panel.
With this preamp, I would have the volume pot at the output, since it has the buffer stage on the output. It has plenty of current to drive the pot and the circuit after it. Best to have the input side of the PCB very close to the RCA jacks.
I have no idea about the potential collectors value of those preamps. Try to make any changes as reversible as possible, and save all the original parts that you are not using. Take pictures and notes so you can return them to original condition if necessary in the future.
Try to mount the MOFI PCB as close to the back panel RCA jacks as possible, so the leads are short. If you have a volume control to the front panel, it is best to have the pot mounted very close to the PCB with a shaft going to the front panel.
With this preamp, I would have the volume pot at the output, since it has the buffer stage on the output. It has plenty of current to drive the pot and the circuit after it. Best to have the input side of the PCB very close to the RCA jacks.
I have no idea about the potential collectors value of those preamps. Try to make any changes as reversible as possible, and save all the original parts that you are not using. Take pictures and notes so you can return them to original condition if necessary in the future.
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thank you hifiamps.
these preamps had an option phono board that is not present in my units, so plenty of room to mount the clone near the jacks.
I will think about the pots. To me it is a bit weird to show knobs on a unit that do not do as they are labeled.
I never upgraded the signal section of this 101, just the supply section. As I am listening to it now, it is not horrible, but noticeably harsh in the mids and highs and a bit loose in the bass compared to the clone.
Probably would sound so much better if I replaced the transistors and caps in the signal section, assuming good matches for the transistors are even available.
these preamps had an option phono board that is not present in my units, so plenty of room to mount the clone near the jacks.
I will think about the pots. To me it is a bit weird to show knobs on a unit that do not do as they are labeled.
I never upgraded the signal section of this 101, just the supply section. As I am listening to it now, it is not horrible, but noticeably harsh in the mids and highs and a bit loose in the bass compared to the clone.
Probably would sound so much better if I replaced the transistors and caps in the signal section, assuming good matches for the transistors are even available.
Regarding the Hafler DH101 preamps. I found this: https://docs.google.com/spreadsheets/d/1hvdkCcaFyQri_itAl2JF9IO1B2QGGzeNElr2GSn7xXI/edit?gid=0#gid=0