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 Post subject: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Mar Sat 13, 2010 6:26 pm 
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Subject:
This is for people who have or want to modify a Talking House transmitter.

History of Talking House:
Talking house is well known. They have gone through different models, the last, TH5.0 version. Some early models did not sound great, others good, but even with in the same model number, there was variation. Talking House was bought by Radio Systems and re-branded "I A.M. Radio". Apparently since Radio Sys bought TH they made mods. I talked to them and they were vague about the improvements made, but this video between a modified TH5.0 and a stock TH4.3 sound demo gives you an idea (starting about 3:00).

http://www.youtube.com/watch?v=NQ2_ooYHcuY

I called the folks at "i AM radio" and gather their changes did NOT involve IC chips? The changes they alluded to were some discrete components (capacitors, resistors?). The audio limiter circuit was mentioned. I gather reading the Web some found different audio sources (level, impedance, equalized) gave different quality. Any Ideas? There are no schematics, so it will have to be reverse engineered. The chips on this unit are:

(click to enlarge, then again, then again)
Image

BA3313L (an ALC chip, automatic limiter circuit)
LM386 (I think to drive the onboard monitoring speaker?)
LM358N (dual op amp, VCO-volt cont'l oscillator)
Positive Linear Voltage Regulator by ST 24CD something
ISD4003-05MP (dual 5 min message recording play back chip)

The most obvious IC that does audio is the ALC chip BA3313L. It's closest to the audio inputs (line and Mic) for "LIVE BROADCAST". This is the area that no doubt can be adjusted. I am guessing some changes in capacitor value, quality and resistor values might change audio?

Can anyone tell me how to test this. I have audio Generator and scope.... I have monitored the antenna with the scope and got a look at both audio and RF and it looks OK with some distortion. I'll post pictures but it's hard to capture it with a camera.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Feb Sat 05, 2011 1:40 am, edited 3 times in total.

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 Post subject:
PostPosted: Mar Sun 14, 2010 7:12 am 
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I am focused on the audio input and limiter stage.... which makes most sense. Even if there are changes down stream, if the source is bad or crippled right from the input, it will affect overall sound. I did some quick and dirty circuit tracing (sorry poor labels, but if you have unit open it's apparent). I looked around the BA3313L (ALC) chip. It makes more sense with the application link below. The BA3313L has two channels and one is not used. I will be able to get a better picture when I take the board out and look at the trace under the board. This guess is just from ohm meter, capacitor meter and reading the codes on the components.

Image

here is the application notes for the BA3313L

http://pdf1.alldatasheet.com/datasheet- ... 3313L.html

The obvious thing is stereo sources are just tied together with two 100K resistors... I think a better choice might be two .15uF caps and 20K resistors.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Mar Sun 14, 2010 7:23 pm, edited 1 time in total.

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 Post subject:
PostPosted: Mar Sun 14, 2010 1:25 pm 
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Interesting, not much help but I had a TH 5.0 here that belonged to wife's cousin who sells real estate, playing music it was a sorry pos...

That one had some changes in the form of caps and resistors tacked in on the top of the board, looked like factory modification and modulated probably 125% or more... Didn't sound too bad on voice but was unusable otherwise... I don't know if she still has it, can ask...

Tom


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 Post subject:
PostPosted: Mar Sun 14, 2010 5:52 pm 
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Edit: I had only tried an iPod as input.... Just tried my computer using WMP, Windows Media Player, with equalizer ..... The sound is improved from adiquate to very good, near good AM BC station quality, showing proper input is key. Clarity, bass, treble are good using the computer with some tweak of the equalizer. The WMP has "SRS WOW Effects" page with "True bass" and WOW Effects, normal/large speaker headphone settings, which has great affect on sound quality, improving bass with out clipping or distortion. I suspect it is a form of compression/limiting for bass freqs. I first tried to listen to TH with a small battery portable with no tone controls in the same room as the TH. The small radio was swamped with signal when with in feet of the TH unit/antenna. The issue with AM is the amplitude and quality you start with. With out a good source and sophisticated audio limiter/compressor you are at the mercy of the input. The computer I assume is a poor mans limiter/compressor/gate and equalizer. With more control it does help the sound quality.

