I changed the guts of my PC’s headphone amplifier box to LM1875 using two of the kits I had bought from ebay.
The ICs are supplied by 2x14Vdc unregulated . I use it to drive a set of AKG K240 sextet (Nom. Imp. 600 Ohm, sensitivity 88dB SPL/mW) and a set of Sennheiser Urbanite (Nom. Impedance18 Ohm, Sensitivity 118dB SPL/mW)
Very satisfied with it acoustically. Measurements will follow.
George
The ICs are supplied by 2x14Vdc unregulated . I use it to drive a set of AKG K240 sextet (Nom. Imp. 600 Ohm, sensitivity 88dB SPL/mW) and a set of Sennheiser Urbanite (Nom. Impedance18 Ohm, Sensitivity 118dB SPL/mW)
Very satisfied with it acoustically. Measurements will follow.
George
Attachments
That's an interesting build.
I've never thought of using something like an LM1875 for a headphone amp.
Did you keep the 22x gain?
How is the sensitivity of the volume control?
I'm guessing that since the power output is presumably less than 1w to drive headphones the chips run very cool?
I've never thought of using something like an LM1875 for a headphone amp.
Did you keep the 22x gain?
How is the sensitivity of the volume control?
I'm guessing that since the power output is presumably less than 1w to drive headphones the chips run very cool?
Last edited:
I remember I had built such an LM1875 but in inverted mode decades ago when that IC was a new thing. I had compared it acoustically to two other discrete builds one class AB, the other A (JLH 69). It was as good as any of them. All eventually went to friends and I was left using the head out of my external sound carts.
Some years ago I had built a smallish amplifier see pics, it was good but marginal in driving the K240.This is the one that was replaced by the LM1875 when I decided to use two of the kits I had bought dirty cheap from ebay 1-2 months ago.
True, the x22 gain is a lot, I had to pad down some 12 dB at the DAC output for to have the volume pot functioning properly at low settings.
I may try later on to reduce the x22 gain but I don’t know if lowering it will be enough before hitting the instability limit (x10 for that chip)
The K240 need some 10-15mW for highish SPL, I’ll measure in time. With 600Ohm load this amp with this psu, clips at around 80mW.
The chips are bolted to the thin aluminum chassis (electrically isolated). They run cool.
George
Some years ago I had built a smallish amplifier see pics, it was good but marginal in driving the K240.This is the one that was replaced by the LM1875 when I decided to use two of the kits I had bought dirty cheap from ebay 1-2 months ago.
True, the x22 gain is a lot, I had to pad down some 12 dB at the DAC output for to have the volume pot functioning properly at low settings.
I may try later on to reduce the x22 gain but I don’t know if lowering it will be enough before hitting the instability limit (x10 for that chip)
The K240 need some 10-15mW for highish SPL, I’ll measure in time. With 600Ohm load this amp with this psu, clips at around 80mW.
The chips are bolted to the thin aluminum chassis (electrically isolated). They run cool.
George
Attachments
A cabinet for a friend's hypex, alongwith harness. The RCA and speaker terminals aren't the best - only had these to hand. With no option to get new ones because of the lockdown here.
Happy to make more if anyone wants it. PM if so.
Happy to make more if anyone wants it. PM if so.
Attachments
I understand that the way audio equipment sounds is far more important than how it looks. Having said that, I really like the aesthetics of your amp. I love how you've back-lit the volume knob. Very subtle, very cool.
Here are some measurements done on the LM1875 amplifier of post #21 driving a pair of AKG K240 Sextette (600 Ohm)
1st attachment is tabulated results, 2nd att. same data drawn as a diagram.Test signal was 997Hz sinusoid.
The notes of how I perceived the resultant sound level when wearing the headphones was done with an 6.5 cycle repeated burst tone of 997Hz.