35Z5 wrote:
Interesting, not much help but I had a TH 5.0 here that belonged to wife's cousin who sells real estate, playing music it was a sorry pos...

That one had some changes in the form of caps and resistors tacked in on the top of the board, looked like factory modification and modulated probably 125% or more... Didn't sound too bad on voice but was unusable otherwise... I don't know if she still has it, can ask... Tom

The TH5.0 I have sounds good music, but needs something (see note above). That was always the issue, they seem to vary. The input line-in is somewhat sensitive. The iPod has about 32 ohm impedance for typical "ear buds" sounds OK. Some have used a matching transformer and say that helps. You can easily over-modulate so that is not the issue. It just needs TONE control, a little more bass, treble. It has bandwidth. TH has good range, making the most of the 100mw with that tuned antenna section.

Tom, if you can get a hold of it again and slide the cover back, take a good pic, notes, that would be great. I see some suspect places where value changes, extra cap might help. You say it did not help? I really think the BA3313L is implementation has questionable choices in capacitors, resistors and circuit.

AMT3000 has control over compression and limiter. It seems easy to put that circuit inside the Talking house and bypass that BA3313L. One thing I'll try is a professional compressor/limiter on eBay. Than use that as the input to the line-in. If that helps... I'll try to bypass that BA3313L, which looks like one resistor disconnected would do it.

(Edit: The next test is to used spectran (audio analysis), read the outgoing audio, going into Talking House and the audio out of the receiving radio, than compare. Looking at modulation on the scope does not substitute for seeing audio freq spectrum, more important the ear. There is no doubt I can make improvements. The way to go is take the board out and experiment with some circuit changes.)

ANY SUGGESTIONS, WILD GUESSING WELCOMED.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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 Post subject:
PostPosted: Mar Mon 15, 2010 5:09 pm 
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The first thing I am going to change is the audio input where two 100K resistors tie the left and right of a stereo source together as a mixer. I am going to add a capacitor and reduce the resistor such as (approx numbers)

1uF + 50K ohm
or
1.5uF + 33K ohm
or
2uF + 25K ohm

The idea is keep the time constant in the 50ms range to pass bass Freq. I don't think this will make a big change but it will be a mixer. A little more hunting I found the changes Radio System made to the TH5.0 are resistors and one capacitor? (so I was told) If any one has a modified version of a TH5.0 let me know.

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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 Post subject:
PostPosted: Mar Mon 15, 2010 7:13 pm 
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Location: Alger, MI
Which resistors and capacitors were changed?

From what I have read, it is the bass response which is somewhat lacking on these units. If so, it would be reasonable to assume that the audio coupling capacitors would need to be increased in value to improve the bass response.

It would be quite easy to drive the unit with an audio signal generator and monitor with an o'scope both the audio output of the alc chip on one channel and the modulated rf output on the second channel. Then do a sweep from 10hz to 15khz and watch the response. I would then increase the coupling capacitor values and do another sweep. When I get my unit, I may try this.

Regards,

Ed


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 Post subject:
PostPosted: Mar Mon 15, 2010 10:06 pm 
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Is there a schematic of the entire unit available?

Dave


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 Post subject:
PostPosted: Mar Tue 16, 2010 3:33 am 
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etech wrote:
Which resistors and capacitors were changed?

From what I have read, it is the bass response which is somewhat lacking on these units. If so, it would be reasonable to assume that the audio coupling capacitors would need to be increased in value to improve the bass response.

It would be quite easy to drive the unit with an audio signal generator and monitor with an o'scope both the audio output of the alc chip on one channel and the modulated rf output on the second channel. Then do a sweep from 10hz to 15khz and watch the response. I would then increase the coupling capacitor values and do another sweep. When I get my unit, I may try this.

Regards, Ed


Hi Ed, are you getting one of these soon? Ha ha
That is a great way to check it. I will have to try it. I need to get a new audio generator. The demo audio Gen software timed out. There are some others that can sweep and do different signals.

Called them today to order the power supplies and talked to John again (one of the TH techs). We had a nice conversation. I tried to get him to give up a little more info. Basically he said one of the engineers fiddled around with it and changed a few parts... he was sure it was not major.

Suspect 220pF on pin 1 (out) or the 100uF on pin 5 (in) are critical.

The spec for the 8313L chip says the the capacitor 47uF (pin 2) and the 3.9K resistor on pin 5 are critical, min values. I wrote 3.8K on mine, but that was measured. The specs for the chip say if these are not selected properly the ALC will work too much.

They "ground" pin 9 via a capacitor. It might be interesting to remove the capacitor and put a resistor in there or both.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Mar Tue 16, 2010 4:37 am, edited 4 times in total.

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 Post subject:
PostPosted: Mar Tue 16, 2010 3:35 am 
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Dave Doughty wrote:
Is there a schematic of the entire unit available? Dave

No, unfortunately. If I take the board out of the case, I can get a good look at the trace and all the parts... It looks fairly straightforward to remove. Except for some off the shelf IC chips there are just parts, transistors, caps, resistors, diodes and inductors. It is just an AM transmitter...... The output self tune output (motorized inductors) has a patent on it. If I look that up I am sure it will be clear how that works. I am going to ignore the output as an issue.

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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 Post subject:
PostPosted: Mar Tue 16, 2010 2:02 pm 
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Location: Alger, MI
Quote:
Suspect 220pF on pin 1 (out) or the 100uF on pin 5 (in) are critical.


Yes, those would be a good starting point. I can't imagine the cap on pin 1 (output) would be 220pf. According to the application note, it should be more like 10uf. I would measure the value by removing one lead from the circuit. Then install a cap which would be double or triple that value. Maybe more, like 100uf instead of 10uf. Then I would re-sweep the circuit.

I would also measure the value of the input cap on pin 5 by removing one lead from the circuit and then I would double or triple that value too. The input cap may not be as critical, since the op amp input would be high impedance.

Ed


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 Post subject:
PostPosted: Mar Tue 16, 2010 5:40 pm 
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etech wrote:
Quote:
Suspect 220pF on pin 1 (out) or the 100uF on pin 5 (in) are critical.


Yes, those would be a good starting point. I can't imagine the cap on pin 1 (output) would be 220pf. According to the application note, it should be more like 10uf. I would measure the value by removing one lead from the circuit. Then install a cap which would be double or triple that value. Maybe more, like 100uf instead of 10uf. Then I would re-sweep the circuit.

I would also measure the value of the input cap on pin 5 by removing one lead from the circuit and then I would double or triple that value too. The input cap may not be as critical, since the op amp input would be high impedance. Ed

Thanks for looking Ed. Great observation. Here is my latest test (not the sweep test and no modification yet):

Test set up iPod headphone jack feeding Talking House. Bottom of same iPod (line-out) feeding a no name car FM transmitter. Source was MP3 music, alternative rock/pop. A few rooms away, a Aiwa AM/FM stereo headphone jack feed into computer sound card line-in, running audio spectrum analysis program. I switched between FM and AM and took screen shots. The Aiwa stereo had all it's magic off (equalizer, surround sound, filters, bass and BBE off).

Image

Strong AM and FM Commercial Station not much different.
No control over source. AM was a 50's oldie music and FM was rock music.
Image

The perceived loudness was not much different between FM and AM, despite the computer programs RMS input display (upper left), but FM was louder. The volume of the Talking House was controlled by the iPod volume control and was a little over half. The "line-out" on the bottom of my iPod does not affect the iPod's line-out. Keeping the iPod on half (headphone vol), no more than 60% keeps Talking House from distorting. This leads me to believe the limiter is not doing a great job, clipping the input too much.

Here is Wiki's description of what Freqs sound like what.

Frequency (Hz) Octave Description
16 to 32 1st The human threshold of feeling, and the lowest pedal notes of a pipe organ.

32 to 512 2nd to 5th Rhythm frequencies, where the lower and upper bass notes lie.

512 to 2048 6th to 7th Defines human speech intelligibility, gives a horn-like or tinny quality to sound.

2048 to 8192 8th to 9th Gives presence to speech, where labial and fricative sounds lie.

8192 to 16384 10th Brilliance, the sounds of bells and the ringing of cymbals. In speech, the sound of the letter "S" (8000-11000 Hz)

Talking house could use more 50-100Hz bass but also the 5-10K was not great. The 10-20K really rolled off, more than I thought, but it is AM and not too far off from commercial AM, based on a crude test, with "help" from the receiver (see below).