3rd att. Is a collection of REW screenshots from amplifier’s output voltage distortion (64k FFT) . Signal was fed to the sound card attenuated
4th att. Is waveform and it’s FFT of the AC 100Hz ripple superimposed on the DC at the input of the multiple CR PSU filter. Upper section is when amplifier is idling, lower section when amplifier is driven at the verge of clipping (7.46Vrms output)
5th att. Is waveform and it’s FFT of the AC 100Hz superimposed on the DC at the output of the multiple CR PSU filter. Again upper section is when amplifier is idling, lower section when amplifier is driven at the verge of clipping (7.46Vrms output)
Photos show the way I mounted the sound level meter to face the capsule of the headphone.
George
1st attachment is tabulated results, 2nd att. same data drawn as a diagram.Test signal was 997Hz sinusoid.
The notes of how I perceived the resultant sound level when wearing the headphones was done with an 6.5 cycle repeated burst tone of 997Hz.
3rd att. Is a collection of REW screenshots from amplifier’s output voltage distortion (64k FFT) . Signal was fed to the sound card attenuated
4th att. Is waveform and it’s FFT of the AC 100Hz ripple superimposed on the DC at the input of the multiple CR PSU filter. Upper section is when amplifier is idling, lower section when amplifier is driven at the verge of clipping (7.46Vrms output)
5th att. Is waveform and it’s FFT of the AC 100Hz superimposed on the DC at the output of the multiple CR PSU filter. Again upper section is when amplifier is idling, lower section when amplifier is driven at the verge of clipping (7.46Vrms output)
Photos show the way I mounted the sound level meter to face the capsule of the headphone.
George
Attachments
Ok how does it sound ? 
Hi George please tell what decision about what exactly!? I suspect hypersensitivity again in this policor world but I am not aware of any wrongdoing in this thread.
The intent of this thread is to post diy audio builds. Stay on topic
Please don’t try to sidestep the Moderation decision, or this thread too will be locked.
George
Hi George please tell what decision about what exactly!? I suspect hypersensitivity again in this policor world but I am not aware of any wrongdoing in this thread.
Last edited:
Decision is to stay away from dealing with Cov social impact (politics) and medical issues (potent for dangerous misinformation).
Closed threads and deleted posts in this thread were of such a nature.
This thread will hopefully remain open with member's cooperation if it deals only with diy builds.
George
My wishes to you Jean-Paul and to all for good health (biological and psychological).
This hobby is a blessing in these circumstances I guess.
On your question of how this amplifier sounds, I can say that with the AKG the bass if very well controlled, deep and punchy and the overall spectrum is reproduced effortlessly at high SPLs. (these K240 have a wonderful midrange clarity)
I haven’t done any electrical measurement with the amplifier driving the easier Sennheisers yet.
George
This hobby is a blessing in these circumstances I guess.
On your question of how this amplifier sounds, I can say that with the AKG the bass if very well controlled, deep and punchy and the overall spectrum is reproduced effortlessly at high SPLs. (these K240 have a wonderful midrange clarity)
I haven’t done any electrical measurement with the amplifier driving the easier Sennheisers yet.
George
> mounted the sound level meter to face the capsule of the headphone.
That headphone is designed to "seal" to the head, and have a controlled volume-space around the ear. Your open-cell foam minimally fills space but does not seal.
Here's my 10-cent "head". The cushion sits on the plywood approximately like a head, with a space. A better model would add an "earlobe" (or similar fill) and maybe some hair (absorption).
I know from real-head use that the fit and seal of a K240 or HD201 has a major influence on bass, and exact location changes the extreme highs.
That headphone is designed to "seal" to the head, and have a controlled volume-space around the ear. Your open-cell foam minimally fills space but does not seal.
Here's my 10-cent "head". The cushion sits on the plywood approximately like a head, with a space. A better model would add an "earlobe" (or similar fill) and maybe some hair (absorption).
I know from real-head use that the fit and seal of a K240 or HD201 has a major influence on bass, and exact location changes the extreme highs.
Attachments
* Found a bad solder joint in my SET amp. Left channel would sometimes cut out after warming up for a while. De-solder and re-solder fixed it.
* Made an A/B switch box.