The Talking House does have bandwidth, because it bleeds 10hz above and below very nicely. That may be just because I'm only 100 feet + one dry wall / light door away. The loop on the Aiwa is a home made 1'x1' deal on the wall behind a dresser. It's 90 degrees to the Talking house, ie not pointed at it. Range is not an issue with the talking house, but sound can be improved.

Picture of Aiwa receiver "magic" on, AM deficiency in bass and upper treble clearly improved. However I would say the (artificial) bass had a little "boomey" affect, but you could hear bass galore. Backing off the magic bass boost a little sounded better. The spectrum picture does not tell the whole story, ear still rules. The treble boost did wonders for highs and you could hear cymbals more clearly with higher highs..
Image

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Mar Tue 16, 2010 6:50 pm, edited 8 times in total.

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 Post subject:
PostPosted: Mar Tue 16, 2010 6:09 pm 
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gmcjetpilot wrote:
8192 to 16384 10th Brilliance, the sounds of bells and the ringing of cymbals. In speech, the sound of the letter "S" (8000-11000 Hz)



Ummm leaves me out in the cold, my left ear is only good for about 7K and the right, maybe half that...

BTW, Sue said she thinks she still has the TH Tx, recently went through a move and still has some stuff to unpack... Probably by the time I get it, you'll have this thing figured out... But as I stated it was horrid, I left it hooked up maybe five minutes... Input was from line out of an AKAI tuner, without any correction, but still the 6888/6GY6 Tx sound great with same... Speaking of which, the ones we've been building have a nearly flat freq response, plenty of bottom and by the sig gen hang in there to 8K+... As I stated, can't hear it, have only seen it on the scope...

Tom


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 Post subject:
PostPosted: Mar Tue 16, 2010 6:13 pm 
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35Z5 wrote:
Ummm leaves me out in the cold, my left ear is only good for about 7K and the right, maybe half that...

BTW, Sue said she thinks she still has the TH Tx, recently went through a move and still has some stuff to unpack... Probably by the time I get it, you'll have this thing figured out... Tom

Thanks Tom that would be great if you can peek into Sue's talking house..... and see what you see. Cheers George

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 Post subject:
PostPosted: Mar Thu 18, 2010 2:07 pm 
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etech wrote:
Yes, those would be a good starting point. I can't imagine the cap on pin 1 (output) would be 220pf. According to the application note, it should be more like 10uf. Ed

The code is 220 on the small ceramic so I assume 220pF or nF, either way it is way smaller than 10uF. So I tried to jump it with a biggest non-polarized cap I had, a 0.5uF (big 600 volt). It did not like it, feed back. I just tried to tack it on in parallel with the existing 220 cap. I have not had time to take the board out and do it right. I'm going to make a mouser order and get some low voltage stuff (caps and currents) to sub into the circuit.

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 Post subject: Talking House Transmitter Modifications
PostPosted: Nov Thu 11, 2010 7:49 pm 
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Has anyone come up with circuit changes to the earlier TH models TH2- TH 4.XX ? to bring up the bass response? Ive been trying to locate information on what changes a person can make and cant come up with anything. There has to be a way to improve the sound quality of the early versions. I am using the TH 5 and that sounds excellent, but also have ohter versions below the TH 5 that need the bass response boosted. EQs dont do the same to the audio as the TH 5 puts out. The TH 5 is just more full sounding and sounds close to a regular AM broad cast station. The the others are narrow in sound.
Thanks Guys, any updates to the TH Transmitters will be apriciated.
Joe


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 Post subject: Re: Talking House Transmitter Modifications
PostPosted: Nov Fri 19, 2010 11:21 pm 
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RadioJoe6 wrote:
Has anyone come up with circuit changes to the earlier TH models TH2- TH 4.XX ? Joe

I just started playing with it lately. I buttoned it up, decided to just use it. With some "tricks" with antenna and chassis ground it sounds pretty good.

I found the higher FREQ to be a better carrier wave, but lower FREQ was more power. Just by ear the high FREQ sounds better. I am talking about a 5.0 TH.

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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 Post subject:
PostPosted: Nov Sun 21, 2010 7:50 pm 
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Doing some research on HUM with TH which clearly lowers the audio quality I found some good info from the Part 15 web forums. These are links to individual threads with some info or links I extracted. If you read all this there is good info that will no doubt help. In no particular order of importance.

TH Extensive mods, this guys did some great mods. He was some what less spacific in some areas, but it's a good post.
http://part15.us/node/2419

Also:

Why does my Transmitter Hum?
http://part15.us/node/479
http://www.northcountryradio.com/Articles/humred.htm
http://kenneke.com/~jon/pixie/pixietips.html
http://www.bluejeanscable.com/articles/humrejection.htm
http://www.epanorama.net/documents/grou ... rcuit.html
http://www.epanorama.net/documents/grou ... lving.html
http://lists.contesting.com/pipermail/t ... 15534.html
http://web.archive.org/web/200108251945 ... DIY/ground


talking house 2 power supply requirements
http://part15.us/node/1968


Hum in AM Signal
http://part15.us/node/2473


http://part15.us/node/2508
use two 12 volt lead sealed batterys, about 7.5 Amps each. I charge then in parallel but run them in series to a adjustible voltage regulator for what ever the voltage is that is required, 16-18?

I usually just recharge when the transmitter is not being used. This took care of the hum problem with the talking house. ( along with an outside external anttnna) I also run ground loop isolators in the audio leads and a ground wires right to the same point on a cold water pipe from each accessory I have attached to the transmitter ( EQ, SIMA SVS4 Switcher,and audio sources.
Radio Joe


http://part15.us/node/855
It doesn't know the words...
-But seriously folks, hum can be RF from the wire antenna being coupled back into the DC input to the transmitter. A greater value capacitor to ground on the DC input can be a real lifesaver. Also shielded wire and toroid cores are good to have around to decouple audio and DC to the transmitter from a variety of sources, including computer equipment. Also, remember ground the shield only on one end of the wire pair. Other wise you are guaranteed to have a ground loop. And remember, if it won't stop humming you may have to teach it the words.

http://part15.us/node/2484
Then spent 3 days getting the hum out. I had the antenna on my metal roof, and could not get all the hum out till I moved the antenna away from the building.


Further I found this but can't find the jumpers myself:
I rediscovered a fine-point about setting one of them up which I'd forgotten. The subject is grounding, and the three jumpers labeled S1, S2 and S3.

In recent months coverage at 1680 kHz has not been what it once was, and I thought maybe it would be time to think about buried ground radials, a hassle I'd like to avoid, but then I discovered S1, which connects transmitter ground to audio ground, was off, in which case an inductor prevents RF from reaching the audio ground. By simply jumpering S1 the old signal is back again.

S2 and S3 are also jumpered, creating a ground path through the power supply

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 Post subject:
PostPosted: Feb Sat 05, 2011 1:36 am 
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A nice Gentleman on the internet shared some ideas for
modification. He sent me pictures and I added notes to make it
clear. These are thumbnails. Click to bring it up. Click again to get
full size. It's easier to save to your computer for viewing. The are
about 1024 x 725 pixel.

He did other mods to another TH, which are way more involved for
other reasons than just audio fidelity. One was an active lowpass
filter for audio (circuit board, IC's power), to avoid interfere the
neighbour channels. Also to avoid interfere a low pass chebyshev
filter is added to the RF, external to the unit in the antenna feed
line. The mods below are for audio fidelity.

I have not done the mods my self, so by all means do them at your
own risk. The total parts needed: (3) capacitors, (1) potentiometer,
(1) RCA phone jack and (2) two-pin headers.

Image
Image
Image

The original .047 uF (C301) capacitor goes to 1-10 uF, and the
(C337) 47 pF goes to 470-1800 pF for the mod.

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Feb Thu 10, 2011 2:04 am, edited 1 time in total.

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 Post subject:
PostPosted: Feb Sat 05, 2011 5:10 am 
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Location: Indianapolis, IN
Thanks GMCJetpilot---didn't notice this thread before your message... Thanks for mod. posting...

Having trouble with image host with my dial-up connection---am PM'ing you my e-mail hoping you can e-mail images directly to me...

John


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 Post subject:
PostPosted: Feb Sat 05, 2011 9:06 pm 
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Location: Alger, MI
When I get a chance, I will have to give these mods a try. I suspect changing C301 from a .047uf to a 10uf will improve the low frequency response.

Ed


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