* Currently making a 3-way speaker with some drivers that have been in my stash for a while. Seas P25REX-DD, 10-FM, Audax TM020J5. Cut panels for a test box today. My name is Dave -- I have a speaker sickness.
Left channel would sometimes cut out after warming up for a while. De-solder and re-solder fixed it. * Made an A/B switch box.
* Currently making a 3-way speaker with some drivers that have been in my stash for a while. Seas P25REX-DD, 10-FM, Audax TM020J5. Cut panels for a test box today. My name is Dave -- I have a speaker sickness.
Attachments
Thanks, zman. I built that amp about 10 years ago from a kit offered here.
KT88 SE Complete Kit
The basic kit supplied most of the circuit parts and plans, but I sourced my own iron, and built the case myself. Really enjoyed the build, and I have grown very fond of the sound.
Last edited:
Thank you Paul for your remarks and suggestion.
May I only clarify that my intent of mounting the sound level meter against the capsule, was to achieve repeatability during testing of sound pressure level output vs excitation level at a single mid frequency (997Hz), not for taking a frequency response in the acoustic domain.
Your mounting suggestion on the other hand is applicable to both types of measurement.
A byproduct of my testing results with the repeated tone burst of 997Hz through the AKGs was to put some confidence on the maximum dynamic range (DR) estimation I can handle.
Under the most silent ambient environment in my house I could perceive tone bursts down to 34dB SPL, though only down to 40dB SPL when in proximity to the fan of my tower PC. (*) .
The upper limit of the dynamic range varies too, now depending on the duration of the high SPL tone. For single short bursts of 5ms duration I can handle the 115dB SPL. For single burst of 10ms, 109dB SPL. For 20ms, 106dB SPL. For 40ms, 103dB SPL. For 80ms, to 160ms 97dB SPL. For 160 to 320ms, 94dB SPL. For 320 to 640ms 91dB SPL. For longer lasting bursts I can listen without discomfort up to 85-88dB SPL.
The ear drum stiffens quite fast with high SPLs, so what one gains by handling more and more higher SPLs due to eardrum stiffening, he misses from the bottom of the just-perceived low SPLs.
Now given that the FFF crescendi in classic music last somewhere in the range from 160 to 320ms, my through-headphones DR capabilities for short time listening is in the vicinity of 70 dB and for longer time -typical listening to the music – closer to 60db.
(*)AKGs are semi-open acoustically, do not isolate at mid/high frequencies.
George
I took advantage of a moment to do some repairs to some speakers that are of the “white van” variety, designed to sell that is. Cones separated from the rotten foam suspensions on both.
They are rated at 200 watts, but have minuscule magnets on the 10” woofers, and no crossovers.
The smaller drivers are treated to small capacitors. The person that had been using these had an older 150w Kenwood amp on them, am thinking it was just a bit much since the guy likes to come in early and crank it up.
Any idea what kind of power these things would appropriately be given?
They are rated at 200 watts, but have minuscule magnets on the 10” woofers, and no crossovers.
The smaller drivers are treated to small capacitors. The person that had been using these had an older 150w Kenwood amp on them, am thinking it was just a bit much since the guy likes to come in early and crank it up.
Any idea what kind of power these things would appropriately be given?
Attachments
SSMH 12AU7 variant
TKD pot
AMRG resistors
Audio Note Kaisei elcos
Polystyrene caps
Neutrik jacks
Large yellow electrical Junction box is temporary corona home for it
Obviously not yet finished. Will spend today wiring it up.
TKD pot
AMRG resistors
Audio Note Kaisei elcos
Polystyrene caps
Neutrik jacks
Large yellow electrical Junction box is temporary corona home for it
Obviously not yet finished. Will spend today wiring it up.
Attachments
Last edited:
Glad you asked.
1) it’s an audio project
2) it’s not something I would normally spend time on
3) they were already in our workshop
4) I’m definitely not about to try and find replacements during this time
Sheesh, just because I haven’t copied an amp design and continued to try and build it with odd parts...
Am going to replace the amp running these, am thinking something less than 60W this time around.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.